Validation of Pedestrian Lower Limb Injury Assessment using Subsystem Impactors

Validation of Pedestrian Lower Limb Injury Assessment using Subsystem Impactors Yukou Takahashi Miwako Ikeda Iwao Imaizumi Yuji Kikuchi Satoru Takeishi Honda R&D Co., Ltd. 212 IRCOBI Conference September 12 nd, 212 Trinity College Dublin, Ireland 1

Outline Background Objective Predictor of Tibia Fracture Development and Validation of Legform Models Correlation of Injury Measures between Human and Legform Models Factors for Difference in Tibia Fracture Measure Correlation Discussion Conclusions 2

Pedestrian Test Procedure EEVC Subsystem Impactors Child Adult Headform Headform Upper Legform Adult Headform FlexPLI Flexible Pedestrian Legform Impactor Legform EEVC Legform Rigid Bones Flexible Bones Final Version FlexGTR Jointly developed by JARI and JAMA

Past Studies Matsui et al. (21) Comparison of time histories of impact force, knee shear displacement and knee bending angle between EEVC legform tests and PMHS tests by Kajzer et al. EEVC legform does not have sufficient biofidelity Konosu et al. (29) Impact simulations using EEVC legform and human FE models against multiple simplified vehicle models No correlation between EEVC legform upper tibia acceleration and human tibia bending moment (R=.1) JAMA and JARI (29) Impact simulations using FlexPLI and human FE models against multiple simplified vehicle models Good correlation between FlexPLI tibia bending moment and human tibia bending moment (R=.9)

Past Studies Validity of the use of tibia bending moment as a predictor of human tibia fracture needs further clarifications No comprehensive comparison has been made as to the correlation of all injury measures Factors for the difference in the correlation have not been clarified

Objective Investigate difference of correlation with human body between EEVC legform and FlexPLI for all injury measures Clarify factors for difference in correlation from a viewpoint of stiffness of tibia and injury measures used Identification of Predictor of Human Tibia Fracture Impact simulations using a human FE model against multiple simplified vehicle models Correlation Analysis of Human and Legform Measures Impact simulations using EEVC legform and FlexPLI FE models against multiple simplified vehicle models Comparison of correlation for all injury measures Clarification of factors for correlation difference Tibia fracture measures Additional simulations using simplified vehicle models and leg component model 9

Candidate Predictors Shear Force Bending Moment Candidate Predictors Shear force, tensile force, bending moment Acceleration Assumption Bone fails when maximum von Mises stress exceeds the limit Tensile Force Investigate correlation between maximum von Mises stress and maximum candidate predictors 11

Force (kn) GTR9-4-2 Simplified Vehicle Model 15 kg Structure Rigid BP SP BLE Shell Rigid Body Geometric Parameters H1 H2 H3 BP SP L2 L1 BLE L2: positive in rearward direction 15 1 5 Stiffness Curves (BP/SP) level A level B level C level D 2 4 6 8 1 12 Deflection (mm) Levels of Parameters Parameter Unit Level 1 Level 2 Level 3 K1 (BLE thickness) mm.4.6 - K2 (BP stiffness) - B C D K3 (SP stiffness) - A C D H1 (BLE height) mm 65 7 75 H2 (BP height) mm 45 49 53 H3 (SP height) mm 25 27 35 L1 (BLE lead) mm 125 2 275 L2 (SP lead) mm -2 3 12

Simplified Vehicle Model Model K1 K2 K3 H1 H2 H3 L1 L2 S1.4 B A 65 45 25 125-2 S2.4 B C 7 49 27 2 S3.4 B D 75 53 35 275 3 S4.4 C A 65 49 27 275 3 S5.4 C C 7 53 35 125-2 S6.4 C D 75 45 25 2 S7.4 D A 7 45 35 2 3 S8.4 D C 75 49 25 275-2 S9.4 D D 65 53 27 125 S1.6 B A 75 53 27 2-2 S11.6 B C 65 45 35 275 S12.6 B D 7 49 25 125 3 S13.6 C A 7 53 25 275 S14.6 C C 75 45 27 125 3 S15.6 C D 65 49 35 2-2 S16.6 D A 75 49 35 125 S17.6 D C 65 53 25 2 3 S18.6 D D 7 45 27 275-2 13

Pedestrian Model Meniscus LCL Pelvis Model Sacroiliac Cartilage Pelvic Bone Pubic Symphysis Knee Model Sacrum Acetabulum Cartilage ACL C5 C6 C7 Neck Model Lumber Model L1 L2 L3 L4 L5 C1 C2 C3 C4 PCL MCL 14

Pedestrian Model Validation Pelvis Thigh Knee Body Region /Tissue Isolated pelvis Isolated femur Femur+flesh Isolated ligament Isolated knee joint Loading Rate Loading Configuration Properties Quasi-static Dynamic, 1 rate Quasi-static Dynamic, 1 rate Quasi-static Dynamic, 1 rate Quasi-static Dynamic, 3 rates Dynamic, 1 rate Leg Isolated tibia Quasi-static Dynamic, 1 rate Isolated fibula Tibia+fibula+ flesh Quasi-static Dynamic, 1 rate Quasi-static Dynamic, 1 rate Lateral compression Iliac / acetabulum loadings 3-point bending 3-point bending Tension 4-point bending 3-point bending 3-point bending 3-point bending 3-point bending Whole body 4 km/h impact Lateral impact 1 small sedan, 1 large SUV Force-deflection Force-deflection Moment-deflection Force-deflection Moment-deflection Force-deflection Moment-angle Force-deflection Moment-deflection Force-deflection Moment-deflection Force-deflection Moment-deflection Head, T1, T8, pelvis trajectories Pelvis and lower limb injury distribution 15

Impact Simulation Setup Model Setup Measurement Location Side View Back View 4 km/h Tibia-1 Tibia-2 Tibia-3 Tibia-4 FlexPLI Tibia Moment Measurement Tibia-1 Tibia-2 Tibia-3 Tibia-4 2º 16

Acceleration (m/s 2 ) Tensile Force (N) Bending Moment (Nm) Shear Force (N) GTR9-4-2 Results of Correlation Analysis 4 km/h Tensile Bend Shear 18 different simplified vehicle models 5 4 3 2 1 4, 3, 2, 1, Bending Moment R=.79 1 2 Von Mises Stress (MPa) Acceleration R=.32 1 2 Von Mises Stress (MPa) Maximum tibia bending moment best correlates with maximum local von Mises stress of tibia 1,5 1, 5 1,5 1, 5 Shear Force R=.17 1 2 Von Mises Stress (MPa) Tensile Force R=.35 1 2 Von Mises Stress (MPa) Maximum tibia acceleration poorly correlates with maximum von Mises stress of tibia 17

Legform Models Femur shaft Tibia shaft Structure Cantilever Shear potentiometer Steel plates Bending potentiometer Accelerometer Femur shaft (Rigid Body) Tibia shaft (Rigid Body) EEVC Legform Model Cantilever (Shell) Damper Joint Form (Solid) Validation Matrix Component Quasi-static knee bending Quasi-static knee shearing Assembly Dynamic certification test Vehicle test Femur shaft Knee joint Tibia shaft Structure Femur bone core Core spacer Core binder Exterior housing Ligament springs Ligament wire cables Tibia strain gages Tibia bone core Femur bone core (Solid) Core binder (Rigid) Ligament wire cables (Bar) Tibia bone core (Solid) FlexPLI Model Neoprene (Solid) Rubber (Solid) Exterior housing (Rigid) Validation Matrix Component Bone core 3-pt bending Femur 3-pt bending Knee 3-pt bending Tibia 3-pt bending Assembly Pendulum test Simplified vehicle test Vehicle test 19

Validation against Car Test 12 EEVC Legform 12 Upper Tibia Acceleration (G) 4 8 4 Experiment Simulation Experiment +/- 15% Passenger car Sport car SUV Knee Bending Angle (deg) FlexPLI 8 4 Passenger car Sport car SUV Passenger Car Sport Car SUV 4 4 Moment (Nm) 3 2 1 Moment (Nm) 3 2 1 Moment (Nm) 3 2 1 Tibia-1 Tibia-2 Tibia-3 Tibia-4 Tibia-1 Tibia-2 Tibia-3 Tibia-4 Tibia-1 Tibia-2 Tibia-3 Tibia-4 3 3 3 Elongation (mm) 2 1 ACL PCL MCL Elongation (mm) 2 1 ACL PCL MCL Elongation (mm) 2 1 ACL PCL MCL 2

Impact Simulations EEVC FlexPLI Legform 4 km/h 4 km/h Injury Human Measure EEVC Legform FlexPLI 4 km/h Tibia Fracture Tibia Bending Moment Upper Tibia Acceleration Tibia Bending Moment MCL Failure MCL Elongation Knee Bending Angle MCL Elongation ACL Failure ACL Elongation Knee Shear Displacement ACL Elongation 18 simplified vehicle models Investigate correlation of tibia and knee injury measures with human model for both EEVC legform and FlexPLI models 22

Legform Model Tibia Moment (Nm) Legform Model MCL Elongation (mm) Legform Model ACL Elongation (mm) Legform Model Tibia Acceleration (G) Legform Model Knee Bending Angle (deg) Legform Model Knee Shear Disp. (mm) GTR9-4-2 Results of Correlation Analysis Tibia Fracture Measure MCL Failure Measure ACL Failure Measure EEVC Legform 6 4 2 R =.22 25 5 Human Model Tibia Momemt (Nm) 25 2 15 1 5 R =.75 1 2 3 Human Model MCL Elongation (mm) 8 6 4 2 R =.9 2 4 6 Human Model ACL Elongation (mm) FlexPLI 5 4 3 2 1 R =.87 25 5 Human Model Tibia Momemt (Nm) 4 3 2 1 R =.56 1 2 3 Human Model MCL Elongation (mm) 15 1 5 R =.71 2 4 6 Human Model ACL Elongation (mm) FlexPLI showed much better correlation than EEVC legform for tibia fracture and ACL failure measures EEVC legform tibia fracture measure showed a negative correlation 23

Force (kn) Force (kn) GTR9-4-2 Simplified Vehicle Impact Simulation Baseline Model 65 mm 45 mm 275 mm 25 mm BP SP 3 mm BLE BP/SP Stiffness SP Location 15 BP 15 SP 1 1 Base Stiff 5 Base Stiff 4 8 12 Deflection (mm) 5 4 8 12 Deflection (mm) -2 mm mm 3 mm 25

Simplified Vehicle Impact Simulation EEVC Legform Model Stiffness of Tibia Case Stiffness Steel Material parameters of steel Bone Flexural rigidity = 555.6 Nm 2 Simulation Matrix Case Stiffness SP Stiffness Location Case BP SP (L2 in mm) Tibia BP SP Tibia SP Location (L2 in mm) V1-B Base Base Bone 3 V1-S Base Base Steel 3 V2-B Stiff Base Bone 3 V2-S Stiff Base Steel 3 V3-B Base Stiff Bone 3 V3-S Base Stiff Steel 3 V4-B Base Stiff Bone V4-S Base Stiff Steel V5-B Base Stiff Bone -2 V5-S Base Stiff Steel -2 26

Normalized Measure Normalized Measure 2.5 2. 1.5 1..5. 2.5 2. 1.5 1..5. V1 V2 V3 Results Effect of BP/SP Stiffness Tibia Bending Moment @ BP Height Baseline Stiff BP Stiff SP Normalized Measure Effect of SP Location Tibia Bending Moment @ BP Height V3 V4 V5 SP Forward Normalized Measure 2.5 2. 1.5 1..5. 2.5 2. 1.5 1..5. Tibia Acceleration @ BP Height V1 V2 V3 Baseline Stiff BP Stiff SP Tibia Acceleration @ BP Height V3 V4 V5 SP Forward Bone Steel Bone Steel 27

Force (kn) GTR9-4-2 Isolated Leg Impact Simulation EEVC Legform Model Isolated Leg Model (Stiffness = Bone) 1 8 6 4 Ram Stiffness Curves 2.5 kn 5. kn 4 km/h 2 15kg Ram Model (Rigid Body) H 5 1 15 2 Deflection (mm) Simulation Matrix Case Impact Height (H in mm) Impactor Stiffness (Force level in kn) Case Impact Height (H in mm) Impactor Stiffness (Force level in kn) H1-S1 25 2.5 H1-S2 25 5. H2-S1 35 2.5 H2-S2 35 5. H3-S1 45 2.5 H3-S2 45 5. 28

Force (kn) GTR9-4-2 Results H3 H2 H1 1 8 6 4 2 S2 S1 5 1 15 2 Deflection (mm) 3. Tibia Bending Moment@ Impact Height 3. Tibia Acceleration @ Impact Height Normalized Measure 2.5 2. 1.5 1..5. Normalized Measure H1 H2 H3 H1 H2 H3 H1 H2 H3 H1 H2 H3 S1 S2 S1 S2 2.5 2. 1.5 1..5. Both bending moment and acceleration are almost two times higher for S2 (5. kn) relative to S1 (2.5 kn) Acceleration does not depend on impact height, while bending moment is highly dependent on impact height 29

Normalized Measure Normalized Measure GTR9-4-2 Discussion 2.5 2. Effect of SP Location Tibia Bending Moment @ BP Height 2.5 2. Tibia Acceleration @ BP Height Bone Steel BP BLE 1.5 1..5 1.5 1..5 SP V5 V4 V3. V3 V4 V5. V3 V4 V5 SP Forward SP Forward Total Force (kn) 25 2 15 1 5 Tibia Stiffness = Bone Total Applied Force (BP+SP) V3 V4 V5 Total Force (kn) 25 2 15 1 5 Tibia Stiffness = Steel V3 V4 V5 5 1 15 Time (ms) 5 1 15 Time (ms) 31

Normalized Measure Normalized Measure GTR9-4-2 Discussion 3. Tibia Bending Moment@ Impact Height 3. Tibia Acceleration @ Impact Height 2.5 2. 1.5 1..5 2.5 2. 1.5 1..5. Acceleration H1 H2 H3 H1 H2 H3 H1 H2 H3 H1 H2 H3 S1 S2 S1 S2 Solely determined by applied force magnitude. SP forward Increased total force Increased acceleration Bending Moment Dependent on both magnitude and location of applied force SP forward Increased total force Lower effective location Increased moment Decreased moment 32

Conclusions Peak tibia bending moment best correlated with peak stress Correlation with human injury measures was found to be significantly improved for FlexPLI relative to EEVC legform for tibia fracture and ACL failure measures Excessive tibia stiffness resulted in higher sensitivity of tibia fracture measures to vehicle stiffness and geometric characteristics Tibia acceleration was found to be solely determined by applied force magnitude, while tibia bending moment depended on both magnitude and location of applied force Differences in tibia stiffness and tibia fracture measures resulted in significantly different trend of tibia fracture measures when vehicle geometry was changed 34

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