Gurson

Dual-Phase steel is an advanced high strength steel that
are used recently in auto-body for energy absorption.
Fracture is an noticeable factor in crashworthiness of
vehicle impact loading. Failure prediction of DP800 was
investigated in this studying. There are different fracture
criteria for damage modeling, but the material behavior
cannot be simulated by using them, so a new approach
have been used in this studying. The Gurson model in
conjunction with the Johnson-Cook damage model is
applied to simulate correctly the material behavior. By
using a new method in this research, in shear fracture
and ductile fracture the active mechanisms are JohnsonCook damage model and Gurson model respectively.
Finally, the crashworthiness of a B-Pillar in different
conditions is simulated and the fracture is predicted.

Ductile damage modeling within the Small Punch Test (SPT) is extensively investigated. The capabilities of the SPT to reliably estimate fracture and damage properties are thoroughly discussed and emphasis is placed on the use of notched specimens. First, different notch profiles are analyzed and constraint conditions quantified. The role of the notch shape is comprehensively examined from both triaxiality and notch fabrication perspectives. Afterwards, a methodology is presented to extract the micromechanical-based ductile damage parameters from the load-displacement curve of notched SPT samples. Furthermore, Gurson-Tvergaard-Needleman model predictions from a top-down approach are employed to gain insight into the mechanisms governing crack initiation and subsequent propagation in small punch experiments. An accurate assessment of micromechanical toughness parameters from the SPT is of tremendous relevance when little material is available.

An original and rather simple micromechanical approach is proposed for the case of a rigid plastic von Mises matrix containing multiple spherical cavities and subjected to linear velocities on the boundary. The approach couples mean-field homogenization with Gurson's single cavity stress-strain solution. The actual porous microstructure is modeled alternatively as spherical rigid plastic inclusions in a homogenized Gurson matrix phase and the volume fractions are determined from a maximum packing argument. The alternative microstructures are homogenized with the Generalized self-consistent (GSC) and Mori-Tanaka (MT) models which are formulated with the secant method and second statistical moments of per phase strain fields. Numerical predictions of effective yield envelopes in the plane of hydrostatic and von Mises stresses are verified against full-field finite element (FE) and analytical results for a large range of porosities. No fitting or empirical parameters are used in GSC or MT. It is found that the agreement between GSC and FE predictions is excellent, except when both the porosity and the stress triaxiality are small. The evolution of porosity as a function of the mean accumulated plastic strain in the solid matrix phase of the original microstructure is computed and illustrated for two effective stress triaxiality ratios.