California Glass Expert Performs a Failure Analysis of Sparkling Liquor Bottle Failures

A bottling line for sparkling drinks was suffering from a high rate of  bottle failures on the bottling line. In addition, several bottles failed on the shelf after bottling. Read Consulting was asked to perform a glass failure analysis to determine the cause of failure of three bottles that had failed "on the shelf". Two of the three bottles were from the same mold cavity, and both failed at the exact same height from the base (2 1/4"). The third bottle failed at 2 1/2" above the base. All three failure origins were the same. All three failures started on the outside of the bottle. All three had "crack arrest lines " near the origin. In addition, All three had no visible mechanical damage to the bottle exterior at the origin.  The presence of the crack arrest line confirms a delayed failure. These factors indicate that the failures are caused by defects caused by the bottle manufacturing process. This is a manufacturing defect that must be corrected by the bottle manufacturer.

California Window Expert Performs Tempered Glass Failure Analysis

California glass expert was asked to perform a glass failure analysis on a glass door that failed spontaneously, The failure analysis lab located the failure origin. The glass experts then examined the fracture surface at the origin, and they determined that the root cause of the failure was a nickel sulfide particle. The failure origin magnified 200X is shown in the color photograph. This photo-micrograph was taken using Nomarski interference contrast. In it one can see that there is a spherical particle at the origin. Using energy dispersion spectroscopy (EDS) the elemental composition of the particle was determined. The chart shows that elemental composition of the particle is nickel (Ni) and sulfur (S). After the thermal tempering process, this particle, over time, went through a post temper phase change that generated tensile stresses and cracking which eventually caused failure. It is important to note that the particle is composed of only two elements, Ni and S.     

California Glass Expert Examines an Aircraft Windshield Failure

Read Consulting failure analysis lab performed a glass failure analysis on a failed aircraft windshield. The  windshield of a turbo-prop aircraft suddenly cracked during descent through clouds. Initially it was thought that static electricity had caused the glass failure. Initially it was proposed that the static electricity sought the aircraft "ground" through heating wires in the windshield. The failure analysis determined that the failure was caused by impact to the outer layer of the windshield. This is demonstrated by the crushed glass at the origin and the subsurface conchoidal fracture around the origin. The flight was in icy conditions; it is possible that a piece of ice came off the propeller and impacted the windshield. 

Glass Expert Discusses Modern Auto Windshields

California glass expert has been involved with evaluation automobile windshields. One way car manufacturers can  increase automobile mileage is to decrease weight. A part of this effort has been to reduce the weight of automobile windshields. This is done by reducing the thickness of the windshield. Upper left is a representative cross section of a modern windshield. The glass is only 2mm thick, and the polyvinyl butyral (PVB) inter-layer is only 0.07 mm thick. On the positive side, this reduces weight and improves the mileage. On the negative side, this windshield is prone to cracking. Upper right is a photograph of a windshield failure. The crack that was started by an impact from a rock. This crack formed immediately and has grown continuously for several months. Older windshields were thicker and were less prone to this sort of cracking. 

Glass Expert Performs a Window Defect Analysis

California glass expert was asked to analyze a window defect that appears as a streak in the window. The glass failure analysis showed that the streaks in the window were  strings of bubbles near the surface of the glass. Upper right is a photograph of the window defect which appears as streaks. Upper left is a macro-photograph of the near surface bubbles that cause the defect. This is a manufacturing defect.

Glass Failure Analysis: Tempered Glass Pot Cover

California glass expert performs a root cause failure analysis on a failed tempered glass pot cover. The pot cover failed "spontaneously" in the users home, and the handle with captured glass was submitted to the California failure analysis lab for evaluation. The failure was caused by the interaction of the handle hardware (i.e. cup washer) with the tempered glass. Crush damage from the cup washer that caused the failure. The series of photo micro graphs above demonstrate the findings. The lesson to be learned here is: there should be no glass-to-metal contact with tempered glass. This type of contact raises the probability of failure. In the case of tempered glass the failure appears to be spontaneous.    

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.

Tempered Glass Expert Discusses Glass Edge Finish

California glass expert discusses the importance of edge finish on tempered glass. Tempered soda lime glass has replaced low expansion borosilicate glass for small oven doors and glass tops for cookware. This reduces costs, but can reduce reliability. One important aspect of these tempered glass pieces is the edge quality. Poor edge finishing can introduce defects that can cause eventual failure. There are three common edge defects. These are chipping, missed seaming and "dry" seaming. Normally these pieces are scribed and broken, seamed with a wet belt sander and tempered. These three edge defects are illustrated by the figures. Read Consulting failure analysis lab has looked at numerous tempered glass failures that have originated at the edge; thus, edge finish is extremely important for any glass piece that can be preferentially heated in the center.

California Glass Expert Witness Discusses Bending Failure of Tempered Glass

California Glass Expert performs a failure analysis on a tempered glass oven door that failed in bending. Normally the fracture surface of tempered glass shows two sets of Wallner lines that are separated by a band of mist hackle. However if the tempered glass window failure is due to bending, the band of mist hackle is shifted toward the tensile side of the bend. Upper left is a photo of the tempered glass failure. The failure originated at an edge and progressed inward. A representative fracture surface is shown on the right, and the failure origin is shown on the left.

California Glass Expert Examines the Edge of Tempered Glass

California glass expert uses a grazing angle surface profilometer (GASP) to study the compressive stresses at the edge of a tempered glass oven door. The edge effects during the air quench step of the thermal temper process are said to lower the surface stress to zero near the edge of the glass article. In fact, fragmentation tests of tempered glass pieces yield a "picture frame" around the edge of the part. Fir this reason, a GASP was used to examine surface stress at the edge. Upper left is an image of the GASP interference pattern in the center of a tempered glass toaster oven door. The surface compressive stress measures 17,000 psi. Upper right is a similar image measured near the edge of the part. In this region the fringes curve, and they show the surface stress going to zero. This is important because any damage to the glass in this region of reduced surface compression stress is more likely to cause failure. 

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.

Failure Analysis: "Exploding" Coffee Pot

California failure analysis expert was presented with the claim that a coffee pot had "exploded" when replaced on the coffee warmer in a convenience store.First of all, there is no "stored" energy to cause an explosion. The coffee is not under pressure, and the pot is made from annealed borosilicate glass. In addition, the broken pot had been destroyed. To prove that the pot is annealed glass. The California glass expert broke an exemplar pot. It broke into large shards and the fracture surfaces were typical of those of annealed glass. Without available stored energy, an explosion is physically impossible; therefore, the injured party must have either dropped the pot or hit it against a hard object.

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 Glass Expert Performs a Failure Analysis on a Glass Bowl

A glass failure analysis was performed on a glass mixing bowl. An overview of the failed glass bowl is shown in the upper left photograph. This bowl failed as a result of thermal stresses. The crack originated at the bottom of the bowl and spread in one direction around the entire bottom. The thermal stresses were such that the crack never reached terminal velocity. In addition, a great portion of the fracture surface was featureless. The failure analysis revealed that this was a low stress crack driven by thermal stresses.

California Glass Expert Discusses Nickel Sulfide in Tempered Glass

In glass failure analysis one uses evidence such as the the attached photograph to demonstrate that a nickel sulfide particle can initiate tempered glass failure. The NiS particle is at the center of expanding Wallner lines. The Wallner lines are used by the glass failure analysis expert to track the direction of the crack growth. In this case the Wallner lines are spreading from a single point; thus, this is the failure origin and the NiS particle is the cause of the tempered glass failure. The California glass expert has seen numerous examples of this type of glass failure.

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.

Pyrex Glass Failure Analysis: Glass Baking Dish Failure Analysis

California glass expert witness performed a failure analysis on a pyrex glass baking dish. This dish was made from pyrex borosilicate glass, and the glass failure occured as the dish was being removed from the oven. The failure initiated at an internal glass defect. The defect appears to be a colapsed bubble (seed) in the bottom of the dish. The upper left (Mag 8X) photomicrgraph is an overview of the failure origin. Upper right is a higher power (Mag 40X) magnification of the origin. It appears as if the bubble colapsed during hot forming of the pyrex glass baking dish. Because the surfaces of the bubble did not re-weld, a stress riser was created that caused later failure as a result of thermal stresses created during normal use.

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.