Glass Expert Witness Discusses Tempered Glass Fracture Surface

California failure analysis expert witness examines two distinct fracture surfaces for tempered glass failures.
According to the tempered glass expert witness, the surfaces of tempered glass are under compressive stress. This stress is balanced by an "equivalent" tensile stress in the center of the glass. Tempered glass failures are really the end result of self destruction. The mid-plane tensile stresses take control of any defect that enters the center of the glass pane and drives the crack to the point that the original piece becomes a large number of almost cubic diced pieces. , under normal conditions, the fracture surface consists of two sets of Wallner lines separated by a central zone of mist hackle (upper  photo-micro-graph). The fracture surface for a tempered glass piece that failed as a result of bending is distinct. The fracture surface shows a shift of the central mist hackle toward the convex side of the bend. In this case, the Wallner  lines have essentially disappeared (lower photo-micro-graph).