Failure Analysis of Glass Pitcher

An injury occured to a woman when she poured cold liquid into a warm glass pitcher. The bottom of the pitcher separated from the handle and fell onto her foot and cut the top of her foot severly. The subject pitcher was lost; therefore, Read Consulting was asked to examine an exemplar from the same store and perform a root cause failure analysis. An accident reconstruction was performed. The upper left photograph is of the exemplar pitcher. This appears to be a hand made glass object (there are no parting seams from a mold). In this case, the main part is made first, and the handle is made separately. Later, the handle is attached to the main body. Both pieces are heated till they are soft and the preformed handle is pressed onto the pitcher. If the main body is not hot enough, thermal stresses can be generated that can create cracks on the inner surface of the vessel. This is a product defect that can cause failure. Such cracks were observed on the new examplar. The red arrow inthe left photo shows the general locationof a crack. A closeup of the handle bottom clearly shows cracking (arrow in lower center photograph). This pitcher also failed when cold water was poured into it while it was warm. The cold liquid caused interior tensile stresses. The failure initiated at a pre-existing crack (i.e. manufacturing defect) near the bottom of the handle (upper right photograph). In this case the handle portion of the pitcher separated from the rest of the body.