Tibia Index (TI)

Overview

The Tibia Index (TI) injury metric uses A-P Moment (Y), L-M Moment (X), and Axial Force (Z) to understand the combined loading of compression and bending moment during frontal crashes. The leg has upper and lower tibia load cells that can be used to calculate TI.

Signals

• Tibia A-P Moment (Y)
• Tibia L-M Moment (X)
• Tibia Axial Force (Z)

Calculation

Calculation from SAE 1727 [1]

1. Filter Tibia Force and Moment data (CFC = 600)
2. Apply Tibia Moment Correction
3. Calculate TI using Equation 1 [1]

$$\tag{Equation 1}TI = ABS(\frac{M_r}{M_c}) + ABS(\frac{F_z}{F_c})$$ $$\tag{Equation 2}M_r = (M_x^2 + M_y^2)^{1/2}$$

Hybrid-III Dummy Tibia Upper and Lower Load Cells [1]. The Y-Axis is into the page.

Tibia Index Critical Values

Critical value from Mertz et al. [2], Craig et al [3], and Kuppa et al. [4].

ATD	$F_c$ (kN)	$M_c$ (N-m)
HIII - M95	50.0	307
HIII - M50	35.9	225
HIII - F05	22.9	115
THOR - M50	12.0	240
THOR - F05	8.6	146

Injury Criteria

Injury criteria for tibia from IIHS [5],

Criteria	IARV	Good-Acceptable	Acceptable - Marginal	Marginal - Poor
Tibia-Femur Displacement (mm)	-15	-12	-15	-18
Tibia Index (Upper, Lower)	1.00	0.80	1.00	1.20
Tibia Force (kN)	-8.0	-4.0	-6.0	-8.0

References

[1] "Calculation Guideline for Impact Testing" No. J1727-2015-02 SAE International. SAE Technical Report, 2015.

[2] Mertz, Harold J. "Anthropomorphic test devices." Accidental injury: Biomechanics and prevention. New York, NY: Springer New York, 1993. 66-84.

[3] Craig, M., et al. "Injury criteria for the THOR 50th male ATD." National Highway Traffic Safety Administration (2020).

[4] Kuppa, Shashi, et al. "Lower extremity injuries and associated injury criteria." No. 2001-06-0160. SAE Technical Paper, 2001.

[5] "Frontal Offset Crashworthiness Evaluation - Guidelines for Rating Injury Measures" No. 2009-06. Insurance Institute for Highway Safety (IIHS), 2009.