Stress Concentration


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stress concentration

[′stres ‚kän·sən‚trā·shən]
(mechanics)
A condition in which a stress distribution has high localized stresses; usually induced by an abrupt change in the shape of a member; in the vicinity of notches, holes, changes in diameter of a shaft, and so forth, maximum stress is several times greater than where there is no geometrical discontinuity.

Stress Concentration

 

(in elasticity theory), the concentration of large stresses on small areas adjacent to points of abrupt changes in the shape of the surface or cross section of a deformed body. The factors leading to stress concentration (”stress concentrators”) may be openings, cavities, cracks, grooves, incisions, corners, protrusions, sharp edges, or engraving, as well as various surface irregularities, such as notches, scratches, markings, and irregularities of welded seams.

The distribution of stresses σ (see Figure 1) is characterized by a sharp change in the stressed state, accompanied by rapid attenuation of stresses with increasing distance from the stressed zone. The higher the maximum stress at the site of concentration relative to the nominal stress (the average normal tensile stress at the narrowest cross section of the specimen), the more pronounced the attenuation of stress with increasing distance from the most highly stressed zone.

Figure 1. Stress concentration under tension of force P on a band of width b with a circular opening of diameter d

A measure of stress concentration is the stress concentration factor, ασ = σmaxn and ατ= τmaxn, where σn and τn are the nominal normal and tangential stresses, respectively. The values of ασ and αT are not related to the properties of the material but rather depend on the type of stress concentrator, on its sharpness, absolute size, and size relative to the specimen, and on the type of deformation and stressed state. In addition to the geometric stress concentration factors (those given above), there is also a technical stress concentration factor, which takes into account the structure and plastic properties of the material.

The nature of stress distribution and the values of stress at concentration sites are determined by using the theory of elasticity and plasticity only for a few types of concentrators, because of the great difficulty of solving such problems. In most cases, stress concentration is studied using the methods of photoelas-ticity or lacquer coatings or by tensometry. Stress-relief notches, reinforcement of the edges of openings and recesses, and stiffen-ers in plates are used to reduce or eliminate stress concentration. Strengthening of the material in the stress concentration zone is achieved by various types of treatment.

stress concentration

Localized stress (usually as a result of localized loading or changes in geometry) which is significantly higher than the average stress.
References in periodicals archive ?
Such grips prevent local stress concentrations by utilizing rotating shafts on the upper and lower fixture.
When the stress concentration at the notch's root causes the stress of a certain element to reach the set value (fracture stress [[sigma].sub.[Florin]]), the element will fail and be deleted, so that the stress is redistributed and new stress concentration is induced.
It can be seen from the longitudinal section in Figure 5 that the stress concentration lies in the roof plate position on the front face of the working surface under four distance conditions between the working surface and fault.
At the same time, when the dense shear zone appears, the stress concentration will also occur here.
When the Ca addition increased to 0.64%, the increasing amount of [Mg.sub.2]Ca and other larger second phase which can cause stress concentration lead to the decrease of the elongation and increase of strength.
[6, 7] conducted compressive tests and numerical simulations on the axial splitting failure characteristics of brittle materials with prefabricated holes, which found that the origination and propagation of cracks started from the area of tensile stress concentration of the hole.
Effect of labial frenum notch size and palatal vault depth on stress concentration in a maxillary complete denture: a finite element study.
The ANSYS[R] general purpose program was used to obtain the concentration factors of both types of t-joints [3]; other authors have used programs of lower cost and of their own development, that at the University of Sarajevo called AlfaK[R] [9], which is used to analyze stress concentration factors for different shapes.
As the roof is prone to large area movement, the stress concentration of the roof and floor is high; the vertical stress is in the range of 24-26 MPa; the stress concentration coefficient is in the range of 1.92-2.08, and the stress concentration of the roof is greater than that of the floor.
Although stress concentration in vicinity of regularly located circular openings under axial tension is well researched [1], in this work the problem was investigated in aspect of transverse bending of cellular beam, when simultaneous action of shear force and bending moment take place and pure bending.
Figure 4 plots stress concentration factors (SCFs) computed for each tested dent based on strain gage measurements, where the SCF is the ratio of stress measured in the dent to stress measured in the base pipe.