Papers by Keyword: Sheet

Abstract: The influence of the stress state on damage evolution, fracture behavior, and component performance is well established for proportional loading conditions. In contrast, many industrial sheet-forming processes involve non-proportional loading paths, which can significantly alter material hardening and fracture responses. Recent results have shown, that load direction changes affect damage evolution in the dual-phase steel DP800. This paper aims to investigate to what extend these results can be transferred to the aluminum alloy AA6082-T6. Therefore, specimens are first prestrained in uniaxial tension and subsequently reloaded either in the same direction or orthogonally, using additional tensile tests. Fracture strains during the subsequent tensile tests are determined by Aramis DIC. Orthogonal load direction changes lead to an increased fracture strain for DP800, but decreased fracture strain for AA6082. While the observed behavior of DP800 can be attributed to the void morphology, which is established during prestraining, the results of AA6082 indicate different damage mechanisms which cause this behavior.

Abstract: The research team studied the hardness of cold-rolled sheets of varying thicknesses containing 0.08% carbon. Greater thickness correlated with lower mean hardness. The hardness was found to drop in the middle of a plate and to increase gradually towards the edges. This pattern was observed regardless of the thickness of thin cold-rolled sheet steel. The change in hardness may indicate uneven accumulated strain in the sheets rolled to a desired value. Pre-hardened sheets were analyzed to find whether the hardness was homogeneous through the thickness. The material was hardened by axial tensioning. Analysis showed that at greater accumulated strain, the through-thickness hardness was affected as well. However, the difference was less pronounced at the edge as well as in the middle of sheets. The paper shows graphs of the hardness distribution through thickness.

Abstract: It is known that metallic materials are characterized by anisotropy of their mechanical properties, with this being attributed to the conditions during the manufacturing process. For sheet metals, this anisotropy occurs symmetrically to the three orthogonal axes of the rolling, transverse and normal direction. This characteristic is referred to as orthotropic behaviour and manifests itself, for example, in earing during cupping tests. Therefore, orthotropic yield criteria are highly relevant for the numerical simulation of sheet metal forming processes. The Lankford coefficient, also known as the r-value, is a good experimental measure for characterizing orthotropic ductile behaviour of sheets, and can easily aid in parameter identification for yield criteria such as the Hill approaches. In the present investigations, Lankford coefficients were determined as a function of local strain in uniaxial tensile tests through high-resolution digital image correlation. The sample direction was varied between 0°, 45° and 90° to the rolling direction and the test temperature varied from RT to 350 °C at three different strain rates (0.01-1 s^-1). By means of a novel backward analysis, the measuring range for the Lankford coefficients was positioned exactly in the necking area. An increase in temperatures showed a decrease in the initial Lankford coefficient. The results showed non-constant Lankford coefficients and commence the course of a natural exponential function depending on the local strain. Regardless of strain rate, the results revealed that the Lankford coefficients (r-values) at 150 °C, 250 °C and 350 °C approaches a steady-state of r = 1.14 with strains greater than 50 %.

Abstract: Little research has been carried out in validating, fiber reinforced polymer (FRP) concrete strengthened column and the effective using partial wrapping. Also the effect of several parameter on strengthen column using the partial wrapping sheet of desired width and thickness around column have not been found out. To this end, a nonlinear 3D finite element model has been developed in current study for CFRP strengthened reinforced concrete column to simulate the behavior accompanied by the effect of partial wrapping with emphasis on load capacity and failure mode. The finite element simulation of CFRP strengthened RC columns is performed using commercial finite element program ABAQUS. Modelling was conducted on reinforced concrete columns with dimensions of 160 x 250 x 960 mm. The finite element model incorporates the nonlinear material behavior of concrete, bilinear stress-strain curve of steel and linear elastic behavior of CFRP material. The concrete was modeled using a plastic damage model. The performance of the FE model was studied by simulating experimental columns from the literature. The load, and strain of CFRP obtained from the FE study were compared with the corresponding experimental results. The FEM results agreed well with the experiments. In addition, to enhance our understanding of the behavior of strengthened reinforced concrete column capacity using partial wrapping the effect of changing the spacing between the CFRP sheets and number of layers were examined. The increase number of layers and decrease spacing give a higher ultimate load capacity, and delay the failure.

Abstract: Molten Mg-AZ31 cools and solidifies to a sheet in horizontal twin-roll casting. In the present investigation, this process was numerically analyzed in two dimensions under various conditions. Steady-state solutions were obtained including plastic deformation after solidification. Based on results of the analyses, an optimum process schedule was proposed for production of a sheet of 1 mm in thickness where the sheet thickness decreased from 3 mm through a couple of transitions during operation. However, the schedule was recommended up to 2 mm in thickness due to the restriction in strength of the sleeve material.

Abstract: In cosmetic dentistry, bleaching and laminate veneer methods are common treatments to improve the appearance of teeth. However, there are limitations to these treatments, as they damage the enamel which are not capable of recovering naturally. In this study, novel hydroxyapatite (HAp) sheets, which enable both enamel restoration and aesthetic treatments, were developed. Results indicated that the lower range of the sintering temperatures, of the pulsed laser deposition targets, produced lighter shades of amorphous Calcium phosphate (ACP) sheets. Subsequently, the post-annealing process of the sheets induced crystallization processes of the ACP sheets, to form HAp sheets, and improved the shade rank of the sheet. The shade rank of the developed sheet (6.8 ± 0.2) was almost comparable to the average shade rank of the teeth of Japanese people, within a range of 6.5 to 7.0.

Abstract: Extensive efforts are underway worldwide to develop new steels with substantial fractions of retained austenite, for lightweight automobile manufacturing and other applications requiring improved combinations of strength and formability. It is likely that microalloying can provide product enhancements in these emerging products, such as Q&P, TBF, medium-Mn TRIP, etc. and this paper examines the expected behavior of niobium using inferences based on published AHSS literature and principles of Nb microalloying. Some benefits of Nb in terms of microstructure refinement and precipitation strengthening have been reported. The potential influences of Nb are complex due to the sensitivity of Nb dissolution and precipitation to chemical composition and processing; differences in the expected role of Nb are pointed out with respect to different product forms produced via hot-rolling or annealing after cold-rolling, and microstructures with or without substantial quantities of primary ferrite. Some issues that warrant further examination are identified, as a deep understanding of Nb microalloying and other fundamental behaviors will be needed to optimize the performance of these next-generation steels.

Abstract: Sheet metal forming processes allow for production of lightweight and durable goods. For this reason, drawing operations have been widely used across the automotive, aviation and construction industries and for production of various components of machines. Despite the popularity of deep-drawing steel sheet metal, non-ferrous materials, such as aluminium, magnesium and titanium are also used for such purposes. Titanium materials seem to be particularly attractive due to a beneficial ratio of strength to density and excellent corrosion resistance in the most of technological environments. However, titanium and its alloys belong to a group of materials with low tribological properties and tendencies for galling and build-up of layers of the deformed material on the tool surface. Therefore, this study will discuss the results of the investigations concerning selection of technological lubricants based on vegetable oils used for the operation of forming of sheet metal made of commercially pure titanium (Grade 2). The focus of the experiment is on lubricants based on vegetable oils i.e. rapeseed oil, sunflower oil and olive oil. The main lubricating additive was boric acid and stearic acid. The study presents the results of the determination of friction coefficient during a strip drawing test.

Abstract: This study presents the findings of numerical simulations of forming process for an inspection hole cover with stiffening ribs made of thin grade 2 titanium sheet metal. The numerical simulation was carried out using the FEM method with PAMStamp 2G software. Numerical calculations were performed with consideration for the phenomenon of material strain hardening and anisotropy of plastic properties of the sheet metal formed. Properties of the grade 2 titanium alloy analysed in the simulations were adopted based on the results of the empirical studies. Adequate parameters of the forming process were selected in order to eliminate unfavourable phenomena of losing of material coherence and sheet metal wrinkling. The effect of conditions of friction between the sheet metal and tool and pressure force of the blank holder on the forming process was investigated. The analysis of the distribution of plastic strain and reduction in wall thickness of the drawn parts can be used for determination of the effect of changes in selected parameters and orientation of the specimen on the process of drawn part forming. The quality of drawn parts was assessed based on the shape inaccuracy determined during simulation of forming. The inaccuracy depended on the conditions of the process and strength properties of the titanium sheet metal.

Abstract: This paper introduces motor rotor blanking die design process through specific terms of the process of stamping all. Mould design process is for structural analysis and process analysis of the parts diagram, based on it to determine the technology methods, select the structure of the mould, and make a necessary calculation to determine stock layout and the size of the work part. And choose a suitable punching machine. Finally, choose the parts from the manual of mould.This design also includes the use of AutoCAD software mapping die assembly and major parts map using UG and Pro/E software for 3D solid modeling and animation design simulation process. In addition, the punch and die processing choose WEDM and Programming. So consider the structural design of WEDM of the specific methods to avoid the conflict between design and processing, and guarantee the production reasonable.