Stress concentration

About: Stress concentration is a research topic. Over the lifetime, 23250 publications have been published within this topic receiving 422911 citations.

An approach for the stress analysis of transversely isotropic biphasic cartilage under impact load.

Abstract: Stress analysis of contact models for isotropic articular cartilage under impacting loads shows high shear stresses at the interface with the subchondral bone and normal compressive stresses near the surface of the cartilage. These stress distributions are not consistent, with lesions observed on the cartilage surface of rabbit patellae from blunt impact, for example, to the patello-femoral joint. The purpose of the present study was to analyze, using the elastic capabilities of a finite element code, the stress distribution in more morphologically realistic transversely isotropic biphasic contact models of cartilage. The elastic properties of an incompressible material, equivalent to those of the transversely isotropic biphasic material at time zero, were derived algebraically using stress-strain relations. Results of the stress analysis showed the highest shear stresses on the surface of the solid skeleton of the cartilage and tensile stresses in the zone of contact. These results can help explain the mechanisms responsible for surface injuries observed during blunt insult experiments.

A multiple‐crack model of brittle fracture: 1. Non‐time‐dependent simulations

Abstract: A numerical multiple-crack interaction model is developed to simulate the failure process in brittle solids containing significant populations of flaws. The model, which is two dimensional, allows for the growth of microcracks on a regular array of potential crack sites. Individual cracks may be oriented vertically, horizontally, or at 45° to the sample axes. Quasi-static equilibrium equations are expressed in terms of finite difference approximations and are solved by applying a Renormalization Group theory approach. More than 5800 potential crack sites are included in the current version of the model. We have successfully duplicated a variety of brittle fracture phenomena observed in laboratory rock mechanics studies by employing a limited number of parameters and relations in the model. Included in the model are (1) Lame constants λ and μ for intact material, (2) a coefficient of friction for friction on cracks, (3) a normal stress-dependent crack closure algorithm and (4) an initial crack population. A fracture mechanics approach is used to determine crack growth. Approximate stress intensity factors are computed for all cracks, and when critical values are exceeded, cracks are allowed to grow in either mode I (tension) or mode II (in-plane shear). Simulations are performed by specifying a combination of stress and strain boundary conditions. The model is capable of duplicating experimentally observed features such as elastic moduli, dilatancy, acoustic velocities, peak strength, Mohr-Coulomb failure envelope and, to a limited degree, crack coalescence. A mode II critical stress intensity factor was required to produce a concave failure envelope, as is observed in laboratory experiments. This curvature in the failure envelope reflects a transition from mode I crack growth at low confining pressure to mode II growth at high confining pressure.

Plastic shear bands and fracture toughness improvements of nanoparticle filled polymers: A multiscale analytical model

Abstract: In this paper a multiscale model is provided to assess the toughening improvements in nanoparticle filled polymers caused by the formation of localised plastic shear bands, initiated by the stress concentrations around nanoparticles. The model quantifies the energy absorbed at the nanoscale and accounts for the emergence of an interphase zone around the nanoparticles. It is proved that the elastic properties of the interphase, which are different from those of the matrix, due to chemical interactions, highly affect the stress field rising around particles and the energy dissipation at the nanoscale.

Crack size effects on the chemical driving force for aqueous corrosion fatigue

Abstract: Small crack size accelerates corrosion fatigue propagation through high strength 4130 steel in aqueous 3 pct NaCl. The size effect is attributed to crack geometry dependent mass transport and electrochemical reaction processes which govern embrittlement. For vacuum or moist air, growth rates are defined by stress intensity range independent of crack size (0.1 to 40 mm) and applied maximum stress (0.10 to 0.95 Φys). In contrast small (0.1 to 2 mm) surface elliptical and edge cracks in saltwater grow up to 500 times faster than long (15 to 40 mm) cracks at constant δK. Small cracks grow along prior austenite grain boundaries, while long cracks propagate by a brittle transgranular mode associated with tempered martensite. The small crack acceleration is maximum at low δK levels and decreases with increasing crack length at constant stress, or with increasing stress at constant small crack size. Reductions in corrosion fatigue growth rate correlate with increased brittle transgranular cracking. Crack mouth opening, proportional to the crack solution volume to surface area ratio, determines the environmental enhancement of growth rate and the proportions of inter- and transgranular cracking. Small cracks grow at rapid rates because of enhanced hydrogen production, traceable to increased hydrolytic acidification and reduced oxygen inhibition within the occluded cell.