Thoracic Trauma Index (TTI)

Overview

Thoracic Trauma Index (TTI) is used for side impact scenarios to evaluate vehicle occupant injuries. This injury criteria uses the maximum of rib acclerations and lower spine accelerations. Due to TTI using positive acceleration for calculation, right side impacts accelerations are inverted in order to alter the polarity for the calculation.

Inputs

Signals:

• Upper Rib Acceleration (G's) (Y)
• Lower Rib Acceleration (G's) (Y)
• Lower Spine Acceleration (G's) (Y)

Constants:

• Skip Bias Removal
• Impact Side (Left or Right)

Optional:

• Age (years) - For Cadaver, Animal or Human Tests
• Mass (kg) - For Cadaver, Animal or Human Tests

Calculation

For ATD Tests:

Calculation from SAE 1727 [1].

1. Apply NHTSA FIR100 Filter
   • Filter signals at CFC = 180
   • Subsample data to 1600 Hz (Time Step = 0.000625)
   • Remove the bias from the signal
   • Perform FIR100 Filter
2. Calculate TTI using Equation 1

$$\tag{Equation 1}TTI = \frac{(a_{max,\,rib} + a_{max,\,lowerspine})}{2}$$

$a_{max,\,rib}$ = the larger maximum of the upper and lower rib acceleration

For Cadaver, Animal, or Human Tests:

Calculation from Eppinger et al. [2] and Kuppa et al. [3],

1. Follow Step 1 from ATD test calculations

2. Normalize Upper Spine using age and mass of the subject

   $$\tag{Equation 2}Upper\,Rib\,Acceleration_{Normalized} = Upper\,Rib\,Acceleration * 1.3 - 2.02$$

3. Calculate TTI using Equation 3

$$\tag{Equation 3}TTI = 1.4 * age + \frac{(a_{max,\,rib} + a_{max,\,lowerspine})}{2} * (mass/75)$$

$a_{max, rib}$ = the larger maximum of the normalized upper rib and lower rib accelerations

Injury Criteria

Injury criteria from Trella et al. [4].

Car Type	TII Injury Limit (G's)
2 Door	85
4 Door	90

References

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

[2] Eppinger, Rolf H., Jeffrey H. Marcus, and Richard M. Morgan. "Development of dummy and injury index for NHTSA's thoracic side impact protection research program." SAE transactions (1984): 359-387.

[3] Kuppa, Shashi. "Injury criteria for side impact dummies." Washington, DC: National Transportation Biomechanics Research Center, National Highway Saftey Administration, US DOT 67 (2004).

[4] Trella, Thomas J., and Randa Radwan Samaha. "MOTOR VEHICLE SAFETY STANDARD 214 SIDE IMPACT COLLISION." Crashworthiness and Occupant Protection in Transportation Systems: Presented at the Winter Annual Meeting of the American Society of Mechanical Engineers. American Society of Mechanical Engineers, 1995.