Experimental and numerical study on the relationship between creep crack growth properties and fracture mechanisms
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27/4/04
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Experimental and Numerical Study on the Relationship between Creep Crack Growth Properties and Fracture Mechanisms MASAAKI TABUCHI, JECHANG HA, HIROMICHI HONGO, TAKASHI WATANABE, and TOSHIMITSU YOKOBORI, Jr. Evaluation of creep crack growth properties taking microscopic aspects into account is effective for developing more accurate life prediction of structural components. The present study investigated the relationship between creep crack growth properties and microscopic fracture aspects for austenitic alloy 800H and 316 stainless steel. The growth rate of wedge-type intergranular and transgranular creep crack could be characterized by creep ductility. Creep damages formed ahead of the void-type crack tip accelerated the crack growth rate. Based on these experimental results, a three-dimensional finite element method (FEM) code, which simulates creep crack growth, has been developed. The effect of creep ductility on da/dt vs C* relations could be simulated based on the critical strain criteria. The diffusion of vacancies toward crack tip would accelerate the crack growth under creep conditions. The change of vacancy concentration during creep was computed for a three-dimensional compact-type (CT) specimen model by solving the diffusive equation under multiaxial stress field. The experimental results that crack growth was accelerated by creep damages formed ahead of the crack tip could be successfully simulated.
I.
INTRODUCTION
UNDERSTANDING of creep crack growth properties is important for the reliability assessment of high-temperature structural components. Creep crack growth properties are affected by microscopic fracture mechanisms, which change dependent on temperatures and loading conditions. For longterm services, creep crack growth by grain-boundary cavitation[1] is often observed. In most high-temperature components operated under multiaxial stress condition, creep crack grows accompanied with microcavities, voids and microcracks ahead of the crack tip. The type IV creep crack observed in the heat-affected zone of high Cr steel weldment is a typical void-type crack under multiaxial stress condition.[2] Because the creep crack growth properties are influenced by creep damages formed ahead of the crack tip, some analytical models taking damage effect into account are proposed.[1,3,4] Therefore, it would be effective to evaluate the creep crack growth properties taking microscopic aspects into account for developing more accurate life prediction methods of structural components. However, there are few experimental and numerical studies from a viewpoint of microscopic mechanisms.[5–8] In the present work, creep crack growth tests were conducted using compact-type (CT) specimen of austenitic alloy 800H and 316 stainless steel at various temperatures and loading levels. Creep crack growth behavior was character-
MASAAKI TABUCHI, Group Leader, JECHANG HA, Research Fellow, HIROMICHI HONGO, Senior Researcher, and TAKASHI WATANABE, Senior Researcher, are with High Temperature Material
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