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Comparison of aPLI and FlexPLI-UBM Advanced Pedestrian Legforms Jason Stammen, NHTSA Brian Suntay, Transportation Research Center Inc. SAE Government/Industry Meeting 2020

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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 Impactors4

FlexPLI

aPLI

FlexPLI-UBM

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: Center (L0), 9 m/s9

T_max

T_reb

aPLI UBM FlexPLI

Test Results: Outboard (L ± 4), 9 m/s10

T_max

T_reb

aPLI UBM FlexPLI

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

Comparison of aPLI and FlexPLI-UBM Advanced Pedestrian Legforms

Jason Stammen, NHTSABrian Suntay, Transportation Research Center Inc.

SAE Government/Industry Meeting 2020