Showing papers in "Strength of Materials in 1977"

The effect of low temperatures on the rate and microfractographic features of the development of a fatigue crack in low-carbon steel

Abstract: Several investigations of the development of a fatigue crack at low temperatures have indicated that with a decrease in temperature the rate of the growth of the crack decreases [1-3]. However, as a result of tests of mediumand low-carbon steels at temperatures of +20 to --160~ it has been established that tnheeffect of reduced temperature on the growth rate of a crack depends substantially upon the value of the amplitude of stress [1-4] and that the growth rate of a crack decreases at low amplitudes and increases at higher ones. In addition, in [5] it was shown that in 15G2AFDps steel at reduced temperature the growth rate of a crack does not always change steadily. Until a certain temperature (--95~ it decreases at all amplitudes and then depending upon the level of stresses either continues to decrease or increases and then again decreases. Regrettably the complex configuration of a crack in the cylindrical samples used in these investigations very much complicates a quantitative analysis of the stresses in the vicinity of its contour. A similar inconsistent temperature relationship of the propagation rate of a crack was observed in testing high-temperature tempered 65G steel [6]. Until now the reasons for this behavior of materials have not been studied.

Moment scheme of the finite-element method in geometrically nonlinear problems regarding the strength and stability of shells

Abstract: 1. The finite-element method may be successfully and effectively used in solving problems regarding the strength and stability of sloping and nonsloping shells and plates. The rejection of the simplifying hypotheses made in the theory of shells and also the allowance made for the rigid displacement of the body enables the results of the theory of thin plates and shells to be refined, the limits of its applicability to be established, and a faster convergence of the results to be achieved as compared with other versions of the finite-element method. 2. The algorithm employed for the solution of geometrically nonlinear problems offers the possibility of studying the hypercritical behavior of sloping and nonsloping shells in the best possible way. 3. The version of the MSFE here described may also be used in solving physically nonlinear problems and problems regarding the dynamics of plates and shells.

Determining fracture toughness from the results of fatigue tests in circular bending

Abstract: 1. A method has been proposed for determining the stress concentration factor in a cylindrical specimen with unilateral crack loaded in cantilever bending, based on the method of measuring the elastic ompliance of a specimen. Results obrained by this method for 15G2AFDps steel and boiler steel are in good agreement with test data for specimens in eccentric tension. 2. It was es tablished that the value of the dimensionless, coefficient Y2 at one and the same relative crack length\(\bar l\) has little dependence on the relative area\(\bar F\) in a wide range of variation of the latter and the crack shape.

Effect of plastic constraint on the fracture toughness of ductile steels

Abstract: 1. An analysis was made of the phenomenon of an increase in values of critical stress intensity factor KQ calculated by the secant method with increasing specimen dimensions. An interpretation of this phenomenon was also presented which explains the reasons for the undervaluing of much research data on the fracture toughness of ductile steels. 2. It was shown that, by applying narrow, slit-shaped grooves of a certain optimum depth (B/Bn≃1.5) to the lateral surfaces of CT specimens, one can significantly (by a factor greater than 2) reduce the dimensional requirement with regard to the specimen that will ensure the achievement of reliable values of KIc for steel in the plastic state.

Crystallography of cleavage in BCC metals

Abstract: 1. Due to the high degree of symmetry of cubic crystals and the large range of possible slip systems, the calculated minimum values of F(α) function maxima for various cleavage systems do not differ significantly, but allowing for crystal anisotropy substantially affects which crystallographic plane should be given preference from the point of view of ease of cleavage. It is therefore essential to take elastic anisotropy into account when making calculations on the Ayres and Stein model. 2. The method of setting the stress field at the crack tip, is also important. Calculations using various types of stress tensor component may lead to various conclusions about the plane of easy cleavage. Calculations for a crack in an anisotropic crystal are most correct, and formulas for a dislocation in an isotropic medium are the least accurate. 3. The results of calculations on the given model accord satisfactorily with experimental data for crystals of W. Mo, and α-Fe (see Table 3), whereas the results of Ayres and Stein and those obtained according to the minimum surface energy criterion cannot explain all the experimental data. 4. Of the two types of slip system characteristic of bcc metals at moderate and low temperatures, i.e., {011} 〈111〉 and {112} 〈111〉, the minimum values of F(α) function maxima are higher in the system {112} 〈111〉 for all four cleavage systems studied. Taking into account the differing mobility of dislocations in these systems, one may expect that the first or the second system may control the processes of stress relaxation at the crack tip, depending upon the temperature.

Study of the connection between metal fatigue endurance and the level of cyclic ine lastic strain

Abstract: 1. For the materials tested the magnitude of inelastic strain per cycle in the stabilization stage of the inelastic strain process is a characteristic of the intensity of the fatigue damage accumulation in individual testpieces under identical loading conditions, characterized by stress amplitude. 2. It has been shown on the basis of mathematical statistical methods that scatter in endurance values of the relatively linear regression equation in coordinates logΔe-log Nf is essentially less than for the regression equation in coordinates σ-log Nf, and may be used to increase the forecasting accuracy for longterm endurance of materials and constructional elements.

Influence of machining methods on the residual-stress distribution and fatigue strength of steel ShKh15 specimens

Abstract: 1. When an ordinary grinding wheel of the EB40SM2K type and a diamond wheel are used to grind steel ShKh15 specimens to the same surface finish, the latter tool produces in the specimen surface layers (δ≤0.05 mm) residual compressive stresses which increase the fatigue limit of the steel by 25–28% over the level recorded for specimens ground with the wheel EB40SM2K. 2. Roller hardening of the roll-bearing steel ShKh15 produces a substantial increase in the depth of penetration of residual compressive stresses (δ≤2 mm); this produces a 10–12% increase in the fatigue strength compared with that of specimens prepared by ordinary grinding. 3. The residual compressive stresses produced in specimen surface layers as a result of grinding with a diamond wheel and roller hardening remain practically unaffected when the specimens are fatigued in rotating bending. 4. The zone of nucleation and growth of fatigue cracks in high-strength steels of the ShKh15 type is, as a rule, in the region of the influence of the maximum combined tensile stress; depending on the finishing machining operation, surface finish produced, and combined stress distribution over the specimen cross section, this zone may be situated either on the specimen surface or in the specimen interior.

The resistance to deformation and failure of cylindrical tubular elements of industrial glass under the action of external and internal pressure

Abstract: 1 A method of investigating the resistance to deformation and failure of glass tubular elements with loading by an external pressure of up to 2500 kgf/cm2 was developed 2 It was established that the failing stress of 13c glass tubular elements loaded by an external pressure is equal to the strength of this glass under conditions of uniform biaxial compression 3 Failure of glass and sitall in cyclic compression is prepared for gradually and occurs significantly earlier than in static loading It is caused by the preferential growth of surface defects causing significant stress concentration and may be observed visually in the early stage of damage

Experimental investigation of the structural aspect of fracture initiation in specimens of hard alloys of WC-20% Co loaded in unixial compression

Abstract: 1. In compression tests, fracture and plastic deformation of individual carbide grains occur long before the appearance of the main crack. 2. The carbide grains which undergo plastic deformation are, as a rule, locally loaded in multiaxial compression. 3. Fractured carbide grains are loaded in three-point or cantilever bending or by crack opening.

Influence of temperature on the anisotropy of the yield point of fredeformed carbon steel

Abstract: 1. The test temperature has a marked influence on the anisotropy of plastic deformation of steel. Regardless of the degree of preliminary deformation, the greatest anisotropy is observed between 100 and 300°C. On cooling, the anisotropy of the yield points decreases. 2. At room temperature and elevated temperatures, the directions in which the yield points are maximal coincide with the direction of the predeformation. At low temperatures these directions do not coincide; the degree of disorientation depends on the temperature, and is 45° at t=−196°C. 3. The circle diagrams characterizing the anisotropy of steel at various temperatures are closely approximated by Eq. (1), which involves three anisotropy parameters which depend practically linearly on the degree of plastic deformation.