Abstract A research on the microstructure and mechanical properties of the dissimilar joint was carried out so as to understand the effects of post-weld heat treatment (PWHT) on microstructural evolution, microhardness, tensile and flexural properties of the dissimilar friction stir welded (FSWed) joint. The results showed that there is a sufficient and rather complicated material mixing in the nugget zone (NZ). After PWHT, the grains in the joint area except for the NZ demonstrated a grain refinement with more homogeneous and equiaxed grains. Fine and clustered SiC particles in the NZ are confirmed by scanning electron microscope (SEM). In addition, the microhardness values of nugget zones both in as-welded and PWHT condition exhibited a higher Vickers compared to that of AA6061-O. Furthermore, a mean tensile strength of 183.30 MPa that demonstrates a 52.22% increase in tensile strength is also observed in the transverse tensile tests subsequent to PWHT. Considering the three-point bending test results, it is explicit that an increase of 121.96% in the bending extension is obtained as there is no significant increase in maximum bending force after the PWHT.

Abstract In this paper, weldability of magnesium alloys by friction stir welding (FSW) method which is difficult to join by the fusion welding have been investigated experimentally and numerically. To this end, the connection of magnesium alloys was performed using different welding parameters. AZ31 Mg-alloy plates were friction stir welded at rotation speed of 1200 rev/min and translational speeds of 80,100,120,140 mm/min. Temperature evolution in the weld zone during welding was measured by using embedded K-type thermocouples. The temperature measurements on both advancing and retreading sides were performed by ten thermocouples. Tensile and Vickers hardness tests were conducted to evaluate the mechanical properties and the hardness distribution on the weld, respectively. During FSW, heat is generated by the friction and plastic deformation. Knowledge of the temperature distribution is requisite since mechanical properties and microstructure are substantially affected by the heat generation. It was observed that the heat generated during the FSW process was increasing and the grain structure was refined as the translational speed was decreasing. In the finite element analyses, modeling of the FSW process were carried out by ANSYS software to determine the temperature and stress distributions in the welded joint during FSW. An APDL (ANSYS Parametric Design Language) code was developed to simulate FSW process. Transient nonlinear finite element analyses were performed at two stages which the first step is thermal analysis which heat transfer from the pin and shoulder to the plates was modeled and the second is the structural analysis which the temperature data obtained from the thermal analysis in the first stage is used.

Abstract This study deals with the dynamic behavior of a cracked beam subjected to a concentrated force traveling at a constant velocity. Dynamic analyses for a hinged-hinged cracked beam resting on elastic supports under the action of a moving load are carried out by the finite element method. For the beam having rectangular cross-section, element formulation for crack element is developed by using the principles of fracture mechanics. In the numerical analysis, Newmark integration method is employed in order to calculate the dynamic response of the beam. The effects of crack depth, crack location, elastic support and load velocity on the dynamic displacements calculated for different locations on the beam are investigated. The results related to the dynamic response of the beam are presented in 3D graphs.