Tibia Force

Description

Tibia Force reports peak axial compression at an upper or lower left/right tibia load cell. It compares the peak with the ATD's available reference value and reports THOR AIS 2+ risk when applicable [1] [2].

When this feature is available

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

The required measurement set includes:

• The signal attachment must be an upper or lower tibia location, such as TIBIA - LEFT UPPER, TIBIA - RIGHT UPPER, TIBIA - LEFT LOWER, or TIBIA - RIGHT LOWER.
• The group must contain a force channel with:
  • Axis: Z - LOCAL
  • Units: NEWTONS

WebSAT checks each tibia attachment independently and enables Tibia Force if any supported left- or right-side measurement set contains the required channel.

Settings

This feature has no settings.

How WebSAT processes the data

1. Validate the Z-force channel at the supported tibia attachment.
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. Use the attachment to select the upper- or lower-tibia IARV and THOR risk relationship.
8. Report the peak, percent of IARV, and available injury risk.

Reference values and injury risk

The Hybrid III values follow the published ATD IARVs; THOR and THOR-LX values follow the corresponding THOR injury-criteria definitions [1] [2].

ATD	Upper tibia IARV (N)	Lower tibia IARV (N)
Hybrid III 95th male	-9820	-9820
Hybrid III 50th male	-8000	-8000
Hybrid III 5th female	-5100	-5100
THOR 50th male	-7011	-8017
THOR 5th female	-4000	-3800
Hybrid III 50th male with THOR-LX legs	-5577	-5861
Hybrid III 5th female with THOR-LX legs	-4000	-3800

A negative sign denotes compression in the ATD coordinate convention. WebSAT compares force magnitudes when calculating percent of IARV. SID-IIs does not have a tibia-force IARV in the available ATD reference data.

For THOR results, WebSAT uses the peak compressive force in kilonewtons to calculate AIS 2+ probability. It uses separate relationships for the upper and lower tibia [2]:

$P(AIS\,2+\mid\text{upper})=\frac{1}{1+e^{5.7415-0.8189F_{upper}}}$

$P(AIS\,2+\mid\text{lower})=\frac{1}{1+e^{3.7544-0.4683F_{lower}}}$

Other supported ATDs receive IARV and percent-IARV output without a tibia-force probability.

Results

The summary reports test, occupant, tibia attachment, peak compression, peak time, IARV, percent of IARV, and THOR AIS 2+ probability when available. A time-history plot shows the processed force and governing peak.

Tibia-force summary for the available upper- and lower-tibia measurements from both front-seat occupants in test 10099.

Filtered axial tibia-force history for the selected occupant and attachment.

References

[1] 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.

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