THE MICROSCOPY OF CATASTROPHIC TIRE FAILURES

Tires sometimes suffer catastrophic failure during travel on highways, resulting in a scatter of tire fragments along the pavement and berms . A large number of these fragments, including partial and whole tires , were collected and examined microscopically The goal was to determin e what sort of evidence might be ''read'' from these fragments via the optical stereo microscope using examinations of 7x to 60x. It was fou nd that these fragments contain a wealth of well preserved information . Rubber tear lines and other fracture topographies are readable, allo wing the failure analyst to determine directions of fracture/tear prop agation which make it possible to postulate modes of separation. The f eatures of torn surfaces that are normally encountered in laboratory t esting are modified in tire failures due to the presence of adjoining compounds, complex shapes, and nonrubber components. Guidelines have b een established to account for these complicating variables. A concept of ''directional anisotropy'' aids the analyst in understanding produ ct failure surfaces. Additional items surveyed in this post mortem stu dy were the condition at wire belt ends and indications of wire corros ion.