Materials Science Forum Vols. 575-578

Abstract: For the short glass fiber reinforced high density polyethylene (HDPE), a high shearing stress-induced HDPE and MAH functional reaction method was introduced which was achieved by increasing the twin screw extruder rotation speed during melting extrusion process. The results show that the graft degree of consequent HDPE-g(b)-MAH product has been increased from 0.14% of the thermal-induced one to 0.77% by the high shearing stress-induced one when the rotation speed of the screw increases from 100r/min to 800r/min. Therefore, the mechanical properties of the GF/HDPE composites are greatly improved, namely, its tensile-strength, bending-strength and the notch impact absorbed work are increased from 21.43MPa, 15.49MPa and 12.82kJ/m2 to 30.18MPa, 29.72MPa and 19.12kJ/m2 respectively. The corresponding simulations through the commercial Moldflow soft show a good agreement with these experimental data.

Abstract: The heavy 125MN Plunger is weight 140 ton, its heat treatment process include two part, one is heat and another is quenching in order to attain certain hardness on its surface and toughness on its body. Differential temperature heat process were made in well resistance furnace, the heat time include warm-up and holding period and high-speed increasing period. The total time is about 30-40 hours.The differential heat treatment process is an essential step in the production of heavy plunger, and it determines the hardness distribution on the sample surface. In this paper, a program to calculate real-time temperature during the heat treatment process was developed based on a great deal of experiments. Using this subroutine program the temperature field of hollow heavy plunger during differential heat treatment process was calculated. The result shows that the simulated temperature was agreed with the real temperature in the warm-up and holding period of the heat treatment process. In the calculation temperature field ,based on the convectional heat transfer coefficient and radiate heat transfer coefficient, the corrected heat transfer coefficient were induced to compose comprehensive heat transfer coefficient. The temperature predicted in warm-up and holding period were correct, the error was below 1%. At the high-speed increasing period, the time when the external temperature reach enacting was predict accurately. So the computer simulation can give real time prediction to decide parameters of the heat treatment process. The result also show that the program developed is sample and applied , it fit for predicting temperature at workshop real time and it is available to deal with complex process .

Abstract: In the present work, there are presented the results of experimental studies on the basis of regression analysis and FEM-based modeling of the processes of aluminum alloys preforms and semi-finished products manufacture including such widely known processes as cutting rolled products by shear and thixotropic stamping (stamping of metal during crystallization). It is investigated the influence of technological heredity created by variation of cant angles of end surfaces and mono- and poly-directional pulling-down by shear in cutting rolled blanks on stability of the process of subsequent longitudinal upsetting while producing preforms for bulk stamping. As a result of studying the ways of eliminating such negative consequences of technological heredity and increasing high-strength aluminum alloys technological plasticity, there is revealed the possibility of using phase transitions (from solid to liquid state and back) while manufacturing semifinished products in thixotropic conditions close to superplastic deformation.

Abstract: A simulator based on rigid-plastic finite element method is developed for simulating the plastic flow of material in forging processes. In the forging process likes backward extrusion, a workpiece normally undergoes large deformation around the tool corners that causes severe distortion of elements in finite element analysis. Since the distorted elements may induce instability of numerical calculation and divergence of nonlinear solution in finite element analysis, a computational technique of using the Euler’s fixed meshing method is proposed to deal with large deformation problem by replacing the conventional way of applying complicated remeshing schemes when using the Lagrange’s elements. With this method, the initial elements are generated to fix into a specified analytical region with particles implanted as markers to form the body of a workpiece. The particles are allowed to flow between the elements after each deformation step to show the deforming pattern of material. The proposed method is found to be effective in simulating complicated material flow inside die cavity which has many sharp edges, and also the extrusion of relatively slender parts like fins. In this paper, the formulation of rigid-plastic finite element method based on plasticity theory for slightly compressible material is introduced, and the advantages of the proposed method as compared to conventional one are discussed.

Abstract: Laser forming of a micro-structural element involves a complex thermoplastic process. Numerous efforts had been made on the mechanisms of laser forming for macro-size elements, such as temperature gradient mechanism, buckling mechanism and upsetting mechanism, etc. It is found that the three mechanisms cannot depict fully the process of deformation in the macro-size element forming, let alone meet the needs of the micro-size one. Considering the laser inducing thermal stresses with size factors differing from the conventional analysis, it is essential to reveal the mechanisms dominating the forming process to accurately control the bending angle of a tiny plate. By studying the thermal transfer and elastic-plastic deformation of micro-structural element laser forming, the forming mechanism is explained within the micro size. The finite element model for laser bending is constructed for simulation. The stimulation results are agreement with the experimental data.

Abstract: Based on the observations that high temperature accelerates creep rate of polymer while physical ageing plays a reverse role, and that there is an analogy between the influences of stress and temperature on the intrinsic times of polymers, the time-ageing time superposition principle (TASP) and the time-temperature-stress superposition principle (TTSSP) are used to evaluate the long-term creep behavior of poly(methyl methacrylate) (PMMA). PMMA specimens were aged for 2 to 120 hours at identical temperature, their short-term creep strains with 2-hour test duration were measured under various stress levels ranging from 14 to 30 MPa at room temperature, and modeled by means of time-ageing time equivalence and time-stress equivalence. The results show that the creep rate increases with stress, but decreases with ageing time. The ageing time shift factors vary with the stresses at which the shifts are applied. The ageing shift rate is independent on imposed stress in linear viscoelastic region, while it decreases with increasing stress when the material behaves in a nonlinear viscoelastic manner. The master creep compliance curve up to about 1-month at reference ageing time 120 hours and stress 18 MPa, which is nearly 2.5 decades longer than the test duration, is constructed by shifting the creep curves horizontally along the logarithmic time axis. The result illustrates that TTSSP, combined with TASP, provides an effective accelerated test technique for long-term mechanical behaviors of polymers.

Abstract: It is considered that Ti-Cr coatings can improve strength, hardness, wear resistance and corrosion resistance of base control alloys as these coatings combine the advantages of both Ti coating and Cr coating. In this study, the Ti-Cr coatings were deposited by diffusion method. The effects of deposition temperatures on the compositions and microstructures of the Ti-Cr coatings on 45# carbon steel were investigated. The coatings formed consisted of three layers. The outer layer contained Ti and Cr carbides beneath which a diffusion layer was developed. The inner layer was enriched in Ti and Cr. At low temperature (800°C) the outer layer of Ti-Cr coatings was dominated by TiC. Increasing deposition temperature led to the enhanced diffusion of Cr and a Cr7C3 and Cr23C6-dominated outer layer was identified. The growth process of Ti-Cr coating was analyzed and simulated.

Abstract: This study evaluated fatigue crack growth characteristics, Besides consider compressive residual stress effect and verified the most suitable shot peening velocity. Fatigue crack growth delay effect was compressive residual stress, but over peening did action projecting velocity that accelerate fatigue crack growth rate. X-ray diffraction technique according to crack length direction was applied to fatigue fractured surface. Fracture mechanics parameters could be estimated by the measurement of X-ray parameters, and the fractography observation was performed using a scanning electron microscope (SEM) for fatigue fracture surface. As the shot peening velocity increases, striation width increased. The changes in X-ray material parameters described above are directly related to the process of fatigue until the initiation of fatigue crack and X-ray diffraction pattern is thought that failure prediction with stress distribution is possible.

Abstract: The Cam nose part of the Automobile's Cam shaft is strongly bumped with rocker arm or valve-lift. Therefore abnormal wear such as unfair-wear and early-wear occur in the surface. This abnormal wear causes a defect that bad timing open and close actions of the engine valve happen in the combustion chamber so the fuel gas will be combustion imperfect. Therefore, the Cam shaft has to be high hardness and wear resistance. In this study, high frequency heat treatment method was accomplished for wear test for material SM53C.

Abstract: The effect of second quenching temperature in zero time holding on 20MnV steel's strength and hardness was studied by the orthogonal regressive principle. The microstructure and property of the steel after austenite inverse phase transformation quenching in zero time holding were analyzed. Experiment results showed that the fine lath martensite of 20MnV steel was obtained through austenite inverse phase transformation quenching in zero time holding at 830°C-930°C. Within the range of Experiment's temperature, the structure of this steel quenched at 830°C is the finest. The microstructure will become coarse and the strength and hardness will become lower if the temperature goes up. The property of this steel can be increased remarkably by austenite inverse phase transformation quenching in zero time holding at lower temperature.