Numerical simulation of fracture in cup drawing

International Journal of Material Forming, 2016

Experimental and numerical cup drawing process has been investigated on 0.65 mm zinc sheets. The cup exhibits anisotropic earrings due to the material microstructure. The material formability is studied through elliptical bulge tests in the rolling, diagonal and transverse direction. High anisotropy of the formability is observed. The numerical simulation of cup drawing is then made and demonstrates the correct fitting with experimental results. A stress formability criterion developed by Jansen et al. [14] is then implemented into a finite element method software and applied to predict the material rupture observed for some process conditions. The risk zone of the cup is subjected to some strain path changes according to the simulation whereas the strain value does not explain the rupture according to the experimental formability measured by the bulge tests. It has been shown that the rupture is due to some critical stresses, which are reached in the risk zone of the cup. The use of the stress criterion and its non-dependence on the strain path change allows the fracture prediction. Finally, the numerical fracture propagation by the Bkill element method^, as briefly discussed by Bouchard et al. [4], is used and shows a good similarity with the experience.

Computers & Structures, 2002

The continuum damage model for ductile damage and ductile fracture is applied to metal forming and crack propagation by finite element method. The highly nonlinear equilibrium equation is formulated in order to include geometric, material nonlinearities and frictional contact condition. The effect of friction on the damage concentration is shown in the upsetting process. Then it is verified that the ductile fracture using this damage model is reasonable by the comparison with the experimental result in CCT specimen. The influence of the hole at the crack tip is shown through the numerical simulations of edge-cracked plates with different hole size. Finally, the strain energy release rate in this damage model is compared with J-integral using ABAQUS to relate the result of damage analysis to the concept of fracture mechanics.

2015

In this paper, an anisotropic formulation of the Gurson-Tvergaard-Needleman (GTN) damage model is used for simulating the deep-drawing of a rectangular box made from an AA6016-T4 metallic sheet. The model is implemented as a VUMAT routine in the ABAQUS/Explicit finite-element code. The material parameters involved in the constitutive relationships are determined by means of an identification procedure that combines the response surface methodology (RSM) and the simulation of a uniaxial tensile test. In order to assess the predictive performances of the GTN model, different levels of the blank-holding force are assumed in the finite-element analysis of the deep-drawing process. The comparison between the numerical results and experimental data shows not only a good accuracy of the fracture predictions, but also the capability of the GTN model to provide a realistic description of the material response during the whole forming process.

Drawing is one of the most important processes for forming sheet metal parts. It is used to manufacture parts in industries such as automobile, aerospace and home appliance, etc. The parts produced include cooking pans, kitchen sinks, automobile panels, gas tanks, fountain pen caps, etc. A deep drawn cup has different regions like, flange, corner radius, side walls and flat bottom. The values of stresses and strains vary throughout the cup (i.e in different regions). The objective of the present work is to perform an experimental investigation of major and minor strains in the different regions of deep drawn cups. In this work, the cups are drawn with different blank thickness and major strain and minor strain are measured in different regions of the cup. Also a comparison is made by drawing graphs between major strain(y axis) and minor strain (x axis) for cups drawn with different sheet thickness. By performing this study it will be possible to find out which region of the cup is strained maximum, hence where exactly fracture is likely to occur. Also, areas which are not stressed can be identified and in those areas, heat treatment is not necessary. It will also be possible to know which sheet thickness can take a maximum and minimum amount of stresses and strains. The material selected for this work is Brass. The diameter and heights of cups drawn are 200mm and 40mm respectively. The sheet thickness selected is 0.71, 0.8and 0.88mm. This work was carried out at Metal industries, Sanathnagar, New modern stone company, Hyderabad and metal forming lab of CBIT. The studies revealed that the die corner radius, region (neck) of the cup has maximum strain. Hence this region is the source for a fracture to take place.

Deep drawing is a forming process widely used in aerospace, military, automotive, and various industries. One of the essential useful parameters in the quality of deep-drawn products is Blank Holder Force (BHF). By Controlling BHF during the process, formability has been improved, reduced forming energy, and sheet thickness. Tearing is one of the most common and crucial defects in this process due to high radial stress in the cup's wall, resulting in many limitations in this field. In this process, the blank holder force plays an indispensable role in causing tearing. Therefore, controlling blank holder force during the process would be inevitable to avoid tearing or even wrinkling. This study aims to calculate the tearing limit with new criteria in analytical dominating plasticity Equations based on the slab Method. The St14 sheet with 1 mm thickness and 200 mm diameter is used in this study. The maximum blank holder force in each stage of punch stroke with new criteria based o...

International Journal of Material Forming, 2008

Journal of Materials Processing Technology, 2006

In this contribution, Lemaitre's ductile damage model is coupled with Hill's orthotropic plasticity criterion. The coupling between damaging and material behaviour is accounted for within the framework of Continuum Damage Mechanics (CDM). The resulting constitutive equations are implemented in the Abaqus/Explicit code, for the prediction of fracture onset in sheet metal forming processes. The damage evolution law takes into account the important effect of micro-crack closure, which dramatically decreases the rate of damage growth under compressive paths.

Computational Mechanics, 2011

Damage-induced ductile crack initiation and propagation is modeled using a constitutive law with asymmetrical contraction of the yield surface, and tip remeshing combined with a nonlocal strain technique. In practice, this means that the void fraction depends on a nonlocal strain. Finite strain plasticity is used with smoothing of the complementarity conditions. The prototype constitutive laws take into account pressure sensitivity and the Lode angle effect in the fracture strain. Two plane idealizations are tested: plane stress and plane strain. Thickness variation in the former is included by imposing a null out-of-plane stress. In plane strain, pressure unknowns and bubble enrichment are adopted to avoid locking and ensure stability of the equilibrium equations. This approach allows the representation of some 3D effects, such as necking. The nonlocal approach is applied to the strains so that the void fraction value evolves up to one and this is verified numerically. Two verification examples are proposed and one validation example is shown, illustrating the excellent results of the proposed method.

2007

The continuum mechanical simulation of the microstructural damage process is important in the study of ductile fracture mechanics. In this paper, the continuum damage mechanics framework for ductile materials developed by Lemaitre has been validated experimentally and numerically for A533-B1 alloy steel under triaxial stress conditions. An experimental procedure to identify the damage parameters was established and the experimental calibrated damage parameters were then used in a finite element model. A fully coupled constitutive elastic-plastic-damage model has been developed and implemented inside the ABAQUS implicit FEA code. The model is based on a simplified Lemaitre ductile damage model whose return mapping stage requires the solution of only one scalar non-linear equation. A local crack growth criterion based on the critical damage parameter was proposed; the validity of this criterion was examined by comparing the simulation with the experimental results on standard three point bending (3PB) test. The critical load at crack growth initiation and the fracture toughness, J Ic , has also been predicted from the simulation. These numerically predicted values compared favourably with those obtained from experiments.

The International Journal of Advanced Manufacturing Technology, 2007

This paper presents analyses of tensile instability in the hydromechanical deep drawing process of cylindrical cups. Analytical models are developed based on Barlat-Lian and Hill's non-quadratic yield criteria and the maximum permissible fluid pressure, above which rupture occurs, is achieved, assuming plane strain tensile failure. The influences of process and material variables on this critical fluid pressure are investigated. The theoretical results are compared with results obtained from experiments to verify the validity of the proposed analytical approaches.

International Journal of Material Forming, 2008

International Journal of Engineering Science, 1990

coupled theory of elasticity and continuum damage mechanics is formulated here. It is assumed that the material undergoes damage with small elastic strains. The hypothesis of elastic energy equivalence is used in order to produce the proposed coupling. The damage variable used represents average material degradation which reflects the various types of damage at the microscale level like nucleation and growth of voids, cavities, micro-cracks and other microscopic defects.

cmm.il.pw.edu.pl

Two damage models are used in this study to predict ductile fracture of an aluminium alloy during metal forming process. The first one is developed in the framework of phenomenological approach of damage mechanics. The second model is the micromechanical Gurson, Tveergaard and Needleman (GTN) constitutive law describing the three physical mechanisms of ductile fracture: nucleation, growth and coalescence of cavities. In the second model, the voids coalescence onset is modelled using the critical porosity. The value of this material parameter is determined from calibration with experimental tensile test results. These two models have been implemented into the finite elements code Abaqus using the Vectorized User MATerial (VUMAT) subroutine and employed to simulate the forging process of cylindrical and flanged specimens. The confrontation between the predictions of these models and the experimental results shows the capability of these two constitutive laws to predict the evolution forging force. However, the GTN model fails to capture the failure of the two workpieces, which are essentially subjected to compressive loading.

Computer Methods in Applied Mechanics and Engineering, 1979

The paper reviews recent work on fundamentals of elastic-plastic finite-element analysis and its applications to the mechanics of crack opening and growth in ductile solids. The presentation begins with a precise formu~tion of incremental equilibrium equations and their finite-element forms in a marines valid for deformations of arbitrary magnitude. Special features of computational procedures are outlined for accuracy in view of the near-incompressibility of elastic-plastic response. Applications to crack mechanics include the analysis of large plastic deformations at a progressively opening crack tip, the determination of J integral values and of limitations to I characterizations of the intensity of the crack tip field, and the determination of crack tip fields in stable crack growth.