Advances in Test Techniques to Characterize Fatigue and Fracture Properties for Safety Critical Applications

Abstract

This paper is a review of developments of note at BISS that impact structural integrity. A test system and procedure were developed to determine J_1c for the case of a through crack in the wall of a pressure vessel subject to internal pressure. More recently, an online scanner was developed and integrated with an automated test system to track damage growth in carbon fibre reinforced plastics under static and cyclic loading. By far the most significant development, from a scientific perspective, is a path-breaking discovery that the well-known mean stress (or residual stress) effect on metal fatigue may be attributed to environmental action. A variety of specially designed experiments proved that the mean stress effect becomes negligible in high vacuum. Further research involving the development of a new test procedure led to the establishment of a unique relationship between computed near-tip residual stress and a threshold stress intensity required for the onset of (atmospheric) fatigue crack extension. All this research required concomitant development of test techniques unavailable from the typical ‘black box’ test equipment associated with conventional fatigue testing.