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Numerical Assessment of a Safety System to Minimize Injuries during a Cyclist Run-Over

Numerical Assessment of a Safety System to Minimize Injuries during a Cyclist Run-Over Hindawi Applied Bionics and Biomechanics Volume 2021, Article ID 9922210, 13 pages https://doi.org/10.1155/2021/9922210 Research Article Numerical Assessment of a Safety System to Minimize Injuries during a Cyclist Run-Over 1 1 2 E. H. López-García , M. F. Carbajal-Romero , J. A. Flores-Campos , and C. R. Torres-SanMiguel Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica Sección de Estudios de Posgrado e Investigación, Azcapotzalco, 02519 CDMX, Mexico Instituto Politécnico Nacional, Unidad Profesional Interdisciplinaria en Ingeniería y Tecnologías Avanzadas, 07340 CDMX, Mexico Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica Sección de Estudios de Posgrado e Investigación, Zacatenco, 07738 CDMX, Mexico Correspondence should be addressed to C. R. Torres-SanMiguel; ctorress@ipn.mx Received 19 March 2021; Revised 18 July 2021; Accepted 11 August 2021; Published 27 August 2021 Academic Editor: Wen-Ming Chen Copyright © 2021 E. H. López-García et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. The World Health Organization has reported that 1.35 million people die on the roads every year due to road traffic accidents. This paper focuses on exploring a passive safety system that reduces lesions in the overtaking run-over scenario. Methods. Head Injury Criterion (HIC) and Combined Thoracic Index (CTI) were evaluated through numerical simulations using LS-Dyna®; in order to compare the computed results, three different speed scenarios were carried out (velocity of running over 40, 50, 60 km/h). Results. The computed results were divided into groups, A for the run-over test without a passive security system and B for the run-over test with a passive security system. For case A.1, the HIC15 was 3325. For case A.2, the HIC15 was 1510, and for case A.3, the HIC 15 was 1208. For case B.1, the HIC15 2605, for case B.2, the HIC15 was 1282, and for case B.3, the HIC was 730. Conclusion. The comparative results show that the passive safety system installed on the bicycle has an increased benefit impact on the severity of the injury on vulnerable road users, decreasing the probability of cranioencephalic lesions in all study cases. In addition, the thorax injuries are cut down only in the impact scenario at a speed of 40 km/h. 52,000 in 2013 [2]. In the United States, 783 cases of cyclist 1. Introduction deaths due to motor vehicle crashes were reported in 2017 The World Health Organization (WHO) reported 1.35 mil- [4], while in Mexico, the cases of death of cyclists in road lion deaths in a year due to road traffic crashes [1]. This accidents totaled 199 in the same year [5]. The cyclist run- problem was the leading cause of death in people between over scenarios can be identified according to different char- 15 and 29 years in 2012 [2]. A specific group called vulner- acteristics. The Pedestrian and Bicycle Crash Analysis Tool able road users (VUR) that include motorcyclist, cyclist, (PBCAT) distinguishes around 79 scenarios that consider and pedestrians are exposed to a greater danger during their different factors such as the vehicle’s position before the circulation inroads because they do not have any structure impact, the direction in which one respects the other, and that protects them from a road accident and is more suscep- the impact causes [6]. The scenario reported a greater prob- ability of cyclist death, where the motor vehicle is moving in tible suffer severe or deadly injuries [3]. The cyclist run-over is the smallest group among all road accidents, representing the same direction as the cyclist and the bicycle is reached in 4% of the victims. Although the numbers of deaths due to the rear side by the front of the car; this scenario is called the the cyclist run-over are a few, it was informed around overtaking scenario [7, 8]. Also, in National Highway Traffic 2 Applied Bionics and Biomechanics Safety Administration (NHTSA) in the database called Table 1: Characteristics of run-over tests. Fatality Analysis Reporting System (FARS) from 2008 to Case A.1 2012, the crash scenario that presented the highest death rate Automobile speed Cyclist speed of the cyclist in the United States is the overtaking crash sce- nario [9], repeating this trend in subsequent years until 60 km/h 0 km/h 2017, which is the last update. It is essential to consider the Case A.2 Group A (without passive type of motor vehicle studied because this directly affects Automobile speed Cyclist speed security system) the severity of the injury that a cyclist can present since its 50 km/h 0 km/h geometric characteristics alter the VUR kinematics. The data Case A.3 issued by the NHTSA show that passenger cars have the sec- Automobile speed Cyclist speed ond place in deaths caused to cyclists [10–12]. In different 40 km/h 0 km/h industrial designs, existing systems are used to decrease inju- ries in vulnerable road users, as shown below: the patent [13] Case B.1 presents a bumper used in children’s bicycles that has the Automobile speed Cyclist speed function of attenuating the frontal collision in front of any 60 km/h 0 km/h surface to protect the bicycle upon impact and reduce the Case B.2 impact force and protect the user. Similarly, the patent Group B (with passive Automobile speed Cyclist speed [14] presents a pneumatic bumper with an internal chamber security system) 50 km/h 0 km/h that stores air, which is released controlled when the front Case B.3 and rear parts of the bumper cushion impact. Also, the device [15] is designed to be used in motor vehicles. It has Automobile speed Cyclist speed two subsystems, an impact mitigation device placed in the 40 km/h 0 km/h front of the vehicle, responsible for absorbing minor impacts that do not exceed the material’s yield point, and an internal bumper that deforms plastically and absorbs the impact Bicycle and cyclist position was proposed before the energy. The patent [16] consists of a U-shaped bumper vehicle’s impact to measure injuries generated under the joined at the motorcycle to protect the vehicle structure from cyclist’s head. The initial position before impact can be seen possible shocks. The device [17] is a rigid structure installed in Figure 1. on the front or rear of a bicycle to protect the damage by an Three meshed models corresponding to the vehicle, bicy- impact. Finally, the patent [18] shows a bumper placed on cle, and cyclist were used, described in detail below. The auto- the rear wheel of the bicycle, serving as a support for a light mobile model consists of a meshed geometry compatible with source projected towards the ground, marking the minimum the Ls-Dyna® software of a Toyota Yaris 2010, developed by safe distance for the circulation of the cyclist to prevent road George Mason University, contracted by the Federal Highway accidents caused by the lack of vision towards the cyclist. Administration (FHWA). This model has validations under The research is aimed at proposing a framework used to the various frontal and lateral impact tests and a substantial perform vehicle-bicycle crash simulations to investigate the barrier impact [20]. The anthropomorphic virtual dummy effects of the rear rubber bumper on cyclist injuries. The used during the simulations to represent the cyclist run-over novelty is the rear passive safety system rubber bumper scenario corresponds to a male Hybrid III percentile 50th, and the numerical analysis carried out. The modeling developed by the Livermore Software Technology Corpora- methods used to predict biomechanical responses for run- tion, developing the LS-Dyna® software. The bicycle model over simulations are well-established and can help predict was developed in the SolidWorks® Computer-Aided Design biomechanical response in this scenario. A sedan vehicle (CAD) software to later export the geometry to the LS- was chosen for this study due to its high commercial Dyna® software, where it proceeded to mesh and configure demand and its incidence in cyclists’ road accidents. In addi- the corresponding contacts and joints. The bicycle frame was tion, the head and chest lesions suffered by the cyclist are based on the Bicyclist and bike targets specifications manual evaluated since those are the body’s main region that causes version 1.1, developed by CATS/4a companies, to provide a person’s death in run-over scenarios. the necessary specifications of a cyclist objective vehicle detec- tion tests. This research used the size of bicycles for an average man in the Dutch population [21]. The characteristics of the 2. Materials and Methods vehicle, dummy, and bicycle model are shown in Table 2. The bicycle frame and wheel discretization were made Three cyclists’ crash impact simulations were carried out using the finite element method by Ls-Dyna® Software, with shell elements. The element type used in the model through a detailed analysis due to the high nonlinearities, was quadrangular elements with 4 nodes, and we used the the inertial components, and the short duration of the mesh algorithm provided by the LS-PrePost® software to phenomenon. All the simulations are carried out in the create a preliminary mesh, then carried out a manual mesh refinement process to achieve a high mesh quality, especially overtaking crash scenario, where the car impacts the bicy- cle’s rear wheel while the bicycle and the vehicle are in the in areas of interest of the model, where correct discretization same direction [19]. The characteristics for each case of is critical for the reliability of the results. To ensure that the run-over are described in Table 1. quality of the mesh was acceptable, mesh quality checks Applied Bionics and Biomechanics 3 Figure 1: Initial position cyclist/automobile. aligned with the centers of the wheels [22]. Therefore, the Table 2: Toyota Yaris 2012 and Hybrid III 50th percentile characteristics [20, 21]. parameters necessary for the bicycle frame to be considered safe must meet two conditions: Model characteristics Yaris 2012 Hybrid 50th Bicycle Number of parts 919 115 12 (i) The frame must not suffer any visible fracture [22] Number nodes 393165 7353 53314 (ii) The permanent deformation measured between the Number of solid elements 15234 2644 — wheel axles’ centers must not exceed 40 mm [22] Number of shell elements 358457 1606 56724 Figure 2 shows the diagram for the frame drop safety test Number of beam elements 4685 3 — and frame impact safety test. Number of restriction joints 19 48 — 2.1. Passive Safety Device. The strain energy density influ- ences the severity of cyclist’s injuries. This property quan- shown in Table 3 were carried out, where it was observed tifies the stored and dissipated energy in a material when it that the mesh of the bicycle parts had a good quality, espe- suffers a deformation. This energy is quantified from the dif- cially in critical areas for the results. ferent parts of the virtual dummy that represents the cyclist’s The LS-Dyna® software has a large number of material body. Therefore, the passive safety device seeks to dissipate models used for different applications. For this research, to the most significant deformation energy before the cyclist’s represent the behavior of the metallic parts, bicycle, and body hits the car’s surface. The graphic method of material the passive safety device, we used the MAT_PIECEWISE_ selection is used, also called the Ashby method [24]. LINEAR_PLASTICITY model. The material selected for The device was based on automotive bumpers systems the bicycle frame was AISI 4130 steel, a common material consisting of a frame, an energy absorber, and a plastic fas- for bicycle frames. In order to properly simulate impact cia. A passive safety system was designed, consisting of a behavior, the material’s linear and nonlinear mechanical frame made of ASIS 201 stainless steel and a polyurethane properties are needed to be configured appropriately within rubber elastic energy absorption system. These materials LS-PrePost®. Table 4 shows the parameters necessary to were chosen due to their high capacity to absorb impact define those mechanical properties. energy. The frame part is responsible for absorbing the most The bicycle frame was validated through the tests outstanding amount of plastic deformation energy from described in Mexican Standards nmx-d-198-2-1985 and being run over by a vehicle. In contrast, the polyurethane nmx-d-198-3-1985, specifically in points 4.3.1 and 4.3.2 cor- rubber parts seek to protect minor impacts by absorbing responding to the mass impact test in frame-scissor assem- the most significant elastic deformation energy. The assem- bly and drop of the frame-scissor assembly, respectively, bly of the system is carried out through arrangements of which were performed in LS-Dyna®. The frame drop safety nuts and screws. The system dimensions were established test consists of fixing the frame’s rear axle, then a mass for the bumper’s average height, which was used to place (M1) of 70 kg must be fixed on the seat post, and the assem- the bicycle’s passive safety system. Since the average height bly is dropped on a steel anvil [22]. The conditions necessary of a vehicle’s bumper is 500 mm [25], the system must be for the bicycle frame to be considered safe are as follows: placed within this measurement. Figure 3 shows how the passive safety system is mounted on a bicycle. (i) The frame must not suffer any visible fracture [22] The passive safety device’s frame was discretized simi- larly to the bicycle’s frame by using shell elements to opti- (ii) The permanent deformation measured between the mize computational resources without sacrificing accuracy. initial and final position of the center of the front Mesh quality check results are shown in Table 2. The mate- axle of the wheel must not exceed 60 mm [22] rial model was again MAT_PIECEWISE_LINEAR_PLAS- In the frame impact safety test, a mass (M) of 22.5 kg was TICITY due to the characteristics already described; the dropped from a height (a) of 180 mm and hit the front part mechanical properties necessary to simulate the correct 4 Applied Bionics and Biomechanics Table 3: Mesh quality checks for bicycle and passive security system model. Acceptable Percentage of valid Percentage of valid Variable Definition value elements elements The ratio between the largest and smallest Aspect ratio <10 99.76% 99.86% dimensions of an element Skewness Angular deviation of the element from an ideal shape <45 97.51% 99.95% The angle between the normal two planes is formed by Warp angle <100 99.36% 99.46% split the quadrilateral element along the diagonals Table 4: Mechanical properties of AISI 4130 and AISI 201 Steel. Material Mass density. (Ton/mm ) E (MPa) Poisson’s ratio σ (MPa) σf (MPa) εe nE (MPa) YS R f t 7:850 × 205 × 10 0:29 460:00 914:481 0:224 0:1456 2:48 AISI 4130 −9 3 0:27 360:00 1377:5 :03715 0:2099 2:61 AISI 201 7:810 × 10 200 × 10 E = Young s modulus; σ = yield stress; σf = true fracture stress; εe = true fracture strain; n = strain hardening exponent; E = tangent modulus. YS R f t Figure 2: Frame drop safety test and frame impact safety test [23]. impact behavior are shown in Table 3. In polymer blocks, imum deformation was 3 mm, indicating that this value is the MAT_MOONEY-RIVLIN_RUBBER model specialized established by the standard on which the tests are based. in this group of materials was used. The mechanical proper- The axis deformation at the front scissors was measured ties necessary to simulate the behavior of this part of the pas- at the maximum position when the impactor is not in con- sive safety device are shown in Table 5. tact with the bicycle’s frame to measure the permanent deformation in it. Figure 5 shows the stages of the frame impact test and the results where the permanent deforma- 3. Results tion (without load) presented in the frontal part of the frame was 16.7 mm, being within the tolerable limits of permanent deformation indicated by the standards on which the simu- The safety framework tests were carried out to bring the fol- lowing results. First, the front scissors’ axis’s deformation lations are based. was measured at the maximum position upon reaching rest (at time t = 2000 ms) against the position instants before hit- 3.1. Vehicle-Cyclist Impact Simulations. Bodily, the injuries ting the rigid wall (at time t = 752:0 ms). Figure 4 shows the happen when its resistance exceeds the withstand energy. stages of the frame drop test and the results, where the max- Thus, for an object to lose speed, its energy of motion must Applied Bionics and Biomechanics 5 Support plate Polymer block Rigid frame Polymer block Mounting plates Support plate Figure 3: Passive security system fixed to the bicycle. Table 5: Mechanical properties of polyurethane rubber with be transferred to another object. This transfer of energy also Mooney-Rivlin formulation. occurs in the case of an accident in the human body. The kinetic energy dissipated during the cyclist’s collision is 3 Mass density (Ton/mm ) Poisson’s ratio AB transformed into the structure deformation, leaving less 1:20 × 0:27 1:24 0:01 residual energy to be absorbed for the mechanical properties of the hard and soft tissue. The dispersion of kinetic energy, A and B are the constants of the Mooney-Rivlin constitutive equation for rubber. In the case of polyurethane rubber, the corresponding coefficients both in space and in time, is determinant in reducing the are A =1:24 and B =0:01 [26]. severity of injuries and can make the difference between sur- viving and not. The most severely injured body areas are the where A is the maximum value of 3 ms clip spinal accel- head and thorax. In this research, Head Injury Criterion max eration (As), D is the maximum value of the dummy (HIC) and Combined Thoracic Index (CTI) determine the max deflection (D), and A and D are the respective intercepts energy generated during the cyclist’s collision. These injury int int as defined above. rates are calculated according to the following equations. The dummy used has accelerometers in different parts of A suitable measurement to scale the possible cranioence- the body. For example, the accelerometer location in the phalic injuries is used the HIC. This criterion reflects the head is at node 133919, while that of the thorax is node change in acceleration that the passenger’s head undergoes 135705, shown in Figure 6. Those nodes measure the accel- moments after the collision. The calculation is performed by erations, and the LSDyna software calculates the HIC and selecting the maximum limits of integration of the area under CTI reached during the run-over. the acceleration curve. NHTSA and AAMA (American Asso- This section shows the results of simulations performed ciation of Medical Assistants) have established a time interval with the characteristics mentioned in Table 6, evaluating of 15 milliseconds after the impact. This interval favors the the cyclist’s head injuries HIC and the CTI index for chest reduction of the HIC calculation error. In addition, this value injuries. The simulation results were compared in two cases provides a more rigorous measurement of injury probability. with the same vehicle’s same speed but with and without a () passive safety system to observe the injuries differences. 2:5 HIC = ðÞ t2 − t1 atðÞdt : ð1Þ t2 − t1 3.2. Comparison between Case A.1 and Case B.1. For the case in which the car moves at 60 km/h, Figure 7 shows the kine- matic of the cyclist in cases A.1 and B.1, while Table 6 shows HIC uses t2 and t1 as a period of deceleration curve, a is the corresponding HIC and CTI values. Finally, Figure 8 the acceleration, and t is the total period of the curve. In order shows the required parameters to assess head and thorax to determine a HIC value, it is necessary to obtain the velocity injury severity at 60 km/h. and acceleration of the body at the moment of impact. There- By using the results of the Combined Thoracic Index fore, the dummy’s dimensional characteristics are crucial to acceleration of the chest center of gravity as well as chest establish a way to generate such kinematic parameters. deflection during a traffic accident, it is possible to know Additionally, the Combined Thoracic Index sums the the probability that the cyclist suffers AIS ≥ 3 and AIS ≥ 5 ribs and skin deflection, measured on cadavers using chest injuries is 99.23% and 43.22%, respectively, for case A.1. bands. However, the chest deflections measured on the For case B.1, the probabilities are 99.58% and 55.77%, dummy represent only the internal chest deflections of the respectively. ribs. Thus, the combined thoracic injury criteria, CTI, is defined with the following equation 3.3. Comparison between Case A.2 and Case B.2. For the case in which the car moves at 50 km/h, Figure 9 shows the kine- A D max max matics of cyclists in cases A.2 and B.2, while Table 6 shows CTI = + , ð2Þ A D int int the corresponding HIC and CTI values. Finally, Figure 10 6 Applied Bionics and Biomechanics t = 752.0 ms. t = 2000 ms. t = 0.0 ms. (a) (b) (c) Permanent deformation = 3 mm 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Time (ms) (d) Figure 4: Front scissors’ deformation: (a) initial position of the frame drop test; (b) moment before impact; (c) maximum permanent deformation position; (d) longitudinal displacement of the center of the front scissors’ axis for the frame drop test. shows the required parameters to assess head and thorax allowed by the Federal Motor Vehicle Safety Standards injury severity at 50 km/h. (FMVSS) [26, 27], and the injuries that the cyclist may have By using the results of the Combined Thoracic Index ranged from moderate to minor. acceleration of the chest center of gravity as well as chest By using the results of the Combined Thoracic Index deflection during a traffic accident, it is possible to know acceleration of chest center of gravity as well as chest deflec- tion during a traffic accident, it is possible to know the prob- the probability that the cyclist suffers AIS ≥ 3 and AIS ≥ 5 injuries is 94.72% and 13.23%, respectively, for case A.2. ability that the cyclist suffers AIS ≥ 3 and AIS ≥ 5 injuries is For case B.2, the probabilities are 97.37% and 21.54%, 97.79% and 24.09%, respectively, for case A.3. For case B.3, respectively. the probabilities are 80.77% and 4.48%, respectively. By obtaining the resulting acceleration graph at the cen- ter of gravity of the cyclist’s head in both cases, it is possible 4. Discussion to know that the HIC15 parameter is 1510 for case A.2, while for case B.2, it is 1282. This difference is because there It shows that the kinematics of the cyclist during impact is is less acceleration in the center of gravity of the cyclist’s quite similar to the results obtained in the present work, as head. After all, the safety device modifies the cyclist’s kine- shown in Figure 14. In addition, the HIC parameters for matics during a collision, causing that the head hits closer cases of 50 km/h and 40 km/h are quite similar when pre- to the center of the vehicle’s windshield, as shown in senting only 9.32% and 6.09% errors, respectively, compared Figure 11(b), which is less rigid than the contour. to their tests. Only when the impact is at 60 km/h, the results differ from each other. It can be explained due to the differ- 3.4. Comparison between Case A.3 and Case B.3. For the case ent geometry between the fronts of the vehicles used because in which the car moves at 40 km/h, Figure 12 shows the the cyclist’s head hits a higher area of the windshield at this cyclist’s kinematics in cases A.3 and B.3, while Table 6 shows speed, which has a higher stiffness, which significantly the corresponding HIC and CTI values. Finally, Figure 13 increases HIC. On the other hand, Raslavicius et al. use shows the required parameters to assess head and thorax a multibody solver, while this work uses a finite element injury severity at 50 km/h. model that can make specificdifferences in body deforma- The HIC and the Abbreviated Injury Scale (AIS) correla- tions in contact during impact [7]. The results obtained tion is estimated life-threatening without the passive security are steady with the severity of the literature’s injuries by system. On the other hand, with the device being installed, agreeing that this crash scenario generates severe or fatal the results show that HIC15 turns out to be close to the limit injuries [8, 28]. Displacement (mm) Applied Bionics and Biomechanics 7 t = 0.3 s t = 0.5 s (a) (b) –10 –20 Permanent deformation = 16.7 mm –30 –40 –50 –60 0 200 400 600 800 1000 1200 1400 Time (ms) (c) Figure 5: Frame deformation: (a) frame contact with impactor; (b) moment after contact with impactor (maximum permanent deformation); (c) longitudinal displacement of the center of the front scissors’ axis for frame impact safety test. Table 6: Evaluation of HIC 15 and CTI with and without a passive safety system. Velocity Case HIC15 AIS head CTI AIS chest AIS ≥ 6 AIS ≥ 5=55:77% 60 km/h A.1 3325 1.933 60 km/h B.1 2605 AIS ≥ 5 2.03 AIS ≥ 5=43:22% AIS ≥ 5 AIS ≥ 5=21:54% 50 km/h A.2 1510 1.62 50 km/h B.2 1282 AIS ≥ 4 1.73 AIS ≥ 5=13:23% AIS ≥ 4 AIS ≥ 5=24:09% 40 km/h A.3 1208 1.76 40 km/h B.3 730 AIS ≥ 3 1.39 AIS ≥ 5=4:48% closer to the windscreen center due to the same principle of deformation energy density, being less rigid, reducing Figure 6: The head and thorax accelerometer location. the possible severity of craniocerebral injuries. It can be seen that the rate of craniocerebral injury for the scenario with the passive safety device installed on the bicycle is consider- ably lower, which influences the probability and severity of The vehicle model used in this work was validated under the various front and lateral impact tests [20], the dummy the injury, going from being incompatible with survival to having a chance of survival. However, with critical and non- model was provided by Livermore Software Technology Corporation, and the bicycle was validated according to reversible injuries, a skull fracture is presented, with a loss of consciousness for more than 24 hours, and intracranial the Mexican Standards nmx-d-198-2-1985 and nmx-d-198- hemorrhage occurs. In the case of the thorax injuries, the 3-1985. A bumper placed at the bicycle’s rear mitigates injuries two cases’ probabilities are similar since it is estimated that there will be a fracture of multiple ribs in both cases. Like- caused by the vehicle’s impact on the cyclist and absorbs wise, there is a 43.22% and 57.77% probability in cases A.1 kinetic energy due to the impact. The system is also useful and B.1, respectively, of complex thoracic injuries with for changing the body’s kinematics. The head hits an area Displacement (mm) 8 Applied Bionics and Biomechanics t = 0.00 ms t = 0.00 ms t = 60 ms t = 60 ms t = 110 ms t = 110 ms t = 143 ms t = 143 ms (a) (b) Figure 7: Impact on a cyclist on the overtaking stage at 60 km/h without a passive safety system (a) and with a passive safety system (b). 200.0 150.0 100.0 50.0 0.0 0.0 50.0 100.0 0 50 100 Time (ms) Time (ms) A.1 A.1 B.1 B.1 (a) (b) –5 –10 –15 –20 –25 0 50 100 150 Time (ms) A.1 B.1 (c) Figure 8: (a) Acceleration in the head and HIC’s gravity center at a speed of 60 km/h. (b) Acceleration of chest gravity center in G’sata speed of 60 km/h. (c) Chest deflection in mm during a traffic accident at a speed of 60 km/h. respiratory difficulty, production of massive hemothorax, referred to in the tables since, due to the setup of the hit- and cardiac rupture or contusion, which fall into the cate- and-run scenarios, and the left lower limb always presents gory of critical injuries with uncertain survival. For the lower injuries far below those generated in the right limb. Both limbs, it is essential to mention that only the right limb is hit and run cases show similar results, where there is a Head acceleration (G′s) Chest deflection (mm) Chest acceleration (G′s) Applied Bionics and Biomechanics 9 t = 0.00 ms t = 0.00 s. t = 80 ms t = 80 ms t = 110 ms t = 130 ms t = 163 ms t = 163 ms (a) (b) Figure 9: Cyclist overtaking impact at 50 km/h without a passive safety system (left) and with a passive safety system (right). 0 0 0 100 0 50 100 150 Time (ms) Time (ms) A.2 A.2 B.2 B.2 (a) (b) 0 50 100 150 –5 –10 Time (ms) –15 A.2 B.2 (c) Figure 10: (a) Acceleration of head gravity center and HIC at a speed of 50 km/h. (b) Acceleration of chest gravity center in G’s at a speed of 50 km/h. (c) Chest deflection in mm during the accident at a speed of 50 km/h. probability of less than 50% of presenting a nondisplaced frac- although this probability is lower when the bicycle has a pas- ture of the femur, an injury categorized as moderate on the sive safety device installed. There are injuries to the cyclist’s AIS scale. In comparison, the probability of presenting an right tibia; injuries, show an AIS = 2 level injury will undoubt- exposed fracture of this bone is less than 20% in both cases, edly occur, indicating a fracture of this bone due to the impact. Head acceleration (G′s) Chest deflection (mm) Chest acceleration (G′s) 10 Applied Bionics and Biomechanics 319.35 mm 269.62 mm (a) (b) Figure 11: Cyclist’s head windshield contact at the vehicle. (a) No passive safety device (b) with a passive safety device. t = 0.00 s t = 0.00 ms t = 100 ms t = 100 ms t = 170 ms t = 170 ms t = 238 ms t = 238 ms (a) (b) Figure 12: Cyclist overtaking impact at 40 km/h without a passive safety system (a) and passive safety system (b). The results show the craniocerebral injury rate for the is estimated that in both cases, there will be a fracture of scenario with the passive safety device fitted to the bicycle multiple ribs, with a probability of practically 100% of pre- is again considerably lower, classified on the AIS-4, which senting an AIS = 3 level injury; likewise, there is a 13.23% is severe, but with probable survival, where cranioencephalic and 21.54% probability in cases A.2 and B.3, respectively, trauma with or without fractures may occur, accompanied with a 13.23% and 21.54% probability of presenting an by unconsciousness and neurological signs such as posttrau- AIS = 3 level injury, respectively. Moreover, case B.3, respec- matic amnesia for 3-12 hours. On the other hand, the most tively, has a 13.23% and 21.54% probability of AIS = 5 tho- likely injuries when the bicycle does not have a passive safety racic injuries, complex injuries with respiratory difficulty, device are categorized at AIS = 5 level, critical injuries where production of massive hemothorax, and cardiac rupture or survival is uncertain. In the case of injuries to the thorax, the contusion, which fall into the category of critical injuries with probabilities between the two cases are again similar, since it uncertain survival [29, 30]. For the lower limbs, in this case, Applied Bionics and Biomechanics 11 0 50 100 150 200 250 0 50 100 150 200 250 Time (ms) Time (ms) A.3 A.3 B.3 B.3 (a) (b) 0 50 100 150 –1 –2 –3 –4 –5 –6 Time (ms) A.3 B.3 (c) Figure 13: (a) Head acceleration in the center of gravity and HIC at a speed of 40 km/h. (b) Chest acceleration in G’s at a speed of 40 km/h. (c) Chest deflection in mm during the accident at a speed of 40 km/h. (2) (1) (1) (2) (3) (4) (3) (4) (a) (b) Figure 14: Cyclist’s kinematics during an overtaking crash. (a) MADYMO run-over simulation; (b) FEM simulation. there is a considerable difference in the probability of injury The results the tables have shown are again considerably to the cyclist’s right femur, since in the case where the bicycle lower, which influences the likelihood and severity of the does not have the safety device installed, the probability of injury, being categorized on the AIS scale as level 3 injuries suffering a nondisplaced fracture is 8.18%. that are serious but not life-threatening and are fully revers- In comparison, if the device is installed, the probability ible, although hospitalization is necessary. On the other increases to 28.4%. In presenting an exposed fracture in this hand, the most likely injuries when the bicycle is not fitted bone, the probability remains less than 20% in both cases, with the passive safety device are categorized at AIS level 4, although it is higher when the bicycle has a passive safety severe, life-threatening injuries, but with probable survival. device installed. The cyclist’s right tibia shows an AIS = 2, In the case of injuries to the thorax, the probabilities between which indicates the fracture of this bone due to the impact. the two cases show a more significant variation than in the Head acceleration (G′s) Chest deflection (mm) Chest acceleration (G′s) 12 Applied Bionics and Biomechanics is the change in the severity of the injury due to the use of previous cases, since the probability of suffering an ASI = 3 or greater injury for the case where the bicycle does not have bicycle helmets during vehicular accidents. The characteris- the passive safety device installed is very close to 100% tics and operation of a bicycle helmet do not significantly (97.79). In contrast, if the bicycle does have this device impact the cyclist’s kinematics during the accident until installed, the probability decreases to 80.77%. The same the cyclist’s head comes into contact with the car [31, 32]. pattern is observed in the probability of suffering injuries ASI = 5 or greater, where case A.3 has 24.09%, while case 5. Conclusions B.1 has 4.48%. For the lower limbs, specifically the cyclist’s right femur, the results between both cases are again quite The passive safety device significantly reduced the severity of similar, approaching the null probability of injury to the craniocerebral injuries by decreasing the magnitude of the femur, whether AIS = 2 or AIS = 3, with a variation of no HIC index by 775, 228, and 478 points for impact speeds more than 2% between the results and a percentage of injury of 60 km/h, 50 km/h, and 40 km/h, respectively. The passive of less than 5%. In the case of cyclist’s right tibia, the results safety device’s use did not significantly reduce the severity of again show that an AIS = 2 level injury will occur, which thoracic injuries at high speeds (60 km/h and 50 km/h); indicates the fracture of this bone injury is a consequence however, it did reduce them at low speeds (40 km/h) by of the impact since the percentage of presenting this injury obtaining a 19.61% less of the probability of suffering an remains at the same value as the previous cases with a injury, presenting an AIS ≥ 5 injury when using the device. 100% probability of fracture. The forces applied to the cyclist’s femur indicated a 28.4% For the cranioencephalic injuries generated in the greater variation in the probability of sustaining an AIS ≥ 2 accident, in all cases where the passive safety device was injury when using the passive safety device. In conclusion, used, the HIC index decreased considerably, reducing the the design fulfilled its primary function by reducing the severity of the injuries by one level according to the AIS severity of cranioencephalic injuries to one level in the AIS scale. However, the impact of this is not minor, as it has system in all cases, which implies the significant decrease several implications. in risk of death by cranioencephalic trauma, especially at low-speed cases in this particular run-over scenario, because (1) In cases where a cyclist is hit at a speed of 60 km/h, this type of injury is the one with the highest risk of mortality the device’s use can reduce the likelihood of injury for cyclists. to such a degree that survival is possible, which is not the case where the device is not fitted Data Availability (2) For the 50 km/h cases, the use of the device can The data used to support the findings of this study are avail- reduce the probability of injury, compared to the able from the corresponding author upon request. results obtained for the run-over cases where the device is not installed, so that the expected injuries correspond to the ASI = 4 level, where survival is Conflicts of Interest likely, as opposed to the AIS = 5 level, where the The authors declare that there is no conflict of interest injuries generated are critical regarding the publication of this paper. (3) In a collision at a speed of 40 km/h, the injuries gen- erated on the cyclist, when using the passive safety Acknowledgments device, are reduced to an AIS = 3 level, where the cyclist’s life is not at risk, although the injuries are The authors acknowledge the financial support for the real- categorized as severe, whereas without the device, ization of this work of the Mexico Government by Consejo the injuries grow to an AIS = 4 level, where the per- Nacional de Ciencia y Tecnología (CONACyT) and the son is likely to die Instituto Politécnico Nacional (IPN). The authors also thank the support of project 20210282 and EDI grant, all by The first limitation of this work is the dummy model SIP/IPN. used. A pedestrian dummy for the collision model was mounted on the bicycle and then used to report the injuries References as a vulnerable road user. For this reason, it is important to corroborate the results with a specific case of the study by [1] WHO, “OMS|10 datos sobre la seguridad vial en el mundo,” means of MADYMO® models. Another limitation of this November 2018, http://www.who.int/features/factfiles/ work is the possibility of using THUMS® anthropomorphic roadsafety/es/. dummies to determine the state of stress and deformation [2] M. Peden, “Informe mundial sobre prevención de los trauma- of soft tissue and hard tissue. Finally, the most critical limi- tismos causados por el tránsito Informe mundial sobre preven- tation is the lack of other experimental dummies to report ción de los traumatismos,” in Informe mundial sobre similar injuries on vulnerable road users. 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[22] Dirección General De Normas, Nmx-d-198/2-1985, “autotran- sporte - bicicletas – especificaciones,” 1985, https://docplayer .es/85390565-Nmx-d-198-autotransporte-bicicletas-metodos- de-prueba-autotransport-bicycles-test-methods.html. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Bionics and Biomechanics Hindawi Publishing Corporation

Numerical Assessment of a Safety System to Minimize Injuries during a Cyclist Run-Over

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Copyright © 2021 E. H. López-García et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Hindawi Applied Bionics and Biomechanics Volume 2021, Article ID 9922210, 13 pages https://doi.org/10.1155/2021/9922210 Research Article Numerical Assessment of a Safety System to Minimize Injuries during a Cyclist Run-Over 1 1 2 E. H. López-García , M. F. Carbajal-Romero , J. A. Flores-Campos , and C. R. Torres-SanMiguel Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica Sección de Estudios de Posgrado e Investigación, Azcapotzalco, 02519 CDMX, Mexico Instituto Politécnico Nacional, Unidad Profesional Interdisciplinaria en Ingeniería y Tecnologías Avanzadas, 07340 CDMX, Mexico Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica Sección de Estudios de Posgrado e Investigación, Zacatenco, 07738 CDMX, Mexico Correspondence should be addressed to C. R. Torres-SanMiguel; ctorress@ipn.mx Received 19 March 2021; Revised 18 July 2021; Accepted 11 August 2021; Published 27 August 2021 Academic Editor: Wen-Ming Chen Copyright © 2021 E. H. López-García et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. The World Health Organization has reported that 1.35 million people die on the roads every year due to road traffic accidents. This paper focuses on exploring a passive safety system that reduces lesions in the overtaking run-over scenario. Methods. Head Injury Criterion (HIC) and Combined Thoracic Index (CTI) were evaluated through numerical simulations using LS-Dyna®; in order to compare the computed results, three different speed scenarios were carried out (velocity of running over 40, 50, 60 km/h). Results. The computed results were divided into groups, A for the run-over test without a passive security system and B for the run-over test with a passive security system. For case A.1, the HIC15 was 3325. For case A.2, the HIC15 was 1510, and for case A.3, the HIC 15 was 1208. For case B.1, the HIC15 2605, for case B.2, the HIC15 was 1282, and for case B.3, the HIC was 730. Conclusion. The comparative results show that the passive safety system installed on the bicycle has an increased benefit impact on the severity of the injury on vulnerable road users, decreasing the probability of cranioencephalic lesions in all study cases. In addition, the thorax injuries are cut down only in the impact scenario at a speed of 40 km/h. 52,000 in 2013 [2]. In the United States, 783 cases of cyclist 1. Introduction deaths due to motor vehicle crashes were reported in 2017 The World Health Organization (WHO) reported 1.35 mil- [4], while in Mexico, the cases of death of cyclists in road lion deaths in a year due to road traffic crashes [1]. This accidents totaled 199 in the same year [5]. The cyclist run- problem was the leading cause of death in people between over scenarios can be identified according to different char- 15 and 29 years in 2012 [2]. A specific group called vulner- acteristics. The Pedestrian and Bicycle Crash Analysis Tool able road users (VUR) that include motorcyclist, cyclist, (PBCAT) distinguishes around 79 scenarios that consider and pedestrians are exposed to a greater danger during their different factors such as the vehicle’s position before the circulation inroads because they do not have any structure impact, the direction in which one respects the other, and that protects them from a road accident and is more suscep- the impact causes [6]. The scenario reported a greater prob- ability of cyclist death, where the motor vehicle is moving in tible suffer severe or deadly injuries [3]. The cyclist run-over is the smallest group among all road accidents, representing the same direction as the cyclist and the bicycle is reached in 4% of the victims. Although the numbers of deaths due to the rear side by the front of the car; this scenario is called the the cyclist run-over are a few, it was informed around overtaking scenario [7, 8]. Also, in National Highway Traffic 2 Applied Bionics and Biomechanics Safety Administration (NHTSA) in the database called Table 1: Characteristics of run-over tests. Fatality Analysis Reporting System (FARS) from 2008 to Case A.1 2012, the crash scenario that presented the highest death rate Automobile speed Cyclist speed of the cyclist in the United States is the overtaking crash sce- nario [9], repeating this trend in subsequent years until 60 km/h 0 km/h 2017, which is the last update. It is essential to consider the Case A.2 Group A (without passive type of motor vehicle studied because this directly affects Automobile speed Cyclist speed security system) the severity of the injury that a cyclist can present since its 50 km/h 0 km/h geometric characteristics alter the VUR kinematics. The data Case A.3 issued by the NHTSA show that passenger cars have the sec- Automobile speed Cyclist speed ond place in deaths caused to cyclists [10–12]. In different 40 km/h 0 km/h industrial designs, existing systems are used to decrease inju- ries in vulnerable road users, as shown below: the patent [13] Case B.1 presents a bumper used in children’s bicycles that has the Automobile speed Cyclist speed function of attenuating the frontal collision in front of any 60 km/h 0 km/h surface to protect the bicycle upon impact and reduce the Case B.2 impact force and protect the user. Similarly, the patent Group B (with passive Automobile speed Cyclist speed [14] presents a pneumatic bumper with an internal chamber security system) 50 km/h 0 km/h that stores air, which is released controlled when the front Case B.3 and rear parts of the bumper cushion impact. Also, the device [15] is designed to be used in motor vehicles. It has Automobile speed Cyclist speed two subsystems, an impact mitigation device placed in the 40 km/h 0 km/h front of the vehicle, responsible for absorbing minor impacts that do not exceed the material’s yield point, and an internal bumper that deforms plastically and absorbs the impact Bicycle and cyclist position was proposed before the energy. The patent [16] consists of a U-shaped bumper vehicle’s impact to measure injuries generated under the joined at the motorcycle to protect the vehicle structure from cyclist’s head. The initial position before impact can be seen possible shocks. The device [17] is a rigid structure installed in Figure 1. on the front or rear of a bicycle to protect the damage by an Three meshed models corresponding to the vehicle, bicy- impact. Finally, the patent [18] shows a bumper placed on cle, and cyclist were used, described in detail below. The auto- the rear wheel of the bicycle, serving as a support for a light mobile model consists of a meshed geometry compatible with source projected towards the ground, marking the minimum the Ls-Dyna® software of a Toyota Yaris 2010, developed by safe distance for the circulation of the cyclist to prevent road George Mason University, contracted by the Federal Highway accidents caused by the lack of vision towards the cyclist. Administration (FHWA). This model has validations under The research is aimed at proposing a framework used to the various frontal and lateral impact tests and a substantial perform vehicle-bicycle crash simulations to investigate the barrier impact [20]. The anthropomorphic virtual dummy effects of the rear rubber bumper on cyclist injuries. The used during the simulations to represent the cyclist run-over novelty is the rear passive safety system rubber bumper scenario corresponds to a male Hybrid III percentile 50th, and the numerical analysis carried out. The modeling developed by the Livermore Software Technology Corpora- methods used to predict biomechanical responses for run- tion, developing the LS-Dyna® software. The bicycle model over simulations are well-established and can help predict was developed in the SolidWorks® Computer-Aided Design biomechanical response in this scenario. A sedan vehicle (CAD) software to later export the geometry to the LS- was chosen for this study due to its high commercial Dyna® software, where it proceeded to mesh and configure demand and its incidence in cyclists’ road accidents. In addi- the corresponding contacts and joints. The bicycle frame was tion, the head and chest lesions suffered by the cyclist are based on the Bicyclist and bike targets specifications manual evaluated since those are the body’s main region that causes version 1.1, developed by CATS/4a companies, to provide a person’s death in run-over scenarios. the necessary specifications of a cyclist objective vehicle detec- tion tests. This research used the size of bicycles for an average man in the Dutch population [21]. The characteristics of the 2. Materials and Methods vehicle, dummy, and bicycle model are shown in Table 2. The bicycle frame and wheel discretization were made Three cyclists’ crash impact simulations were carried out using the finite element method by Ls-Dyna® Software, with shell elements. The element type used in the model through a detailed analysis due to the high nonlinearities, was quadrangular elements with 4 nodes, and we used the the inertial components, and the short duration of the mesh algorithm provided by the LS-PrePost® software to phenomenon. All the simulations are carried out in the create a preliminary mesh, then carried out a manual mesh refinement process to achieve a high mesh quality, especially overtaking crash scenario, where the car impacts the bicy- cle’s rear wheel while the bicycle and the vehicle are in the in areas of interest of the model, where correct discretization same direction [19]. The characteristics for each case of is critical for the reliability of the results. To ensure that the run-over are described in Table 1. quality of the mesh was acceptable, mesh quality checks Applied Bionics and Biomechanics 3 Figure 1: Initial position cyclist/automobile. aligned with the centers of the wheels [22]. Therefore, the Table 2: Toyota Yaris 2012 and Hybrid III 50th percentile characteristics [20, 21]. parameters necessary for the bicycle frame to be considered safe must meet two conditions: Model characteristics Yaris 2012 Hybrid 50th Bicycle Number of parts 919 115 12 (i) The frame must not suffer any visible fracture [22] Number nodes 393165 7353 53314 (ii) The permanent deformation measured between the Number of solid elements 15234 2644 — wheel axles’ centers must not exceed 40 mm [22] Number of shell elements 358457 1606 56724 Figure 2 shows the diagram for the frame drop safety test Number of beam elements 4685 3 — and frame impact safety test. Number of restriction joints 19 48 — 2.1. Passive Safety Device. The strain energy density influ- ences the severity of cyclist’s injuries. This property quan- shown in Table 3 were carried out, where it was observed tifies the stored and dissipated energy in a material when it that the mesh of the bicycle parts had a good quality, espe- suffers a deformation. This energy is quantified from the dif- cially in critical areas for the results. ferent parts of the virtual dummy that represents the cyclist’s The LS-Dyna® software has a large number of material body. Therefore, the passive safety device seeks to dissipate models used for different applications. For this research, to the most significant deformation energy before the cyclist’s represent the behavior of the metallic parts, bicycle, and body hits the car’s surface. The graphic method of material the passive safety device, we used the MAT_PIECEWISE_ selection is used, also called the Ashby method [24]. LINEAR_PLASTICITY model. The material selected for The device was based on automotive bumpers systems the bicycle frame was AISI 4130 steel, a common material consisting of a frame, an energy absorber, and a plastic fas- for bicycle frames. In order to properly simulate impact cia. A passive safety system was designed, consisting of a behavior, the material’s linear and nonlinear mechanical frame made of ASIS 201 stainless steel and a polyurethane properties are needed to be configured appropriately within rubber elastic energy absorption system. These materials LS-PrePost®. Table 4 shows the parameters necessary to were chosen due to their high capacity to absorb impact define those mechanical properties. energy. The frame part is responsible for absorbing the most The bicycle frame was validated through the tests outstanding amount of plastic deformation energy from described in Mexican Standards nmx-d-198-2-1985 and being run over by a vehicle. In contrast, the polyurethane nmx-d-198-3-1985, specifically in points 4.3.1 and 4.3.2 cor- rubber parts seek to protect minor impacts by absorbing responding to the mass impact test in frame-scissor assem- the most significant elastic deformation energy. The assem- bly and drop of the frame-scissor assembly, respectively, bly of the system is carried out through arrangements of which were performed in LS-Dyna®. The frame drop safety nuts and screws. The system dimensions were established test consists of fixing the frame’s rear axle, then a mass for the bumper’s average height, which was used to place (M1) of 70 kg must be fixed on the seat post, and the assem- the bicycle’s passive safety system. Since the average height bly is dropped on a steel anvil [22]. The conditions necessary of a vehicle’s bumper is 500 mm [25], the system must be for the bicycle frame to be considered safe are as follows: placed within this measurement. Figure 3 shows how the passive safety system is mounted on a bicycle. (i) The frame must not suffer any visible fracture [22] The passive safety device’s frame was discretized simi- larly to the bicycle’s frame by using shell elements to opti- (ii) The permanent deformation measured between the mize computational resources without sacrificing accuracy. initial and final position of the center of the front Mesh quality check results are shown in Table 2. The mate- axle of the wheel must not exceed 60 mm [22] rial model was again MAT_PIECEWISE_LINEAR_PLAS- In the frame impact safety test, a mass (M) of 22.5 kg was TICITY due to the characteristics already described; the dropped from a height (a) of 180 mm and hit the front part mechanical properties necessary to simulate the correct 4 Applied Bionics and Biomechanics Table 3: Mesh quality checks for bicycle and passive security system model. Acceptable Percentage of valid Percentage of valid Variable Definition value elements elements The ratio between the largest and smallest Aspect ratio <10 99.76% 99.86% dimensions of an element Skewness Angular deviation of the element from an ideal shape <45 97.51% 99.95% The angle between the normal two planes is formed by Warp angle <100 99.36% 99.46% split the quadrilateral element along the diagonals Table 4: Mechanical properties of AISI 4130 and AISI 201 Steel. Material Mass density. (Ton/mm ) E (MPa) Poisson’s ratio σ (MPa) σf (MPa) εe nE (MPa) YS R f t 7:850 × 205 × 10 0:29 460:00 914:481 0:224 0:1456 2:48 AISI 4130 −9 3 0:27 360:00 1377:5 :03715 0:2099 2:61 AISI 201 7:810 × 10 200 × 10 E = Young s modulus; σ = yield stress; σf = true fracture stress; εe = true fracture strain; n = strain hardening exponent; E = tangent modulus. YS R f t Figure 2: Frame drop safety test and frame impact safety test [23]. impact behavior are shown in Table 3. In polymer blocks, imum deformation was 3 mm, indicating that this value is the MAT_MOONEY-RIVLIN_RUBBER model specialized established by the standard on which the tests are based. in this group of materials was used. The mechanical proper- The axis deformation at the front scissors was measured ties necessary to simulate the behavior of this part of the pas- at the maximum position when the impactor is not in con- sive safety device are shown in Table 5. tact with the bicycle’s frame to measure the permanent deformation in it. Figure 5 shows the stages of the frame impact test and the results where the permanent deforma- 3. Results tion (without load) presented in the frontal part of the frame was 16.7 mm, being within the tolerable limits of permanent deformation indicated by the standards on which the simu- The safety framework tests were carried out to bring the fol- lowing results. First, the front scissors’ axis’s deformation lations are based. was measured at the maximum position upon reaching rest (at time t = 2000 ms) against the position instants before hit- 3.1. Vehicle-Cyclist Impact Simulations. Bodily, the injuries ting the rigid wall (at time t = 752:0 ms). Figure 4 shows the happen when its resistance exceeds the withstand energy. stages of the frame drop test and the results, where the max- Thus, for an object to lose speed, its energy of motion must Applied Bionics and Biomechanics 5 Support plate Polymer block Rigid frame Polymer block Mounting plates Support plate Figure 3: Passive security system fixed to the bicycle. Table 5: Mechanical properties of polyurethane rubber with be transferred to another object. This transfer of energy also Mooney-Rivlin formulation. occurs in the case of an accident in the human body. The kinetic energy dissipated during the cyclist’s collision is 3 Mass density (Ton/mm ) Poisson’s ratio AB transformed into the structure deformation, leaving less 1:20 × 0:27 1:24 0:01 residual energy to be absorbed for the mechanical properties of the hard and soft tissue. The dispersion of kinetic energy, A and B are the constants of the Mooney-Rivlin constitutive equation for rubber. In the case of polyurethane rubber, the corresponding coefficients both in space and in time, is determinant in reducing the are A =1:24 and B =0:01 [26]. severity of injuries and can make the difference between sur- viving and not. The most severely injured body areas are the where A is the maximum value of 3 ms clip spinal accel- head and thorax. In this research, Head Injury Criterion max eration (As), D is the maximum value of the dummy (HIC) and Combined Thoracic Index (CTI) determine the max deflection (D), and A and D are the respective intercepts energy generated during the cyclist’s collision. These injury int int as defined above. rates are calculated according to the following equations. The dummy used has accelerometers in different parts of A suitable measurement to scale the possible cranioence- the body. For example, the accelerometer location in the phalic injuries is used the HIC. This criterion reflects the head is at node 133919, while that of the thorax is node change in acceleration that the passenger’s head undergoes 135705, shown in Figure 6. Those nodes measure the accel- moments after the collision. The calculation is performed by erations, and the LSDyna software calculates the HIC and selecting the maximum limits of integration of the area under CTI reached during the run-over. the acceleration curve. NHTSA and AAMA (American Asso- This section shows the results of simulations performed ciation of Medical Assistants) have established a time interval with the characteristics mentioned in Table 6, evaluating of 15 milliseconds after the impact. This interval favors the the cyclist’s head injuries HIC and the CTI index for chest reduction of the HIC calculation error. In addition, this value injuries. The simulation results were compared in two cases provides a more rigorous measurement of injury probability. with the same vehicle’s same speed but with and without a () passive safety system to observe the injuries differences. 2:5 HIC = ðÞ t2 − t1 atðÞdt : ð1Þ t2 − t1 3.2. Comparison between Case A.1 and Case B.1. For the case in which the car moves at 60 km/h, Figure 7 shows the kine- matic of the cyclist in cases A.1 and B.1, while Table 6 shows HIC uses t2 and t1 as a period of deceleration curve, a is the corresponding HIC and CTI values. Finally, Figure 8 the acceleration, and t is the total period of the curve. In order shows the required parameters to assess head and thorax to determine a HIC value, it is necessary to obtain the velocity injury severity at 60 km/h. and acceleration of the body at the moment of impact. There- By using the results of the Combined Thoracic Index fore, the dummy’s dimensional characteristics are crucial to acceleration of the chest center of gravity as well as chest establish a way to generate such kinematic parameters. deflection during a traffic accident, it is possible to know Additionally, the Combined Thoracic Index sums the the probability that the cyclist suffers AIS ≥ 3 and AIS ≥ 5 ribs and skin deflection, measured on cadavers using chest injuries is 99.23% and 43.22%, respectively, for case A.1. bands. However, the chest deflections measured on the For case B.1, the probabilities are 99.58% and 55.77%, dummy represent only the internal chest deflections of the respectively. ribs. Thus, the combined thoracic injury criteria, CTI, is defined with the following equation 3.3. Comparison between Case A.2 and Case B.2. For the case in which the car moves at 50 km/h, Figure 9 shows the kine- A D max max matics of cyclists in cases A.2 and B.2, while Table 6 shows CTI = + , ð2Þ A D int int the corresponding HIC and CTI values. Finally, Figure 10 6 Applied Bionics and Biomechanics t = 752.0 ms. t = 2000 ms. t = 0.0 ms. (a) (b) (c) Permanent deformation = 3 mm 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Time (ms) (d) Figure 4: Front scissors’ deformation: (a) initial position of the frame drop test; (b) moment before impact; (c) maximum permanent deformation position; (d) longitudinal displacement of the center of the front scissors’ axis for the frame drop test. shows the required parameters to assess head and thorax allowed by the Federal Motor Vehicle Safety Standards injury severity at 50 km/h. (FMVSS) [26, 27], and the injuries that the cyclist may have By using the results of the Combined Thoracic Index ranged from moderate to minor. acceleration of the chest center of gravity as well as chest By using the results of the Combined Thoracic Index deflection during a traffic accident, it is possible to know acceleration of chest center of gravity as well as chest deflec- tion during a traffic accident, it is possible to know the prob- the probability that the cyclist suffers AIS ≥ 3 and AIS ≥ 5 injuries is 94.72% and 13.23%, respectively, for case A.2. ability that the cyclist suffers AIS ≥ 3 and AIS ≥ 5 injuries is For case B.2, the probabilities are 97.37% and 21.54%, 97.79% and 24.09%, respectively, for case A.3. For case B.3, respectively. the probabilities are 80.77% and 4.48%, respectively. By obtaining the resulting acceleration graph at the cen- ter of gravity of the cyclist’s head in both cases, it is possible 4. Discussion to know that the HIC15 parameter is 1510 for case A.2, while for case B.2, it is 1282. This difference is because there It shows that the kinematics of the cyclist during impact is is less acceleration in the center of gravity of the cyclist’s quite similar to the results obtained in the present work, as head. After all, the safety device modifies the cyclist’s kine- shown in Figure 14. In addition, the HIC parameters for matics during a collision, causing that the head hits closer cases of 50 km/h and 40 km/h are quite similar when pre- to the center of the vehicle’s windshield, as shown in senting only 9.32% and 6.09% errors, respectively, compared Figure 11(b), which is less rigid than the contour. to their tests. Only when the impact is at 60 km/h, the results differ from each other. It can be explained due to the differ- 3.4. Comparison between Case A.3 and Case B.3. For the case ent geometry between the fronts of the vehicles used because in which the car moves at 40 km/h, Figure 12 shows the the cyclist’s head hits a higher area of the windshield at this cyclist’s kinematics in cases A.3 and B.3, while Table 6 shows speed, which has a higher stiffness, which significantly the corresponding HIC and CTI values. Finally, Figure 13 increases HIC. On the other hand, Raslavicius et al. use shows the required parameters to assess head and thorax a multibody solver, while this work uses a finite element injury severity at 50 km/h. model that can make specificdifferences in body deforma- The HIC and the Abbreviated Injury Scale (AIS) correla- tions in contact during impact [7]. The results obtained tion is estimated life-threatening without the passive security are steady with the severity of the literature’s injuries by system. On the other hand, with the device being installed, agreeing that this crash scenario generates severe or fatal the results show that HIC15 turns out to be close to the limit injuries [8, 28]. Displacement (mm) Applied Bionics and Biomechanics 7 t = 0.3 s t = 0.5 s (a) (b) –10 –20 Permanent deformation = 16.7 mm –30 –40 –50 –60 0 200 400 600 800 1000 1200 1400 Time (ms) (c) Figure 5: Frame deformation: (a) frame contact with impactor; (b) moment after contact with impactor (maximum permanent deformation); (c) longitudinal displacement of the center of the front scissors’ axis for frame impact safety test. Table 6: Evaluation of HIC 15 and CTI with and without a passive safety system. Velocity Case HIC15 AIS head CTI AIS chest AIS ≥ 6 AIS ≥ 5=55:77% 60 km/h A.1 3325 1.933 60 km/h B.1 2605 AIS ≥ 5 2.03 AIS ≥ 5=43:22% AIS ≥ 5 AIS ≥ 5=21:54% 50 km/h A.2 1510 1.62 50 km/h B.2 1282 AIS ≥ 4 1.73 AIS ≥ 5=13:23% AIS ≥ 4 AIS ≥ 5=24:09% 40 km/h A.3 1208 1.76 40 km/h B.3 730 AIS ≥ 3 1.39 AIS ≥ 5=4:48% closer to the windscreen center due to the same principle of deformation energy density, being less rigid, reducing Figure 6: The head and thorax accelerometer location. the possible severity of craniocerebral injuries. It can be seen that the rate of craniocerebral injury for the scenario with the passive safety device installed on the bicycle is consider- ably lower, which influences the probability and severity of The vehicle model used in this work was validated under the various front and lateral impact tests [20], the dummy the injury, going from being incompatible with survival to having a chance of survival. However, with critical and non- model was provided by Livermore Software Technology Corporation, and the bicycle was validated according to reversible injuries, a skull fracture is presented, with a loss of consciousness for more than 24 hours, and intracranial the Mexican Standards nmx-d-198-2-1985 and nmx-d-198- hemorrhage occurs. In the case of the thorax injuries, the 3-1985. A bumper placed at the bicycle’s rear mitigates injuries two cases’ probabilities are similar since it is estimated that there will be a fracture of multiple ribs in both cases. Like- caused by the vehicle’s impact on the cyclist and absorbs wise, there is a 43.22% and 57.77% probability in cases A.1 kinetic energy due to the impact. The system is also useful and B.1, respectively, of complex thoracic injuries with for changing the body’s kinematics. The head hits an area Displacement (mm) 8 Applied Bionics and Biomechanics t = 0.00 ms t = 0.00 ms t = 60 ms t = 60 ms t = 110 ms t = 110 ms t = 143 ms t = 143 ms (a) (b) Figure 7: Impact on a cyclist on the overtaking stage at 60 km/h without a passive safety system (a) and with a passive safety system (b). 200.0 150.0 100.0 50.0 0.0 0.0 50.0 100.0 0 50 100 Time (ms) Time (ms) A.1 A.1 B.1 B.1 (a) (b) –5 –10 –15 –20 –25 0 50 100 150 Time (ms) A.1 B.1 (c) Figure 8: (a) Acceleration in the head and HIC’s gravity center at a speed of 60 km/h. (b) Acceleration of chest gravity center in G’sata speed of 60 km/h. (c) Chest deflection in mm during a traffic accident at a speed of 60 km/h. respiratory difficulty, production of massive hemothorax, referred to in the tables since, due to the setup of the hit- and cardiac rupture or contusion, which fall into the cate- and-run scenarios, and the left lower limb always presents gory of critical injuries with uncertain survival. For the lower injuries far below those generated in the right limb. Both limbs, it is essential to mention that only the right limb is hit and run cases show similar results, where there is a Head acceleration (G′s) Chest deflection (mm) Chest acceleration (G′s) Applied Bionics and Biomechanics 9 t = 0.00 ms t = 0.00 s. t = 80 ms t = 80 ms t = 110 ms t = 130 ms t = 163 ms t = 163 ms (a) (b) Figure 9: Cyclist overtaking impact at 50 km/h without a passive safety system (left) and with a passive safety system (right). 0 0 0 100 0 50 100 150 Time (ms) Time (ms) A.2 A.2 B.2 B.2 (a) (b) 0 50 100 150 –5 –10 Time (ms) –15 A.2 B.2 (c) Figure 10: (a) Acceleration of head gravity center and HIC at a speed of 50 km/h. (b) Acceleration of chest gravity center in G’s at a speed of 50 km/h. (c) Chest deflection in mm during the accident at a speed of 50 km/h. probability of less than 50% of presenting a nondisplaced frac- although this probability is lower when the bicycle has a pas- ture of the femur, an injury categorized as moderate on the sive safety device installed. There are injuries to the cyclist’s AIS scale. In comparison, the probability of presenting an right tibia; injuries, show an AIS = 2 level injury will undoubt- exposed fracture of this bone is less than 20% in both cases, edly occur, indicating a fracture of this bone due to the impact. Head acceleration (G′s) Chest deflection (mm) Chest acceleration (G′s) 10 Applied Bionics and Biomechanics 319.35 mm 269.62 mm (a) (b) Figure 11: Cyclist’s head windshield contact at the vehicle. (a) No passive safety device (b) with a passive safety device. t = 0.00 s t = 0.00 ms t = 100 ms t = 100 ms t = 170 ms t = 170 ms t = 238 ms t = 238 ms (a) (b) Figure 12: Cyclist overtaking impact at 40 km/h without a passive safety system (a) and passive safety system (b). The results show the craniocerebral injury rate for the is estimated that in both cases, there will be a fracture of scenario with the passive safety device fitted to the bicycle multiple ribs, with a probability of practically 100% of pre- is again considerably lower, classified on the AIS-4, which senting an AIS = 3 level injury; likewise, there is a 13.23% is severe, but with probable survival, where cranioencephalic and 21.54% probability in cases A.2 and B.3, respectively, trauma with or without fractures may occur, accompanied with a 13.23% and 21.54% probability of presenting an by unconsciousness and neurological signs such as posttrau- AIS = 3 level injury, respectively. Moreover, case B.3, respec- matic amnesia for 3-12 hours. On the other hand, the most tively, has a 13.23% and 21.54% probability of AIS = 5 tho- likely injuries when the bicycle does not have a passive safety racic injuries, complex injuries with respiratory difficulty, device are categorized at AIS = 5 level, critical injuries where production of massive hemothorax, and cardiac rupture or survival is uncertain. In the case of injuries to the thorax, the contusion, which fall into the category of critical injuries with probabilities between the two cases are again similar, since it uncertain survival [29, 30]. For the lower limbs, in this case, Applied Bionics and Biomechanics 11 0 50 100 150 200 250 0 50 100 150 200 250 Time (ms) Time (ms) A.3 A.3 B.3 B.3 (a) (b) 0 50 100 150 –1 –2 –3 –4 –5 –6 Time (ms) A.3 B.3 (c) Figure 13: (a) Head acceleration in the center of gravity and HIC at a speed of 40 km/h. (b) Chest acceleration in G’s at a speed of 40 km/h. (c) Chest deflection in mm during the accident at a speed of 40 km/h. (2) (1) (1) (2) (3) (4) (3) (4) (a) (b) Figure 14: Cyclist’s kinematics during an overtaking crash. (a) MADYMO run-over simulation; (b) FEM simulation. there is a considerable difference in the probability of injury The results the tables have shown are again considerably to the cyclist’s right femur, since in the case where the bicycle lower, which influences the likelihood and severity of the does not have the safety device installed, the probability of injury, being categorized on the AIS scale as level 3 injuries suffering a nondisplaced fracture is 8.18%. that are serious but not life-threatening and are fully revers- In comparison, if the device is installed, the probability ible, although hospitalization is necessary. On the other increases to 28.4%. In presenting an exposed fracture in this hand, the most likely injuries when the bicycle is not fitted bone, the probability remains less than 20% in both cases, with the passive safety device are categorized at AIS level 4, although it is higher when the bicycle has a passive safety severe, life-threatening injuries, but with probable survival. device installed. The cyclist’s right tibia shows an AIS = 2, In the case of injuries to the thorax, the probabilities between which indicates the fracture of this bone due to the impact. the two cases show a more significant variation than in the Head acceleration (G′s) Chest deflection (mm) Chest acceleration (G′s) 12 Applied Bionics and Biomechanics is the change in the severity of the injury due to the use of previous cases, since the probability of suffering an ASI = 3 or greater injury for the case where the bicycle does not have bicycle helmets during vehicular accidents. The characteris- the passive safety device installed is very close to 100% tics and operation of a bicycle helmet do not significantly (97.79). In contrast, if the bicycle does have this device impact the cyclist’s kinematics during the accident until installed, the probability decreases to 80.77%. The same the cyclist’s head comes into contact with the car [31, 32]. pattern is observed in the probability of suffering injuries ASI = 5 or greater, where case A.3 has 24.09%, while case 5. Conclusions B.1 has 4.48%. For the lower limbs, specifically the cyclist’s right femur, the results between both cases are again quite The passive safety device significantly reduced the severity of similar, approaching the null probability of injury to the craniocerebral injuries by decreasing the magnitude of the femur, whether AIS = 2 or AIS = 3, with a variation of no HIC index by 775, 228, and 478 points for impact speeds more than 2% between the results and a percentage of injury of 60 km/h, 50 km/h, and 40 km/h, respectively. The passive of less than 5%. In the case of cyclist’s right tibia, the results safety device’s use did not significantly reduce the severity of again show that an AIS = 2 level injury will occur, which thoracic injuries at high speeds (60 km/h and 50 km/h); indicates the fracture of this bone injury is a consequence however, it did reduce them at low speeds (40 km/h) by of the impact since the percentage of presenting this injury obtaining a 19.61% less of the probability of suffering an remains at the same value as the previous cases with a injury, presenting an AIS ≥ 5 injury when using the device. 100% probability of fracture. The forces applied to the cyclist’s femur indicated a 28.4% For the cranioencephalic injuries generated in the greater variation in the probability of sustaining an AIS ≥ 2 accident, in all cases where the passive safety device was injury when using the passive safety device. In conclusion, used, the HIC index decreased considerably, reducing the the design fulfilled its primary function by reducing the severity of the injuries by one level according to the AIS severity of cranioencephalic injuries to one level in the AIS scale. However, the impact of this is not minor, as it has system in all cases, which implies the significant decrease several implications. in risk of death by cranioencephalic trauma, especially at low-speed cases in this particular run-over scenario, because (1) In cases where a cyclist is hit at a speed of 60 km/h, this type of injury is the one with the highest risk of mortality the device’s use can reduce the likelihood of injury for cyclists. to such a degree that survival is possible, which is not the case where the device is not fitted Data Availability (2) For the 50 km/h cases, the use of the device can The data used to support the findings of this study are avail- reduce the probability of injury, compared to the able from the corresponding author upon request. results obtained for the run-over cases where the device is not installed, so that the expected injuries correspond to the ASI = 4 level, where survival is Conflicts of Interest likely, as opposed to the AIS = 5 level, where the The authors declare that there is no conflict of interest injuries generated are critical regarding the publication of this paper. (3) In a collision at a speed of 40 km/h, the injuries gen- erated on the cyclist, when using the passive safety Acknowledgments device, are reduced to an AIS = 3 level, where the cyclist’s life is not at risk, although the injuries are The authors acknowledge the financial support for the real- categorized as severe, whereas without the device, ization of this work of the Mexico Government by Consejo the injuries grow to an AIS = 4 level, where the per- Nacional de Ciencia y Tecnología (CONACyT) and the son is likely to die Instituto Politécnico Nacional (IPN). The authors also thank the support of project 20210282 and EDI grant, all by The first limitation of this work is the dummy model SIP/IPN. used. A pedestrian dummy for the collision model was mounted on the bicycle and then used to report the injuries References as a vulnerable road user. 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Journal

Applied Bionics and BiomechanicsHindawi Publishing Corporation

Published: Aug 27, 2021

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