Failure Analysis Lab Analyzes Shower Door Failure

Installed Shower Door

Top Roller  at Stop

Disassembled Roller

Fracture Surface at Origin

Tempered glass shower doors have been modernized. Recent designs have the doors suspended by rollers that ride on a pipe. In certain cases the door stop is on the top. In this case, the roller is stopped by a rubber bumper. Several of these doors had failed during use, and the glass experts at Read Consulting were asked to perform a failure analysis and suggest solutions to the glass fracture problem.

The two top photographs illustrate how these types of doors are installed. Basically they are hung on two rollers that are bolted to the tempered glass doors using holes cut into the glass. At the end of travel, these doors are stopped when one roller hits a rubber bumper. There is some cushion from the rubber bumper; however, this is not enough.

Glass failure analysis was performed on a representative failed door. In this case, the failure origin was clamped in one of the two rollers. The failure initiated on the interior wall of one of the through holes in the glass. It is believed that the failure forces are created by torsional moments generated because the top of the door is stopped, but the bottom of the door is not. When the door is stopped at the top, the unrestrained bottom creates a large rotation moment. This moment puts high forces on the walls holes in the glass. These forces act on the ground hole walls to cause failure.

The two lower photographs document the glass failure analysis. It is believed that the stopping mechanism must not generate twisting moments. One solution is to put the rubber stopper in the center of the door, not at the top. Another solution is to slowly reduce the door speed (i.e. create drag) before it hits the stop at the top.

Failure Analysis Lab performs Electronic Failure Analysis

Array of Pogo Pins

Top of Pogo Pin at Mag. 30 X

Cross sectioned Pogo Pins at Mag. 5 X

Read Consulting Failure Analysis Labs often perform electronic failure analysis for various manufacturers. The objective is to determine the root cause of the failure and help the manufacturer correct the problem.In this case, a company that assembles an array of Pogo connector pins into an instrument for multiple contacts. Some of the Pogo pin arrays are hand soldered into the equipment; other arrays are assembled using a wave solder machine. The wave soldered arrays had poor contact. Initially we were told that there were two shipment lots of Pogo pin arrays, and it was thought that  one was bad. Read Consulting tested a representative sample from both lots and could find no difference:
1. Through the optical microscope the pins from both lots were found to have good gold plating. On the upper left is a  photomicrograph of the surface of a "bad" pin.
2. In both cases testing the Pogo pins with a needle showed good contact all through the instrument.
3. Samples were cross sectioned and both lots showed good plating on the interior of the Pogo pins. Center photomicrograph.

The client was advised that there was no bad lot. It was suggested that the Pogo pins be wiped with isopropyl alcohol and retested. This test was successful; therefore one must conclude that a contaminant film settled on the contact surfaces during the wave solder operation. The alcohol wipe was added to the procedure.

Tempered Glass Expert Discusses Tempered Glass Fracture Surfaces

Fracture Surface of Thermally
Tempered Glass

Fracture Surface of Chemically
 Tempered Glass

The Glass Expert Witness at Read Consulting have performed hundreds of glass failure analysis on tempered glass pieces. These include both thermally tempered and chemically tempered glass.


Thermally tempered glass has compressive stress on its surfaces. The thickness pf the compressive layer is a function of the over all glass thickness; this thickness is 20% of  the glass thickness. In addition, the resulting fracture surface of thermally tempered glass has distinct characteristics. There are two sets of Wallner lines (which indicate the crack travel direction) separated by a band of mist hackle. In addition, near the surfaces there are parallel markings indicating the surface compressive stresses.

Chemically tempered glass also has its surfaces in compression. For this glass, the compressive layer is very tin; it is on the order of 10µ's. In addition, this thickness is not a function of the glass thickness. It is dictated by the chemical tempering  process. Because the compressive layer is so thin, there are no distinct markings on the fracture surface. Often the fracture surface is featureless, or it will have a single set of Wallner lines indicating the direction of travel.