Digital Image Mechanical Identification (DIMI)

TL;DR

This paper introduces a method to directly identify constitutive damage laws from digital images captured during mechanical tests, utilizing displacement field analysis, equilibrium gap method, and a new stability-enhanced formulation.

Contribution

It presents a novel integrated approach combining image-based displacement estimation, a reconditioned equilibrium gap method, and a direct damage law identification technique.

Findings

Validated on artificial data and real biaxial tension tests

Achieved damage law determination with less than 7% displacement fluctuation residuals

Demonstrated the method's effectiveness in quantifying damage growth laws

Abstract

A continuous pathway from digital images acquired during a mechanical test to quantitative identification of a constitutive law is presented herein based on displacement field analysis. From images, displacement fields are directly estimated within a finite element framework. From the latter, the application of the equilibrium gap method provides the means for rigidity field evaluation. In the present case, a reconditioned formulation is proposed for a better stability. Last, postulating a specific form of a damage law, a linear system is formed that gives a direct access to the (non-linear) damage growth law in one step. The two last procedures are presented, validated on an artificial case, and applied to the case of a biaxial tension of a composite sample driven up to failure. A quantitative estimate of the quality of the determination is proposed, and in the last application, it is shown that no more than 7% of the displacement field fluctuations are not accounted for by the determined damage law.