Glass Expert Performs Failure Analy on Low E Windows

California failure analysis lab was asked to determine why windows in an expensive hilltop home failed. The windows in question were Lo- E windows that were tinted to absorb infra-red light. At this location two south facing, side-by-side windows cracked. The window expert at Read Consulting was asked to perform a glass failure analysis to determine the root cause of the failure. For this failure analysis the site of the origin was cut from the window and  the failure origin was examined using a low power optical microscope. Both windows failed in an identical manner. Thermal expansion of the center of the Low-E window put the ground glass window edges in tension.A damage site from either the window sizing or window seaming processes was activated by the thermally generated stresses and cracked these windows. Please refer to the photographs above.    

Window Expert Discusses Metal Clad Wood WIndows

As a result of a window failure analysis performed by a failure analysis expert, several observations were made with respect to metal clad wood windows. The perception is that these windows are almost maintenance free. The outside metal cladding does not need painting, and the wood layer is inside, so it requires minimal maintenance. Numerous window failure analysis has shown that under certain circumstances, water enters through poor seals on the seams of the metal cladding. Once the water enters, the wood swells, and the seam openings worsen. Worse is that the wood cannot dry out because of the metal barrier. In addition, the metal cladding on the windows heat up to 140°F and higher. This is a "composting" environment that causes the wet wood behind the cladding to rot. In the early stages, the window damage is not visible because it is behind the metal cover. Eventually, the wood becomes weak and the window can no longer protect the interior of the building. Often this happens before the home owner is aware that there is a problem.

Glass Expert Witness Discusses Window Failure

Glass failure analysis expert discusses interesting window failure, that of a piece of antique window glass. The window expert performed a failure analysis that determined the failure initiated at crush damage from the scribing operation, and it started as a bending crack. It then transformed into a "thermal crack". That is the crack front was driven by thermally generated stresses ( either residual stresses or temperature differential generated stresses). Termal cracks tend to wander, and after this crack initiatiated it wandered and almost created a semi-circle (crack growth is indicated by the arrows in the above photographs). This window failure is interesting because this glass was made in the 1930's, and it was ground and polished. Present flat glass (i.e. float glass) is solidified on liquid tin and does not require glass machining (i.e.grinding and polishing). Also, modern float glass processing is better controlled than the previous roll forming processes.