Session: DA-03-01 Fatigue (joint with M&F and C&S)

Paper Number: 62779

Start Time: Thursday, July 15, 2021, 09:00 AM

62779 - Microstructural Based FEM-Calculation of Stress/Strain Fields in Steel AISI 316L and Its Validation by Digital Image Correlation 

Abstract

The prediction of some damage mechanisms, such as fatigue in e.g. piping, requires the consideration of the microstructure, since crack initiation starts at the microscopic scale, i.e. within or between grains. Therefore, it is important to know the local strain/stress state, which, due to the misorientation of neighboring grains, can reach much higher values than the nominal (macroscopic) ones. A finite element model for the calculation of stress/strains and the formation of crack networks  based on the measured anisotropic microstructure of austenitic stainless steel AISI 316L was developed at Paul Scherrer Institut (PSI) in Switzerland (PSI). This hysteresis energy-based mesoscale model uses the sizes and crystallographic orientations of the grains, measured with 2- and 3-dimensional electron back scattering diffraction (EBSD) to generate a representative volume element (RVE) of the material. The anisotropic elastic properties and the anisotropic plastic behavior of each single crystal of the RVE, defined through the evolution of shear deformation in the slip plane with the highest Schmid factor, is considered. Concerning single crystal properties are preliminary determined by a standard tensile test followed by an inverse parameter analysis. A four-parameter damage model used for crack initiation and growth, based on the accumulated inelastic hysteresis energy, is applied. Beside the calculation of local stresses and strains in the microstructure, this (PSI-SNF) model allows the calculation of high and low cycle fatigue lifetime and to perform sensitivity studies, e.g. to analyze the influence of e.g. grain sizes or multiaxial loading on the stress-strain curves.

The local strains in the microstructure, calculated by the PSI-SNF model were validated by the crystal plasticity finite element (CPFEM) code CAPSUL and by measurements with a digital image correlation system (DIC). Good agreement between strains evaluated with these three different methods were observed for strains up to about 4%, meaning that the PSI-SNF model can be successfully applied in the strain range of LCF and HCF.

Furthermore, aspects such as the influence of 2D or 3D EBSD data and the approximation with corresponding columnar, synthetic or real grain geometries in the FE-modelling on the accuracy of the calculated strains, are also discussed.

 

 

 

Presenting Author: Markus Niffenegger Paul Scherrer Institut

Authors:

Markus Niffenegger Paul Scherrer Institut
Vicente Herrera-Solaz Paul Scherrer Institut