Biaxial experiments and numerical analyses on damage prediction in metal forming processes

Michael Brünig,Steffen Gerke,Marco Schmidt

doi:10.1051/matecconf/20168003001

Michael Brünig, Steffen Gerke + Show 1 more

Open Access

https://doi.org/10.1051/matecconf/20168003001

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Abstract

The paper discusses an anisotropic continuum damage and failure model for ductile metals. The phenomenological approach is based on kinematic definition of damage tensors and takes into account the effect of stress state on damage conditions and damage strain evolution laws. Different branches of these criteria based on experimental studies and numerical simulations are considered corresponding to various microscopic damage and fracture mechanisms depending on stress intensity, stress triaxiality and the Lode parameter. Experiments with biaxially loaded specimens and corresponding numerical simulations have been performed showing that they cover a wide range of stress states in combined tension, shear and compression regimes. Digital image correlation technique has been used to analyze current strain states in critical regions of the specimens. Damage behavior for shear-compression loading conditions appearing in metal forming processes is discussed in detail.

Highlights

Numerical calculations for optimization of forming processes currently receive remarkable attention because products of modern metal forming processes have to fulfill economic, environmental and material strength requirements caused by the increasing demands of the customers
Accurate modeling and numerical simulation of large inelastic deformations as well as of damage and failure behavior in materials and structures are of keen interest for many metal forming processes
In various experiments and forming operations with ductile metals large and often localized inelastic deformations occur which may be accompanied by different damage and fracture mechanisms on the micro- and meso-scales

Summary

Introduction

Characteristics of damage and failure mechanisms depend on stress state acting in a material point. For example during tension loading with high positive stress triaxialities damage in ductile metals is mainly caused by nucleation, growth and coalescence of micro-voids whereas during shear and compression loading with nearly zero or negative stress triaxialities the main damage mechanisms on the micro-scale are formation, growth and coalescence of micro-shear-cracks. Can be obtained by numerical simulations considering representative volume elements under various loading conditions [1,2,3,4,5] These microscopic numerical calculations allow detailed analysis of individual behavior of microdefects and it was possible to detect a number of damage and failure mechanisms which have not been revealed by experiments alone. Biaxial experiments with new shear-tension-specimens in combination with numerical simulations have been proposed by [13, 14] to study stress-state-dependent damage and failure processes. Numerical simulations based on the proposed continuum model have been performed and numerical results will be used to explain stress-state-dependent damage and failure processes especially in the regime of negative stress triaxialities

Continuum damage model

G trAel 1

Experiments and numerical simulations

Conclusions