High temperature sensitivity of notched AISI 304L stainless steel tests W.Y. Lu a, * , M.F. Horstemeyer a , J.S. Korellis a , R.B. Grishabar b,1 , D. Mosher a a Materials and Engineering Sciences Center, Sandia National Laboratories, Livermore, CA 94551-0969, USA b University of California, Davis, CA 95616, USA Abstract Experiments were designed to determine the failure characteristics of AISI 304L stainless steel under dierent stress triaxialities and temperatures up to 70% of melt. The data show that as temperature increases the displacement to failure of notched tensile specimens increases. The complex interaction of deformation mechanisms, such as twinning and dynamic recrystallization, appears to negate the damage accumulation at higher temperatures. Microstructural analyses and ®nite element simulations indicate that voids nucleate, grow, and coalesce more rapidly as temperature and triaxiality increase. Finite element simulations were performed to analyze temperature dependence on the Cocks± Ashby void growth model. The ®nite element simulations qualitatively show a double-knee that was observed in the notched experimental specimens after loading. The combined experimental±numerical study indicates that failure can be de®ned at several points in the notch tests when: (1) macrovoids starts to form, (2) the load drop-o occurs, and (3) total perforation of the specimen occurs. These three points occur simultaneously in ambient conditions but occur at dierent displacements at higher temperatures. Ó 1998 Elsevier Science Ltd. All rights reserved. 1. Introduction Except for the small temperature changes that Bridgman imposed on notch tests [1], very little has been accomplished in the way of determining hydrostatic eects of materials at high homolo- gous temperatures [2]. This study examines the void growth (or damage evolution) in 304L stain- less steel up to 70% of the melt temperature. Notch specimens with varying radii were pulled under displacement control with a constant applied temperature. Finite element analyses at ambient and high temperatures complemented the experi- mental study to give insight into the physical mechanisms that cause void evolution for varying temperatures. Finite element simulations were required to de- termine the damage model parameters in which the load±displacement response depends on both plasticity and damage. Plasticity was indepen- dently characterized through compression testing. The experimental investigation included: perform- ing compression tests at various temperatures for determination of plasticity model parameters, de- veloping high temperature tensile test capabilities, performing ambient and high temperature notched specimen tensile tests, and studying deformation microstructures of the notched specimens. It is conceivable that void growth should arise from the driving mechanisms of inelasticity alone. Theoretical and Applied Fracture Mechanics 30 (1998) 139±152 * Corresponding author. Tel.: 1 510 294 3181; fax: 1 510 294 1459; e-mail: wy_lu@sandia.gov. 1 Currently at W.L. Gore and Associates Inc. 0167-8442/98/$ ± see front matter Ó 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 1 6 7 - 8 4 4 2 ( 9 8 ) 0 0 0 5 1 - 2