Femur Force

Description

Femur Force reports the peak axial compressive load in a left or right femur and compares it with the occupant's available injury assessment reference value. Supported ATDs also receive an AIS 2+ femur-injury probability [1] [2].

When this feature is available

Femur Force becomes available when either the current curve selection or any loaded test contains a femur measurement set that meets the requirements. Only channels with a usable data status count.

The required measurement set includes:

• The signal attachment must be FEMUR - LEFT or FEMUR - RIGHT.
• The group must contain a force channel with:
  • Axis: Z - LOCAL
  • Units: NEWTONS

WebSAT checks each femur independently and enables Femur Force if any left- or right-side measurement set contains the required channel.

Settings

This feature has no settings.

How WebSAT processes the data

1. Validate the left- or right-femur Z-force channel.
2. Convert the force signal to newtons.
3. Filter the signal at CFC 600.
4. Trim pre-zero data when it is present.
5. Apply the expected compression polarity.
6. Find the peak compressive force and its time.
7. Compare the peak with the occupant's ATD-specific IARV.
8. Report the peak, percent of IARV, and AIS 2+ probability when supported.

Reference values and injury risk

The Hybrid III values follow the published ATD IARVs, and the THOR value follows the THOR injury-criteria report [4] [5].

ATD	Femur compression IARV (N)
Hybrid III 5th female	-6805
Hybrid III 50th male	-10008
Hybrid III 95th male	-12700
Hybrid III 6-year-old	-2310
THOR 50th male	-10577
THOR 5th female	-6510

A negative sign denotes compression in the ATD coordinate convention. WebSAT compares force magnitudes when calculating percent of IARV.

Hybrid III 50th male and 5th female use the NCAP AIS 2+ logistic relationships. For THOR, WebSAT uses the peak compressive femur force in kilonewtons in this AIS 2+ relationship [3] [4]:

$P(AIS\,2+)=\Phi\left(\frac{\ln(1.299F_{LC})-2.62}{0.3014}\right)$

WebSAT leaves probability blank for unsupported ATDs.

Results

The summary reports test, occupant, left/right attachment, peak compression, peak time, IARV, percent of IARV, and AIS 2+ probability. The detail plot shows the filtered femur-force history and peak.

Femur-force summary for the left and right femurs of both front-seat occupants in test 10099.

Filtered femur-force history for the selected occupant and attachment.

References

[1] Insurance Institute for Highway Safety. Frontal Offset Crashworthiness Evaluation—Guidelines for Rating Injury Measures, 2009.

[2] Eppinger, R. et al. Development of Improved Injury Criteria for the Assessment of Advanced Automotive Restraint Systems: II, 1999.

[3] National Highway Traffic Safety Administration. Federal Motor Vehicle Safety Standards; Occupant Crash Protection; Final Rule. Federal Register, 65(208), 2000.

[4] Craig, M. et al. Injury Criteria for the THOR 50th Male ATD. National Highway Traffic Safety Administration, 2020.

[5] Mertz, H. J., Irwin, A. L., and Prasad, P. “Biomechanical and Scaling Bases for Frontal and Side Impact Injury Assessment Reference Values.” Stapp Car Crash Journal, 47, 2003, pp. 155–188. SAE Technical Paper 2003-22-0009.