Microstructure-based models predict abrasion of high strength steels

When striving for material and process optimisation, traditional constitutive mechanical material models lack knowledge on material microstructural parameters such as grain size, shape, orientation, etc. Whereas micromechanical models are reliable tools to effectively link microstructural features to material properties and, thus, performance.

Traditional constitutive mechanical material models are relied upon in many real-scale applications to tackle mechanical issues such as buckling, damage, fatigue, etc. These models are generally calibrated experimentally to reproduce stress-strain curves as accurate as possible. They are then used to predict the real deformation by applying macroscopic boundary conditions.

Unfortunately, such approach is lacking knowledge on material microstructural features – grain size, shape, crystallographic orientation, etc. – which are rounded and homogenised in material model parameters.

Especially for multiphase materials, material microstructural features highlight the material’s anisotropy in the mechanical response. Microstructure-based models, also called micro-mechanical models, are advanced multi-scale approaches linking microscale parameters representing the grain anisotropy (e.g. dislocation density, plane and direction) to macro-scale parameters defining the polycrystalline response.

The scale transition in this approach deals with iterative loops of homogenisation-localisation of stress and/or strain at the RVE (=representative volume element) and single grain scales, respectively. Thus, stress distribution at the RVE scale is more accurately predicted considering initial texture details. Texture based post-processing of the results allows to trace causal factors of the material failure in fatigue, wear or other loading conditions.

BEHH wear modelling ocas

Example of 80×80 µm² RVE representing Von Mises equivalent stress map in an FCC steel under uniaxial tensile test

Being aware of the increasing use of micromechanical modelling approach in material optimisation for complex applications, OCAS is more and more involved in several projects sharing knowledge on this topic and participates in e.g. IMMARS (= Integrated Material Modelling for Abrasion Resistant Steels), a European RFCS project aiming at optimising wear grades for agricultural machinery such as ploughing tines and rotary tillers. This project is dealing with multi-scale approach involving modelling and experimental testing at the microscale to bring knowledge on wear failure mechanisms in such application and link it to material’s microstructure (grain size, distribution, shape, TRIP effect, etc.) using crystal plasticity models (CPFEM) combined with mesoscale damage models.

“Micromechanical models start to become reliable tools to effectively link microstructural features to material properties and, thus, performance.”

Haithem Ben Hamouda, Research engineer Applications & Solutions department, OCAS