Failure Analysis of Broken Drinking Glass

Glass expert performs a failure analysis on a broken drinking glass from a restaurant. As the glass was being filled with cold water, the drinking glass split into two equal halves. The failed drinking glass was made of thick glass, and its rim was tempered. A failure analysis was performed by a glass failure analysis expert, and he discovered that the failure had initiated at a minor damage site on the interior wall of the tumbler. It is hypothesized that the failure was caused by thermal shock. The cold water was poured into a glass recently removed from the dish washer; in this case, the glass had not cooled sufficiently before the interior wall was chilled by the cold water. The cold water rapidly cooled the interior wall and put it into tension. The tensile stresses caused by surface chilling caused the glass to crack. The damage on the interior is believed to have been caused by normal restaurant handling. Tumblers made from thicker glass cool more slowly, and these are more likely to exhibit this type of failure during rush periods in a restaurant. Curiously, this particular glass split perfectly in half.

The upper left photograph is an overview of the failed glass. Upper right is a 40X photomicrograph of 1/2 of the failure origin.

Nickel Sulfide Particles in Tempered Glass

Glass failure analysis expert witness performs a failure analysis on a tempered glass window. The failure was initiated by a nickel sulfide, NiS particle. The glass failure analysis expert was able to retrieve both halves of the failure origin. One side of the failure origin contained the protruding NiS particle. On the other side of the failure origin there was a hole out of which the NiS particle had pulled out when the two halves of the failure origin were separated. Above are two photographs of the two halves of the failure origin retrieved during the failure analysis. These photomicrographs were taken at 100X magnification using Nomarski interference contrast optics. This is a manufacturing defect. The NiS entered the glass during the melting operation.

Glass Expert Performs a Bottle Failure Analysis

A California Glass failure analysis expert witness was asked to examine a failed wine bottle. A portion of the bottle top broke off midway down the cork as the cork was being removed. The root cause failure analysis revealed that the bottle had received a impact to the side. The distinct Wallner lines (see the photomicrograph above) located near the origin demonstrate that the impact was severe. The interaction of the crack front with the vibrations generated by the impact caused very visible Wallner lines. There was no manufacturing defect associated with this failure. When and how the impact occured cannot be determined from this failure analysis.

Glass Expert Analyzes WIndow Damage

Glass failure analysis expert analyzes scratched windows on new construction. There have been numerous occasions where a glass expert has been brought in the determine the cause of window scratching. This is often on new construction that has a stucco exterior. Post construction window claening is critical because of adhered construction materials. Removal of these materials is difficult because of their adhesion. Therefore, cleaning crews should not use blades to remove debris. In many cases abrasive debris such as stucco or cement can be captured by the blade and scratch the glass as the blade is being drawn across the surface. Abrasives can also be captured by dry cloths and pads and can also cause window scratching. The photographs above show the resulting window scratches. Upper left is a sample of cloth related window scratching, and upper right is a sample of metal blade related window scratches. These are window cleaning related and are not manufacturing defects. Only experienced window cleaners should be assigned to clean windows on new construction.

WIndow Defect Analysis

Glass failure analysis expert witness has analyzed numerous cases of window damage. Often a metal blade is used by the window cleaners. In many cases the window damage is found on new construction. GANA has specific window cleaniong instructions that forbid the use of metal blades. The concern is that the blades pick up abrasive particles that get between the blade and the window glass and cause glass scratching when the blade is moved across its surface. In the case of scratched tempered glass, there is a consern that glass particles have attached themselves to the window surface during the tempering process. Later cleaning will dislodge these particles and they will cause scratching. The california failure analysis expert has examined unscratched clean windows that have streaks that were shown to be adhered glass particles. This observation proves two things:

1. Cleaning tempered windows with adhered particles can be done without scratching. Use of a blade during cleaning of tempered glass will cause scratching and the abrasive is not necessarily adhered glass. It can also be dirt or abrasive materials such as concrete or stucco.

2. Microscopic examination can be used to determine if there are glass particles stuck to the surface of tempered glass.

Above are two microphotographs of a tempered glass surface found to have adhered glass. Upper left is 25X magnification and upper right is a 200X magnification. This window was cleaned before the pattern of adhered glass was discovered. Tempered glass window cleaning defects can be avoided even when there are adhered glass particles. On ther other hand, it is extremely risky to use metal blades for window cleaning if window scratches are a problem.

GLass Expert Discusses Nickel Sulfide Spontaneous Failures

Glass failure analysis expert witness demonstrates that in the case of the spontaneous failure of tempered glass, the tempered glass failure is caused by the NiS particle. The failed glass door was taken apart to reveal the NiS particle. At this point the Wallner lines surrounding the NiS particle were located. The Wallner lines domonstrate that the NiS particle is in the center of the failure origin, and must be the cause of failure. The upper left photograph is a 20X photomicrograph of the NiS particle and its surroundings taken using Nomarski optics. Upper right is the same photomicrograph upon which arrows have been placed to show the crack travel directions as indicated by the Wallner lines. One can see that the NiS particle is at the center of the origin, and is the cause of the failure.

Glass Expert Performs Failure Analysis of Drinking Glass

In order to simulate potential cracking of a heavy bottom drinking glass still hot from a commercial dishwasher, a glass was immersed in 140°F water till stabile. The glass was removed and ice water was then poured into the glass. A glass failure analysis expert witness then performed a failure analysis on the resulting cracked drinking glass. The drinking glass tested is not new; therefore, there is random handling damage present both inside and outside the tumbler. The upper left photo shows the overall cracking resulting from thermal shock. To the right is a photograph of the cracked bottom of the glass. The location of the crack origin is indicated. The crack started in the center of the bottom on the inside surface. When the ice water hit the hot interior bottom, it put the interior surface in tension, and this started the glass cracking. Upper right is a 25X photomicrograph of the crack origin. The failure began at a point where there is a small bruise. It is important to see that there is no major handling damage at this origin. This is because the failure was driven by thermal stresses not mechanical stresses. In addition, the initial part of the crack at the origin is not straight. The direction of the stresses are changing even when the crack is initiating.

GLass Expert Discusses Chill Cracks

Glass failure analysis expert witness discusses a common glass bottle manufacturing defect. After the bottle has been formed it is removed hot from the clam shell tool. If it encounters any localized cooling at this stage, it can form a manufacturing defect called a "chill crack". Thermal shock cause the cooled area to shrink, and this causes localized tensile stresses. This event can create a small crack that can cause later failure of the bottle. Above are two photos of the same chill crack. Upper left is a 20X photomicrograph, and upper right is a 40X photomicrograph. To start, this crack is less than 0.1" long, and it has grown to be approximately 0.7" long. The bottling line has had numerous failures from this lot of bottles, and the cause has been traced back to this type of chill crack.

Cosmetic Bottle Failure Analysis

Glass failure analysis expert witness performs failure analysis on a broken small cosmetic bottle. This bottle failure occured when it was being capped on the line. The objective of the analysis was to determine the cause of the failure and to advise the bottle manufacturer. The bottle broke into two pieces, and these are shown in the upper left photograph. Upper right is a 20X photomicrograph of the failure origin. This failure originated as a result of a "chill crack" which is a manufacturing defect formed when, exiting the clam shell tool, the hot bottle touched an unprotected metal tool. The cold spot created a chill crack that eventually caused the bottle failure. The manufacturer is presently correcting the manufacturing problem. In the meantime, only bottles from another supplier are being used.

Glass Failure Analysis Of Bottle Defect

California Glass Expert Witness was assigned to determine the cause of failure of wine bottles at the manufacturing facility. During processing the bottles had a higher than normal failure rate. A root cause failure analysis was performed by the glass failure analysis expert witness. He inspected a large number of whole bottles and removed those with visible defects. In addition failure analysis was performed on those bottles that failed in manufacturing. Above left is a photomicrograph of a "crush" or "bruise" found on one of the unbroken bottles. This type of defect was found on several bottles. This bottle defect appears to be a result of impact damage. Curiously, there is an open surface bubble (i.e. seed) in the vacinity of the bruise. Upper right is a photomicrograph of the fracture surface of one of the failed bottles. The origin of this failure is at the same location on the bottle as the bruises found on whole bottles. In addition, this failure started at a small diameter bruise. The repetitive nature of the location and the nature of the defect indicates that this manufacturing defect is caused by the glass handling machinery either at the bottle manufacturing facility or at the bottling plant. Also, this damage is severe enough to cause bottle failure.

Product Liability, Chair Failure Analysis

Failure analysis expert witness examined a failed hospital chair. The chair failed during a breast X-ray examination. The chair had been altered 3 years prior to the failure, and the machine shop that had made the alterations was accused of causing the fatigue failure. Examination of the chair discovered hammer marks on a critical region of the chair. The chair owner had performed repairs two days prior to the accident. The nature of the repairs was such that the hammer marks would have been appropriate. Therefore, the failure was attributed to user error. This fatigue fracture was not the result of a product defect. Therefore, product liability was not in question.

Failure Analysis Expert Witness Analyzes a Pipe Fatigue Failure

Failure analysis expert analyzes a pipe failure. In this case the failed brass pipe supported a gauge. The gauge was cantilevered on the 6" long pipe and valve assembly. This assembly was attached to a pump, and the pump vibrations acted on the assembly and caused a metal fatigue failure to initiate ar the root of the male pipe thread where the thread exited the 'T' fitting. This is the most vulnerable point. The moment is maximum at this point and the root of the thread was a stress concentrator that magnified the stresses caused by the vibrations. The photographs above summarize the failure. Upper left shows an overview of the failure. The pipe failure occured where the pipe entered into the 'T' fitting. Upper right is an 8X photomicrograph ofthe fracture surface. The fatigue failure initiated at the root of the pipe thread. It then proceeded to the left as shown by the arrows. Fundimentally, the vibrating weight of the cantilevered, unsupported gauge caused the failure.

Wine Bottle Failure Analysis

Glass Failure Analysis Expert Witness Performs Wine Bottle Failure Analysis. In this product liability case the user was injured as the cork was being extracted. The glass failure expert witness performed a glass failure analysis and determined that the bottle failure initiated at the very top of the bottle. Thus, the cork screw could not have caused the damage that initiated the failure. Unopened bottles from the same case were examined, and it was discovered that the rod that pushed the cork in was very close to the glass in three of the four bottles that were examined. This indicates that the failed bottle was damaged during the corking operation. In addition, the forces used to extract the cork drove the pre-existing crack to failure. The photograph on the upper left is of the failed bottle top. In this photo the origin and crack travel direction are indicated. Upper right is a top down photo of a cork from one of the unopened bottles. The impression made in the cork is from the rod that pushed the compressed cork into the bottle. One can see from the impression that the rod was not centered. This indicates that the subject bottle failed due to corking damage. This is a manufacturing defect.

Failure Analysis Expert Witness Examines Failed Rivet

A failure analysis expert witness performed a rivet fialure analysis of a rivet involved in a ladder failure. The failed rivet, which is a hollow end rivet, was found to be too short for the intended application. The photo on the upper left is a cross section of the failed rivet in question. The clinch allowance of this rivet was inadequate and over time the folded over portion failed from fatigue and allowed the joint to open. The center photograph is of a similar rivet. One can see that this rivet has very little left to grip on the hollow end. This rivet has not failed; however, it does show significant deterioration. Upper right is a rivet that has the proper clinch allowance. In additon, this rivet does not show any signs of deterioration.