On discontinuities when computing the stress-field from the strain: a finite volume discretization

TL;DR

This paper develops a finite volume discretization method for computing heterogeneous stress fields from strain data, addressing stability issues and handling discontinuities in complex geometries and deformations.

Contribution

It introduces a finite volume discretization for a hyperbolic PDE system to accurately compute stress fields from deformation data, including discontinuities and irregular geometries.

Findings

Validated with finite element data

Successfully applied to experimental tension test

Captured stress discontinuities at interfaces

Abstract

Recently, a widely applicable system of hyperbolic partial differential equations has been derived that enables the deterministic computation of a full heterogeneous stress field from a measured deformation field, for example, from a strain field obtained via digital image correlation. This information enables the determination of material properties, making this approach an alternative to finite element model updating or the virtual fields method. This article focuses on developing a finite volume discretization of this system of equations to address instabilities that arise from violations of the Courant-Friedrichs-Lewy condition. The developed discretization enables the system of equations to be applied to irregular geometries and finite deformation. We determine how, in general, one may translate knowledge of the traction at the boundary into boundary conditions, so that the numerical method can be applied to a variety of loading conditions. We analyse the solution structure in the case of deformation discontinuities, and the results are applied to account for discontinuities at the interfaces between finite volumes (this has relevance to other applications such as composite materials). Interestingly, the discontinuities cause reflection and transmission of the principal stresses. The finite volume discretization is validated using data output from commercial finite element software. Furthermore, the discretization is applied to an experimental uniaxial tension test with plastic deformation and necking. The strain field is obtained using digital image correlation, and the stress field is computed using the developed finite volume discretization. Together, these give the stress-strain behavior for each material element.