Swing Set Failure Analysis

California failure analysis expert analyzes forces necessary to cause a swing set to fail. There are times that it is claimed that a swing set failed under "normal use" conditions. Tests were performed to determine what minimum forces are necessary to cause the chain to be pulled from the 'S' hook that holds it to the top of the swing set. Exemplar assemblies were put together and tested. The photographs above show the testing of an assembly. These tests showed that at least 400 pounds minimum is needed to pull the chain out. The above chain/'S' hook orientation required the minimum force. Other orientations required higher forces. This indicates that a child swinging on the saet could not generate the necessary forces to cause the chain to pull out of the 'S' hook.

Window Expert Discusses Metal Clad Wood WIndows

As a result of a window failure analysis performed by a failure analysis expert, several observations were made with respect to metal clad wood windows. The perception is that these windows are almost maintenance free. The outside metal cladding does not need painting, and the wood layer is inside, so it requires minimal maintenance. Numerous window failure analysis has shown that under certain circumstances, water enters through poor seals on the seams of the metal cladding. Once the water enters, the wood swells, and the seam openings worsen. Worse is that the wood cannot dry out because of the metal barrier. In addition, the metal cladding on the windows heat up to 140°F and higher. This is a "composting" environment that causes the wet wood behind the cladding to rot. In the early stages, the window damage is not visible because it is behind the metal cover. Eventually, the wood becomes weak and the window can no longer protect the interior of the building. Often this happens before the home owner is aware that there is a problem.

Broken Cutting Tool Failure Analysis

California failure analysis expert performs examines a failed cutting tool. In this case the cutting tool consisted of a carbide cutting tip brazed to a mild steel "post". The failure of the post initiated as a fatigue crack at a grinding mark where the post was shaped to accept the carbide cutting tip. The final failure ended as a 45° bending overload. The failure was caused by high machining forces caused by the absence of lubricant. The upper left photomicrograph is an overviewof the fracture surface. It shows the two phases of the crack. Upper right shows the grinding mark where the fracture initiated.

Plumbing Failure Analysis

Northern California failure analysis expert often performs plumbing failure analysis. In this case, the corrosion expert examines plumbing in numerous houses that was plugged due to brass dezincification of yellwo brass. In this case the zinc in the copper zinc alloy corrodes selectively and this leaves a white deposit on the interior of the pipe. The white material is a combination of zinc oxide and zinc carbonate. Above is an example of significant dezincification; however this pipe is still fairly open. One can see that the flow of the water is from the brass to the copper and the corrosion product is being dragged into the copper pipe from the corroding brass fitting that is soldered to it. As the brass contioues to corrode, the fitting can become clogged and its strength will significantly decline.

Failure Analysis Expert Examines a Broken Champagne Bottle

A California failure analysis expert witness was asked to perform a glass failure analysis on a champagne bottle that had failed "spotnaeously". Because champagne is under pressure and in glass, there are warnings not to use a cork screw to remove the cork. However, there are cases where the cork is stuck and people will use a tool to extract the cork. The danger is that the tool can damage the inner wall of the bottle neck and initiate a crack that will cause bottle failure. In the present case, a tool was used to pry the cork out and it caused "chatter" damage on the inner wall of the neck very near the top. This damage initiate a crack that finally caused bottle failure. Upper left is a 20X photomicrograph of the damage to the neck inner wall. Upper right is a 20X photomicrograph of the failure origin on the fracture surface. Again, because a champagne bottle is under pressure, one should never use a tool to remove a stubborn cork. There was no manufacturing defect; this bottle failed as a result of handling damage.

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.

Glass Expert Examines a Tempered Glass Window Failure

California failure analysis expert uses glass fractography to perform a glass failure analysis on a tempered glass window failure. The glass fracture analysis showed that the window failure was a result of heating the glass in the center. Due to the heat, the center of the window expanded. This created additional tensile stress on the window edges. Although the window edge was ground and chamfered, there was enough residual damage at the edge that the thermal stresses were able to cause window failure. Upper left shows the failure initiation site on the edge of the window. Upper right is a 40X photo micrograph of the origin on one of the fracture surfaces. The glass fracture analysis showed that the glass failure initiated on the window's edge face and propogated inward until the tensile center of the tempered glass window was reached. At this point the residual tempering stresses caused the entire window to self destruct into small "cubic" pieces. This may be a manufacturing defect because of the severity of the edge damage.

Failure Analysis Expert Examines a Plumbing Failure

A failure analysis was performed on a plumbing failure. The line is a corrugated water line to a bathroom sink. The pipe failure occured at a bend in the water supply line it was due to stress corrosion of the yellow brass line. Microscopic examination of the largest crack showed that there was also dezincification associated with the stress corrosion cracking. Upper left is an overview of the corrugated water supply line. It is cracked where there is mechanical deformation of the brass tubing. The upper right photo is a 10X photomicrograph of the major crack. There are regions of the crack surface where the yellow brass has "red brass" regions. This indicates that there was selective corrosion of the zinc rich portions of the alloy. That is brass dezincification has occured at the crack tip.

Failure Analysis Expert Examines a Corrosion Failure

Corrosion engineer performed a metallurgy failure analysis to determine the cause of prematurely failing burners in a particular brand of gas grill. The burners in question would fail completely after two or three years of service. The failure analysis of the burner revealed that the grill manufacturer made the subject gas burners from an inferior grade of stainless steel. They used a relatively obscure alloy (J1). This alloy is a variation on 304 stainless steel. The 304 alloy contains 18% chromium (Cr), 8% nickel (Ni) and 2% maximum manganese (Mn), and it allows a maximum of 0.08% carbon (C). The J1 alloy allows the same amount of C but contains only 15% Cr; it also has 4% Ni and 8% Mn. Because the Cr is the active ingredient for the corrosion resistence of stainless steel, the J1 alloy will perform poorly in a corrosive environment. A by-product of burning propane in a gas grill is water. In addition, the burner is hot with other contaminants on it; a corrosion expert would state that this is a corrsive environment. Upper left is a photograph of a burner that failed prematurely. Upper right is an unetched metallugraphic sample of a piece of this burner. One can clearly see that the burner surface shows grain bounbary corrosion. It is believed that the low level of Cr and the presence of water and carbon makes the J1 alloy susceptable to stainless steel corrosion and unsuitable for gas grill burners. This product defect analysis indicates that this is a not a manufacturing defect but design defect.

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.

Failure Analysis Expert Examines Bottle Failure

Glass failure analysis expert witness prepared numerous bottle failures of "off the shelf" 12 oz beer bottles by over pressuring them with a hydraulic pump. These tests were needed to generate bottle failures of a known origin in order to examine the crack patterns, the fracture surfaces and the failure origins. Numerous bottles were broken, and even though the locations of the failure origins varied (i.e. some were on the body and others on the heel), they all had identical characteristics. They initiated as a single crack parallel to the bottle axis. Also, the origin was always on the outer surface of the bottle and located at a minor external glass defect. In addition, the failure initiated as a fracture mirror. The fracture mirror was surrounded by mist hackle. The failure shown here initiated at the heel of the bottle. an overview of the failed bottle is shown in the two upper left photographs. The initial crack is parallel to the bottle axis, and it wraps around the heel. At both ends of the initial straight crack the crack fans out. On the upper right is a 40X photomicrograph of the failure origin. The mirror fracture and mist hackle border are clearly visible. The minor defect at the origin is just the weakest part of thisstandard bottle. This bottle failed at 410 psi. This was not a defective bottle. This would not be a product liability case.

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.

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 Discusses Tempered Glass Fracture Surfaces

California glass expert witness discusses crack travel directions during tempered glass failure. During tempered glass failure the glass sheet "self destructs" because the internal residual stresses are tensile and drive the failure. Essentially the glass failure results in the glass breaking into tiny cubes. This means that the crack is constantly changing directions. The California failure analysis expert has observed that the crack breaks through and travels in two directions. This is shown in the 20X photomicrograph above. Even though the crack is spreading in two directions, this does not indicate that this piece contains a failure origin. This is an interesting special case where the crack is spreading from a point, but it is not exiting the origin.

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.

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 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 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.