Fracture toughness estimation of ductile materials using a modified energy method of the small punch test
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The fracture property estimation of ductile materials with small volumes at room temperature was performed experimentally and analytically in this study. A modified energy method of the small punch test (SPT) was applied to estimate fracture toughness based on the membrane stretch analysis. The effective strain was assumed to be the average value of center strain and contact boundary strain. To overcome the problem involved in strain calculation by microscopic observation, one relatively simple correlation which related effective fracture strain to displacement was proposed. The results obtained by the modified energy model and conventional experiment were in good agreement. Furthermore, a three-dimensional finite element model was established successfully. The influence of ball diameter and center hole diameter in the lower die on the SPT was analyzed by detailed discussion. Finally, the applicability and accuracy of the modified energy model based on the SPT were proved. An economic, effective energy method can be obtained from the present study to assess the properties of in-service components and micrometer scale materials.
I. INTRODUCTION
In engineering practice, the aging, embrittlement and irradiation degradation analysis of structural materials are requisites in the consideration of in-service components. However, the strong volume constraint of irradiated materials restricts the application of a standard test in the field of nuclear engineering. Most of the current conventional techniques are also not accessible to surface engineering due to limitations in terms of the thin surface nanocrystalline layer.1,2 It is realized that the small-scale techniques could be available methods for mechanical property estimation of micro or nanometer scale materials. 3,4 The hardness, elastic and plastic properties can be extracted from the experimental curves with small deviation.5 Alternatively, miniature specimen tests hold several advantages over uniaxial tension and compression with bulk materials in the field of novel alloy. Hence, the small-scale techniques have attracted worldwide interest in the past decade. As a part of the small-scale techniques, the small punch test (SPT) is an effective and promising methodology to test materials extracted from in-service components using a miniature disk sample, which has the merits of being economical and nearly nondestructive. The load–displacement (L–D) curves, which play a key role in small-scale tests,6 are also considered in the SPT. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.205 J. Mater. Res., Vol. 29, No. 15, Aug 14, 2014
http://journals.cambridge.org
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Well-established evaluation approaches for the elastic modulus,7 yield strength,8 and tensile strength9 have been derived. In addition, taking into account the fracture mechanics under different conditions, the feasibility of the SPT for ductile–brittle transition temperature,10 creep properties11 and irradiated damage12 is identified. Developmen
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