Glass Failure Analysis, Coffee Pot Failure

 Read Consulting failure analysis laboratory was asked to examine a failed coffee pot that had been abraded with a cleaning pad and then subjected to a series of thermal shock cycles. The pot was heated to 190°C then immediately immersed in 10°C water. The pot appeared to survive till the 51st cycle. On this cycle a crack across the bottom appeared. Glass failure analysis performed on the fracture surfaces revealed a glass fatigue failure. The failure initiated at the location of abrasive damage and the flaw grew incrementally after each quench. It is unique to find actual fatigue in a brittle material. Apparently, the thermal shock stress was short term enough to allow incremental growth. Once the crack started, each quench caused the crack to advance and stop. The result is a crack arrest line.

Coffee Pot Failure Analysis

A failure analysis was performed on a glass coffee press. In this case the glass coffee pot is a 0.085" thick borosilicate glass 3.7" diameter cylinder that is 7" high. It had received a blow on the top rim, and it broke into approximately 10 pieces. Because the pot is a cylinder, the blow from the outside on the rim created tensile stress on the inside of the pot and compressive stress on the outside of the pot. This is reflected in the fracture surface above. The crack traveled faster on the inside half of the glass fracture surface. It finished as twist hackle on the outside half of the glass fracture surface.