Iranian Journal of Materials Forming
Volume:6 Issue: 1, Winter and Spring 2019

Single point incremental sheet forming (SPISF) has demonstrated significant potential to form complex sheet metal parts without using component-specific tools and is suitable for fabricating low-volume functional sheet metal parts economically. In the SPIF process, a ball nose tool moves along a predefined tool path to form the sheet. This work aims to optimize the formability and forming forces of Al/Cu bimetal sheet formed by the single-point incremental forming process. Two levels of tool diameter, step size, tool path and sheet arrangement were considered as the input process parameters. The process parameters influential in the formability and forming forces have been identified using the statistical tool (response table, main effect plot and ANOVA). Analysis of variance (ANOVA) was used to indicate potential differences among the means of variables by testing the amount of population within each sample, which enabled it to show the effects of input variables on output ones. A multi response optimization was conducted to find the optimum values for input parameters by response surface methodology (RSM), and the confirmatory experiment revealed the reliability of RSM for this approach.

Equal channel angular rolling (ECAR) is a severe  plastic deformation (SPD) technique which has been used to produce metal sheets with ultra-fine grain structure. In the present work, the relationships between the mechanical properties and microstructure of samples during the ECAR process have been investigated. The Rietveld method was applied to analyze the X-ray diffraction pattern and to determine the microstructural characteristics including the crystallite size, microstrain, and dislocation density. It was observed that the average crystallite size and dislocation density increased by increasing the strain during the ECAR process. The results showed that ECAR is a procedure intended to obtain meaningful structural refinement appearing in a crystallite. It can be justified by using Taylor equation that the mechanical properties are related to the dislocation density. The ECAR process strongly increases the yield strength and microhardness due to an increase in the dislocation density over a wide range of strain.

This research work has been carried out to study the effect of different Ca contents (0.5, 1.0, 1.5, 2.0 and 3.0) on the microstructure and porosity content of ZK60 alloys. The samples were examined by using optical and scanning electron microscopy (SEM) to evaluate the modification efficiency of the alloy with different Ca concentrations. The cast specimens were modified, homogenized and extruded at 350 °C at an extrusion ratio of 12:1. The experimental results showed that the addition of Ca brings about the precipitation of a new phase and refines the as-cast grains. It was also found that the presence of Ca at higher concentrations (>2 wt. %) results in the formation of hard Ca-rich intermetallics segregated in cell boundaries. Hot-extrusion was found to be powerful in breaking the eutectic network and changing the size and morphology of Ca-rich intermetallic phase. By applying the extrusion process and increasing Ca concentration (up to 2.0 wt. %), the porosity percentage decreased from 13.62% to 6.34% and 7.11% to 3.89% for ZK60 and ZK60+3%Ca alloys, respectively.

In the present investigation, two dimensional elastoplastic finite element analysis was conducted to assess the deformation characteristics of Al 1100 alloy during continuous confined strip shearing (C2S2) process. The results of simulations showed that the plastic strain distribution across the deformed sample is non-uniform irrespective of the amount of friction and C2S2 die angle. The most uniform distribution of equivalent strain is achieved when the friction coefficient and die angle are equal to 0.3 and 90˚ respectively.  It was also observed that the maximum damage factor is located in the inner regions of the cross section of the plate similar to the conventional ECAP processing of soft materials with higher strain hardenability. According to a set of simulations, executed at different frictions and die angles, it was demonstrated that the safest condition is achieved during deformation with a friction coefficient of 0.3 and die angles of 90˚ and 110˚. Besides, the analysis of the equivalent strain rate pattern showed that the width of the deformation zone decreases by increasing the friction coefficient and decreasing the C2S2 die angle.

The new class of wrought γ-γ/ Co-base superalloys, which are based on Co-Al-W system,  was developed by conventional hot working routes with a high volume fraction of γ/ precipitates and good mechanical properties. The aim of the present study was to predict the flow stress and hot deformation modeling of a novel γ-γ/ Co-base superalloy. The hot compression tests were carried out over a wide range of temperatures (950°C-1200°C) and strain rates (0.001s-1-1s-1). The flow stress analysis, constitutive approach and microstructure characterization revealed that dynamic recrystallization (DRX) occurred at a high temperature regime (1100°C-1200°C) but not at a low one (950°C-1050°C) due to the presence of γ/ precipitates. The hot deformation characteristic was studied using the hyperbolic sine equation on each of the above-mentioned regimes and the ANN approach on the overall conditions. The constitutive method indicated good potential for the prediction of the flow stress at each separated regime, but the ANN model represented a much more appropriate performance. The outstanding predictability of the ANN model regardless of the γ/ phase participation during the thermomechanical processing under the overall deformation conditions can be considered as another achievement of the proposed approach.

In this study, two-dimensional finite element modeling was used to study the simultaneous effect of the cell shape and regular cell distribution on the anisotropy of the elastic properties of 316L stainless steel foam. In this way, the uniaxial compressive stress-strain curve was predicted using a geometric model and fully solid 316L stainless steel. The results showed that the elastic tangent and the yield strength increase significantly if the direction of the loading is parallel to the major cell dimension. Besides, the regular cell distribution affects the above properties, and the sharp drop in the mechanical properties is observed when the maximum shear stress plane is parallel with the plane including higher cell density. In addition, the finite element modeling showed that the elastic properties of porous 316L stainless steel are anisotropic and the optimum conditions depend entirely on the shape of the cells and the loading direction in the regular cell distribution foam.

Understanding crack growth behavior in engineering components subjected to cyclic fatigue loadings is necessary for design and maintenance purpose. Fatigue crack growth (FCG) rate strongly depends on the applied loading characteristics in a nonlinear manner, and when the mechanical loadings combine with environmental attacks, this dependency will be more complicated. Since, the experimental investigation of FCG behavior under various loading and environmental conditions is time-consuming and expensive, applying a reliable methodology for prediction of this property is essential. In this regard, a modeling technique based on least square support vector machine (LSSVM) framework is employed for prediction of FCG behavior of three different alloys including, Ti-6Al-4V alloy and two Cu-strengthened high strength low alloy (HSLA) steels in the air and corrosive media. The parameters of the developed model were calculated employing the coupled simulated annealing optimization technique. The performance and accuracy of the developed models were tested and validated by their ability to predict the experimental data. Statistical error analyses indicated that the developed model can satisfactorily represent the experimental data with high accuracy.