Authors: Hong Wei Ji, Huai Wen Wang
Abstract: Short span compressive experiments of molded pulp specimens were carried out on the SHIMADZU material test machine, resulting in the stress-strain curves. The analytic results indicate that the material density and the loading rate are the two major factors that influence the stress-strain relationships of the molded pulp materials. With the increase of material’s density, elastic modulus and ultimate strength both increase. With the increase of loading rate, elastic modulus decreases whereas ultimate strength increases. By analyzing the test results and the existing models, an improved stress-strain model for molded pulp material, with the two factors taken into consideration, has been proposed. The model coefficients are obtained by fitting against the short span compressive experimental data for the materials with different densities under different loading rate. Comparison made between the experimental results and calculated results indicates that the proposed model can well fit the stress-strain curves of molded pulp.
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Authors: Ming Tu Ma, Yan Zhao, Gang Fang, Yi Feng
Abstract: In this paper, the high speed tension experiments have been performed on ultra high strength bullet proof steel. The samples were cut from the bullet proof steel plate after hard-module quenching with thickness of 3.7 mm. The mechanical properties at strain rates of 0.001 s-1, 0.01 s-1, 0.1 s-1 and 1 s-1 were carried out on MTS810, while those at higher strain rates of 200 s-1, 500s-1 and 1000s-1 were tested on HTM5020 high speed tension tester and Hopkinson bar. The data from the high-speed tension experiments were fitted via Johnson-Cook constitutive equation, and the fracture surface of each sample was analyzed by SEM. The results indicate that, the shoot-resistance capability of bullet proof steel is closely related to its strength, thickness and flow behaviors under high strain rate. The shoot-resistance will be improved in the case of higher strength and better matching between strength and elongation. The Johnson-Cook equation fitted via experimental data provides fundament to numerical simulation. With the increase of strain rate, the size and depth of dimple trend to decrease and the depth of dimple changes less in steel with lower strength and higher elongation. The SEM analysis of fracture is benefit for further understanding of deformation and fracture mode under high strain rate.
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Authors: Ling Mei Guo, Yan An Lv, Zhi Fang Deng, Yang Wang
Abstract: Uniaxial tension tests for filled silicone rubber were performed at high strain rates using a split Hopkinson tension bar system. Quasi-static tension tests were carried out using an Instron-E3000 material test system. The grip fixture was designed to reliably connect the tensile specimen with the incident/transmitted bars. The method to increase the signal-noise ratio of the stress pulse in the transmitted bar was proposed. The effect of specimen gage length-to-width ratio on the stress-strain responses was experimentally studied. The suitable specimen geometry was determined by means of experimental investigation and finite element analysis. The automated grid method was used to capture the deformation information of the tensile specimen. Experiments indicate that the tension responses of silicone rubber exhibit the apparent hyper-elastic and rate-dependent characteristics. The values of tensile modulus increase with the increase of strain rate. The stress at a given elongation increases with the increase of strain rate.
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