Numerical study of the flange earring of deep-drawing sheets with stronger anisotropy

A Barlat–Lian anisotropy yield function is introduced into a quasi-flow corner theory of elastic–plastic finite deformation and the elastic–plastic large deformation finite element formulation based on the principle of virtual velocity and the discrete Kirchhoff triangle plate shell element model. The focus of the present researches is on the numerical simulation of the flange earring of deep-drawing process of circular sheets with stronger anisotropy, based on which, the schemes for controlling the flange earring are proposed.     

Analysis of crease-wrinkle interaction for thin sheets

In this paper, geometrically non-linear post-buckling analyses were performed to study the effect of sheet thickness, deployment angle, and load ratio on the crease-wrinkle interaction. A square sheet configuration with a single transverse crease was modeled using thin shell elements. The analysis proceeded by initially providing a realistic deployed state of a creased membrane sheet. Then an uneven corner loading was applied to introduce wrinkling. The effects of the induced anisotropy from the crease on the fine-scale detail of the wrinkle evolution, as a function of sheet thickness, loading, and crease deployment angle were systematically investigated. Significant differences were found in sheet compliance and crease-wrinkle interaction as these parameters were varied.     

Effect of planar anisotropy on wrinkle formation tendencies in curved sheets

Wrinkle formation tendencies in the form of short-wavelength shallow buckling modes are investigated for sheet materials exhibiting planar anisotropy. The critical state for the onset of these short-wavelength shallow modes are determined from plastic bifurcation theory. A local analysis is performed by considering the current deformed state of a sheet element in a doubly-curved, biaxial plane stress state. The planar anisotropy is prescribed using recently proposed anisotropic yield criteria. Parametric studies are performed to assess the effects of the various material and geometric parameters on wrinkling.     

Role of plastic anisotropy and its evolution on springback

Springback angles and anticlastic curvatures reported for a series of draw-bend tests have been analyzed in detail using a new anisotropic hardening model, four common sheet metal yield functions, and finite element procedures developed for this problem. A common lot of 6022-T4 aluminum alloy was used for all testing in order to reduce material variation. The new anisotropic hardening model extends existing mixed kinematic/isotropic and nonlinear kinematic formulations. It replicates three principal characteristics observed in uniaxial tension/compression test reversals: a transient region with low yield stress and high strain hardening, and a permanent offset of the flow stress at large subsequent strains. This hardening model was implemented in ABAQUS in conjunction with four yield functions: von Mises, Hill quadratic, Barlat three-parameter, and Barlat 1996. The simulated springback angle depended intimately on both hardening law after the strain reversal and on the plastic anisotropy. The springback angle at low back forces was controlled by the hardening law, while at higher back forces the anticlastic curvature, which depends principally on yield surface shape, controlled the springback angle. Simulations utilizing Barlat's 1996 yield function showed remarkable agreement with all measurements, in contrast to simulations with the other three yield functions.     

Friction stir butt welding thin aluminum alloy sheets

0.8-mm-thick alclad 2024-T4 aluminum alloy sheets were friction stir butt welded. A 15-mm diameter shoulder tool was used to guarantee sufficient heat input during welding. A 0.08-mm shoulder plunge depth was adopted to reduce sheet thickness reduction. Sound joints were obtained at rotating speeds from 400 to 1000 rpm and welding speeds from 50 to 150 mm/min. A thickness reduction of 6% was achieved at 1000 rpm and 50 mm/min. Secondary phases firstly precipitated at the black lines in the stir zone (SZ). The hardness of the SZ showed a decrease about 6% compared with the base metal. A maximum tensile strength of 399.5 MPa and an elongation of 5.6% were achieved at 1000 rpm and 150 mm/min. The fracture morphologies showed typical ductile fracture mode.     

The role of plastic anisotropy deformation in fretting wear predictions

The deformation occurring under fretting conditions occurs over length scales of the same order as the grain size, so the plastic anisotropy plays a significant role in the very local region near the contact edge during fretting process. The present study first describes plastic anisotropy by unified anisotropy plastic model coupling with Archard's wear law on the fretting behavior incorporating the effect of wear debris into such a quantitative model. The finite element method, utilizing this model, is used to analyze gross slip fretting conditions. The implementation of the wear simulation tool together with anisotropy cyclic plasticity analysis during fretting process is applied to the wear depth simulation. The present study validates the experiment phenomena from numerical simulation that failure location of the specimens under the flat-on-flat configuration is very close to the trailing edge. The scar at the trailing edge is much deeper than any other locations and the larger relative slip range resulted in considerably deeper surface damage. Another interesting discovery is that when material with different orientations the degree of wear also develops differently and the quantitative prediction is given.     

Identification of sheet metal plastic anisotropy using heterogeneous biaxial tensile tests

The plastic behavior of anisotropic steel and aluminum sheets is identified by combining the results of classical uniaxial tensile tests and heterogeneous biaxial tensile tests on non-standard cruciform specimens specifically designed for obtaining a high sensitivity of strain fields to material anisotropy. The strain fields are measured on the surface of the specimens by means of an image correlation method. The 8-parameter anisotropic yield function proposed by Ferron et al. [1] is adopted for identification. On the one hand, the results of uniaxial tensile tests are analyzed to determine the strain-hardening parameters and yield function parameters related to transverse strain-anisotropy (angular variation of the anisotropy coefficient R) and stress-anisotropy (angular variation of the yield stress σ). On the other hand, strain fields measured in the biaxial tests are used as input data in an optimization procedure that consists of fitting simulated fields with experimental ones in order to determine the material parameters describing the shape of the yield surface in the biaxial stretching range. The identified yield function is validated using experimental data issued from biaxial tests that were not considered during the optimization process.     

Microscopy of cell cultures through thin plastic films

Microscopy of cells growing in vessels containing plastic films as a substrate or as a transparent window is facilitated by a contact cap on the objective or the contact objectives for intravital microscopy. When applied to microscopical examination of living cells through a thin film, the cap considerably improves the conditions of observation with high-power dry objectives and makes it possible to use water- and oil-immersion objectives.     

Effect of deformation-dependent material parameters on forming limits of thin sheets

Material properties are deformation history dependent. To take this fact into consideration in forming limit analysis, the material parameters are defined as functions of strain using the Voce equation. These history-dependent material parameters are incorporated in the M–K analysis based on Hill's 1993 yield criterion in which all material parameters are independent, so that the effect of each of these history-dependent parameters on forming limits can be investigated individually. The analysis shows that history-dependent material properties have a significant influence on forming limits. An increasing r-value will increase the limit strain under plane strain (FLD₀), which is different from the traditional M–K analysis. Comparison of predicted results with experimental data illustrates that the consideration of history-dependent material properties can improve forming limit predictions considerably.     

A simple light guide for coupling to thin scintillator sheets

A simple light guide configuration for coupling to thin scintillator sheets is described. Its light collection properties are similar to those of the more conventional “twisted strip” guide and it offers the advantages of compactness and reduced cost.     

Closed-form solution for wedge cutting force through thin metal sheets

A simple kinematic model is developed which describes the main features of the process of the cutting of a plate by a rigid wedge. It is assumed in this model that the plate material curls up into two inclined cylinders as the wedge advances into the plate. This results in membrane stretching up to fracture of the material near the wedge tip, while the “flaps” in the wake of the cut undergo cylindrical bending. Self-consistent, single-term formulas for the indentation force and the energy absorption are arrived at by relating the “far-field” and “near-tip” deformation events through a single geometric parameter, the instantaneous rolling radius. Further analysis of this solution reveals a weak dependence on the wedge angle and a strong dependence on friction coefficient. The final equation for the approximate cutting force over a range of wedge semiangles 10° ≤ θ ≤ 30° and friction coefficients 0.1 ≤ μ ≤ 0.4 is: F = 3.28σ₀(δ_t)^0.2l^0.4t^1.6μ^0.4, which is identical in form and characteristics to the empirical results recently reported by Lu and Calladine [Int. J. Mech. Sci.32, 295–313 (1990)].This analysis is believed to resolve a controversy recently developed in the literature over the interpretation of plate cutting experiments.     

Fretting damage in thin sheets: Analysis of an experimental configuration

A method for evaluating fretting damage in thin sheets was developed for AISI 301 stainless steel in full hard condition in contact with AISI 52100 steel and cast ANSI A356 aluminum. Samples were subjected to fretting and then were subsequently fatigue tested to determine the impact of the fretting damage on fatigue life. A finite element model of the experimental configuration was used to determine the response for the experimental conditions imposed. The values of Fatemi-Socie critical-plane fatigue damage parameter are shown to correspond to the trends in the observed residual fatigue life for contact with AISI 52100 steel.     

Effects of plastic anisotropy and yield criteria on prediction of forming limit curves

The effects of yield criteria on predictions of the right-hand side of forming limit diagrams (FLDs) are investigated. Predictions of limit strains are determined from an initial imperfection model based on the early work of Marciniak and Kuczynski (1967). Particular attention is placed on the effect of normal plastic anisotropy on limit strains during biaxial sheet stretching. The anisotropic yield criteria investigated in this paper include Hill’s (1948) quadratic criterion, Hosford’s (1979) higher-order criterion, and case 4 of Hill’s (1979) non-quadratic criterion. Several important characteristics of the yield surface shape are discussed and a new parameter that quantifies some of these aspects is introduced. Similar to the work of Barlat (1987), this parameter is based on the relative position of plane strain on the yield surface and can be used to predict the various effects of yield criteria on limit strains. Results indicate that predictions of FLD are very sensitive to selection of yield criteria.     

A method to include plastic anisotropy to orthogonal micromachining of fcc single crystals

Micro-abrasive jet machining (μ-AJM) is a fast and flexible technique for micro-patterning of brittle materials and can be combined with patterned mask made from a material with excellent photolithographic properties. Here, we demonstrate a fabrication method for the realization of a passive micromixer with third-dimensional feature by using a μ-AJM process with employing photopolymer as a mask on a glass slide target. We fabricated the mask using SU8, a photosensitive polymer, applied as a micro-pattern for μ-AJM process. The design and fabrication of the proposed micromixer is the first reported for such a device. Three glass layers were successfully bonded in a single step using a direct bonding method. These three bonded glass layers with micro-patterns etched on them were the realization of third-dimension feature on the micromixer design.     

Minimizing manufacturing costs for thin injection molded plastic components

Minimizing the cost of manufacturing a plastic component is very important in the highly competitive plastic injection molding industry. The current approach of R&D work focuses on optimizing the dimensions of the plastic component, particularly in reducing the thickness of the component during product design, the first phase of manufacturing, in order to minimize the manufacturing cost. This approach treats the component dimensions established in the product design phase as the given input, and uses optimization techniques to reduce the manufacturing cost of mold design and molding for producing the component. In most cases, the current approach provides the correct solution for minimizing the manufacturing cost. However, when the approach is applied to a thin component, typically when miniaturizing products, it has problems finding the true minimum manufacturing cost. This paper analyses the shortcomings of the current approach for handling thin plastic components and proposes a method to overcome them. A worked example is used to illustrate the problems and compare the differences when using the current approach and the new method proposed in the paper.     

Minimizing manufacturing costs for thin injection molded plastic components

Minimizing the cost of manufacturing a plastic component is very important in the highly competitive plastic injection molding industry. The current approach of R&D work focuses on optimizing the dimensions of the plastic component, particularly in reducing the thickness of the component during product design, the first phase of manufacturing, in order to minimize the manufacturing cost. This approach treats the component dimensions established in the product design phase as the given input, and uses optimization techniques to reduce the manufacturing cost of mold design and molding for producing the component. In most cases, the current approach provides the correct solution for minimizing the manufacturing cost. However, when the approach is applied to a thin component, typically when miniaturizing products, it has problems finding the true minimum manufacturing cost. This paper analyses the shortcomings of the current approach for handling thin plastic components and proposes a method to overcome them. A worked example is used to illustrate the problems and compare the differences when using the current approach and the new method proposed in the paper.     

Butt autogenous laser welding of AA 2024 aluminium alloy thin sheets with a Yb:YAG disk laser

Higher productivity, lower distortion and better penetration are the main advantages provided by laser welding in comparison with conventional processes. A Trumpf TruDisk 2002 Yb:YAG disk laser is used in this work to increases productivity and quality. Aluminium alloys lead to many technological issues in laser welding, resulting in shallow penetration and defects. In particular, AA 2024 aluminium alloy in a thin sheet is investigated in this paper, being it is used extensively in the automotive and aerospace industries. Bead-on-plate and butt autogenous laser welding tests with continuous wave emission on 1.25 mm thick AA 2024 aluminium alloy sheets were examined morphologically and micro-structurally. The geometric and mechanical features of the welding bead were evaluated via a three-level experimental plan. In addition to the power and speed which are traditionally referred to, beam defocusing was considered as an additional governing factor in a central composite design scheme because it massively affects keyhole conditions. Softening in the fused zone is discussed via Vickers micro-hardness testing and magnesium loss through energy dispersive spectrometry. After properly performing the modelling and optimisation of the fused zone and the cross-section shape factor as the response variables, the laser welding conditions for thin sheets of AA 2024 aluminium alloy are suggested. X-ray and tensile tests were conducted on the specimens obtained with the recommended processing parameters to characterise the AA 2024 disk laser welded beads.