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.

CA Glass Expert Performs Bottle Failure Analysis

Overview of Assembled Bottle 8X Mag.

View of Origin on Bottle 40X Mag.

View of Origin on Neck 40X Mag.

California glass expert was asked perform a glass failure analysis on numerous small cosmetic bottles. These bottles all failed where the neck intersected the shoulder of the bottle. Microscopic photos of a representative failure are given above. The glass fracture originates on the outside of the bottle and progresses inward before going around the bottle. These glass failures were found in the filling line, and the bottle manufacturer was notified. The root cause of these failures was determined to be a check (chill check?) in the neck where it intersects the bottle shoulder. This is a manufacturing defect that affects product liability.

Product Liability Expert Asses Changing Part Suppliers

Product liability is strongly dependent on part quality. This is a big issue when changing part suppliers, and there are times a product liability expert must be hired to examine parts from the new supplier.

In this case the supplier of a molded nylon part was changed and plastic failure analysis tests showed that the thread strength of the replacement part was inadequate. The possibilities considered were a change in the poloymer, improper glass filling and incomplete thread geometry. The new supplier actually failed on all three counts. He substituted a different polymer, he used shorter glass fibers, and he did not properly mold the part. A failure analysis expert performed a root cause failure analysis which indicated that incomplete molding of the threads was the main cause of the decrease in strength. A failure analysis expert cross sectioned representative parts and found the female threads were incomplete, and these provided inadequate strength. The cross section photomicrograph on the upper left shows the representative threads of a part from the original supplier. Upper right is that of the alternate supplier. One can see that the alternate supplier had formed incomplete threads.

Glass Expert Performs Bottle Failure Analysis

A glass failure expert witness performs a failure analysis on a failed cosmetic bottle. As received, the top of the bottle had broken off. Upper left is a photograph of 'as receceived' failed bottle. Approximately one half of the bottle finish had broken off. Read Consulting performed a glass failure analysis to determine if this failure was a manufacturing defect, or it failed as a result of shipping damage. The upper right photomicrograph is 30X view of the failure origin. The failure initiated at a bruise (small impact damage) on the top of the finish. Three of nine bottles from the same molding cavity also had damage to the top of the finish. In this shipping lot there were over thirty five bottles from other cavities, and none of these showed damage. Thus, the glass failure analysis expert witness believes that this product defect occured during manufacturing. However, both the shipping methods and the manufacturing proceedures will be reviewed for product liability improvement.

Champagne Bottle Glass Failure Analysis

Glass failure expert performed a complete glass failure analysis on numerous champagne bottles that had failed in the riddling process. These bottles are used for riddling and they are made from a large amount of re-cycled glass. Several of these bottle failures initiated at a site that had a piece of unmelted cullet (Note: Cullet is ground glass that is re-melted). The photographs above show one such failure from two vantages. The "lump" of unmelted cullet was larger in diameter than the thickness of the glass (0.120"). The bottle manufactrurer was made aware of the manufacturing process problem and is in the process of fixing it. This is a manufacturing defect that could potentially become a product liability.

Grinding Wheel Failure Analysis

Failure analysis expert witness performed a failure analysis on a broken grinding wheel. This is part of a product liability case where it was claimed that the wheel broke apart during normal use and injured the user. Examination of the wheel showed that the wheel had been broken by someone clamping it and breaking off a piece. The upper left photograph shows the failed wheel. this wheel has the paper label bent over. This indicates that the wheel did not spontaneously fail. Upper right is a photomicrograph of the paper label opposite the break. Visible is a linear array of marks indicating that this wheel had been held in a clamp (such as a vice). This evidence shows that the subject grinding wheel did not fail spontaneously as described by the injured user. There was no product defect or manufacturing defect with respect to this wheel.

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.

Glass Expert Discusses Exploding Tempered Glass

Classic Symetrical Temper Stresses

Three Photomicrographs of

Poor Temper Fracture Patterns

There has been some concern about glass oven wear made from tempered soda lime glass exploding while in use. A Glass failure analysis expert witness performed fractography on a thick glass jar that had been "tempered". Because this is a prototype piece, the temper was not done correctly. When the glass jar surface was abraded prior to thermal shock testing, it exploded violently. Recent tests by this glass expert on properly tempered glass had shown no "explosion". The glass merely cracked in place. Failure analysis of the two types of glass revealed some interesting differences. The non-exploding tempered glass showed symetrical stresses in the glass. The photomicrograph on the top left is representative of the stress pattern for standard tempered glass. In this case, the outer surfaces were under approximately the same compression, and the center of the glass was in tension; this is demonstrated by the "mist hackle" in the center of the fracture surface. Also, there are two sets of symetrical Wallner lines on either side of the center mist hackle. In the case of the exploding glass jar, the temper was found to be non symetrical and not uniform. In some regions the fracture surface had the mist hacklemuch nearer one surface; in addition, one surface does not appear to have been in compression. Other areas on this jar showed weak or very weak surface compressive stresses. The other three photomicrographs demonstrate thiese results. At this point the glass failure expert believes that improperly tempered glass oven ware can "explode". This manufacturing defect may be a product liability and could pose some danger to the user.

Glass Failure Analysis of Tramp Glass

As a part of a product liability case, a glass failure expert was asked to determine if a piece of "tramp glass" found by a consumer (Upper left photo) was put into the bottle after it was opened. There was a companion bottle from the same six pack that also had glass contamination(upper right photo). If the tramp glass in the subject bottle was planted, then the glass in the "sister bottle" was also put in by the consumer. These were "twist off" bottles; therefore, it was decided that if the torque needed to remove the cap on the sister bottle was low, this would indicate the cap had been previously removed by the consumer. The removal torque was measured on the sister bottle, and it was twice that measured on control bottles. Thus, the cap on the sister bottle had not been removed, and the glass contamination entered this bottle during bottle manufacturing or bottle filling. From this it was concluded that the tramp glass in the subject bottle is also a manufacturing defect.

Glass Expert Analyzes Wine Bottle Defect

A glass expert was asked to examine poor quality bottles received by a winery. The issue was whether this product defect would significantly lower the strength of the bottle and would present a product liability problem. The photo on the upper left is a photograph of the manufacturing defect. It is a 4 inch horizontal "gash". The center picture is a photo-micrograph of the defect cross-section. The cross-section shows that the edges of the defect are rounded. This is a molding defect that occured when the glass was at or above the its softening point. The edges of the defect are rounded; therefore, in the opinion of a manufacturing engineer, they are unlikely to cause a low stress bottle failure. The picture on the upper right is a photo-micrograph of the top of the defect. There is a thin sheet of glass over the center mound of the defect. It is believed that this defect was formed in the blow molding step of the bottle manufacturing process.

Beer Bottle Impact Failure Analysis

Glass failure expert analyzed a failed beer bottle to determine if there was a product defect. It was stated that the bottle exploded when it was put into a cooler filled with ice. The failure analysis revealed that the bottle had been hit with a sharp object. The photograph on the left is the bottle after re-assembly. The photograph in the center is a closeup of the failure origin from the outside of the bottle, The photo on the right is the failure origin from the inside of the bottle. The hertzian cone from the impact is readily visible. It is obvious that this bottle broke after it was hit on the side. Thus there are no product liability issues or manufacturing defects associated with this failure.

Manufacturing Engineer and Product Liability

Product Liability, Design Defects and Manufacturing Defects are obvious arenas for an experienced manufacturing engineer or process engineer. He has the insight to best evaluate manufacturing defects in product liability cases. Naturally, he must first perform a complete root cause failure analysis to determine if there was product misuse, a manufacturing defect or a design defect. Naturally it is a benifit if the chosen engineer has experience with similar products, materials and processes in question. This is an asset because he can relate the defect back to a specific process step. In addition, he will be familiar with what is necessary for correct product development. An example is a case where a product failed after a short time in service. He is best qualified to determine if the product or process development procedures were thorough and proper. For example, he can determine if the proper accelerated life tests were performed to determine the product performance over its expected lifetime. Product development and process development usually occur in four stages: concept, bread board, pilot production and full production. An important aspect of this cycle is to determine if there are potential circumstances during normal use that might cause product failure and/or personnel injury. Documented tests must be performed to prove that the hypothetical degradation mechanisms do not cause premature product failure. If this is not done, an unreliable or dangerous product (i.e. poor product safety) may be put on the market. An experienced manufacturing engineer is the best prepared to determine if the product was properly developed to allow for proper product quality. This insight can only be gained from direct hands on manufacturing experience.