Engineering criterion for rupture of brittle particles in a ductile matrix including particle size and stress triaxiality effects

AbstractCatastrophic failure due to cleavage fracture is caused by the rapid propagation of a micro-crack in the vicinity of a macroscopic flaw. Micro-cracks are initiated at second-phase brittle particles, present in the steel in different sizes and distributed randomly in the volume. The current understanding is that such particles rupture when overloaded by the plastically deforming matrix. To predict the experimentally observed statistical nature of cleavage fracture under different constraint conditions, it is pertinent to develop a particle size and constraint dependent criterion for the failure of a brittle particle in a ductile matrix.In this work the failure energy of an elastic-brittle spherical particle in a ductile matrix is analysed. Several loading conditions were examined, from constrained-uniaxial through to plane strain with varying levels of constraint. To develop a size dependent condition, results for multiple particle radii were investigated within a fixed matrix volume. The particle and matrix were deformed initially; subsequently nodes along the particle mid-plane were released progressively imitating crack opening. The energy associated with particle rupture was determined from the change in reaction force before and after release and corresponding opening displacements.The results for each loading case show clear linear relation between rupture energy and particle size. Further the results show the dependence of rupture energy on constraint, with a distinct increase of failure probability with increasing constraint. Finally, an expression for particle rupture dependence on size, stress triaxiality, and plastic strain level is derived. It is intended that this model will then be used to advance continuum-based local approach models to cleavage and meso-scale models for distributed interacting micro-cracks

Two-parameter fracture characterization of a welded pipe in the presence of residual stresses

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.In this paper two-parameter fracture characterization of elastic and elastic-plastic stress/strain field around a crack front is presented for a welded pipe component containing a circumferential through-thickness crack. A macro function programmed in PYTHON is used to compute the constraint parameters (T-stress, Tz and Q factors) of the specimen in the open source finite element package Code_Aster. Data obtained from literature was employed to support three-dimensional finite element models developed in this research to study the impact of high magnitude repair-weld residual stresses. Complete distributions of the Tstress, Tz and Q-factors were obtained along a 3D crack front in the presence of residual stresses. The effects of stresses (residual and operational) on the constraint parameters are studied. It is shown that a two-parameter methodology provides effective characterization of three dimensional elastic–plastic crack tips constraint

Experimental and numerical analyses of microstructure evolution of Cu-Cr-Zr alloys during severe plastic deformation

We have performed a constitutive experimental, FEM and discrete complex based studies for two copper alloys subjected to ECAP and MDF deformation processes. This combination of methods allows for recognising complementary microstructural effects, such as micro- and macrolocalization phenomena, coupled dislocation cells and grains evolution, inhomogeneities of triple junction network and ultrafine grain emergenc

About the first experiment at JINR nuclotron deuteron beam with energy 2.52 gev on investigation of transmutation of I-129, NP-237, PU-238 and PU-239 in the field of neutrons generated in pbtarget with U-blanket

The experiment described in this communication is a part of the scientific program „Investigations of physical aspects of electronuclear method of energy production and transmutation of radioactive waste of atomic energetic using relativistic beams from the JINR Synchrophasotron/Nuclotron“ - the project „Energy plus Transmutation“. The performing of the first experiment at deuteron beam with energy 2.52 GeV at the electronuclear setup which consists of Pb-target with U-blanket (206.4 kg of natural uranium) and transmutation samples and its preliminary results are described. The hermetic samples of isotopes of I-129, Np-237, Pu-238 and Pu-239 which are produced in atomic reactors and industry setups which use nuclear materials and nuclear technologies were irradiated in the field of electronuclear neutrons produced in the Pbtarget surrounded with the U-blanket setup “Energy plus transmutation”. The estimations of its transmutations (radioecological aspect) were obtained in result of measurements of gamma activities of these samples. The information about space-energy distribution of neutrons in the volume of the Pb-target and the U-blanket was obtained with help of sets of activation threshold detectors (Al, V, Cu, Co, Y, In, I, Ta, Au, W, Bi and other), solid state nuclear track detectors, He-3 neutron detectors and nuclear emulsions

Fatigue corrosion crack extension across the interface of an elastic bi-material

In this work crack propagation in a bi-material composed of a thin elastic layer ideally bonded to a large elastic substrate is studied. A flaw is assumed existing on the surface of the layer. Cracks nucleate from the flaw and propagate through the bi-material. The cracks have realistic geometrical shapes, where the crack tip is an integral part of the crack surface. Thus the crack propagation is associated with a crack surface evolution. Material loss due to corrosion of the crack surface is the physical ground for the evolution. A controlling mechanism for the surface advancement is the rupture of a brittle corrosion-protective film, which is continually building-up along the corroding surface. The rate of surface evolution is a function of the degree of protective film damage, caused by the surface straining. This leads to a moving boundary formulation, for which a numerical solution is proposed. Fatigue loading is considered as a suitable way to maintain crack evolution at a constant peak load level. Under the assumed model, the cracks always pass the interface. The elastic mismatch is shown to influence the growth rate variation around the interface. Crack extensions are presented as functions of the elastic mismatch and as functions of the initial flaw size. It is shown how the results can be used in designing bi-material systems. A typical morphology evolution of a crack passing through an interface with a weak-stiff transition is presented. An example of fatigue corrosion fracture is offered, which shows that the crack morphology of the model resembles the one observed in reality. It is concluded that the realistic crack geometry is an effective concept and the moving boundary formulation could be a very successful tool for simulating realistic crack propagation

Evolution of fatigue crack corrosion from surface irregularities

A moving boundary model is presented for crack nucleation and growth from surface flaws. It concerns with chemical attack that results in material dissolution. A controlling mechanism for evolution is the rupture of a brittle corrosion-protective film that is built up along the corroding surface. The evolution rate is a function of the degree of protective film damage caused by the surface straining. The problem is formulated for an elastic body containing a single and double pits. Low-frequency cyclic loading is considered. Numerical solution is proposed. The behaviours of a growing crack and of two competing cracks are described. Stages of incubation, blunting and steady-state growth characterise a single crack evolution. The steady-state growth rate is found independent of the initial geometry. Stages of independent growth, interactive growth and arrest of one crack characterise the evolution of two competing cracks. The lengths of the arrested cracks are presented as functions of the ratio between the pit depth for a series of different distances between the pits. It is emphasized that the solutions correspond to a homogeneous material. Further work is required to account for the material microstructure