Mertz neck injury assessment

Description

Mertz evaluates an individual neck force or bending-moment history against an ATD-specific injury assessment reference value (IARV). Force assessments account for both load magnitude and duration; bending moments use fixed flexion and extension limits [1] [2] [3].

When this feature is available

Mertz becomes available when either the current curve selection or any loaded test contains the upper-neck measurement required for the selected Neck Load Type. Only channels with a usable data status count.

The required measurement depends on the selected load type:

• Shear Force: upper-neck X - LOCAL force
• Axial Force: upper-neck Z - LOCAL force
• Bending Moment: upper-neck Y - LOCAL moment
• Bending Moment with Apply Moment Correction selected: upper-neck Y - LOCAL moment and X - LOCAL force

WebSAT checks each occupant or test subject independently. The button becomes available if any measurement set contains the inputs for the selected settings.

Settings

• Neck Load Type selects Shear Force, Axial Force, or Bending Moment. The button label changes to show the selected load type.
• Apply Moment Correction corrects the bending moment to the occipital-condyle location. This option is selected by default and applies only to Bending Moment. It requires the companion upper-neck X - LOCAL force.

How WebSAT processes the data

1. Identify the load type and direction from the signal axis, units, and attachment.
2. Convert the signal to the standard force or moment units.
3. Apply the required impact-test filtering.
4. If Bending Moment and Apply Moment Correction are selected, correct the measured Y moment to the occipital-condyle location with the companion force channel.
5. Build the peak-versus-duration history for the processed signal.
6. Compare every point with the applicable ATD-specific IARV curve or fixed moment limit.
7. Report the governing load, duration, and maximum percent of the reference value.

Reference values and injury risk

Force-versus-duration curves

The force curves are piecewise linear between the listed time/load points. The coordinates are the Hybrid III-family IARVs published by Mertz, Irwin, and Prasad [1] [2]. Reference [1] is the corrected 2016 republication of the original 2003 paper. Positive loads represent tension or forward shear; compression values are negative. Only ATDs with populated curves can receive a force percent-IARV result.

ATD	Tension curve: time (ms) → load (N)	Compression curve: time (ms) → load (N)	Shear curve: time (ms) → load (N)
Hybrid III 95th male	0 → 5030; 38 → 4420; 49 → 1330	0 → -4830; 33 → -1330	0 → 3740; 27 → 1810; 38 → 1810; 49 → 1330
Hybrid III 50th male	0 → 3300; 35 → 2900; 45 → 1100	0 → -4000; 30 → -1100	0 → 3100; 25 → 1500; 35 → 1100
Hybrid III 5th female	0 → 2620; 28 → 2310; 36 → 690	0 → -2520; 24 → -690	0 → 1950; 20 → 950; 28 → 950; 36 → 690

Bending-moment limits

The fixed flexion and extension limits are from the same published ATD IARV framework [1] [2] [3].

ATD	Flexion limit (N·m)	Extension limit (N·m)
Hybrid III 95th male	252	-128
Hybrid III 50th male	190	-57
Hybrid III 5th female	95	-49
Hybrid III 10-year-old	125	-40
Hybrid III 6-year-old	60	-30
Hybrid III 3-year-old	42	-21
CRABI 18-month	29	-15
CRABI 12-month	27	-14
CRABI 6-month	25	-13
THOR 5th female	88.1	-94
SID-IIs 5th female	95	-49

Mertz results are expressed as a percentage of the governing curve or moment limit. This function does not convert the result into an AIS probability.

Example duration-dependent upper-neck tension reference curve [1].

Example forward/rearward shear reference curves [1].

Results

The summary identifies the test, occupant, load type, positive peak and duration, negative peak and duration, maximum percentage of the IARV curve, and the channel used. Supporting plots show the processed load and reference curve.

Mertz shear summary for the left- and right-front-seat occupants in the sample test.

Forward-shear duration curve for the selected left-front-seat occupant compared with the applicable IARV curve.

Rear-shear duration curve for the selected left-front-seat occupant compared with the applicable IARV curve.

References

[1] Mertz, H. J., Irwin, A. L., and Prasad, P. “Biomechanical and Scaling Basis for Frontal and Side Impact Injury Assessment Reference Values.” 60th Stapp Car Crash Conference, 2016. SAE Technical Paper 2016-22-0018. https://doi.org/10.4271/2016-22-0018.

[2] Mertz, H. J., Irwin, A. L., and Prasad, P. “Biomechanical and Scaling Bases for Frontal and Side Impact Injury Assessment Reference Values.” 47th Stapp Car Crash Conference, 2003. SAE Technical Paper 2003-22-0009. https://doi.org/10.4271/2003-22-0009.

[3] Mertz, H. J. “Anthropomorphic Test Devices.” In Accidental Injury: Biomechanics and Prevention. Springer, 1993, pp. 66–84.