13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- different elevated temperatures [4-5]. This paper reports the dependence of shear localization and fracture on plastic anisotropy of the material. Three types of automotive sheet materials, namely IF steel (BCC structure), AA5754 aluminum alloy (FCC) and AZ31 magnesium alloy (HCP) are examined. Digital image correlation (DIC) [6-7] is used to follow the development of deformation pattern during tensile deformation. The role of anisotropy in relation to damage and fracture process is also examined through a variety of surface analysis techniques including optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray tomography. 2. Experimental The three sheet materials used in the present study were 0.7 mm thick IF steel, 2mm thick AA5754 in O-temper and 2mm thick AZ31 in O-temper. IF steel has a BCC structure, AA5754 FCC and AZ31 HCP. The initial texture is measured by EBSD using TSL OIM software for all three materials. Uniaxial tensile tests are performed at room temperature using ASTM E-8 specimens. Prior to the tests, an ink pattern is applied to each specimen surface. A commercial available optical strain measuring system, Aramis based on digital image correlation is used for DIC measurements. Plastic anisotropy of metallic materials is usually represented by the plastic strain ratio, r-value, that is defined as [8] (1) where εl, εw, and εt are longitudinal, width, and thickness strains, respectively. As thickness strain is difficult to measure, longitudinal and width strains are usually measured to determine the r-value based on the incompressibility criterion along with the assumption of uniform strain distribution over the gage length [8]. In practice, r-value represents material resistance to thinning. In steels, it is generally accepted that higher the r value, higher the FLD. However, in materials with small amount of plasticity, r-value is not a sensitive parameter. Another parameter, the contraction ratio, q-value, similar to a Poisson’s ratio in elasticity, has been proposed and defined as [9] l w q ε ε =− (1) It is easily seen that q=r/(1+r). After tensile tests, necked and fractured specimens are collected for damage and fracture observations using optical microscopy, SEM and X-ray tomography. 3. Results and discussion l w w t w r ε ε ε ε ε + = = −
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