Biofidelity of the Hybrid III and Thor Knee-Thigh-Hip Complex [Shashi Kuppa] 2003 SAE Government/industry meeting

SLIDE 1:
KNEE-THIGH-HIP INJURIES AND KNEE/FEMUR COMPLIANCE OF THE HYBRID III, THOR-Lx AND HUMAN CADAVERS

Shashi Kuppa, NHTSA
Jonathan Rupp, UMTRI
Larry Schneider, UMTRI


SLIDE 2:
KTH INJURY SCENARIO IN FRONTAL CRASHES
(diagram of pelvis/femur/patella/tibia and fibula as lower half of seated vehicle passenger)

-> Force applied at the knee is transmitted throught the thigh and to the hip (bolster to knee impact force)

-> body motion forward


SLIDE 3:
Michigan CIREN Center

photo & xrays accompanying diagram (see slide 2) indicating mechanisms of injury.

bar chart 
HIP INJURIES IN FRONTAL CRASHES
1989-1990:	 3
1991-1993:	11
1994-1995:	18
1997-1999:	17


SLIDE 4:
bar chart: RISK OF AIS +2 INJURY IN DIFFERENT RESTRAINT ENVIRONMENTS (NASS/CDS 1992-2001) 

Head
 - bag + belt	<2%
 - bag only	>4%
 - belt only	<2%
 - unrestrained	10%

neck
 - bag + belt	<2%
 - bag only	<2%
 - belt only	<2%
 - unrestrained	<2%

thorax/abd
 - bag + belt	<2%
 - bag only	>2%
 - belt only	>2%
 - unrestrained	 5%

upperex
 - bag + belt	<2%
 - bag only	<2%
 - belt only	 2%
 - unrestrained	<2%

lowerex
 - bag + belt	<4%
 - bag only	 7%
 - belt only	>2%
 - unrestrained	<10%

KTH
 - bag + belt	 2%
 - bag only	<4%
 - belt only	<2%
 - unrestrained

below knee
 - bag + belt	<2%
 - bag only	 4%
 - belt only	<2%
 - unrestrained	 4%


SLIDE 5:

bar chart ANNUAL LLI PER 100 FRONT SEAT OCCUPANTS IN DIFFERENT RESTRAINT ENVIRONMENTS (NASS/CDS 1993-2001

LLI (years) per 100 occupants
Head/Face
 - bag + belt	<1
 - bag only	2.5
 - belt only	<1
 - unrestrained	5.5

neck
 - bag + belt	
 - bag only	<1
 - belt only	
 - unrestrained	<1

thorax/abd
 - bag + belt	1
 - bag only	>1
 - belt only	<1
 - unrestrained	>3

upperex
 - bag + belt	<2
 - bag only	<2
 - belt only	<2
 - unrestrained	 2

lowerex
 - bag + belt	 2
 - bag only	<7
 - belt only	<2
 - unrestrained	<8

KTH
 - bag + belt	<1
 - bag only	 3
 - belt only	 1
 - unrestrained	 5

below knee
 - bag + belt	 1
 - bag only	<4
 - belt only	>1
 - unrestrained	<3


SLIDE 6:
bar chart RISK OF KTH INJURIES OF RESTRAINED OCCUPANTS BY AIR BAG PRESENCE (NASS/CDS 1993-2001)


SLIDE 7:
RISK OF KTH INJURIES IN AIR BAG EQUIPPED VEHICLES BY VEHICLE MODEL YEAR (NASS/CDS 1993-2001)
3 point belt restrained occupants


SLIDE 8:
FMVSS 208 AND NCAP TEST DATA

FMVSS 208 (unrestrained HIII dummy in 48kph frontal crash)

NCAP (restrained HIII dummy in 56kph frontal crash


SLIDE 9:
LOADING RATES IN PREVIOUS STUDIES
FORCE (kN) vs TIME (ms)
- melvin 1976.  lightly padded impactor
- melvin 1980. sled, padded knee stop
- powell 1975. rigid impactor
- leung 1983. sled, padded knee stop
- cheng 1984. sled, 1983 VW Rabbit bolster
- FMVSS 208 compliance test. results from a 2000 Taurus


SLIDE 10:
INERTIAL EFFECTS ON LOADING OF THE KTH COMPLEX


SLIDE 11:
EFFECT OF JOINT COMPLIANCES ON SHORT- AND LONG-DURATION LOADS


SLIDE 12:
UMTRI HIP TOLERANCE TESTING
schematic of test ficxture

pneumatic accelerator
- weighted pla
- hexcel

center portion
- impact surface
- ram
- applied force load cell
- molded knee interface

reaction force 
 - load cel (rigidly mounted)


SLIDE 13:
RATE OF LOADING IN UMTRI KNEE IMPACT TESTS
FORCE (kN) vs TIME (ms)
typical loading rates in FMVSS 208 tests are also less than 300 N/ms while the loading rates in previous research were 400-3000 N/ms.


SLIDE 14:
FEMUR TOLERANCE TESTING
- same apparatus as hip tolerance tests
- same specimens as those used in the hip tolerance tests with hip disarticulated and the head of femur inserted in an acetabular cup fixed to the support


SLIDE 15:
FEMUR TOLERANCE TESTING
- The femur is stronger than the acetagbulum (P<0.01) 
- Hip tolerance is 72+/-7% of femur tolerance


SLIDE 16:
RESULTS OF IMPACT TESTS
- Neutral posture hip fracture tolerance is 5.7+/-1.4kN
- femur facture tolerance is 7.6+/-1.6kN
- femoral neck is the weakest part of the femur.
- Using the displacement of the ram and the force applied at the knee:
	* the stiffness of knee-thigh-hip complex is 233N/mm
	* the stiffness of knee-femur complex is 370+/-80N/mm


SLIDE 17:
STIFFNESS OF HUMAN CADAVER KNEE/FEMUR COMPLEX AT LOADING RATES SEEN IN 30mph FRONTAL CRASHES (FMVSS208)

Most of the knee-femur axial compliance is due to femur bending rather than the compliance at the knee joint


SLIDE 18:
HYBRID III KNEE-THIGH-HIP COMPLEX
- Hybrid III knee-thigh stiffness based on fixed femur skeletal response of knee+distal femur sections by Horsch and Patric (1076)

[illustration of HIII complex, indicating femur casting, rigid femur, femur load cell, and knee skin and knee padding]

- Compliance of knee padding was selected such that HIII knee+distal femur response matches the Horsch-Patric data

- Donnelly and Roberts (1987) found the Hybrid III to produce three times greater force than cadaveric subjects in whole-body knee impact tests


SLIDE 19:
THOR KNEE-THIGH-HIP COMPLEX
- To better match Donnelly & Roberts data, Thor has a compliant element in the mid femur and redistributes some of the thigh mass to the flesh

[illustration of HIII complex, indicating femur casting, compliant femur, femur load cell, rigid knee cap, knee skin & knee padding]

- The knee design is similar to the Hybrid III knee with similar impact response characteristics. It has rigid hemispherical knee caps intended to provide more human-like interaction with the knee bolster.


SLIDE 20:
KNEE-FEMUR COMPLIANCE OF HYBRID III, THOR AND CADAVER IN MOLDED KNEE INTERFACE LOADING AT RATES SIMILAR TO THAT SEEN IN 30mph FRONTAL CRASHES

Initial stiffness (1800N/mm) of HIII knee-femur is due to compression of knee padding. After about 2mm, the HIII stiffness increases to 8100N/mm, which reflects the rigidity of the femur and the limited compliance offered by knee padding.


SLIDE 21:
COMPLIANCE OF ATDs AT TYPICAL LOADING RATES SEEN IN FMVSS 208 FRONTAL CRASHES

Thor knee/femur compliance = 3x cadaver knee/femur compliance

hybrid III knee/femur compliance = 16x cadaver knee/femur compliance

the Thor has a less stiff force deflection response than the Hybrid III dummy due to the compliant element in the Thor femur


SLIDE 22:
BIOFIDELITY OF ATDs
- Biofidelity of an ATD's knee-thigh complex depends on knee/femur stiffness, as well as inertial contributions of the knee/femur complex and other body regions.

- In order to address mass-coupling issues, knee impacts to whole body cadavers and ATDs (free back condition) will be conducted.

- Though the Thor knee-femur stiffness is 3 times greater than that of human cadavers, its response under dynamic knee loading, such as in frontal crashes, may be similar to that of human cadavers.


SLIDE 23:
NEW KNEE BOLSTER DESIGNS
With the advent of new knee bolster designs, such as inflatable bolsters, the biofidelity of the knee-thigh-hip complex of the ATD and appropriate injury criteria will become crucial to ensure adequate protection for the KTH complex in frontal crashes