LOW‐TEMPERATURE AUTOFRETTAGE: AN IMPROVED TECHNIQUE TO ENHANCE THE FATIGUE RESISTANCE OF THICK‐WALLED TUBES AGAINST PULSATING INTERNAL PRESSURE

Abstract

Abstract— It is shown that autofrettage at low temperatures is superior to autofrettage at room temperature in enhancing the fatigue resistance of thick‐walled tubes against pulsating internal pressure. The physical reason is based on the well‐known temperature dependence of the mechanical behaviour of metals and alloys which generally exhibit an enhancement of both the yield stress and strain hardening behaviour at lower temperatures. As a consequence, significantly larger compressive residual hoop stresses can be introduced during pressurization at low temperatures than at room temperature. Experimental data obtained on thick‐walled tubes of the metastable austenitic stainless steel AISI 304 L which were subjected to pulsating internal pressure at room temperature after autofrettage at temperatures between‐110°C and room temperature are presented. These data demonstrate convincingly the advantages offered by low‐temperature autofrettage in enhancing both the fatigue life in the finite‐life region and the fatigue endurance limit in comparison with autofrettage at room temperature. In conclusion, some specific materials requirements for optimum low‐temperature autofrettage performance are discussed.