Chapter 13 DIC Measurement of Anisotropy for Plastically Deformed Thermoplastic Kenichi Sakaue and Sho Higuchi Abstract The present research examines the deformation-induced anisotropy in the necking part of thermoplastic. Firstly, a uniaxial tensile force is applied to the large polycarbonate specimen to create the necking part. Then, small specimens are cut off from the large deformed specimen with various cutting angle to the initial tensile direction. The small specimens are used to evaluate the stress-strain curves. The results show that the elastic modulus and the maximum stress depend on the cutting angle to the initial tensile direction. Therefore, it is confirmed that the plastic deformation-induced anisotropy. Moreover, it is revealed that the dependence of the cutting angle on the elastic modulus and the maximum stress can be expressed by the anisotropic elastic constitutive equation and Tsai-Hill criterion, respectively. Keywords Thermoplastic · Necking · Deformation-induced anisotropy · Elasto-plasticity · Digital image correlation 13.1 Introduction The necking phenomenon of thermoplastic is frequently observed if the thermoplastics specimen is subjected to a uniaxial tensile force. It is well-known that the deformation-induced anisotropic characteristics appears in the necking part by the orientation of the molecular chains. The deformation-induced anisotropic characteristics of the thermoplastics have been studied through many experiments. These researches revealed that the elastic modulus and the maximum stress increases in the extending direction, and these characteristics depends on the value of the pre-strain [1]. Also, the researches on the numerical analyses have been performed to reproduce the deformation-induced anisotropy in thermoplastics materials. For example, the molecular chain network theory [2] and the composite inclusion model [3] are proposed for the finite element simulations. As mentioned above, the deformation-induced anisotropy of thermoplastics has been investigated by many studies mainly through experiments. However, the purposes of the most researches are to examine the existence of anisotropy and to evaluate the relationship between pre-strain and anisotropy. Therefore, the strain distribution has not been measured. It is necessary to acquire the strain distribution by full-field strain measurement methods in order to confirm the validity of the anisotropic constitutive model of the deformed materials and the method of finite element analysis. In this study, a uniaxial tensile test is performed to the specimen cut off from the necking part of the large polycarbonate sheet. In order to obtain the strain distribution, digital image correlation method, DIC, is used. In addition, the anisotropic mechanical characteristics are evaluated by the anisotropic elastic constitutive equation and Tsai-Hill criterion, respectively. 13.2 Test Method Polycarbonate sheet with 3 mm thickness (Iupilon, Mitsubishi Engineering Plastics Co., Ltd) is used as the test material. Firstly, the large specimens are used to create deformation-induced anisotropic characteristics in the necking part by a uniaxial tensile test. Then, the small specimens are cut off from the necking part of the large specimen and are used to K. Sakaue ( ) · S. Higuchi Department of Mechanical Engineering, Shibaura Institute of Technology, Koto-ku, Tokyo, Japan e-mail: sakaue@sic.shibaura-it.ac.jp; md19059@shibaura-it.ac.jp © The Society for Experimental Mechanics, Inc. 2021 M.-T. Lin et al. (eds.), Advancement of Optical Methods & Digital Image Correlation in Experimental Mechanics, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59773-3_13 95
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