Inverse modelling approach in 3-point bending for elasto- plastic material parameter identification of thin spring steel

C Mertin,G Hirt,K Huse

doi:10.1088/1742-6596/734/3/032011

C Mertin, G Hirt + Show 1 more

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https://doi.org/10.1088/1742-6596/734/3/032011

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Abstract

Under process conditions such as bending of flat wire made from high strength spring steel, the occurring strains are many times higher than the maximum strains determined from uniaxial tensile tests. To determine the elasto-plastic material behaviour of high strength spring steel (X10CrNi18-8), an inverse modelling approach using a simple testing method is presented. A 3-point bending test with the resulting force-displacement measurements is used for the inverse analysis. The inverse approach is used for determining the Young's modulus and hardening parameters of the Ludwik-Hollomon's law for bending of high strength spring steel. FE simulations with the optimised material data meet the experimentally measured punch forces during bending. The optimised material data considerably enhances the springback prediction.

Highlights

For the electrical industry, springs made from high strength flat wire with distinct elastic properties are formed by multi-stage bending processes
Under process conditions such as bending of flat wire made from high strength spring steel, the occurring strains are many times higher than the maximum strains determined from uniaxial tensile tests
The results show that material data from tensile test are not adequate to predict the punch force in v-bending [4]

Summary

Introduction

Springs made from high strength flat wire with distinct elastic properties are formed by multi-stage bending processes. In order to determine the material properties for the required level of strain in the Finite Element Method (FEM) of bending processes, an inverse modelling approach by means of a 3-point bending test is presented. The basic principle of inverse modelling is to optimise input parameters iteratively by minimising a cost function, e.g. least squares method, which evaluates the difference between the experimental and the simulated response of a physical system. One advantage of this inverse approach is that the material parameters are determined under similar load conditions as in the manufacturing of the components. The results show that material data from tensile test are not adequate to predict the punch force in v-bending [4]

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Results

Conclusion