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.

Botle Manufacturing Defect

Glass failure analysis expert performs a root cause failure analysis on a bottle failure. In this case a manufacturing defect was causing numerous failures on a manufacturing line. The tops of these small bottles were coming off. The upper left photomicrograph is with the two halves of the bottle re-assembled. The upper right photomicrograph is of one of the glass fracture surfaces. The failures were occuring just below the transfer ring at a glass molding defect. The molding defect is a fold in the glass that acts as a stress concentrator. The lower left photograph is of an unused bottle with the defect. This is an unacceptable manufacturing defect and the parts werre returned as non-conforming.

Wine Bottle Failure Analysis

Glass failure analysis expert locates the origin of a failed wine bottle. Thye failure origin is at the top of the bottle on the inside rim. The origin is a crush spot on the inner rim. This was too high to be caused by a cork screw. It is believed that the damage occured before the bottle was purchased. Root cause of the failure is mechanical damage to the top of the bottle on the inner rim of the neck.

Glass Damage from Weld Spatter

At a new condminium complex, numerous windows were discovered to have been damaged by weld spatter. Upper left is a photograph of typical damage found on the affected windows. A glass expert examined the damage to determine if the windows could be repaired. A glass failure analysis was performed to evaluate the damage level. Microscopic examination showed that the damage was below the surface. The damage depth varied from 0.05 mm to 0.3 mm deep. The photo on the upper right is a 20X photo micrograph of the glass damage. The round part of damage is 0.3 mm deep. The failure analysis expert deems these windows unrepairable. They must be replaced.

Glass Expert Performs Sauce Bottle Glass Failure Analysis

Glass expert peformed a bottle failure analysis on a broken bottle of steak sauce . Intitally it was stated that this was a new and unopened bottle; however, examination revealed that there was sauce on the bottle threads. In addition, the "band" below the plastic lid was not connected. From this it was concluded that the bottle had been opened in the past. The fracture surface was examined and the root cause failure analysis showed the origin to be located on the bottle "shoulder ring" which is just below the plastic lid band. Upper left is a photomicrograph of the a portion of the fracture surface that includes the origin (indicated by the arrow). Upper right is a higher power photomicrograph using Nomarski optics of the failure origin. In this case the failure originated at the site of chipping damage to the bottle (arrows indicate the initial crack direction). This is not a manufacturing defect.

Failure Analysis Expert Discusses Metal Fatigue

Failure analysis was performed on a failed pin from a large tractor. The upper right gives an overview of the pin. Upper left is a close up of the fracture surface. The fatigue crack originated at the top of the photo and progressed downward until the final overload failure.

GLass Expert Analyzes Wine Bottle Failure

Glass expert analyzed several leaking wine bottles that eventually broke in half. All the bottle failures occured on the heal. Also, during failure analysis, it was discovered that all of the bottle failures were made in one cavity of a multi-cavity bow mold tool. Bottles from the other cavities did not have this problem. These bottles were made from very thick dark glass. It is believed that the failures were initiated as chill cracks. However, more process development work must be done at the factory to correct this manufacturing defect. Two suggestions are to eliminate any drafts in the factory and increase the amount of post mold flame heating on the conveyer. Bottles made from thick glass are more likely the have this glass failure mode.

Glass Expert Analyzes Wine Bottle Failure

Tempered Glass Expert Shows Multple Views of Nickel Sulfide Particle

The result of a failure analysis, a glass expert presents several views of a 180µ diameter origin (nickel sulfide particle) of a failed tempered glass door. The upper left photomicrograph is taken with a low power optical microscope and it includes the NiS particle and the initial Wallner lines. Upper right and lower left are taken with a high power optical microscope. with and without Nomarski. Finally lower right is an Scanning electron microscope photomicrograph of the same particle. The inportance here is that the distinct shape and surface of a NiS particle makes it identifiable with an optical microscope.

Glass Failure Analysis of Laminated and Tempered GLass

Glass failure analysis was performed by a failure analysis expert on a large laminated window of which one layer was tempered glass. The tempered half of the lamination failed. The other half of the window held the system together, and this allowed a failure analysis to be performed. The upper left photo is an over view of the window failure. The arrow indicates the general location of the failure origin of the tempered glass layer. The upper right photo is a closeup of the origin. The arrow indicates the location of a nickel sulfide particle (NiS) that caused the failure. It was reported that the tempered glass had been heat soaked. In this case the heat soak test (HST) did not eliminate on this window before it was sold.

Failure Analysis Expert shows Nickel Sulfide Particle

Failure analysis expert observed a nickel sulfide particle using Nomarski optics. The various colors show different elevations of the surface around the particle. This particle was at the origin of a failed tempered glass door. This is an interesting result of a glass failure analysis performed on the door.

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.

Failure Analysis Expert Performs Glass Failure Analysis

Glass expert performs a failure analysis on a failed tempered glass door. The spontaneous glass failure was analyzed to determine the cause of failure. This was one of several doors that failed spontaneously on a new high rise. Fortunately the door did not fall apart; thus, the failure origin could be preserved. The upper left photo shows the failure origin (arrow). The origin was taken apart, and at the center was a spherical 180 micron diameter nickel sulfide particle, NiS particle. During the glass failure analysis, a scanning electron microscope, SEM, image of the particle is shown in the upper right. Elemental analysis of the particle showed it to consist of nickel and sulfur. The SEM image also shows initial Wallner lines that are spiral in shape and are leaving the particle. This identifies the NiS particle as the cause of the failure

Glass Failure Expert Looks at Tempered Glass Failure

Glass expert analyzed a broken tempered glass door. He was able to preserve the origin and perform a failure analysis. The spontaneous glass failure started in the center of the window and was caused by a nickel sulfide particle (NiS particle). This failure mechanism is well known and has been documented by others. In this case, the glass expert spent some time documenting the initial crack growth. The upper left photomicrograph shows two sets of Wallner lines spreading away from the general location of the 100 micron diameter spherical nickel sulfide particle. The photomicrograph on the upper right shows a circular crack arrest line surrounding the NiS particle. This circular artifact identifies the NiS particle (a manufacturing defect) as the cause of the failure. In addition, it also indicates that the crack stopped at least once before the glass went to failure. At first the crack started as a round crack due to the stresses from the nickel sulfide particle. Later the residual stresses in the glass took control. The circular crack opened up and turned into the classic sets of Wallner lines found in root cause failure analysis of tempered glass.

Glass Expert Discusses Construction Defect

Glass expert analyzed a failed shower enclosement wall made from tempered glass. The failure occured before the homeowner warranty had failed. The contractor refused to replace the glass panel. It was his opinion was that the homeowner had damaged the panel and was responsible. Glass failure analysis determined that the failure initiated under the frame. In addition, there was no damage to the metal frame (i.e. there were no "dings" or "dents"). Therefore, the panel had failed spontaneously as was claimed by the homeowner. The upper left photograph is an overview of the failed panel. Here one can see that the failure emanates from the lower right corner. The upper right photograph is a close up of the corner. As a result of the analysis, the contractor agreed to honor the warranty and replace the tempered glass panel.

Hot Dip Galvanized v.Electro-Galvanized Nails

Metallurgy expert describes the difference between hot dip galvanized nails and electro-galvanized nails. Manufacturers have changed from hot dip galvanizing to electro-galvanizing. The zinc is a sacraficial materail; therefore, the protection afforded by the galvanize layer (zinc) depends on the zinc thickness. All other things being equal, the electro-galvanized nails with the much thinner zinc layer (t= 0.000065"), right photo, will rust sooner than the hot dip galvanized (t= 0.0015"), left photo. It is reccomended that hot dipped nails be used for critical applications.

Glass Expert Analyses a Broken Bottle

Glass failure anlysis expert witness performs a root cause failure analysis on a broken bottle. This bottle broke into pieces (lowerleft figure). A failure analysis determined that the failure origin was in the bottle neck under the plastic cap (lower right figure). The glass expert removed the cap and the the residual polish (top left figure). The neck was cut open from the side opposite the visible crack, and the failure analysis revealed that the failure originated (arrow) at a damage site on the interior of the bottle neck (top right figure). Further study is required to determine the source of the damage.

CPVC Plastic Failure Analysis of Hot Water Pipe Fitting

Plastic failure expert performs a failure analysis on a failed CPVC 90° 3/4 inch elbow. This elbow was in a 150°F hot water recirculation system in a large facility. Plastic fatigue was the alledged cause of failure. However, a plastic failure analysis found no evidence of fatigue. Instead, the detailed root cause failure analysis indicated that this elbow had molding defects and had deteriorated in service; in the top left photograph one can see that the CPVC inner and outer surfaces have turned brown. The failure originated at a stress concentration point caused by the interior 90° angle. It initiated as a brittle fracture on the outside. It then became an overload failure in mid thickness. Finally, there were layer separations toward the interior of the elbow. The photo on the right is of the vent hole. This shows that the CPVC came out in layers. Thus, during plastic molding there were layers of CPVC that did not "recombine". Given that this elbow is formulated to operate continuosly at 180°F, this elbow was a defective product due to both plastic molding defects and plastic formulation problems.

Glass Expert Performs Failure Analysis of Glass to Metal Seals

California failure analysis expert and manufacturing engineer was engaged to perform a root cause failure analysis of shallow cracking in the seal glass. These glass to metal seals were made by one manufacturer and then sent out to another processor to be plated. The photograph on the left shows two sight glasses. The body of the seal has male pipe thread and there is a screw driver slot on the top. The intent is for these seals to be screwed into a container wall. The glass window allows one to view the container interior (i.e. see the fluid level). The photomicrograph on the right shows a typical crack. These cracks occured during plating; they are always shallow and always associated with the one of the screw driver slots. The "rainbow" that is seen is due to the air wedge created by the shallow crack. The stress pattern of these seals is symetrical; therefore, sealing stresses are not implicated. Because glass only fails in tension and because these cracks are associated with a screw driver slot, the glass expert believes that they occur when the seals come out of the hot plating bath (195°F) and cool rapidly either in the air or when spray rinsed.

Machine Controls: Factory Safety or Manufacturing Safety Issue

Factory safety expert witness was engaged to determine the cause of a worker injury to an experienced operator/supervisor. The superviser was threading the machine with plastic sheet material when her hand was crushed. The accepted practice for threading was to feed the plastic sheet from the top and reach underneath to pull it through while another operator (i.e helper) pressed the "advance" (Arrow C) function on the control panel. In this instance the helper accidentally pushed the start button ( Arrow A). Both buttons are the same color and are very near each other. When the supervisor realized that her hand was being squeezed by the machines heated platens, she ordered the operator to "stop" the machine. The operator pressed the red stop button (Arrow B) instead of the E-stop. The stop button stops the machine after it has completed a full cycle. The "E-Stop" immediately stops all functions. Since the machine completed its cycle, the supervisor's hand was severly injured. This is a case of poor machine design with respect to machine safety and operator safety. Because both the advance and start buttons are adjacent and the same color, it is forseable that one could push the wrong button. In addition to the "helper"the emergency stop and the "stop" buttons are the same color and perform the same apparent function (i.e. it is forseeable that an operator would assume that both perform the same function). Machine guards are not appropriate because the operator must reach in to the thread the machine; in addition, the machine must be on for the threading operation to be performed.

Solution: Provide an on/off foot switch to control the advance function. This assures operator safety by allowing the person threading the machine to have absolute control over starting and stopping the machine as it is being threaded.