Application of Micromechanical Models to the Prediction of Ductile Fracture

Abstract

The ductile fracture behavior of different specimens is analyzed by continuum damage-mechanics techniques. A model introduced by Gurson and modified by Needleman and Tvergaard has been implemented in the finite element program package, ADINA. The damage parameters of the model are measured and calculated from smooth tension tests, and the characteristic material distance is estimated from compact tension experiments. A steel, ASTM A710, and a weld metal for the steel, ASTM A508, are investigated. The damage parameters determined from the smooth bars are used to predict the deformation and fracture behavior of notched round bars and of sidegrooved compact specimens. For the weld metal, a side-grooved WOL-X-specimen is also simulated. In every case, a satisfactory agreement of prediction and experiment is observed. In order to investigate the influence of the stress state (constraint) in cracked specimens, a series of numerical computations of different specimen geometries and loading situations is performed utilizing the same set of parameters of the ASTM A710 steel. The slopes of the predicted J-resistance curves increase with increasing ratio of tension versus bending load and with decreasing relative crack length.

A computational approach to ductile crack growth under large scale yielding conditions

“…The J-values in these plots were computed using the line integral on a contour remote from the tip. The trends follow those brought out in earlier modeling work by Sun and Schmitt (1990) and in the systematic experimental studies of the effect of constraint by Hancock et al (1993) and Joyce and Link (1994). The deeply-cracked CT and TPB specimens have the highest constraint and lowest resistance curves, while the center-cracked panel (CCP) has the lowest constraint and the highest resistance curve.…”

“…They focused on the interaction between the void nearest the crack tip and the tip itself by treating large voids as discrete entities and by modeling a second population of much smaller voids using the Gurson relation. In work which is closest in spirit to that developed here, Sun and Schmitt (1990) and Brocks et al (1995) have adopted a version of the computational model proposed by Needleman and Tvergaard and have applied the model to analyze fully plastic cracking behavior of tough steels for various specimen geometries. Work based on a local failure criterion was originated and pursued independently by Rousselier (1987) and coworkers, who developed their own mechanics model for void damage as an alternative to the Gurson model.…”

Micromechanical Coupled Study of Crack Growth Initiation Criterion in Pressure Vessel Steel

“…This result is in accordance with previous research [11,12]. Therefore the FE size o f 0.25 X 0.25 mm in ligament is adopted.…”

Experimental and Numerical Investigation of Void Nucleation in an AlMgSi Alloy

“…A more commonly applied procedure for determining the micromechanical parameters is based on a dual approach involving experimental testing as well as FE analyses of axisymmetric tensile specimens (see e.g. [12]). The FE analyses calculate the macroscopic response of the specimens using the constitutive equations of-the Gurson model.…”