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.

Porcelain Failure Analysis

California failure analysis lab is able to show similarities between glass failure analysis and porcelain failure analysis. The predominant tool for tracking a crack in glass is to look at "Wallner lines" These can tell the direction of travel of a crack in glass. This allows the glass failure expert to trace the crack back to the origin. He can then analyze the origin microscopically to determine the root cause of the failure. Glass is a smooth material, and the Wallner lines are readily visible. Porcelain is also a brittle material, and it also fails in a brittle manner. The difference is that the porcelain fracture surface is grainy and artifacts on the porcelain fracture surface (such as Wallner lines) are very difficult to see. Above are photographs of the fracture surfaces of two bending failures, one glass and one porcelain. The Wallner lines on the glass fracture surface are obvious and readily visible. The Wallner lines on the porcelain surface are very difficult to see and are best seen in oblique light. A sample of each is given above for the reader to see the differences/

California Failure Analysis Expert Witness Examines Failed Glass Pool Tiles

California glass expert performed a failure analysis on several broken glass tiles. These tiles were above the water line in a swimming pool. The failed tiles were removed and submitted for failure analysis. It was impossible to open the tiles to examine the fracture surface. The thin set mortar had "squeezed" into the crack and was firmly holding the tile pieces together. The tiles were soaked overnight in muriatic acid to allow separation. They could then be pulled apart to expose the fracture surface for failure analysis. The figure above is an 8X photomicrograph of a representative fracture surface. All the failures initiated on the backside of the tile. It appears that the glass tile backside was forced against a small hard particle during mounting in the thin set mortar. The failure initiated at a point on the glass tile backside and srpead into the tile (indicated by the arrows). The root cause of the glass fracture was inpact against a hard particle, The fact that the mortar had squeezed into the crack indicated that the glass tile failure occured during mounting. Perhaps the tile setter was using a mallet to align the glass tiles.

Glass Fracture Due to Liquid Pressure

Glass failure analysis expert witness performs a failure analysis on a hollow glass tube that failed due to internal pressure. The glass fracture initiated at a small bruise on the outer surface of the glass tube. The upper left 25X photomicrograph gives an overview of the failure. One can see that the glass fracture analysis determined that the failure initiated at a small bruise. The upper right 100X photomicrograph gives more detail of the origin. This was a manufacturing defect because the bruise was created during manufacturing.

Shaping Flat Glass

Glass expert describes the condition of the edges of windows, mirrors and other flat glass pieces. Almost all flat glass pieces are shaped from larger pieces using glass scribe and break techniques. Thus the edge of the part has two distinct sides. The photograph above is a microscopic picture of a the edge of an automobile mirror that was shaped in automatic scribing machinery. The top of the photomicrograph is the surface where the scribing tool has created controlled glass damage (i.e. crush). In general the damage is uniform. This photo imcorporates the start of the glass scribing, and this point always has more significant damage. Glass failure analysis determined that glass cracking due to thermal stresses initiated at the start point. Glass fracture analysis indicates that glass cracking always starts at the weakest point under tensile stresses.

Botle Manufacturing Defect

Glass failure analysis expert performs a root cause failure analysis on a bottle failure. In this case a manufacturing defect was causing numerous failures on a manufacturing line. The tops of these small bottles were coming off. The upper left photomicrograph is with the two halves of the bottle re-assembled. The upper right photomicrograph is of one of the glass fracture surfaces. The failures were occuring just below the transfer ring at a glass molding defect. The molding defect is a fold in the glass that acts as a stress concentrator. The lower left photograph is of an unused bottle with the defect. This is an unacceptable manufacturing defect and the parts werre returned as non-conforming.