[en] Meaning of C* concept is discussed. It is shown that this concept is only a global approach of material force rate concept. The field of Csub(i)sup(*) (material force rate densities) is more representative of creep crack growth than C* integral. As application corrected expressions of C* are proposed for non isothermal cases, strain hardening creep and effect of material elasticity

[en] Among the topics discussed are: fracture analysis methods evaluation; instability prediction using the K sub R-curve approach; and the deformation failure assessment diagram. Consideration is also given to: instability prediction based on the modified J, J sub M-resistance curve approach; and stable crack growth and instability prediction on the V by means of the V sub R-curve method

[en] Short communication

[en] In dense silicon nitride the effect of grain elongation on crack propagation was studied using scanning electron microscopy. The crack front profile could be interpreted by both intergranular and transgranular crack deflection. This crack front deflection was characterized by means of a median deflection angle, which was computed from the surface trajectories of stable cracks. This method was applied to the evaluation of cracks in a set of hot-pressed silicon nitride materials, in which the grain elongation was varied in a controlled way of changing the additive concentration. It was found that the crack front deflection at the start of the critical crack propagation increased with grain elongation. At the same time, it was observed that room temperature fracture toughness increased with the median deflection angle. This indicates that crack front deflection contributes to the correlation between fracture toughness and grain elongation. (orig.)

[en] Short communication

[en] Short communication

[en] Short communication

[en] Creep crack initiation and creep crack growth behaviours were studied in two creep ductile materials, an austenitic stainless steel and a low alloy ferritic steel. A number of limitations of the global approach to creep cracking, in which unique correlations between time to initiation or creep crack growth rate and the load-geometry parameter, C^*, are shown. A local approach to creep cracking is developed in the austenitic steel. In this material a damage function based on the measurement of intergranular damage in notched specimens is established and then applied ahead of the crack tip to simulate numerically crack growth. A good agreement between observed and calculated crack growth curves is obtained using crack initiation data. (orig.)

[en] The thrust of this work was to investigate published J material resistance and stress-strain data applicable to the understanding of crack propagation in tough ductile steels, particularly SA 106 Grade B pipe steel. This data has been assembled from PIFRAC, AECB report INFO-0254-1 and Ontario Hydro sources and has been uniformly formatted and presented to facilitate comparison and assessment. While the data is in many aspects incomplete it has enabled an evaluation of the influence of temperature, specimen thickness and specimen orientation to be made in the context of the experimental J-R curves so determined. Comparisons of the stress-strain data within the Ramburg-Osgood formulation are also considered. A further component of this report addresses the development of the required software to utilize what is referred to as the engineering approach to elasto-plastic analysis to investigate the load carrying capacity of selected cracked pipe geometries which are representative of applied crack propagation studies associated with piping systems in the nuclear industry. Three specific geometries and loading situations, identified as Condition A, B and C have been evaluated; the results are presented and illustrate the variation in applied load as a function of an initial and final crack extension leading to instability

[en] A simple model for predicting the initiation of crack growth during plastic fracture is evaluated. The model is based on requiring equilibrium between applied loads and an assumed stress distribution in the uncracked ligament near the crack. The fracture parameters required are the material's ultimate tensile strength and a process-zone size at the crack tip that is determined from simple fracture tests. The Crack Plane Equilibrium model predicts crack-growth initiation for the crack geometries studied with sufficient accuracy to warrant extending it for investigating other geometries and for predicting stable crack growth and the onset of unstable crack growth