Glass Bottle Failure Analysis

Larger Point Impact (1/8" Dia.)

Fracture Surface at Origin
of 1/8" at 40X

Small Point Impact (1/32" Dia.)

Fracture Surface at Origin
of 1/32" at 40X

Often bottles and other glass objects fail as a result of "point impact". Given here are two examples of point impact failure origins discovered as a result of glass failure analysis performed at the Read Consulting Failure Analysis Lab. The origin is found by tracing the crack backwards on the fracture surface. Often there is a crushed glass region at the point of impact. This blog demonstrates two impact failures. Shown are the are both the impact point on the free surface and the origin as observed on the fracture surface as viewed at 40X using an optical microscope.  

California Failure Anal

California Failure Analysis lab performed an electronic failure analysis on Pogo pin spring loaded contacts (Pogo connector pins) to determine the cause of intermittent open circuits. Electronic testing had detected that there were times when the spring loaded pin was depressed, the circuit would open and there would be an interruption of the signal. The cross section of a single Pogo (upper left) showed that the  the structure was entirely made of gold plated parts (pin, spring and outer
 case).  However, there was some concern that the inner wall of the case
was defective. For additional failure analysis, a sample case was split open (photo-micrograph on the right) and the inner surface was found to have horizontal machining marks,  not be plated, to be corroded and contaminated with plating salts. These plating defects indicate that the intermittent contact problem will worsen with time. These results are not surprising since the case is really a deep blind hole, and this makes it impossible to properly clean and plate  the interior. The vendor being analyzed is an overseas vendor that was to replace a reliable US supplier. These parts are unusable.

California Glass Expert Discusses Bottle Failure Analysis

A California failure analysis expert has been testing the strength of beer bottles by causing them to fail from pressure overload. In all cases the origin always had a mirror region at the origin. The presence of the mirror region indicates that the crack initially grows slowly. Theoretically, the mist hackle  indicates that the crack velocity has reached its terminal velocity. As a part of bottle failure analysis, the absence of this mirror region would indicate that the bottle did not fail as a result of internal pressure. In addition, the presence of crushed glass and mechanical damage at the origin would indicate that the bottle had been hit by a hard object.

Safety Glass Expert Performs Tempered Glass Analysis

Glass failure analysis often requires understanding of safety glass. Normal window glass is in the annealed state. Therefore, it will break into large sharp shards that can injure a person who breaks through it. In order to reduce the probability of failure and the possibility of injury two types of safety glass have been developed. The first is laminated safety glass, and the other is tempered safety glass (i.e. surface compression stress >10,000 psi). Automobile windshields and hurricane resistance windows are made from laminated safety glass. These are special applications, and laminated safety glass is appropriate, even though it is more expensive. In most other safety glass applications, thermally tempered safety glass is used. These windows are safer because they are stronger and because they break into small "blocks" when they fail. These two factors significantly reduce but do not eliminate the probability of injury to anyone that breaks through the glass. There are two prevalent techniques to evaluate the level of temper in glass. One is to measure the surface compression stress with a grazing angle surface profilometer (GASP); the other is to break the tempered glass per UL guidelines and measure the area of the largest remaining pieces. The photographs above show the two methods. Upper left is a photograph of the fringe pattern of a tempered 9" X 13" X 4 mm thick glass oven door taken through a Strainoptic Technologies GASP. This image shows the compressive surface stress to be -20,000 psi. Upper right is a photograph of the same door after the UL fragmentation test (i.e. using a center punch to penetrate the compressive layer). One can see that the resulting pieces are extremely small. In general, the pieces are aqlmost cubic.

Glass Fracture, Califirnia Glass ExpertPerforms Bottle Failure Analysis

California failure analysis expert witness was asked to perform a detailed failure analysis of a broken wine bottle. Glass fractography was used to determine the root cause failure mode. The failure originated at damage caused by the prop on the cork screw. The fact that there were two damage sites on opposite sides of the bottle and that the cork was only partially removed, indicates that the force to remove the cork was excessive. The donward force on the prongs crushed the top of the bottle at two places and initiated a crack that was driven by the force needed to move the cork. This failure was not the result of a bottle manufacturing defect; it was caused by the high forces needed to move the cork and the type of cork screw used. Upper left is a photograph of the two pieces of the bottle neck. Upper right is a 20X photomicrograph of the failure origin and the initial part of the crack. The arrows show the initial travel direction of the crack. Also, visible is the "crush point" at the beginning of the failure.

California Coating Expert Performs Failure Analysis of Epoxy Paint

A California coating expert was confronted with a municipal water tank with a rubbery epoxy coating. The complaint was that the epoxy paint was not properly mixed, and it had not cured properly. During the coating failure analysis, the study showed that the epoxy paint was aliphatic amine cured. In addition, the tank was painted in the winter, and it cured at 50°F. Prior to filling with water, the tank interior was given a final inspection. During the inspection the paint layer was found to be rubbery on the sunny side of the tank. Because epoxy is thought to be "cross linked" all were surprised that the paint was rubbery. and they were concerned that the paint adhesion had been compromised. Adhesion tests were positive. The fact is many epoxies 'soften' above their initial cure temperature. In this case, the epoxy paint had cured at or below 50°; thus, on a warm day (T> 70°F) the epoxy will initially be soft. However, over time, the paint will "re-cure" and harden at the higher temperature. The failure analysis demonstrated that there was no product defect.

High Pressure Bottle Failure Analysis Tests

Glass failure analysis requires looking at failed bottles and determining the cause of failure. The failure analysis procedure includes carefully examining the crack pattern and the failure origin. It also helps to have failures with known causes to confirm the conclusions. In this case bottles were purposly broken using hydraulic pressure. Their performance was documented for future use. Numerous bottles were tested, and all showed similar failure characteristics. All bottle failures were caused by "hoop stress"; thus they started as a straight crack parallel to the axis of the bottle and then branched out. Microscopically, all the over pressure glass bottle failures originated as a slow growing crack and formed a distinct fracture mirror surrounded by mist hackle. Upper left is a photograph of a representative over pressure failure. This particular failure originated on the body of the bottle. Others originated on the heel, but all had the same characteristics. Upper right is a 40X photomicrograph the origin of the failure. It consists of a slow growth fracture mirror surrounded by mist hackle. The small arrows indicate the crack travel direction. During falure analysis, a glass failure analysis expert can compare the unknown glass failure to this example to aid in determining the cause of the failure.

Glass Bottle Damage; GLass Bottle Failure Analysis

Glass expert illustrates wine bottle damage that occured during corking. This product defect occured during cork insertion. The "push rod" was off center, and it impacted the top of the bottle. As a result, there was a crush point that would have resulted in a crack during cork removal by the user. Glass failure analysis of broken bottles would have shown the origin at the top of the bottle.

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.

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 Expert Performs a Wine Bottle Failure Analysis

California glass expert performs a failure analysis on a wine bottle failure. In this case the root cause of the failure was due to an impact on the top of the bottle finish. it is apparent that this bottle was hit on the top. This is shown by the photomicrograph.