Failure Analysis of Failed Plastic Chair

Plastic Failure Analysis Expert performs a failure analysis on a plastic "lawn chair" that collapsed when someone sat in it. The right arm separated from the seat. Upper left is a photograph of the subject chair with the separated leg. Fractography, top center photograph, indicates that the failure was progressive (i.e. a fatigue failure). Examination of exemplar chairs at the site showed identical small cracks where the leg joins the side of the seat. All the chairs examined had this manufacturing defect, and these will eventually show fatigue faikure. This is a product defect (design defect) that must be corrected to improve the performance of the chair. Otherwise, this is a product liability that exposes the manufacturer.