Stress Corrosion Cracking in Fibreglass Composite Structures - A Case Study

Abstract

One failure mechanism experienced by fibreglass composite structures is stress corrosion cracking, which occurs in structures under load in a corrosive environment. Over time, stress corrosion cracking attacks the glass fibres, which weakens the structure and can lead to premature failure. Stress corrosion cracking failure is characterized by flat fracture surfaces perpendicular to the fibres at both the macroscopic and microscopic levels. Prevention of stress corrosion cracking includes proper selection of fibre and resin, and use of a protective layer between the glass fibres and the environment. Fibreglass structures that have failed due to stress corrosion cracking include chemical tanks, sewer pipe and pressure vessels. This paper describes the phenomenon of stress corrosion cracking in fibreglass composite structures. It also presents, as a case study, the investigation of the failure of a fibreglass overwrapped compressed air cylinder, used in a self-contained breathing apparatus. The failure was attributed to stress corrosion cracking following exposure to a highly acidic cleaning fluid. The cause of the failure was determined based on the results of fractography, chemical analysis, and stress corrosion tests performed on samples of the accident cylinder.