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.

Glass Expert Performs Failure Analysis on Glass Blender Jar

The glass experts at Read Consulting in Santa Rosa California performed a glass failure analysis on a borosilicate glass blender jar that failed in a glass thermal shock test as a part of product qualification. The jar is operated with a stainless steel spoon inside. It is then subjected to thermal shock test by heating it to 140°F and then pouring a cold  mixture of vodka and ice into the hot jar. The jar must survive this test to qualify. A failure analysis was performed on a jar that failed the test. Upper left is a photograph of the cracked jar in the region of the failure origin. Upper right is a photo micro graph of the origin. The failure originated at a damage site in the interior wall of the jar (presumably caused by the spinning spoon). The failure was driven by thermal stress. Because the jar is made from low expansion glass and this is a standard qualification test, there must be an explanation as to why this jar failed the test. Examination with polarized light indicates that this jar was not completely annealed. This is shown in the center photograph taken with cross polarizers. There are significant residual stresses.

Glass Experts Examine Interior Wall of Champagne Bottles

The gas in champagne and most other sparkling wines results from the addition of a small amount of sugar after fermentation has ended. After the sugar addition, bottle is capped. The sugar reacts with remnant yeast and converts to alcohol and carbon dioxide. Because the bottle is sealed, the CO2 gas enters the wine as a dissolved gas. The conversion of the sugar leaves residue particles in the wine that make it cloudy. When the sugar was added a small amount of clay was also added. The clay combines with the fermentation residue and help with precipitation (i.e. drag it out of solution). In a process called "riddling" the particles are encouraged to deposit in the bottle neck just under the cap. This deposit forms a plug that is then frozen and removed before the bottle is corked.

 In this case the particles were attaching themselves to the interior bottle surface (photo upper left). The wine bottling experts at Read Consulting were asked to  determine the cause of the problem. The problem was intermittent, and it had two potential causes. One hypothesis was that there were ridges on the interior wall that were "catching" the particles as they fell toward the cap. This hypothesis is not likely because the bottles are blow molded, and they should have a smoothe interior wall. Another possible cause was a new coating that was being sprayed on the bottle interior. There were horizontal ridges visible on the bottle; however, it was not possible to determine if these ridges were on the interior or exterior wall. The glass experts at Read Consulting cut a panel from the bottle and examined both surfaces microscopically. The ridges that were visible were on the exterior wall; thus, they were not responsible for the "sticking" particles. After the interior spray coating was eliminated, and the problem was resolved. The manufacturing defect is the interior spray caoting.
 

 

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.

Failure Analysis of Glass Encapsulated Zener Diodes

Failure Analysis Lab examines performs a failure analysis on surface mount glass encapsulated Zener diodes. These diodes were in an appliance control board, and they are surface mounted to the underside a printed circuit board. The entire board is encapsulated in rigid polyurethane. There was a significant yield loss due to cracking of the glass encapsulation around the active assembly. Glass failure analysis determined that the failure origin was at the end of the diode where the glass is in contact with the metal end contact. Examination of  new diodes by glass experts found that the glass was cracked in the same location on new diodes. Thus, the failures were initiated before these diodes were assembled onto the printed circuit board.

Glass Expert Analyzes Drinking Glass Failure

The glass experts at Read Consulting were asked to perform a glass failure analysis on a drinking glass that had failed in a restaurant and had injured a customer. The customer had just filled the glass with cold water and was lifting it when it fell apart causing an injury. failure analysis determined that the failure initiated on the interior surface of the thick bottom of the glass. the fracture surfaces had very few markings. Thus, the forces involved were very low. It appears as if  the glass was still hot after removal from the dishwasher and the cold water created tensile stresses when it hit the bottom of the hot glass. The combination of the  stresses from thermal shock and a preexisting flaw on the glass bottom caused the glass failure. Although the manufacturer warns restaurants to allow these glasses to cool after cleaning and before using, the dynamics in a busy restaurant makes this difficult to do. It is also important to note that the glass on the bottom is over 1/2" thick, and it will cool very slowly.Often waiters will place silverware in glasses when either clearing or serving, and   contact of silverware with the glass bottom can cause damage that can later initiate a failure 

GLass Expert Discusses WIndow Failures and Window Evaluations

Glass experts at Read Consulting provide services as window experts. Read Consulting offers a wide spectrum of window testing and evaluation. Included are glass failure analysis, evaluation of window damage and window scratching, window performance (light transmission testing of low-E windows), problems with laminated glass, temper level of tempered and heat strengthened glass, nickel sulfide induced failures of tempered glass and window distortion. These services are a natural outgrowth of continuous involvement with glass, glass properties and useable items made from glass.