A TWO-SCALE CONSTITUTIVE PARAMETERS IDENTIFICATION PROCEDURE FOR ELASTO-PLASTIC FRACTURE

Constitutive parameters identification for elasto-plastic fracture is a complex problem due to the interplay between two forms of material nonlinearity, viz. plasticity and cohesive fracture. In the present study we examine this problem in relation to Copper specimens covered by Silver used in photovoltaic modules as electrical conductors. Uniaxial tensile tests on un-notched and notched specimens are performed with a tensile stage inside a scanning electron microscope, monitoring crack growth for each imposed far-field displacement. Parameters identification is then performed by considering an elasto-plastic constitutive relation with isotropic hardening for the continuum and a polynomial cohesive zone model (CZM) with two free parameters. For a better numerical-experimental fitting, a four-parameter CZM should be used to independently control the CZM stiffness and the fracture energy. To do so effectively, a constrained optimization procedure with a two-scale objective function is outlined.