Michael Fischlschweiger

An Inverse Finite Element Approach to Calculate Full-Field Forming Strains

A methodology to calculate surface strains from a rectangular grid placed on a forming blank is introduced. This method consists of treating the grid points as nodes of a finite element (FE) model and assigning elements to the grid. The strains are then computed following FE analysis. If higher order elements are used, also more information within the element can be obtained which allows a coarser grid without loss of accuracy. This is the major advantage of the approach presented herein.

A multi-block-spin approach for martensitic phase transformation based on statistical physics

Current strategies in modeling shape memory alloy (SMA) behavior follow either the concept of classical irreversible thermodynamics or the methodology of phenomenological approaches at the micro as well as at the macro space scale. The objective of the present study is to show a new approach in modeling SMAs by using a statistical physics concept without the requirement of evolution equations for internal variables. Thermodynamic principles in connection with the mathematical apparatus of statistical physics allow deriving relevant system properties in analogy to the formalism used for paramagnetic-ferromagnetic systems. As a result the macroscopic strains and the volume fractions of the martensitic variants and their rates are obtained. The multi-block-spin approach further maps the tension compression asymmetry of multivariant SMAs.

The role of phase interface energy in martensitic transformations: A lattice Monte-Carlo simulation

To study martensitic phase transformation we use a micromechanical model based on statistical mechanics. Employing lattice Monte-Carlo simulations with realistic material properties for shape-memory alloys (SMA), we investigate the combined influence of the external stress, temperature, and interface energy between the austenitic and martensitic phase on the transformation kinetics. The one-dimensional model predicts well many features of the martensitic transformation that are observed experimentally. Particularly, we study the influence of the interface energy on the transformation width and the effective compliance. In perspective, the obtained results might be helpful for the design of new SMAs for sensitive smart structures and efficient damping systems.

A space‐time concept for martensitic phase transformation based on statistical physics

Understanding martensitic phase transformation (MPT) is of crucial importance for many engineering applications. Especially in polycrystalline shape memory alloys and steels one can observe phase transformations on several length and time scales. Those are firstly the atomistic length scale (nano scale, nm) and the scale of the crystallites (micro scale, μm), which, in turn, have a certain size and orientation distribution. The transformation kinetics is described on the mesoscale (mm), where an averaging of physical properties is useful and possible within the representative volume element (RVE). A proper handling of the relevant physical properties within the RVE allows to incorporate effective material laws for computations on the macroscale (m). The present study focuses mainly on the aspect of deriving the relevant physical properties on the mesoscale from atomistic and single crystal properties, i.e., on closing the gap in modelling MPT between the nano‐ and microscale resp., and the macroscale. It ...