A step towards numerical evaluation of the local hydrogen susceptibility of punched and cold-formed advanced high strength steel (AHSS) sheets

An experimental and numerical based assessment strategy to evaluate the risk of HE would allow exceeding the current bounds towards new light weight design concepts using modern AHSS. In the current paper a step towards such an assessment strategy is presented. The experimental bases for the model are constant load tests (CLT) on electro-chemically pre-charged and zinc coated notched and punched tensile samples. The overall concentration of lattice and weakly bonded (trapped) hydrogen was measured with thermal differential analysis (TDA). The hydrogen diffusion is modeled by using the trapping formalism proposed by Svoboda-Fischer. Trapping energy and density were determined from electrochemical permeation tests by means of inverse parameter optimization. The evolution of the local stress and strain fields and the hydrogen distribution during the test were simulated in a Finite Element (FE) model of the CLT. Based on the experimental and the numerical results a damage model is suggested to evaluate the local hydrogen embrittlement susceptibility.