Estimation of the Onset of Crack Growth in Ductile Materials

In this paper, the ductile fracture mechanism is discussed. The results of numerical and experimental analyses were used to estimate the onset of crack front growth. It was assumed that the ductile fracture in front of the crack starts at the location along the crack front where the accumulated effective plastic strain reaches a critical value. According to numerous research articles, the critical effective plastic strain depends on the stress triaxiality and the Lode angle. The experimental program was performed using five different specimen geometries, three different materials, and three different temperatures of +20 °C, −20 °C, and −50 °C. Using the experimental data and results of the finite element computations, the critical effective plastic strains were determined for each material and temperature. However, before the critical effective plastic strain was determined, a careful calibration of the stress–strain curves was performed after modification of the Bai–Wierzbicki procedure. It was found that critical effective plastic strain was a function of triaxiality factor and Lode parameter, as expected, and that the fracture locus was useful to estimate the onset of ductile crack growth

Ductile Fracture Mechanisms in the High-strength Steel Hardox-400. Microscopic Observations and Numerical Stress-strain Analysis.

AbstractThis report presents two hypotheses that aim to predict ductile failure due to void growth and due to shear. The former failure mechanism is predicted using measures of both the tridimensional stress level and plastic strain. The latter failure mechanism, which occurs along the shear lips, is predicted by the level of the maximum shear stress. Both hypotheses were verified by the stress and strain field analyses in front of the crack and scanning microscope observations of the fracture surfaces. A numerical 3D elastic-plastic analysis was conducted assuming finite strains. The material used was Hardox-400 ultra-high-strength steel

Numerical Analysis of the Failure Processes of Plates Made of S 960 QC Steel

In the paper a simple geometrical model is proposed to explain the observation that in the certain thin plates made of steels the ductile failure plane is not inclined by 45 degrees to the plane of the maximum principle stress. This angle is smaller. The hypothesis was supported by results of the numerical observations.</jats:p