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Estimation of Armour Backface Velocity

NCJ Number
310408
Date Published
October 2021
Length
10 pages
Annotation

This paper reports on the methodology and findings from a research study that aimed to identify impact conditions where backface velocity of armor may be estimated from clay testing in order to improve the assessment of a wearer’s risk of injury.

Abstract

The velocity of an impact plays a significant role in the response of biological tissue. Current techniques to assess behind-armor blunt trauma (BABT) only measure the static post-test depth in clay and cannot capture the velocity of deformation. Assessments of focal, high-energy impacts that include velocity have been shown to better predict increased injury severity. Previous work has described a technique to estimate the backface velocity (BFV) of armor in clay tests; however, the accuracy of that technique was not reported. To overcome this limitation, experiments have been conducted on ballistic gelatin to measure the BFV of the armor from a subset of the impact conditions previously conducted on clay. The estimates of armor BFV using the conservation of momentum, areal density of the armor, and the area of the clay impression at the impact surface were biased lower than the BFV calculated from high-speed video analysis of ballistic gelatin tests. In other words, the BFV from the gelatin tests tended to be faster than the estimated BFV from clay. Closer inspection of these cases indicated that often many layers of the armor were penetrated, suggesting that the mass of the involved-armor may be overestimated in the calculations. One case exhibited the opposite trend (estimated clay BFV was faster than gelatine BFV). This case involved an impact near the edge of the armor, possibly underestimating the impact area in the clay. This would lead to an underestimation of the mass of the involved-armor, and therefore, an increased BFV estimate. This study begins to identify impact conditions where the BFV of armor can be estimated from clay testing. As velocity may be an important indicator of injury, being able to include a parameter from the backface signature that incorporates it would improve the assessment of injury risk of BABT. (Published Abstract Provided)

Date Published: October 1, 2021