Body Armor Testing

Introduction

When evaluating the ballistic performance of body armor, determining the back face deformation (BFD) during impact is of prime importance since this deformation is what a wearer's body would experience when shot. The current state of the art technique for obtaining this metric is to use clay as a backing material for the armor being tested, and measure the residual deformation in the clay after impact. This is a crude way to evaluate performance since no deformation-time history can be obtained from during the impact. Having deformation-time history data available would enable the performance of different body armors to be rated more effectively and the effect of a shot to be more accurately simulated in the body.

Most high accuracy techniques for high speed shape sensing require line-of-sight to obtain shape data (such as stereo high speed imaging with digital image correlation). This is problematic when using a backing material since line-of-sight is not available. In this project sponsored by the US Army's Test Resource Management Center’s (TRMC) T&E/S&T Program, a sensing layer was developed using fiber-Bragg grating strain sensors that collects data for reconstructing the BFD time history that occurs during ballistic impact.

Contributions

  • Managed and executed ballistic testing toward the development of a sensing layer for body armor testing

  • Developed setup and high-speed imaging technique for gathering deformation data during ballistic tests

  • Designed and fabricated test fixtures that have been used extensively over many different projects

  • Reconfigured and safety-checked high-pressure gas system for improved gas gun performance

  • Authored or coauthored 4 journal articles and 6 conference papers disseminating this work

  • Generated dataset of Kevlar BFD performance with over 300 downloads (doi:/10.17632/728mkms533.1)

Imaging Technique Details

A schematic of the test setup is shown below for obtaining the back face deformation during impact using clear ballistics gel and high-speed photography.

Using the high-speed video obtained using this setup, depth and volume (estimate) are calculated as a function time for the impact. This is achieved through an image processing algorithm that tracks which pixels are a part of the deformation.

Publications

F. Seng, D. Hackney, T. Goode, A. Noevere, A. Hammond, I. Velasco, K. Peters, M. Pankow, S. Schultz, "Dynamic back face deformation measurement with a single optical fibre," Impact Engineering, vol. 150, 2021. doi:10.1016/j.ijimpeng.2020.103800

D. Hackney, T. Goode, F. Seng, M. Pankow, S. Schultz, K. Peters, "Survivability of integrated fiber Bragg grating sensors in ballistic protection fabrics for high velocity impact testing," Optical Fiber Technology, vol. 60, p. 102356, 2020. doi:10.1016/j.yofte.2020.102356

D. Hackney, T. Goode, F. Seng, S. Schultz, M. Pankow, K. Peters, "In-situ strain measurement of ballistic fabrics during impact using fiber Bragg gratings," Optical Fiber Technology, vol. 59, p. 102334, 2020. doi:10.1016/j.yofte.2020.102334

T. Goode, G. Shoemaker, S. Schultz, K. Peters, and M. Pankow, “Soft Body Armor Time-Dependent Back Face Deformation (BFD) with Ballistics Gel Backing,” Composite Structures, 2019. doi:10.1016/j.compstruct.2019.04.025

A. Rocco, A. Noevere, T. Goode, and M. Pankow, “Survivability of Silicone Encased Fiber Bragg Gratings Subject to High Rate Impacts,” in SAMPE, 2018.

D. Hackney, T. Goode, K. Peters, M. Pankow, F. Seng, S. Schultz, and G. Shoemaker, “In-situ measurements of strain in soft body armor with FBG sensors during ballistic impacts,” in Optical Fiber Sensors, 2018.

D. Hackney, F. Seng, A. Noevere, T. Goode, G. Shoemaker, M. Pankow, and K. Peters, “Back Face Deformation Reconstruction of Soft Body Armor During Ballistic Impact Using Fiber Bragg Gratings,” in Society of Experimental Mechanics, 2018.

T. Goode, “Soft Body Armor Back Face Deformation with Ballistics Gel Backing,” North Carolina State University, 2017.

T. Goode, G. Shoemaker, K. Peters, and M. Pankow, “Predicting Body Armor Back Face Deformation (BFD),” in American Society for Composites - Technical Conference, 2017.

D. Hackney, S. Gundyal, T. Goode, K. Peters, F. Seng, S. Schultz, G. Shoemaker, M. Pankow, “Three Dimensional Shape Sensing of Woven Fabrics Using Fiber Bragg Gratings Under Quasi-Static Loading,” in Society of Experimental Mechanics, 2017.

F. Seng, D. Hackney, T. Goode, L. Shumway, A. Hammond, G. Shoemaker, M. Pankow, K. Peters, and S. Schultz, “Dynamic Shape Sensing Using Optical Fiber Strain Sensing,” in International Test and Evaluation Association Test Instrumentation Workshop, 2017.

F. Seng, D. Hackney, T. Goode, L. Shumway, A. Hammond, G. Shoemaker, M. Pankow, K. Peters, and S. Schultz, “Split Hopkinson bar measurement using high-speed full-spectrum fiber Bragg grating interrogation,” Applied Optics, vol. 55, no. 25, pp. 7179–7184, 2016. doi:10.1364/AO.55.007179