SAE 2011 Government / Industry Meeting A Systematic Approach for Improving Occupant Protection in Rollover Crashes Jingwen Hu, PhD University of Michigan Transportation Research Institute King H. Yang, PhD Bioengineering Center, Wayne State University University of Michigan Transportation Research Institute
Significance Rollover crashes are the most dangerous vehicular crashes among all the crash types Although only 2.6 percent of passenger vehicle crashes resulted in rollovers, they accounted 21.1 percent of fatal crashes in the US. (Traffic Safety Facts 2005) In 2005, 10,816 people died in rollover crashes. (FARS 2005) University of Michigan Transportation Research Institute 2
Complex and Random Trip-over Flip-over Turn-over Fall-over Bounce-over Collision University of Michigan Transportation Research Institute 3
Controversy No causal relationship between roof crush and head/neck injury - Moffatt 1975, Malibu test I&II, Crown Victoria tests Occupants are injured as they "dive" into the roof before it crushes Causal relationship between roof crush and head/neck injury Rechnitzer et al. 1998, Friedman and Nash 2001 A weak roof can collapse and buckle in a rollover, imposing forces on an occupant s head inducing injuries University of Michigan Transportation Research Institute 4
Countermeasure Lessons from frontal & side impact Minimal intrusion Effective restraint system Friendly interior design Rollover Belted Occupants - Head to roof contact No systematic approach available University of Michigan Transportation Research Institute 5
FE Models Vehicle Model Dummy Model Neck Model Human Model University of Michigan Transportation Research Institute 6
University of Michigan Transportation Research Institute 7
Vertical Head Excursion (mm) Inversion & Rolling Test Validation 160 140 120 Test simulation-static Simulation-220deg/s Simulation-360deg/s 100 80 60 40 20 0 dummy-static dummy-dynamic human static human dynamic University of Michigan Transportation Research Institute 8
Vertical Acceleration (g) Lateral Acceleration (g) Dolly Test Validation - Driver 80 60 Test Simulation 40 20 0-20 0.3 0.4 0.5 0.6 0.7 0.8 Time (s) 25 20 Test Simulation 15 10 5 0-5 -10 0.3 0.4 0.5 0.6 0.7 0.8 Time (s) University of Michigan Transportation Research Institute 9
Axial Neck Force (N) Vertical Acceleration (g) Curb-trip Validation - Passenger 80 Test Simulation 60 40 20 0-20 -40 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Time (s) 12000 Test Simulation 10000 8000 6000 4000 2000 0-2000 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Time (s) University of Michigan Transportation Research Institute 10
Head-neck Model Validation University of Michigan Transportation Research Institute 11
Three Parametric Studies Roof Crush vs. Occupant Injury Risk IJVD (2010) 54(3) pp. 238-261 Neck Injury Mechanism and Roof Interior Design Spine (2008) 33(23) pp. 2529-2535 Seat Belt Design SAE Journal (2009) 2(1) pp. 904-913 University of Michigan Transportation Research Institute 12
Roof Crush vs. Occupant Injury 13
Roof Crush vs. Occupant Injury Simulated Scenarios Two curb-trips (Impact Mode I and II) One soil-trip (Impact Mode I) Vehicle models Four vehicle models with different roof stiffness Occupants Belted driver and front seat passenger Output Resultant head acceleration Axial neck load University of Michigan Transportation Research Institute 14
Roof Modification Yellow color indicates rigid material Vehicle Model I (SWR = 1.95) Vehicle Model II (SWR = 2.21) Vehicle Model III (SWR = 3.31) Vehicle Model IV (SWR = 3.64) University of Michigan Transportation Research Institute 15
Dummy Responses Regular roof Stronger roof Regular roof Stronger roof University of Michigan Transportation Research Institute 16
Roof Crush (mm) Neck Axial Force (N) Roof Crush and Neck Load vs. Time 300 250 Roof Crush Neck Axial Force 12000 10000 200 8000 150 100 6000 4000 50 2000 0 0-50 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Time (s) -2000 University of Michigan Transportation Research Institute 17
Maximum Neck Force (N) Maximum Neck Force (N) Does roof stiffness matter? Yes! Far-side occupants with two roof-ground impacts in a single roll Soil-trip Curb-trip 12000 12000 10000 10000 8000 8000 6000 6000 4000 4000 2000 2000 0 I II III IV Vehicle Model 0 I II III IV Vehicle Model Increased roof stiffness Increased roof stiffness University of Michigan Transportation Research Institute 18
Vertical Velocity (m/s) Far-side Occupant in Impact Mode I 2 Dummy head - Vehicle model I Dummy head - Vehicle model III 0-2 Far-side dummy contacts the roof Far-side dummy in vehicle model I contacts the ground -4 Far-side dummy in vehicle model III contacts the ground Near-side roof contacts the ground -6 0.80 0.84 0.88 0.92 0.96 1.00 1.04 Time (s) University of Michigan Transportation Research Institute 19
Injury Mechanism Does diving or roof crush induce injuries? Diving Is roof stiffness related to injuries? Yes, but only for far-side occupant when there are two roof-to-ground impacts during a single roll. Can seat belt prevent head-roof impacts? Currently, not so much. University of Michigan Transportation Research Institute 20
Head Excursion vs. Head Room Typical head room 10 cm (4 ) Head excursion.. 20 cm (8 ) Moffatt and James 2005 University of Michigan Transportation Research Institute 21
A Systematic Approach IF we have a rigid roof? Head & neck injury risk will mainly depend on the restraint system IF we have a perfect restraint system? Roof stiffness will play a very significant role. In reality, there is no rigid roof or perfect restraint system During a head-to-roof contact, roof interior will play a major role. A combination of vehicle, restraint system, and roof interior design optimization University of Michigan Transportation Research Institute 22
Neck Injury Mechanism and Roof Interior Design 23
Cadaver Tests Nightingale et al. 1997 n=6 n=6 n=6 n=4-15º 0º +15º +30º University of Michigan Transportation Research Institute 24
Neck Injury Mechanism in Near-Vertex Impact Neck injury mechanisms are dependent on the neck orientation and impact direction. Padding will add constraints to the head, in turn, will increase the risk of neck injury. If the neck can escape from the direction of momentum, the risk of neck injury will be greatly reduced. University of Michigan Transportation Research Institute 25
Human Head- Neck Simulation Impact directions University of Michigan Transportation Research Institute 26
Average Maximum Principal Strain Human Head- Neck Simulation Level COF Padding thickness Padding stiffness Impact velocity AP surface angle Lateral surface angle 1 0.0 0.63 cm Soft 1.0 m/s -15º 0º 2 0.2 1.27 cm Middle 2.0 m/s 0º 15º 3 0.5 2.54 cm Hard 3.0 m/s 15º 30º 4 1.0 5.08 cm Rigid 4.0 m/s 30º 45º 0.030 0.025 Level 1 Level 2 Level 3 Level 4 0.020 0.015 0.010 0.005 0.000 COF Padding thickness Padding stiffness Velocity AP angle Lateral angle Factors University of Michigan Transportation Research Institute 27
Friction COF=0.0 COF=0.5 University of Michigan Transportation Research Institute 28
Foam Effect COF=0.0 COF=0.8 COF=0.8 sliding University of Michigan Transportation Research Institute 29
Seat Belt Design 30
Dummy and Human Model for Seat Belt Design University of Michigan Transportation Research Institute 31
Seat Belt Effectiveness Two portions of vertical excursions Slack Pretensioner latch plate Lapbelt angle Clearance Portion I Portion II University of Michigan Transportation Research Institute 32
New Seat Belt Designs Not effective Not effective Effective a) 4-Point Seatbelt (Rouhana et al. 2004) b) 3+2-Point Seatbelt (Bostrom et al. 2005) c) Double-Lapbelt (New design) University of Michigan Transportation Research Institute 33
Summary Roof crush Roof stiffness Diving is the major injury mechanism, but roof stiffness can affect injury risk in diving Low friction padding reduce injury risk Seatbelt design reduce impact velocity Lapbelt design is crucial for rollover safety A combination of vehicle, restraint system, and roof interior design optimization University of Michigan Transportation Research Institute 34
SAE 2011 Government / Industry Meeting A Systematic Approach for Improving Occupant Protection in Rollover Crashes Jingwen Hu, PhD University of Michigan Transportation Research Institute King H. Yang, PhD Bioengineering Center, Wayne State University University of Michigan Transportation Research Institute