Papers by Keyword: Strain Distribution

Abstract: Perforated metal sheets with numerous holes created by punching are used for various purposes, ranging from automotive parts to daily kitchen products, in applications such as ventilation, soundproofing, shielding from sound and light, and weight reduction. However, the plastic forming of thin metal sheets has generally been limited to materials of uniform thickness and quality. It has not been the subject of significant technological development or research. Most current products have flat shapes or are simply bent, and there are few precedents for machining methods that apply strong forces to the hole edges. In the drawing process, in which a strong force is applied to the hole edge, changes in tensile and compressive deformation occur due to discontinuities in deformation resistance. This results in non-uniform sheet thickness caused by a combination of deformation in the holes and no deformation in the surrounding sheet. Therefore, clarifying the drawing characteristics of perforated sheets will contribute to progress in plastic forming.

Abstract: Severe plastic deformation (SPD) with strong shear component is required to promote both grain refinement and texture randomization. When Asymmetric rolling (AR) is applied as asymmetric accumulative roll bonding (AARB), it enables the production of architectured microstructures and metallic composites. Finite element (FE) simulations of AR and AARB were employed to understand the influence of pass thickness reduction (PTR) on the through thickness variation of the velocity gradient. The influence of the PTR up to a total thickness reduction of 50% and the effect of a single 50% reduction step in a bi-layer bonding condition was analyzed. The influence of these process parameters on the strain and rigid body rotation components was compared with the experimental data obtained on an AA1050 aluminum. A better shear to compression ratio across the sheet thickness is achieved by PTRs lower than 30%; at a PTR of 50% the texture is dominated by the frictional shear generated at the roll-sheet interface and the process has a stronger compressive character. This indicates that simple ARB followed by AR with smaller PTRs should generate a better shear distribution than AARB alone.

Abstract: Heteroepitaxially grown multilayered thin film structures have been attracted of great interest due to its potential applications in photovoltaic/light emitting/electronics devices. The thin film morphology plays an important role in enhancing its related physical properties. It is not easy to simulate the multi-layered thin film structures due to the influence of the interface/surface fluctuation. However, the phase field method, based on thermodynamics and Cahn-Hilliard diffusion model, can predict the thin film morphologies without tracking the interfaces. In this paper, a new phase field model was developed for predicting multi-layer structures with multi-order parameters. The morphologies with strain distributions of the quantum wells, quantum dots and buffer layers structures were investigated in the current study. We found that the strain distribution has a strong effect on the suface/interface morphologies in the multilayered structures. Some simulation results are consistent with experimental observations.

Abstract: Advanced materials such as aluminum alloys and composites offer great potential for weight reduction applications in automotive and aerospace vehicles construction. In order to investigate the feasibility of using such materials in the form of laminates, sheet bulging with single-layer aluminum and the aluminum/Composite laminate with the carbon cloth as the middle layer is investigated under uniform liquid pressure conditions. The aluminum sheet stress-strain, wall thickness distribution, carbon fiber radius stress-strain distribution and the effect of die entrance radius etc. are discussed and compared in details. FE results validate that the numerical method can predict the same fracture regions for bulging-blank as observed in experimental tests. Furthermore, the study validates that multi-layer sheet hydro-bulging process with composite fiber as a middle layer is not feasible to form laminates due to rupture of composite fibers near edge regions. Further study is needed to improve the methodology.

Abstract: Roll forming is a continuous profile production process to form sheet metal progressively into the desired shape with closer tolerances. The process offers several advantages such as complex geometrical shapes, high strength, dimensional accuracy, closer tolerances, better quality and consistency, high production rate, improved conformity, and good surface finish. Several parts of automobile body are produced with this process. Nowadays roll forming technology draws more attentions than before in the automotive industry. In this paper, A Finite Element Method applied to study von mises stress, equivalent plastic strain, thickness, plastic strain, longitudinal strain and spring back of the metal sheet with ribs formed by roll forming process. The thickness variation was almost -6.144%.

Abstract: The dynamic strain distribution behavior of a mortar block blasting was experimentally investigated. A small-scale blasting experiment using a mortar block with well-defined property was conducted and the dynamic strain distribution on the mortal block surface was analyzed using a Digital Image Correlation (DIC) method to establish the effective method for investigating the relationship between blast design and fracture mechanism. The block was blasted by simultaneous detonation of Composition C4 explosive charges with an electric detonator in two boreholes. The behavior of the block surface was observed by two high-speed cameras for three-dimensional DIC analysis and it was also measured by a strain-gauge for comparison. The three-dimensional displacements of the free surface of the block were obtained and dynamic strain distributions were computed. A point strain profile extracted from the analyzed strain distribution data was compared with a directly observed strain profile by the strain gauge.

Abstract: This study aimed to analyze the impact of the weld location of TWBs of different thickness ratios on dissimilar steels, particularly on its height, which is known as the rigid hemispherical punch bulging formability. Laser welding was conducted on St12 (0.8 mm) and St16 (1.2 mm) samples using three different width ratios (1:2, 1:1, and 2:1). Then, the microstructure and microhardness of the TWBs and welded joints were tested. Finally, a rigid hemispherical punch bulging formability test was conducted to obtain the bulging formability of the TWBs for the study. Further, the results were compared to the bulging formability of the parent metal. The results show that the microstructure of welds contain all types of ferrites, bainites and lath martensites. The hardness on both sides of the weld is different, and it appears to be an asymmetric distribution. The hardness of the weld seam and heat-affected zone is much higher than the parent metal. The limit dome of the TWBs is lower for each side of the parent metal. When the weld location is parallel to the direction of the principal strain, the bulging formability of TWBs of different thickness ratios is much better. Under certain combinations of material and thickness, the thicker the plate is, the better the bulging formability of the different thickness TWBs is.

Abstract: Damage and microcracks formed by rolling contact fatigue (RCF) were characterized for carburized SCM420 steel. A large number of microcracks were detected beneath the contact surfaces after RCF. The microcrack generation and strain distribution beneath the contact trail depended on the slip ratios of 0 %, -20% and -40 % in the roller pitting test. Such severe slip increased shear strain in the region higher than 160 µm in depth from the contact surface. Compressive stress also gave rise to strain in the region near the surface up to 100 µm in the depth. Those strain gradients may cause a strain incompatibility at the transition layer in which a crack branching was detected.

Abstract: Digital image correlation (DIC) method is a convenient strain analysis method calculating strain from the difference of images between before and after deformation and shows an advantage to apply to any deformation mode or materials as long as significant contrast. We reviewed basic principles of DIC method and then demonstrated strain distribution in tensile deformed ferritic steel and cyclic deformed tempered martensitic steel. Strain distribution in tensile deformed ferritic steel becomes inhomogeneous with lowering temperature due to restriction of slip systems at low temperature. Strain distribution around a fatigue crack in cyclic deformed tempered martensitic steel was visualized by DIC analysis for replica film and strain concentrated on crack tip same as previous report in DIC analysis for specimen surface, which suggests that strain distribution obtained from replica film has an enough reliability. From these results, it can be concluded that DIC analysis is effective method to investigate local deformation and relation between local deformation and fracture behavior in metal materials.

Abstract: In this paper, digital image correlation (DIC) technology and equipment were applied to research strain distribution of CuZn30 metal sheet throughout thickness during three-point bending process. Especially, a parametric study of DIC technique was conducted. The results show that the subset value and step size has a great impact on the strain distribution date. In order to obtain a lower iterations and confidence of the image, reasonable step size and subset value should be decided.