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Phoenix666 writes:

The testing of soft body armor has been a big concern because the deployment of a new kind of fiber—believed to be superior to the previous material—unexpectedly failed in 2003, resulting in the death of a police officer. That and other incidents prompted a 2005 recall of some of the vests made with the new material.

Although the performance of these vests was superior when they were fresh out of the box and in pristine condition, tests later showed that the mechanical properties of the fibers inside the vests began to deteriorate after a few months of normal wear. The new vests were eventually removed from market entirely and the manufacturer was sued by the Department of Justice (DOJ).

[...] The positron annihilation lifetime spectroscopy (PALS) technique provides a molecular-level view of the structure of materials. It has been used for testing materials in other sectors, including porous membranes and semiconductor insulators. For this work, positrons were injected into ballistic fibers and enabled researchers to determine if any voids were created during folding on a scale of less than 5 nanometers.

Using PALS, Holmes and Soles discovered that void levels are very sensitive indicators of damage sustained by the fibers after folding; a larger population of voids means a better chance of fiber failure. The team previously suspected that void creation was a critical component of mechanical degradation, but the small angle X-ray scattering measurements that had been used in the past tended to be less sensitive to voids smaller than 5 nanometers and proved to be inconclusive. The critical damage was occurring on much finer length scales.

Until better materials are developed, do not fold, spindle, or mutilate your bulletproof vest.

Original Submission