Comparison of aPLI and FlexPLI-UBM Advanced Pedestrian Legforms
Jason Stammen, NHTSABrian Suntay, Transportation Research Center Inc.
SAE Government/Industry Meeting 2020
• Upper leg injuries are common for pedestrians in the U.S.1
• Questionable validity of FlexPLI femur measurements in vehicle tests• FlexPLI does not adequately simulate the impact kinematics and bending
loads above the knee• Lack of upper body mass believed to have an effect on leg kinematics and femur measurements• Currently no proposed injury assessment values
• New legforms with upper body mass have been introduced• FlexPLI-UBM (SENIORS)• aPLI (ISO)
• Potential for single legform test to replace two existing (lower/upper leg) tests
2
Motivation
1Mallory et al. Relative Frequency of U.S. Pedestrian Injuries Associated With Risk Measured in Component-Level Pedestrian Tests. DOT HS 812 658
3
Objective
• Perform a preliminary evaluation of the FlexPLI-UBM and aPLI and compare vehicle test results with one another and the current FlexPLI in matched impacts
Pedestrian Legform Impactors5
• FlexPLI (13 kg total mass)• FlexPLI-UBM* (20 kg total mass)
• Bolt-on upper body part (7 kg)• Attaches to existing FlexPLI (13 kg)
• aPLI** (25 kg total mass)• Redesigned legform
• Mass distribution• Contact profile• Knee ligament geometry• Increased femur bone stiffness• Simplified upper body part with onboard DAS and additional instrumentation
**Isshiki et al., Consolidated Technical Specifications for the Advanced Pedestrian Legform Impactor (aPLI), IRCOBI 2018 (modified)
*Zander et al., Development and Evaluation of an Upper Body Mass (UBM) for the Flexible Pedestrian Legform Impactor (FlexPLI) and for Incorporation within Improved Test and Assessment Procedures – Results from SENIORS, IRCOBI 2019
aPLI Setup• Launch carriage
• Designed by Cellbond
• Custom adaptor• Attach to our launch system• Horizontal flight motion
6
FlexPLI-UBM Setup7
Additional support pieces
• Modifications to NHTSA launch carriage (coordinated with HIS)• Addition of UBM support bar to existing launch carriage• Bolt-on attachments
Vehicle Test Setup• 2016 Ford Edge
• Vehicle available• Previous FlexPLI testing• Global platform, higher bumper vehicle
• VRTC launch system unable to reach 11.1 m/s due to increased total mass
• Target velocity 9 m/s
8
Test Matrix (n=1 in each condition)
Legform Target Velocity Impact Location Bottom of LegformHeight from Ground
aPLI
9 m/s
L+4, Passenger25 mm
L0, Center
FlexPLI-UBML+4, Passenger
63 mmL0, Center
FlexPLIL-4, Driver
75 mmL0, Center
L + 4 L0 L - 4
400 mm 400 mm
Test Results: Femur Bending Moment11
357 365
302315
325321
216
151
82
0
50
100
150
200
250
300
350
400
Femur 1 Femur 2 Femur 3
Femur Bending Moment (Nm)
aPLI FlexPLI-UBM FlexPLI
Center
305
246
189
287279 271
151
103
58
0
50
100
150
200
250
300
350
400
Femur 1 Femur 2 Femur 3
Femur Bending Moment (Nm)
aPLI FlexPLI-UBM FlexPLI
Outboard
1
2
3
• Legforms with upper body mass had higher femur moments• Further from knee: FlexPLI and aPLI decreased, Flex-UBM more consistent along length
Test Results: Knee Ligament Elongations12
26.1
4.4
10.3
23.3
8.76.4
18.3
8.2
4.7
0
5
10
15
20
25
30
35
MCL ACL PCL
Knee Ligament Elongations (mm)
aPLI FlexPLI-UBM FlexPLI
29.4
4.2
11.4
28.4
9.07.7
25.7
11.6
6.3
0
5
10
15
20
25
30
35
MCL ACL PCL
Knee Ligament Elongations (mm)
aPLI FlexPLI-UBM FlexPLI
Center Outboard
MCL ACL PCL
• Legforms with upper body mass had higher MCL and PCL
Test Results: Knee Ligament Elongations13
26.1
4.4
10.3
23.3
8.76.4
18.3
8.2
4.7
0
5
10
15
20
25
30
35
MCL ACL PCL
Knee Ligament Elongations (mm)
aPLI FlexPLI-UBM FlexPLI
29.4
4.2
11.4
28.4
9.07.7
25.7
11.6
6.3
0
5
10
15
20
25
30
35
MCL ACL PCL
Knee Ligament Elongations (mm)
aPLI FlexPLI-UBM FlexPLI
Center Outboard
MCL ACL PCL
• Legforms with upper body mass had higher MCL and PCL• ACL different in aPLI: ligament orientation
Test Results: Knee Ligament Elongations14
26.1
4.4
10.3
23.3
8.76.4
18.3
8.2
4.7
0
5
10
15
20
25
30
35
MCL ACL PCL
Knee Ligament Elongations (mm)
aPLI FlexPLI-UBM FlexPLI
29.4
4.2
11.4
28.4
9.07.7
25.7
11.6
6.3
0
5
10
15
20
25
30
35
MCL ACL PCL
Knee Ligament Elongations (mm)
aPLI FlexPLI-UBM FlexPLI
Center Outboard
MCL ACL PCL
• Legforms with upper body mass had higher MCL and PCL• ACL different in aPLI: ligament orientation, secondary peak higher
Test Results: Knee Ligament Elongations15
26.1
810.3
23.3
8.76.4
18.3
8.2
4.7
0
5
10
15
20
25
30
35
MCL ACL PCL
Knee Ligament Elongations (mm)
aPLI FlexPLI-UBM FlexPLI
29.4
7
11.4
28.4
9.07.7
25.7
11.6
6.3
0
5
10
15
20
25
30
35
MCL ACL PCL
Knee Ligament Elongations (mm)
aPLI FlexPLI-UBM FlexPLI
Center Outboard
MCL ACL PCL
• Legforms with upper body mass had higher MCL and PCL• ACL different in aPLI: ligament orientation, secondary peak higher
Overall aPLI peak ACL is more
consistent with other two legforms
Test Results: Tibia Bending Moment16
274
229
158
72
240
193
136
63
221
187
135
65
0
50
100
150
200
250
300
350
400
Tibia 1 Tibia 2 Tibia 3 Tibia 4
Tibia Bending Moment (Nm)
aPLI FlexPLI-UBM FlexPLI
299272
208
102
308
272
192
92
318
263
176
90
0
50
100
150
200
250
300
350
400
Tibia 1 Tibia 2 Tibia 3 Tibia 4
Tibia Bending Moment (Nm)
aPLI FlexPLI-UBM FlexPLI
Center Outboard
1
2
3
4
• Center: legforms similar at all locations• Outboard: Flex-UBM & FlexPLI similar, aPLI higher
Test Results: Center > Outboard (All Legforms)17
0
100
200
300
400
Femur (AVG) Tibia (AVG)
Bending Moment (Nm)
Center Outboard
05
1015202530
MCL ACL PCL
Knee Ligament Elongation (mm)
Center Outboard
FlexPLI
0
100
200
300
400
Femur (AVG) Tibia (AVG)
Bending Moment (Nm)
Center Outboard
05
1015202530
MCL ACL PCL
Knee Ligament Elongation (mm)
Center Outboard
Flex-UBM
0
100
200
300
400
Femur (AVG) Tibia (AVG)
Bending Moment (Nm)
Center Outboard
05
1015202530
MCL ACL PCL
Knee Ligament Elongation (mm)
Center Outboard
aPLI
Discussion• Increased femur bending moments in FlexPLI-UBM & aPLI
• Upper body mass & higher CG location• Lower impact height
• Increased MCL/PCL elongations• Lower impact height
• Varying ACL elongations• Ligament orientation in aPLI
• Relative measurements for 3 legforms• Maybe vehicle shape specific
18
FlexPLI/UBM aPLIHuman Knee From Isshiki et al., IRCOBI 2018
• FlexPLI-UBM and aPLI exhibited more realistic kinematics with respect to human body model simulations
• FlexPLI and FlexPLI-UBM exhibited greater yaw rotation than aPLI at the outboard impact location
• Possibly due to different knee shape
Discussion 19
aPLIFlexPLI
vs
FlexPLI-UBM
Conclusions• Both FlexPLI-UBM and aPLI easy to use and adapt to VRTC system
• At 9 m/s (we are now upgrading our system to achieve 11.1 m/s)
• Preliminary FlexPLI-UBM and aPLI results show:• Increased femur bending moments & MCL/PCL elongations• Varying ACL elongations• Similar tibia bending moments• More realistic kinematics
20
Future Work• Need to better understand how design updates affect legform
response by performing tests that isolate influences of:• Upper body mass• Legform impact height• Knee-bumper interaction• Cruciate ligament orientation
• Testing at 11.1 m/s on the Ford Edge and additional vehicles
• Need to investigate upper leg part of the equation• Upper leg/UBM measurements vs. upper legform in matched pair tests
21