Manufacturing Defect on Tempered Glass Window

Glass failure analysis expert witness performed a root cause failure analysis on window defects found on a recently built custom home. The upper left photograph shows the defect from the building exterior. The window defect resembles a dust or dirt streak and was not detected until the post construction window cleannig. In all cases, the manufacturing defect is in the center of the window, is parallel to the long side and it looks like a streak or scuff. The upper right photograph is a 200X photomicrograph of a portion of the window defect. It is composed of an array of small glass particles strongly adhered to the glass surface. It is believed that these particles were generated during the window sizing process and were a contaminant on the horizontal rollers used in the glass temper process. During glass tempering they came into contact with the hot glass surface and welded to it. This is a manufacturing defect. It is not a construction defect. This defect is often blamed for window scratching from window cleaning operations. However, these particles were visibly obvious and could not be dislodged. Therefore, these particles don't fit the popular window damage model proposed by many window cleaning experts.

Tempered Glass Expert Describes Two Tempered Glass Fracture Surfaces

Glass failure analysis expert witness compares two typical tempered glass fractures. The lower photomicrograph shows a typical thermally tempered glass fracture surface . This piece is from a fully tempered glass sheet. That is; this glass has a surface compression stress of 10,000 psi or more. In addition, the compressive layer on each face is 20% of the thickness. This fracture surface has two sets of Wallner lines separated by mist hackle. The upper photomicrograph shows a representative chemically strengthened glass fracture surface. This one is of a 0.05" thick piece of chemically tempered glass. In this case the compressive layer is approximately 10 microns thick and the compressive stress is approximately the same as thermally tempered glass. The chemically tempered compressive layer is too thin to dominate the fracture. The Wallner lines on this fracture surface are similar to those one would find on the fracture surface of annealed glass.

Product Liability, Chair Failure Analysis

Failure analysis expert witness examined a failed hospital chair. The chair failed during a breast X-ray examination. The chair had been altered 3 years prior to the failure, and the machine shop that had made the alterations was accused of causing the fatigue failure. Examination of the chair discovered hammer marks on a critical region of the chair. The chair owner had performed repairs two days prior to the accident. The nature of the repairs was such that the hammer marks would have been appropriate. Therefore, the failure was attributed to user error. This fatigue fracture was not the result of a product defect. Therefore, product liability was not in question.

Failure Analysis of Wood Shipping Crate Failure

Failure analysis expert witness was asked to perform a root cause failure analysis of a wood shipping crate failure. It rolled over and caused a factory worker injury. The wooden crate in question was loaded with 3mm thick sheets of glass. This crate was designed such that there was a four inch lengthwise gap in the floor. The center section consisted of two short spacers. Therefore, when the crate was loaded onto a standard glass shop cart, the center portion of the stack of glass sheets (estimated weight of 1200 pounds) was unsupported and could press down onto the skids and separate the front floor board from the skid. The upper left photograph shows one end of the crate and the support "fork" of the cart. One can also see that the front floor board has pulled away from the skid. The same thing happend on the other end. Here one can see that the "tensile" nails had pulled out. In addition, the "shear" nails were very near the surface and these separated from the floor board without bending. The shear nails do not meet ASTM D36097 which requires these nails to be centered on the floor board. These nails provided no strength to the floor board. This is a manufacturing defect.