Evaluation of residual stress relaxation and its effect on fatigue strength of AISI 316L stainless steel ground surfaces: Experimental and numerical approaches

• Published in: International journal of fatigue Vol. 48; pp. 109 - 121
• Main Authors: Laamouri, Adnen, Sidhom, Habib, Braham, Chedly
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.03.2013; Elsevier
• Subjects: Applied sciences; Austenitic stainless steels; Bend tests; Bending fatigue; Cyclic hardening; Degradation; Exact sciences and technology; Fatigue; Fatigue limit; FE analyses; Grinding; Grounds; Heat resistant steels; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Residual stress; Residual stress relaxation; Stress relaxation; Cyclic hardening; Fatigue; FE analyses; Grinding; Residual stress relaxation; Austenitic stainless steel; Machining; Mechanical properties; Stress relaxation; Fatigue strength; Stainless steel; Cyclic load; Residual stress; Strain hardening; Strength; Stainless steel-316L
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2012.10.008

► The 3-point and 4-point bending fatigue limits depend strongly on the RS relaxation. ► The stabilized RS are predicted by FE models. ► A cyclic hardening model for the ground layer was considered in the FE models. ► The effect of stabilized RS on fatigue strength was predicted. This paper is aimed at evaluating the residual stress relaxation and its effect on the fatigue strength of AISI 316L steel ground surfaces in comparison to electro-polished surfaces. An experimental evaluation was performed using 3-point and 4-point bending fatigue tests at Rσ=0.1 on two sets of notched specimens finished by electro-polishing and grinding. The residual stress fields were measured at the notch root of specimens, before and after fatigue tests, by means of the X-ray diffraction technique. It was found a degradation of about −35% for the 4-point bending fatigue limit at 2×106 cycles of the ground specimens in comparison to the electro-polished ones. This degradation is associated with a slight relaxation of the grinding residual stresses which remain significant tensile stresses at the stabilized state. While under the 3-point bending test, these residual stresses relax completely and provoke a noticeable increase of the fatigue limit estimated at about 50% in comparison to the 4-point bending fatigue test. The numerical evaluation of residual stress relaxation was carried out by FE analyses of the cyclic hardening behaviour of the ground layer. The isotropic and nonlinear kinematic model proposed by Chaboche was used and calibrated for the base material and the ground layer. The results show that residual stresses relax to a stabilized state characterized by elastic-shakedown response. This stabilization is occurred after the first cycle of the 4-point bending test corresponding to the higher stress concentration (Kt-4p=1.66), while it requires many cycles under the 3-point bending test corresponding to the lower stress concentration (Kt-3p=1.54). The incorporation of stabilized residual stress values into the Dang Van’s criterion has permitted to predict with an acceptable accuracy the fatigue limits under both bending modes.