Glass Expert Witness Discusses Tempered Glass Fracture Surface

California failure analysis expert witness examines two distinct fracture surfaces for tempered glass failures.
According to the tempered glass expert witness, the surfaces of tempered glass are under compressive stress. This stress is balanced by an "equivalent" tensile stress in the center of the glass. Tempered glass failures are really the end result of self destruction. The mid-plane tensile stresses take control of any defect that enters the center of the glass pane and drives the crack to the point that the original piece becomes a large number of almost cubic diced pieces. , under normal conditions, the fracture surface consists of two sets of Wallner lines separated by a central zone of mist hackle (upper  photo-micro-graph). The fracture surface for a tempered glass piece that failed as a result of bending is distinct. The fracture surface shows a shift of the central mist hackle toward the convex side of the bend. In this case, the Wallner  lines have essentially disappeared (lower photo-micro-graph).

California Failure Analysis Lab Examines Stainless Steel Corrosion Failure

Stainless steel corrosion failures often result from grain boundary sensitization. Many 300 series stainless steel alloys come in two grades or more. For example 304 stainless steel comes as 304, 304L and 304H. Each grade has a different amount of carbon (C). the 304 grade allows up to .0.08% C; whereas
304 L allows a maximum of 0.03% C. In corrosive environments, this is critical if the piece is welded or heated in the temperature range from 459°C to 850°C. As the carbon content increases in the alloy, the time for grain boundary sensitization decreases. Grain boundary sensitized stainless steels exhibit rapid corrosion  failure at the grain boundary because the chrome has been tied up by the carbon in the grain boundaries.
In this case the California failure analysis expert performed a corrosion failure analysis on a jacketed pipe made from 304 stainless steel which corroded rapidly as a result of grain boundary sensitization. The alloy was not specified correctly. The design drawings should have specified solution treated 304L or 316L plate for the manufacture of the industrial pipe. The plumbing failure expert  contends that if this were done, the plumbing failure would not have occurred. The equipment designer cannot rely on the supplier to pick the proper materials..  

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.

Tempered Glass Failure: Nickel Sulfide Particle

California failure analysis expert examines glass door failure to determine the root cause of the failure. The subject tempered glass door failed spontaneously, and because the glass was verticle, the broken pane remained intact. Read Consulting failure analysis laboratory was able to obtain the origin and perform a root cause failure analysis. The attached 25X Nomarski photomicrograph demonstrates that the glass failure originates at a nickel sulfide (NiS) particle. Once the glass failure has been initiated, the failure is driven by the residual stresses in the thermally tempered glass.  Glass fracture analysis shows the Wallner lines initiating at and expanding from a NiS particle. NiS particles are common in float glass, but they are only a problem in thermally tempered glass. Read Consulting Laboratory performs similar failure analyses on metals, plastics, ceramics and glass on a regular basis 

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.

Cast Iron Metal Fatigue Failure

California failure analysis expert performs a failure analysis on a failed cast iron "latch lever" from a wood stove. This failure initiated as a fatigue crack at a casting defect. It progressed as a fatigue crack through most of the thickness until the final overload failure. Upper left is a photograph of the backside of the lever, and it shows the casting defect. Upper right is a 10X photo-micro-graph of the fracture surface. Cast iron fracture surfaces are "grainy". Fortunately, oblique lighting reveals the fatigue stria on the fracture surface. When latched, the surface with the casting defect is in compression; it is believed that this is why the crack progressed mostly as a fatigue failure.

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.

Plumbing Failure Analysis: Failure Analysis of a Water Flow Indicator

A California failure analysis expert performs a failure analysis on a broken water flow indicator. This flow indicator was in a large building, and as a result of the failure, there was substantial damage. The flow indicator consisted of a glass dome clamped into a metal housing.The failure originated where the flange of the glass dome contacts the interior wall of the metal housing. The failure initiated at the “half thickness” of the flange on the glass dome and spread left and right. This failure was caused by misalignment of the glass dome with respect to the interior of the glass housing. From this perspective, this is an assembly defect. From another perspective, this is a design defect. The absence of a compliant spacer between the edge of the flange and the wall of the metal housing allows misalignment. A design improvement would be to add a compliant “ring” spacer between the glass dome flange and the interior wall of the metal housing. This failure should be considered a product defect.