Latham Fracture Criterion Research Articles

Numerical modelling of the structural behaviour of thin-walled cast magnesium components using a through-process approach

A through-process methodology for numerical simulations of the structural behaviour of thin-walled cast magnesium components is presented. The methodology consists of casting process simulations using MAGMAsoft, mapping of data from the process simulation onto a FE-mesh (shell elements) and numerical simulations using the explicit FE-code LS-DYNA. In this work, generic High Pressure Die Cast (HPDC) AM60 components have been studied using axial crushing, 3-point bending and 4-point bending tests. The experimental data are applied to obtain a validated methodology for finite element modelling of thin-walled cast components subjected to quasi-static loading. The cast magnesium alloy is modelled using a user-defined material model consisting of an elastic–plastic model based on a modified J2-flow theory and the Cockcroft–Latham fracture criterion. The fracture criterion is coupled with an element erosion algorithm available in LS-DYNA. The constitutive model and fracture criterion are calibrated both with data from material tests and data from the process simulation using MAGMAsoft.

Energy absorption capacity for thin-walled AM60 castings using a shear-bolt principle

The energy absorption potential of high pressure die cast (HPDC) plates made of magnesium alloy AM60 is investigated using a shear-bolt principle. To study the effect of bolt geometry, the tests are performed using bolts with both pentagonal and circular shapes made of high strength steel. It is found that this deformation principle gives an approximately constant average force during the deformation process. A simple empirical model for prediction of the mean shearing force as a function of plate thickness and bolt diameter is proposed. Further, the experiments are simulated numerically using the explicit FE-code LS-DYNA. The numerical simulations are performed using a user-defined material model, consisting of an elastic–plastic model based on a non-associated J2-flow theory and the Cockcroft–Latham fracture criterion. The fracture criterion is coupled with an element erosion algorithm available in LS-DYNA.

Numerical modelling of the structural behaviour of thin-walled cast magnesium components

Axial crushing, 3-point bending and 4-point bending tests have been performed in order to establish an experimental database of the behaviour of generic high pressure die cast (HPDC) AM60 structural components. In this paper, the experimental data are applied to obtain a validated methodology for finite element modelling of thin-walled cast components subjected to quasi-static loading. The HPDC structural components are modelled in LS-DYNA using shell elements. The cast magnesium alloy is modelled using both the classical J2-flow theory and an elastic–plastic model based on a non-associated J2-flow theory. In the latter, the constitutive model includes the Cockcroft–Latham fracture criterion, which is coupled with an element erosion algorithm available in LS-DYNA. It is further possible to define the fracture criterion as a Gauss-distributed stochastic parameter to allow for heterogeneities in the cast material. The constitutive model and fracture criterion are calibrated with data from tension and compression tests. Comparison of experimental and predicted behaviour of HPDC components gives promising results. It is found that the strength difference between uniaxial compression and tension has little influence on the numerical simulations. The fracture criterion of Cockcroft and Latham seems to be an effective approach to predict failure in HPDC components.

Effect of ductile fracture criteria on chevron crack formation and evolution in drawing

The purpose of this study is to clarify the mechanics of ductile fracture in bulk metal forming processes by finite-element analysis and experiments. The author has developed a computer program, based on a conventional computer program involving the finite-element method, by which the behavior of crack propagation after ductile fracture can be analyzed. The phenomenon in which a ‘chevron crack’ appears periodically in the axial direction during drawing has been simulated using the developed computer program. Special attention is focused on the effect of various kinds of ductile fracture criteria on chevron crack formation and evolution during drawing. Results obtained are summarized as follows. First, the analytical results obtained using Gurson's fracture criterion and using Oyane's fracture criterion agree well with the experimental result. Second, the analytical results using Cockcroft and Latham's fracture criterion and using Brozzo et al.'s fracture criterion agree somewhat with the experimental result. Finally, the analytical result obtained using Freudenthal's fracture criterion does not agree with the experimental result.

Finite element analysis on the effect of die clearance on shear planes in fine blanking

Finite element analysis was performed to investigate the effect of the die clearance on shear planes in the fine blanking of a part of an automobile safety belt. For the analysis, AISI1045 was selected as the material, which was used in manufacturing part of an automobile safety belt, and Cockcroft–Latham fracture criterion was applied. The effect of die clearance on die-roll width, die-roll depth, burnish zone, and fracture zone has been investigated in a finite element analysis by a rigid–plastic FEM code, DEFORM-2D. From the analysis, it was found that die-roll width and depth of the shear plane increase with increasing die clearance. The burnish zone decreases with increasing die clearance, but the variation of the fracture zone is the opposite that of the burnish zone, because the increase in die clearance requires less fracture energy. Theoretical predictions were compared with experimental results. There was significant agreement between theory and experiment.

Finite element simulation of the effect of clearance on the forming quality in the blanking process

The clearance between the punch and the die plays an important role in the blanking process. The selection of the clearance will influence the life of the die or punch, the blanking force, the unloading force and the dimensional precision. In this paper, the punch–die clearance values for a given sheet material and thickness are optimized, using the finite element technique and Cockroft and Latham fracture criterion. In the study, the shearing mechanism was studied by simulating the blanking operation of an aluminum alloy 2024. The results of the present paper agree with the previous experimental results.

Validation of the Cockcroft and Latham Fracture Criterion for Cold Heading of Steel Fasteners

Validation of the Cockcroft and Latham Fracture Criterion for Cold Heading of Steel Fasteners

Finite element analysis of optimum clearance in the blanking process

Abstract We propose a methodology to obtain optimum punch-die clearance values for a given sheet material and thickness to be blanked, using the finite-element technique. In the present investigation, the shearing mechanism was studied by simulating the blanking operation of an AISI 304 sheet. Simulation used the FEM program ANSYS and also the Crockroft and Latham fracture criterion. The results of the present paper are in agreement with the results of experimental studies and reflect the results of previous theoretical work.