Deformation and Damage Analysis of a Hybrid‐Forming Tool under Thermal Shock Conditions

Abstract

In the hybrid-forming process for gradient structures [1] inhomogeneous cyclic thermo-mechanical stresses and strains lead to higher risks of failure of the forming tool. The main topic of this paper is the validation of finite element calculations for a tool-like specimen under complex thermo-mechanical loadings in order to predict the material behaviour [3]. To this end thermal shock experiments of tool-like specimens are performed. Optical measuring systems are used for three-dimensional digitalisation of the specimens to get a sufficient amount of data. Results of experimental optical measurings and results of finite element calculations are compared. Additionally, damage analysis using the eddy current method is performed to characterize the surface state of the cyclically thermal shocked specimens. This damage analysis provides data for lifetime prediction models under thermal shock conditions.

FEM Simulation of a Micromechanical Model for Textured Polycrystalline Shape Memory Alloys with n‐Variants

“…In order to solve the discrete state relations, with variant fractions λ ij subjected to the state constraints a Newton type projection method is used (for more details see [6]). Basic principles of the algorithm are taken from [2] and applications are presented in [4].…”

“…To this end the unknowns are collected in a vector X explained below. Additionally, a residual vector is defined which collects the reduced state residuals r ij (see [6]) and the equality constraints for h i = 1 − n j=0 λ ij = 0, i.e.…”

“…Furthermore the projected Jacobi matrix J * (R) (see [6]) is needed to calculate the search direction…”

Simulation of a Hybrid‐Forming Process using Temperature‐ and Rate‐Dependent Viscoplastic Material Models

“…For constitutive modelling of the forming tool (Figure 1 a)) the well known Chaboche model [2] combining plasticity, temperature-, rate-and cycledependency is used. Parameter identification as presented in [3] using results of uniaxial tension-compression tests, results of numerical simulations of these tests and least-squares functionals for experimental and simulated stresses is done for calibration of the constitutive equations. Finite-element modelling of the cyclic thermal loaded forming tool is realized using a three-dimensional finite-element model with tetrahedrical continuum elements (Figure 1 b)).…”