Voids Nucleation at Inclusions of Various Shapes in Front of the Crack in Plane Strain

An analysis is presented of the stress field in and around inclusions of various shapes. Results were obtained by the finite element method. Inclusions were located within elementary cells located at the centre of the specimen next to the crack front. The influence of an in-plane constraint on the stress distribution was tested

Analysis of Stress and Strain Fields in and around Inclusions of Various Shapes in a Cylindrical Specimen Loaded in Tension

A numerical analysis is performed of the stress field in and around inclusions of various shapes. Inclusions both stiffer and more compliant than the metal matrix are analysed. The critical stresses required for inclusion fracture are estimated after observation of cavities and inclusions by scanning electron microscopy. Real inclusions were observed after performing uniaxial loading to different amounts of overall strain. The material tested was Hardox-400 steel

On the role of the process zone in hydrogen assisted cracking-II. Kinetic conditions

Following up the developments of recent work on the geometric and force characteristics of the process zone (PZ) and its role on environmental fracture we discuss here the problem of hydrogen assisted cracking (HAC) in elastoplastic material under kinetic conditions. The analysis is based on the postulate that cracking proceeds in step-wise fashion with an average velocity determined by the ratio Δa/Δtc, where Δa is an average crack jump length and Δtc the time interval between two subsequent jumps. Since Δa has been calculated in our earlier work with the aid of macroscopic considerations, emphasis is put here on the calculation of Δtc by considering the critical accumulation of hydrogen within the PZ. Indeed, this is used to formulate a chemomechanical type fracture criterion which eventually leads to the prediction of velocity vs stress intensity factor graphs. © 1988

Analysis of Stress and Strain Fields in and around Inclusions of Various Shapes in a Cylindrical Specimen Loaded in Tension

A numerical analysis is performed of the stress field in and around inclusions of various shapes. Inclusions both stiffer and more compliant than the metal matrix are analysed. The critical stresses required for inclusion fracture are estimated after observation of cavities and inclusions by scanning electron microscopy. Real inclusions were observed after performing uniaxial loading to different amounts of overall strain. The material tested was Hardox-400 steel

On the length of crack jump during subcritical growth

The stepwise growth of a crack in elastoplastic materials under subcritical conditions is considered by developing a model for the individual jumps. The method is based on the concept of the process zone which was precisely defined in an earlier paper (Engng Fracture Mech. 26, 491-503). It is shown that the length of the jump is given explicitly in terms of the geometric and physical characteristics of the process zone, external loading and environmental conditions. The environment of interest can be either a high temperature or a chemical agent, with emphasis being placed on hydrogen-assisted cracking. Two main results are established within this discrete modelling approach to crack motion. First, a physically based definition of a continuous velocity for the crack tip is possible; and, second, the structure of the velocity vs stress intensity factor curve is theoretically established. © 1987

On the role of the process zone in hydrogen assisted cracking-I. Threshold conditions

In preceding papers we defined the geometric and stress distribution characteristics of the process zone (PZ) for subcritical cracking. Here we apply these results to consider the problem of hydrogen assisted cracking under threshold conditions. In particular, the relation of threshold stress intensity factors (KTH) vs hydrogen pressure (P) for elastoplastic materials is theoretically established in accord with experiments. As a byproduct of the analysis, the mean hydrogen concentration within the PZ is calculated and we use this result in Part II of this work where kinetic conditions are discussed and stress intensity factors (K) vs velocity (V) profiles are obtained. © 1988

On the size and shape of the process zone

We discuss a procedure for determining the size and shape of the process zone in an elastoplastic material. The basic features of Rice-Johnson elastoplastic analysis are utilized together with a linear distribution of the process zone forces and the smooth closure condition for the process zone faces. Three different methods are adopted for the calculation: one based on the elimination of the plastic singularity at the crack tip, another on the balance of energy at the onset of crack motion, and the third on an expression for the crack opening angle. Numerical results pertaining to these calculations are listed. © 1987