مهندسی مکانیک در طراحی جامدات
دانشگاه صنعتي اميركبير
گروه آموزشی مکانیک
In the present study, an attempt was made to analyze formability of aluminum 6061 fiction stir welded blank through incremental forming process. Firstly, series of experiments were carried out to find which joining direction causes higher formability. For this purpose, joints with three different directions (i.e., rolling direction, transverse direction, and diagonal direction) were prepared and formability, that is, formed bowl height until failure was compared. After finding the best direction, effect of welding process parameters, that is, rotational speed, plunge depth, and travel speed on formability was analyzed. Thereafter, effect of incremental forming parameters on thickness distribution was identified. From the results, it was found that joints with diagonal direction cause the higher value of bowl height. It was also resulted that the forming efficiency at optimum welding condition is 73% of parent metal. Furthermore, it was found that along the transverse direction tear and minimum thickness occurs in advancing side.
In the present study, non-linear thermal post-buckling analysis of hybrid laminated composite Timoshenko beams embedded with the shape memory alloy (SMA) wires resting on a non-linear hardening elastic foundation were studied. Mechanical properties of composite media are considered temperature-dependent. The theory of Timoshenko beams and von Kármán’s strain-displacement relations are applied simultaneously in virtual work principles to derive the system of non-linear equilibrium equations. Various types of boundary conditions such as clamped, simply supported, and rolled edges were studied for edge supports. Generalized Differential Quadrature Method (GDQM) was utilized to discrete the equilibrium equations in space domain. Different types of lay-ups, such as symmetric and asymmetric, were considered. Post-buckling paths are depicted for different values of non-linear elastic foundation parameters, volume fractions, pre-strains of the SMA fibers, and boundary conditions. The one-dimensional thermo-mechanical constitutive law suggested by Brinson  is applied to model the SMA wires. Numerical results make it possible to recognize that increases in the volume fraction and pre-strain of SMA lead to a dramatic enhancement in thermal buckling and post-buckling capacity of the beam. Pre-buckling, buckling, and postbuckling behavior of the beam are totally different and this is due to variations among critical buckling, austenite start and finish temperatures. Due to the recovery stress of SMA wires, particular consequences are shown.
In this paper, a complete literature review for thermal contact between fixed and periodic contacting surfaces and also thermal contact between exhaust valve and its seat in internal combustion engines is presented. Furthermore, the effects of some parameters such as contact pressure, contact frequency, the contacting surfaces topography and roughness, curvature radius of surfaces, loading–unloading cycles, gas gap conductance and properties, interface interstitial material properties, surfaces coatings and surfaces temperature on thermal contact conductance are investigated according to the papers presented in this field. The reviewed papers and studies included theoretical/ analytical/experimental and numerical studies on thermal contact conductance. In studying the thermal contact between exhaust valve and its seat, most of the experimental studies include two axial rods as the exhaust valve, and seat and the one ends of both rods are considered at constant and different temperatures. In the experimental methods, the temperatures of multi-points on rods are measured in different conditions, and thermal contact conductance is estimated using them.