Hydrostatic stress

About: Hydrostatic stress is a research topic. Over the lifetime, 1568 publications have been published within this topic receiving 37773 citations.

Atomistic simulation of the effect of trace elements on grain boundary of aluminum

Abstract: Molecular statics simulations are used in conjunction with the Embedded Atom Method to study the segregation tendency of magnesium and the effect of doping on aluminum symmetric tilt grain boundaries (STGB). It is observed that a state of hydrostatic stress exists predominantly near the grain boundary and influences the segregation energy of magnesium. The origin of hydrostatic stress is explained in terms of local geometrical arrangement of atoms at the grain boundary. The energy of a given grain boundary is found to increase with addition of Mg atoms and the increase depends on the normal distance of the atom from the grain boundary.

Effects of Hydrostatic Pressure on the Flow Stress of Cast Iron

Abstract: A theory is developed in this paper to explain the effects of hydrostatic pressure on the deformation of cast iron. It is assumed that a graphite flake in an iron matrix acts as a penny-shaped crack. The external stresses necessary to induce a finite plastic zone near the crack tip are calculated with rough approximation. The analysis provides a qualitative explanation of the following experimental evidences : (1) Superposed hydrostatic pressure increases the flow stress of cast iron. (2) The increase of flow stress due to hydrostatic pressure is reversible with respect to the hydrostatic pressure. (3) Hydrostatic pressure decreases the anisotropy of cast iron usually observed in torsion tests.

Elastic-Plastic Three-Dimensional Finite-Element Analysis of Bulk Metalforming Processes

Abstract: An elastic-plastic three-dimensional finite-element formulation is presented for the study of bulk metalforming problems. The incremental technique is based upon the Prandtl-Reuss flow rule and von Mises’ yield criterion, and incorporates a finite-deformation formulation using correct definitions of stress and strain increment for accurate and efficient solution of large-strain analyses.

Application of fracture mechanics to propagation of stress corrosion crack based on localized hydrogen embrittlement.

Abstract: In order to estimate quantitatively and theoretically, the SCC test results for Al-8%Mg alloy were analyzed with applying the fracture mechanics, based on the presumption that the principal determining parameter in SCC is the localized hydrogen embrittlement at near the crack tip. Theoretically, the high hydrogen concentration is appeared to be unable to produce through the hydrostatic stress induced diffusion only, in the case of lower yield strength materials such as one discussed here. Thus the concentration due to the increase of plastic strain was discussed by the strain field analysis, assumed that the hydrogen content at near the crack tip can increase proportionally with an increase in dislocation density associated with the plastic yielding within the plastic zone. Results of analysis for the moving crack with continuous hydrogen supply from an environment, showed that the extremely high concentration can be induced within the plastic zone, and that the theoretical prediction can be very closely consistent with the actual behavior of the alloy discussed. Nucleation and propagation of SCC crack were also considered with the fracure mechanics.

Torsional Creep of Polycrystalline Metallic Materials under Hydrostatic Pressure at Room Temperature

Abstract: It has been confirmed by the present authors, as the result of the experimental studies they performed of the creep of pure aluminum and pure iron in the normal temperature range below 0, 5Tm, 1Tm being the absolute melting temperature, that the creep rate of polycrystalline metals tends to decrease with the increase in hydrostatic pressure regardless of such a normal temperature range in which its diffusion mechanism is not to be expected theoretically3)13). It has also been confirmed that the effect of hydrostatic pressure on the flow stress of metals can be described satisfactorily by assuming the formulation of yield condition including the first invariant of stressJ1=σkk, (a) J2'=k(k2+CkJ1+DJ12)1/2, and further that the qualitative explanation of creep rate decreasing with hydrostatic pressure of metals subjected to constant load is given uniformly by this yield condition from a side view of continuum mechanics.Secondly, however, in order to understand better the relationship of hydrostatic pressure to the deformation mechanism in plasticity and creep of metals it is necessary to evaluate quantitatively the difference in the intensity of the influence of hydrostatic pressure between these deformations.In the present study, therefore, it has been aimed at to evaluate numerically the change in the structure of metallic materials, i.e. the effects of hydrostatic pressure on the magnitude both of their plastic and of their creep deformation, and with these ends in view, various hydrostatic tests, creep tests and simple torsion tests, of polycrystalline materials, e.g. pure aluminum, pure iron and pure zinc, have been carried out under several levels of hydrostatic pressure at room temperature. It is to be noticed that the torsion test is found effective in the investigation because its stress condition does not cause the change in the form of the test specimens, nor does it enter into the hydrostatic stress component.The results are summarized as follows:(1) There has been little influence of hydrostatic pressure on the plastic flow stress of pure aluminum but on pure iron there has been effect to some extent after leaving plastic defomation, while remarkable influence appears on pure zinc in an early stage of deformtion. On the whole, such effects grows gradually with advanced deformation.(2) The shape of the yield surface that varies with plastic deformation is determined by replacing the parameters both C and D in the Eq. (a) with numerical values. The calculated values of C and D, without regard to the kind of metal, are nearly zero during the shearing strain between zero and 30% but increases rapidly with the advanced shearing strain.(3) On the creep of metals at room temperature, the confining pressure has a distinctive effect of decreasing the creep rate. The numerical values of C and D in the creep process of pure zinc agree with those in their static plastic flow respectively. Therefore, it is clear that the intensity of the influence of hydrostatic pressure on the creep rate is of the same magnitude as that on the static plastic deformation.