Showing papers in "Strength of Materials in 1983"

Fracture toughness of structural alloys under cyclic loading. Communication 2

Abstract: 1. We experimentally confirmed the need to allow for the change in the parameters of the equation of state of structural alloys during cyclic loading (primarily the change in σplc) in evaluating fracture toughness characteristics for cyclic loading. 2. A correlation was established between the size of the fatigue-damage zone calculated from the proposed relation and values of σplc and crack jump size found for the investigated materials. 3. We established the dependence of equation of state characteristics σo.2c and σplc and fracture toughness characteristic Kfc1 for cyclic loading on the value of the ratio σu/σo.2 for structural steels. This dependence, in the absence of direct empirical data on the effect of load cyclicity on equation-of-state parameters, makes it possible to evaluate σo.2c, σplc, and Kfc1 for prescribed cycling regimes from mechanical characteristics of the steels determined in the static loading of smooth specimens. 4. We demonstrated and experimentally confirmed the possibility of using the proposed model to construct the relations Kfc1=f(Nf), determine the size and number of crack jumps during cyclic loading before final fracture, and establish the relationship between fracture toughness characteristics for static and dynamic loading (KIc and KDc), as well as for cyclic loading (Kfc1 and Kfck).

Strength of glass ceramic S0115M and its joints based on optical contact

Abstract: 1 Breaking strength for joints based on optical contact with a contact area of 680 mm2 is 111 MPa for rectangular cross section specimens Specimens with an annular configuration and a contact area of 150 mm2 have the highest ultimate strength σf=245 MPa 2 Ultimate strength in axial tension and compression for cylindrical specimens made of optical glass ceramic with high microroughness of the lateral surfaces RZ≤063 μm is 591 and 2008 MPa respectively, and this exceeds the ultimate breaking strength of joints based on optical contact with an area of 150 mm2 by factors of 24 and 820 3 In absolutely brittle materials of the optical glass ceramic type forces of mutual attraction operate in annular crack zones predicted by the Leonov-Panasyuk model for the limiting condition, and they promote closing together of the crack sides It may be assumed that the magnitude of these mutual attraction forces for the crack sides is not less than the breaking stress for joints based on optical contact established in this way 4 In critical articles of the shell type made of glass and glass ceramic loaded by external hydrostatic pressure, it is possible for cracks to develop during operation It is not possible to detect these cracks visually due to closing together of the sides after removal of a tensile load In order to provide reliable operation of similar articles there is considerable practical interest in the search for experimental methods making it possible to reveal cracks in these objects

Mechanical properties of a high-strength aluminum alloy with shock loading

Abstract: 1. Within the limits of experimental error, the impact compressibility of different aluminum alloys in the test pressure range is weakly dependent on chemical composition, treatment process, and material strength. 2. Resistance to deformation in the high strain rate region increases with increasing strain rate, and the boundary for a marked effect of strain rate on its resistance moves into the region of higher rates. 3. In the case of the absence of a correlation between strength properties with uniaxial stress and uniaxial strain states, their sensitivity to loading rate may be connected with a single viscosity factor.

Damping capacity of rods in a centrifugal-force field

Abstract: One of the factors determining the reliability and longevity of the working blades of turbomachinery is their damping properties, e.g., the capacity of the material to dissipate vibration energy irreversibly. The characteristic operating conditions of the blades -the presence of centrifugal forces and high temperatures-exert a significant influence on the damping capacity of the material. Methods used to investigate the damping capacity of the blade material under conditions that approach the operating conditions as closely as possible are therefore of greatest practical interest. These possibilities are exhibited by equipment that permits determination of the vibration decrement of rods on a rotating disc by exciting vibrations in them kinematically through the disc [i].

Experimental-numerical methods of determining stress concentrations

Abstract: 1. The combination of the experimental methods and the finite-element method can be used successfully to determine the stress-strain state in zones with steep stress gradients, and makes it possible to examine problems which are difficult or impossible to solve by means of the experimental methods. 2. The proposed method simplifies experiments and yields the most complete information on the stress distribution in the given zone, whose accuracy is not inferior to that of the experimental data. 3. Various types of boundary conditions, obtained using various experimental methods, can be used for the contour of the zone.

Temperature relationships of the mechanical properties of the base metal and weld joints of large-diameter pipe

Abstract: 1. The temperature relationships of the strength and deformation properties and the coefficient and modulus of hardening with\(\dot \varepsilon = 200 sec^{ - 1}\) for VSt3kp, 17GS, and 17G1S-u steels and their weld joints were obtained experimentally. 2. The values of the parameters characterizing thermally activated plastic deformation of the investigated steels and their weld joints were established. These results make it possible to predict the values of yield strength for other test conditions. 3. The values of the resistance to rupture of the investigated steels were determined.

Effect of anisotropy and viscosity on the propagation of waves in multilayer cylinders

Abstract: The effect of anisotropy, viscosity, and mode of loading on the wave form in a multilayer cylinder was examined.

Computer modeling of the deformation kinetics in the plastic zone near a crack tip

Abstract: 1. The possibility of describing the kinetics of the development of the plastic zone using a semimicroscopic method that employs phenomenological equation (1) for the rate of local plastic strain and the distribution of dislocation charges Δρ (4), which determine the magnitude of the local stress, is indicated. 2. A pronounced separation of dislocation charges in the plastic zone, which can be interpreted as the outset of plastic rotations in the zone, is detected. 3. For selected parameter values corresponding to real single iron crystals, the deformation in the plastic zone is determined primarily by long-range hardening (by variation in σl as a result of the appearance of Δρ), and the contribution made by local hardening is only several percent. 4. Even at the level of fractions of a percent, deformation in the plastic zone results in the appearance of a new region of local overstress ahead of the crack tip — a region of instabilities. In this region, the deformations have a sign opposite to that of the deformations in the plastic zone. Moreover, large local-stress gradients, which contribute to the development of rotation instability develop here. This effect is apparently decisive for the initiation of a zone of instabilities ahead of the crack tip, and, consequently, for conditions favorable to macrocrack caving.

Thermal shock resistance of blades with protective coatings in a corrosive atmosphere

Abstract: 1. Diffusion impregnation of a blade surface with aluminum; titanium and aluminum; chromium, silicon, and aluminum with yttrium; cobalt, chromium, and aluminum with yttrium, reduces the corrosion rate for high-temperature heat-resistant and low-temperature heatresistant nickel-base alloys in an atmosphere with sea salt. 2. The most effective coating of those tested under thermal cycling conditions for a gas flow containing sea salt is a multicomponent coating of electron beam evaporation and deposition in a vacuum of cobalt-chromium-aluminum-yttrium. Effective blade corrosion protection may also be achieved by applying a chromium-aluminum-silicon-yttrium coating. 3. Thermal shock resistance of blades with coatings is mainly governed by the relationship of base metal and coating properties. Some coatings may reduce blade material to resist thermal fatigue. 4. The presence of sea salt in the gas stream in amounts close to operating conditions leads to high-temperature sea salt corrosion of blades, and also to a reduction in thermal cycling resistance and working capacity.