The aim of the present work is to discuss process parameters effect on microstructure evolution and formation mechanism of ultrafine grains. As plastic deformation technique Equal Channel Angular Pressing (ECAP) method used pure Ti G4 rods processed in order to obtain fine grained micro structure. Equal Chanel Angular Pressing technique was conducted at different processing route, process temperature, pressing velocity with an orthogonal design to critically evaluate the significance of these process parameters with their different levels. The microstructure was observed with optical and electron back scattering diffraction (EBSD) microscope. The mechanical properties were tested with tensile, hardness tests and phase is controlled with XRD analysis.
Four different quasi-static flow curve models were investigated to describe flow curves of austenitic (304) and ferritic (430) stainless steel sheets. Uni-axial tensile tests were carried out and material constants of the models were determined by curve fitting technique. Applicability of these models over the uniform plastic deformation region was evaluated according to the value of nonlinear regression parameter R
IntroductionConstitutive equations give a mathematical representation of the flow stress behavior of materials and involve a particular number of material constants, which are evaluated using limited number of experimental data [1]. These equations are used in finite element (FE) modeling software to simulate the material response under specified loading conditions [2]. Therefore, the accuracy of the numerical simulation largely depends on how accurately the deformation behavior of the material is being represented by the constitutive equation [3]. Many researchers have conducted studies on modeling of flow curves of materials. Singh [4] has investigated suitability of the different constitutive equations for different grain size and temperatures in 316L austenitic stainless steel. Lemoine et al. [5] have compared different constitutive equations for DP 780 and TRIP 780 steel sheets and have recommended the most suitable model for these materials. Li et al. [6] have researched the constitutive relationship of boron steel for the numerical simulation of hot stamping and have attained equations based on strain, strain rate and temperature. In the present work, a comparative study was carried out on Hollomon, Ludwik, Swift and El-Magd models to represent the flow behavior of austenitic (304) and ferritic (430) stainless steel sheets. Uni-axial tensile tests were carried out to determine the material constants of models. Subsequently, the suitability of these models was evaluated by comparing nonlinear regression parameter R 2 and the most suitable model was determined for the test materials.
An experimental study of residual thermal stresses has been carried out in injection molded virgin and recycled high density polyethylene (HDPE) blends. Effects of blend concentrations on residual stresses were investigated under different injection conditions such as melt temperature, mold temperature and cooling time. Layer removal technique was used for measuring residual stresses. In order to determine the relation between the residual stresses and material characteristic of HDPE blends, mechanical and morphological properties of the blends were also investigated. Elastic modulus and impact strength were important key factors for determining the blend characteristics. As a result, it was found that HDPE blends gave higher residual stresses but lower impact strength with higher elastic modulus when recycled concentration was increased. Furthermore, it was seen that shape and size of the crystallites were also effective on residual stresses. Small and spherulitic crystallite structured blends such as 30 % recycled HDPE induced reduction in residual stresses due to easier relaxation with lower elastic modulus and higher impact strength while lamellar crystallite structured blends such as 50 % recycled HDPE gave higher elastic modulus but lower impact strength with higher residual stresses.
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