Interfacial Morphology Prediction of Impact Welding by Eulerian Method

In this paper, results from LS-DYNA numerical simulations are presented with respect to the interfacial morphology of an impact weld of dissimilar sheet materials, i.e., Cu110 (flyer) and CP-Ti (base), both 1 mm thick. These materials were selected as the workpieces since vortices are known to occur at the interface during experimental welding of this material combination. But a conventional Lagrangian numerical method is not capable of capturing this phenomenon due to large element distortions at the interface. Thus, a numerical simulation with the Eulerian method was used to investigate this local, large plastic deformation of materials at high strain rate. Unlike the Lagrangian method, the surrounding air is modelled in the Eulerian method, with a 5 by 5-micron element size in this research, to capture the vortices at the interface. A Johnson-Cook material model, which is widely used for deformation processes at high strain rates, was used for both flyer and base workpieces. Also, a Mie-Grueneisen’s equation of state (EOS) was defined to describe the variation in pressure based on the dynamic condition of materials

Thin Film Superplastic Forming Model for Nanoscale Bulk Metallic Glass Forming

ABSTRACT Geometrically complex, high aspect ratio microstructures have been successfully formed in Bulk Metallic Glass (BMG) via superplastic forming against silicon dies Silicon molds with various nanofeatures were produced using Deep Reactive Ion Etching to achieve high aspect ratio dies over a relatively large area in order to validate these models

An investigation of Hertzian contact in soft materials using photoelastic tomography

Hertzian contact of a rigid sphere and a highly deformable soft solid is investigated using integrated photoelasticity. The experiments are performed by pressing a styrene sphere of 15 mm diameter against a 44 x 44 x 47 mm$^3$ cuboid made of 5% wt. gelatin, inside a circular polariscope, and with a range of forces. The emerging light rays are processed by considering that the retardation of each ray carries the cumulative effect of traversing the contact-induced axisymmetric stress field. Then, assuming Hertzian theory is valid, the retardation is analytically calculated for each ray and compared to the experimental one. Furthermore, a finite element model of the process introduces the effect of finite displacements and strains. Beyond the qualitative comparison of the retardation fields, the experimental, theoretical, and numerical results are quantitatively compared in terms of the maximum equivalent stress, surface displacement, and contact radius dimensions. A favorable agreement is found at lower force levels, where the assumptions of Hertz theory hold, whereas deviations are observed at higher force levels. A major discovery of this work is that at the maximum equivalent stress location, all three components of principal stress can be determined experimentally, and show satisfactory agreement with theoretical and numerical ones in our measurement range. This provides valuable insight into Hertzian contact problems since the maximum equivalent stress controls the initiation of plastic deformation or failure. The measured displacement and contact radii also reasonably agree with the theoretical and numerical ones. Finally, the limitations that arise due to the linearization of this problem are explored

Improvement of Spatial Ability Using Innovative Tools: Alternative View Screen and Physical Model RotatorR

Spatial ability, which is positively correlated with retention and achievement in engineering, mathematics, and science disciplines, has been shown to improve over the course of a Computer-Aided Design course or through targeted training. However, which type of training provides the most beneficial improvements to spatial ability and whether other means would be more effective, is not known. In this research project, two tools for use in spatial ability training were developed and evaluated. One tool, a Physical Model Rotator (PMR), rotates a physical model of an object in synchronous motion with a model of the same object in CAD software. The other training tool, the Alternative View Screen (AVS), provides the user of CAD software with both a solid model (including shading) and a line version view of the object. Students with poor spatial ability were identified through standardized testing and they were then trained over a four week period for one hour each week. The effectiveness of the training tools was evaluated by comparing spatial ability test scores before and after training. Results showed an increase did exist when targeted training was provided. However, this effect was not statistically significant, possibly due to the small sample size

Examining Industry Perspectives Related to Legacy Data and Technology Toolset Implementation

oai:ojs.edgj.org:article/6In this paper, results from a subset of the Purdue Spatial Visualization Test and a self-efficacy test developed by the authors are presented to determine whether certain object shapes, orientations, and types of rotations in standard spatial ability tests cause more difficulty than others and whether a solid object, which includes shading to distinguish different surfaces on the object, would have an effect on the spatial ability test results.  Lower spatial ability scores were observed for more complex object shapes, orientations, and number of rotations on both tests; however, viewing solid images as opposed to line images did not affect the spatial ability scores.  The subjects in this study were engineering students from various disciplines

Prediction of strain gradient hardening during microextrusion

A new formulation is presented to predict the strain distribution through the thickness of the workpiece during forward extrusion. By using shear components, a new model is established to estimate the geometrically necessary dislocation density, which is found to increase with a decrease in the initial and final specimen diameters and an increase in the die angle. Also, strain gradient hardening during forward microextrusion is predicted according to the calculated geometrically necessary dislocation (GND) density. It is found that to experience a significant amount of strain gradient hardening, the diameter of the material should be on the order of 400 mu m or less

Experimental investigation of grain and specimen size effects during electrical-assisted forming

Alternative manufacturing processes such as hot working and electrical-assisted forming (EAF), which involves passing a high density electrical current through the workpiece during deformation, have been shown to increase the potential strain induced in materials and reduce required forces for deformation. While forming at elevated temperatures is common, the EAF process provides more significant improvements in formability without the undesirable effects associated with forming at elevated temperatures. This research investigates the effect of grain size and current density on annealed pure copper during the EAF process. The flow stress reduction effect of the process was shown to decrease with increasing grain sizes. A threshold current density, required to achieve a significant reduction in the flow stresses, becomes more apparent at larger grain sizes, and the value increases with increasing grain size. The effects increase with increasing strain due to dislocations being generated during deformation. Therefore, the dislocation density, related in part by the grain size, appears to be a factor in the EAF process. [DOI: 10.1115/1.4001039