This study demonstrated the initial feasibility of using nondestructive inspection (NDI) penetrant-based methods for detecting fatigue cracks and similar breaches of integrity in chemical protective clothing and shelter materials. Such a technique could provide a simple but direct means of determining remaining life in chemical protective suits and shelters. Chemical protective materials range from coated fabrics to highly engineered multi-layer, multi-film composites. Selected materials were tested using off-the-shelf penetrant systems normally used for inspecting metallic surfaces. Microscopy, biopenetration, and chemical permeation were used to verify the results of penetrant NDI testing. The selected materials were fatigued using a “Gelbo flex tester” to simulate wear and repeated flexing. Controlled diameter and depth punctures were also used to induce material defects.
Fluorescent penetrants applied to Teflon/Nomex or fiberglass/Teflon composite laminates formed large florescent halos around defects which had breached the top layer of Teflon. These easily observed halos show through the translucent coating and were the result of penetrant wicking into the fibrous center layer. The detection success for defects which breached the outer Teflon layer was virtually 100%. Halo indications were typically 7 mm in diameter for a 0.12 mm puncture defect--representing an amplification factor of over 50. When a fatigued sample failed biopenetration, the same fatigue level sample produced positive penetrant testing results. Penetrant NDI results also correlated well with chemical permeation results. Fluorescent indications were observed for controlled punctures which were half as deep as the material thickness. Other types of chemical protective suit and shelter materials were tested, including PVC and butyl coated fabrics. while halos occurred in some of these materials, background coloring of other materials caused interference with the technique.