Action Of Residual Stresses Research Articles

Prospects of improving control over the process of electrochemical machining of the blade airfoil profile using the duplex mode method

The paper discusses the features of machining of a compressor blade airfoil. The problem of airfoil deformations under the action of residual stresses that negatively affect the accuracy of the relative position of the airfoil relative to the blade root is discussed. Methods of compensating for the effect of permanent deformations on the accuracy in blade machining and the impossibility of using this approach when the compressor blade is included in the duplex mode technology of electrochemical machining are specified. The analysis of the pattern of electrochemical machining of the blade airfoil with adjustment of the auxiliary technological base developed by the authors and the use of segmented electrodes showed the effectiveness of its use in order to compensate for airfoil deformations. We suggest measuring the interelectrode gaps in the machining chamber after refixturing the base in order to reduce the total machining time. We also suggest using the modernized electrochemical machining scheme when designing a CNC machine for the machining of a blade airfoil.

Modelling of residually stressed, extended and inflated cylinders with application to aneurysms

The paper presents the localized bifurcation abnormal enlargement associated with certain human diseases such as abdominal aortic aneurysms (AAA), among others. The constitutive framework herewith proposed is constructed relying on the modelling of non-linear elastic materials under the action of residual stresses. The suitable incorporation on the mechanical response of residual stresses in the analysis is regarded important for the formation of aneurysms in soft tissues. From a mechanical perspective, the onset of aneurysms formation can be interpreted through bifurcation conditions, whose localization is relatively sensitive to different material and geometrical parameters as it is shown here. In order to reduce the risk and interpret aneurysm formation, we perform a thorough sensitivity analysis of the effect of design parameters such as tube diameter, length, thickness and strength of the residual stress field on bifurcation of a tube under inflation and extesion. A consistent residually stressed material model is formulated in terms of invariants for a general elastic strain-energy function. The dependence of applied pressure, axial stretch and different geometrical and constitutive parameters on bulging and bending bifurcation is illustrated. The numerical procedure to analyse the bifurcation of the finite deformation boundary-value problem at hand is developed based on the modified Riks method. The proposed formulation is implemented in the general-purpose finite element code ABAQUS using user-defined material subroutines.For a given material model, bulging bifurcation is expected for sufficiently large values of the axial stretch while the onset of bifurcation is found to be the bending mode for small values of the axial stretch. This transition zone from bending bifurcation to bulging bifurcation is analyzed for the different parameters considered.

Relaxation of bending stresses and the reversibility of residual stresses in amorphous soft magnetic alloys

The reversibility of residual bending stresses is revealed in ribbon samples of cobalt- and iron-based amorphous alloys Co69Fe3.7Cr3.8Si12.5B11 and Fe57Co31Si2.9B9.1: the ribbons that are free of applied stresses and bent under the action of residual stresses become completely or incompletely straight upon annealing at the initial temperatures. The influence of annealing on the relaxation of bending stresses is studied. Preliminary annealing is found to sharply decrease the relaxation rate of bending stresses, and the initial stage of fast relaxation of these stresses is absent. Complete straightening of preliminarily annealed ribbons is shown to occur at significantly higher temperatures than that of the initial ribbons. Incomplete straightening of the ribbons is explained by the fact that bending stresses relaxation at high annealing temperatures proceeds due to both reversible anelastic deformation and viscous flow, which is a fully irreversible process. Incomplete reversibility is also caused by irreversible processes, such as the release of excess free volume and clustering (detected by small-angle X-ray scattering). The revealed differences in the relaxation processes that occur in the cobalt- and iron-based amorphous alloys are discussed in terms of different atomic diffusion mobilities in these alloys.

Model of formation of texture in A Nd – Fe – B alloy under severe plastic deformation

The effect of torsional severe plastic deformation (TSPD) at room temperature on sintered isotropic and textured Nd – Fe – B permanent magnets is studied. TSPD followed by annealing produces a dominant orientation of the crystallographic c-axes of grains of Nd2Fe14B in the plane of thin nanocrystalline specimens. A model involving two mechanisms is suggested for explaining the appearing texture, i.e., (a) anisotropic breakage of grains under the action of TSPD and (b ) anisotropic growth of grains in annealing under the action of residual stresses.

On the possibility of development of defects in zirconium parts of thermal reactors during storage prior to and after operation

We have established that technological defects (cracks) in zirconium articles can develop in the course of long-term storage prior to their mounting in a reactor, which is caused by the action of residual stresses and hydrogen. We have considered the conditions of after-operation storage of zirconium articles of the fuel core of thermal reactors in water of the cooling ponds of reactors and in spent-fuel storehouses. The possibility of subsequent hydrogenation of these articles during their storage has been shown. Finally, we have studied the effect of hydrogen, absorbed in the course of storage, on the crack resistance of zirconium articles and the development of defects in them due to delayed hydride cracking.

Hardening of Plates by Local Heating of the Zones of Possible Stress Concentration

We determine optimal parameters of the procedure of local heating of one or two zones of a plate used to induce residual compressive stresses around small-size stress concentrators and study the problem of propagation of cracks in the zone of action of residual stresses. On the basis of the results of numerical calculations, we demonstrate advantages of the procedure of heating two zones as compared with heating of a single zone.

Special features of warping of cast and welded parts at elevated temperatures under the action of residual temperatures

The regular features in warping of cast and welded parts produced from various alloys at elevated temperatures under the action of residual stresses are studied. The warping process under the action of residual stresses is directly reproduced on special cast and welded specimens. The temperature dependence of the warping is shown to behave similarly for various alloys and has an extremum at a specific temperature.

The Effects of Macroscopic Residual Stress on Ring Collapse and Crack Growth in an in-situ Al-Al3Ni Functionally Gradient Material.

The effect of macroscopic residual stress on the fracture of an Al-Al3Ni functionally gradient material (FGM) has been studied. The material has a graded volume fraction of Al3Ni intermetallic particles in a continuous Al phase. Specimens were machined from a thick-walled tube of in-situ Al-Al3Ni FGM that was fabricated by centrifugal casting. The level of macroscopic residual stress present in the hoop direction can be modelled accurately using an uniform temperature change of 160K from an assumed stress free temperature of half the melting point (of the Al matrix). The residual stress distribution changes through-thickness from tension (inner surface) to compression (outer surface). By a superposition of applied and residual stresses a failure (crushing) stress of 130 MPa is obtained. Radial cracks are initiated symmetrically on inner surfaces at positions of maximum applied tensile stress. These cracks do not propagate catastrophically under a constant applied stress, but rather they arrest. Crack opening displacement measurements confirm that as cracks propagate they close under the action of residual stresses. Fractographs show that Al3Ni intermetallic particles fail by transgranular cleavage, and they are surrounded by ductile failure of the continuous Al matrix. The crack path preferentially follows cracked Al3Ni particles.

Distribution of M‐Centres after Annealing in Plastically Deformed LiF Crystals

AbstractThe persistence of M‐centres in glide bands after annealing is explained with the aid of edge dislocations dipoles. On one hand these would cause the segregation of M‐centres, and on the other hand the segregation of the complementary interstitials, migrating in the opposite direction under the action of residual stresses. This slows down the recombination of these defects and consequently the thermal bleaching.