Failure Prediction in Bulk Metal Forming Process

Ameen Topa,Qasim H Shah

doi:10.1155/2014/385065

Abstract

An important concern in metal forming is whether the desired deformation can be accomplished without defects in the final product. Various ductile fracture criteria have been developed and experimentally verified for a limited number of cases of metal forming processes. These criteria are highly dependent on the geometry of the workpiece and cannot be utilized for complicated shapes without experimental verification. However, experimental work is a resource hungry process. This paper proposes the ability of finite element analysis (FEA) software such as LS-DYNA to pinpoint the crack-like flaws in bulk metal forming products. Two different approaches named as arbitrary Lagrangian-Eulerian (ALE) and smooth particle hydrodynamics (SPH) formulations were adopted. The results of the simulations agree well with the experimental work and a comparison between the two formulations has been carried out. Both approximation methods successfully predicted the flow of workpiece material (plastic deformation). However ALE method was able to pinpoint the location of the flaws.

Highlights

In metal forming processes, the term workability refers to the degree of deformation that can be achieved in the workpiece without the occurrence of a defect, that is, the appearance of surface or internal cracks
It can be observed that as the rate of deformation is higher near the end of the compression phase, the strain rate increases at this stage
Since stressstrain relationship at different strain rates was defined in the material model, the strain rate effects are considered in the calculations

Summary

Introduction

In metal forming processes, the term workability refers to the degree of deformation that can be achieved in the workpiece without the occurrence of a defect, that is, the appearance of surface or internal cracks. The propagation of the cracks is of little interest as the main objective is to avoid their initiation These cracks usually appear within regions that are highly strained due to extensive plastic flow of the material during the metal forming process [1]. Rao and coworkers carried on a comparative evaluation of the theoretical failure criteria reported in the published literature They concluded that no theoretical failure criterion can be described as truly geometry-independent for metal forming processes [6]. The development of inexpensive powerful computers technology and the application of finite element method (FEM) into user friendly programs have brought this technology forward This evolution has more or less revolutionized the metal forming analysis [15, 16]. SPH is proven to be a very useful tool in LS-DYNA that can simulate solid and fluid materials [19, 20]

Theoretical Background

Experimental Work

Finite Element Modelling

Results and Discussion

Conclusions