Tempered Glass Oven Door Thermal Shock Test Failures

 Glass experts at Read Consulting  performed a glass failure analysis on several fully tempered glass oven doors that failed in an unexpected manner during thermal shock testing. 100% of these doors failed the glass thermal shock test. The subject tempered glass doors were painted
with a 20µ thick picture frame on one side (top left photo). Using a Strainoptics grazing angle surface profilometer (GASP), the temper stress for all the doors tested (i.e. before thermal shock testing); all doors  measured to have surface compression stresses in excess of 13,000 psi. In the upper right photograph is a typical GASP output for these doors. Therefore one would expect the failure mode to be "dicing".In fact, all the failures initiated with long thermal
 cracks. Only in the later stages of failure did portions of the doors break into small pieces (i.e. dice). A typical failure is shown in the lower left photo. A typical failure origin is shown in the lower right photograph.         The failures initiated under the paint. This indicates that, during thermal shock, tensile stresses were created at the paint-glass interface that overcame the tempered glass compressive surface stresses and initiated a crack. These painted tempered glass oven doors had a 100% failure rate; Identical unpainted doors had a 100% survival rate.

Glass Experts Examine Hotel Window Defect

 The glass experts at Read Consulting performed a window defect analysis on defective windows at a hotel. The windows began to appear dirty, and no amount of cleaning could remove the "dirt". When initially installed, the insulated glass (I.G.) windows appeared normal. However, over time they began to appear perpetually dirty. Using a microscope to look through the glass from surface 1, it appeared that surface #2 was heavily scratched. The window was disassembled and surface #2 was examined directly with a microscope. The defect was found to be in the Low-E coating on surface #2. This is a manufacturing defect and not the fault of the building owners. Product liability rests solely with the manufacturer.

California Window Expert Performs Tempered Glass Failure Analysis

California glass expert was asked to perform a glass failure analysis on a glass door that failed spontaneously, The failure analysis lab located the failure origin. The glass experts then examined the fracture surface at the origin, and they determined that the root cause of the failure was a nickel sulfide particle. The failure origin magnified 200X is shown in the color photograph. This photo-micrograph was taken using Nomarski interference contrast. In it one can see that there is a spherical particle at the origin. Using energy dispersion spectroscopy (EDS) the elemental composition of the particle was determined. The chart shows that elemental composition of the particle is nickel (Ni) and sulfur (S). After the thermal tempering process, this particle, over time, went through a post temper phase change that generated tensile stresses and cracking which eventually caused failure. It is important to note that the particle is composed of only two elements, Ni and S.