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.

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.