A correction method of elastic modulus in compression tests for linear hardening materials
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A correction method of elastic modulus in compression tests for linear hardening materials Wei Liu, State Key Laboratory of Nonlinear Mechanics (LNM), Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China; Key Laboratory of Microgravity (National Microgravity Laboratory), Institute of Mechanics, Chinese Academy of Sciences (CAS), Beijing 100190, China Yong Huan, Jie Dong, and Yujing Dai, State Key Laboratory of Nonlinear Mechanics (LNM), Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China Ding Lan, Key Laboratory of Microgravity (National Microgravity Laboratory), Institute of Mechanics, Chinese Academy of Sciences (CAS), Beijing 100190, China Address all correspondence to Yong Huan at [email protected] (Received 21 September 2015; accepted 23 November 2015)
Abstract A correction method for linear hardening materials is brought forward to obtain the true (or nearly true) modulus of cylindrical specimens with middle aspect ratios in compression tests. By considering the stress concentration near the interface between the specimen and the compression platen caused by slanted contact, a “sandwich” model is developed. A correction formula is derived and all parameters can be obtained from the tested stress–strain curve. Experiments were performed on Al 2024 specimens with four aspect ratios. The corrected results are closer to the intrinsic modulus than the tested values, which verify the effectiveness of the correction method.
Introduction The most commonly employed test for the determination of the static Young’s modulus of a material is probably the uniaxial compression test for solid circular cylinders.[1] It has advantages in specimen preparation and experiment operation, with a simple mechanical model. Studies have shown that some materials, such as ceramics, concrete, graphite, and some composites, exhibit different elastic moduli in tension and compression, which is known as bimodular materials.[2–4] Compression tests are irreplaceable for these bimodular materials and other anisotropic materials, such as unidirectionally reinforced composite materials and highly textured materials deformed by twinning.[5] Furthermore, to understand the behavior of materials under large plastic strains, compression test is more appropriate than the tensile test because the latter is limited by necking.[6] Especially, the compression test is easier for metallic glass to produce plasticity than the tensile test.[7–9] However, the drawback of compression tests is that the tested modulus is usually different from the intrinsic value. It has long been recognized that friction inevitably exists between the loading platens and the upper and lower end surfaces of the cylindrical specimen, which will influence the test results.[1,10] To acquire the compression modulus as reliable as possible, a high aspect ratio (≥8) is recommended by ASTM E9-09.[11] However, specimens of high aspect ratio (>5) can only be used in small deformation tests because they are susceptible to buck
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