Nondestructive Approach for Defect Detection in Hard Armor Protective Inserts

Abstract

Delamination detection in hard body armor is uniquely challenging and has affected the defense acquisition plan while generating uncertainty with respect to ballistic performance. The ability to confidently detect armor delamination is necessary to protect the warfighter and manage risk. The tap test has long been a benchmark in nondestructive inspection (NDI), including the investigation of composite structure delamination. The application of impact-based NDI to composite parts, although widely reported, is still hampered by a number of challenges. In a simple summary, NDI can be characterized as an inverse problem with the goal of inferring the presence of a defect by interpreting and extrapolating the system's "reaction" under controlled conditions. The fundamental challenge is that realistic armor delaminations (e.g. from manufacturing) may be too deep or too slight to be confidently deconvolved from the noise generated by armor system complications using an impact-based NDI approach. The subject research postulates that existing impact-based methods are not sensitive enough to detect small defects in thick-sectioned, finite-geometry, laminar composites such as hard body armor; however, modifications to the impact-based approach may provide greater sensitivity in discerning the presence of small delaminations. The research approach has three objectives: (1) define the target defect in hard armor protective inserts (2) evaluate the capabilities and limitations of impact-based NDI (3) propose methodology improvements that may achieve the desired sensitivity for hard armor inserts. Defect characterization, method sensitivity, potential confounds, and the extension to small defects are discussed. Impact-based NDI is a rudimentary tool that is deceivingly simple, yet versatile and widely applied. Under the right conditions, it can illuminate delamination in complex material systems.Ph.D., Mechanical Engineering and Mechanics -- Drexel University, 202