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We perform the experimental investigation of the specific features of deformation of a straight segment of a Du-200 pipeline made of 20 steel under the conditions of cyclic loading by internal pressure. The tests were carried out on a pneumohydraulic test bench under the conditions close to the plane stressed state with recording circular and axial elastoplastic deformations. The experimental program includes the application of block cyclic loading of a pipe with variable amplitudes and a constant average stress in a cycle. The stress-strain diagrams are obtained for the case of cyclic creep (ratcheting) of the pipe in the circular and axial directions after 100 cycles in each of the three blocks of loading. It is shown that an increase in the loading amplitude (as compared with the load applied in the previous block) strengthens the effect of cyclic creep. Moreover, as a result of returning to the lower level of loading, this effect is neutralized. [ABSTRACT FROM AUTHOR]

Deformation of rectilinear elements of Du 200 pipeline made of 20 steel under cyclic loading with internal pressure has been studied experimentally. Tests were carried out on a pneumohydraulic bench under conditions close to plane stress state, room temperature, and cycle asymmetry under soft loading mode (stress control). Circumferential and axial strains were recorded at three points of a diametrical section located in the middle of the element under study. Two tubular elements were tested at different values of maximum and amplitude stresses based on 100 cycles of loading. Deformation curves (cyclic creep) of tubes in a circular direction have been obtained, the character of which is significantly non-uniform in comparison with deformation of laboratory specimens. It is shown that even a slight increase in maximum (by 4%) and amplitude (by 8%) stresses significantly (up to 50%) increases the cyclic creep strains in the circular direction. Such growth of deformations can be explained by a peculiarity of 20 steel, the deformation diagram of which in the elastoplastic transition area contains a yield point, which determines intensive deformation of the material. Fixed plastic deformations in the axial direction are more than an order smaller than circular ones, and with increasing loading cycles, they change insignificantly and coincide for the two studied tubular elements. [ABSTRACT FROM AUTHOR]

The effect of heat treatment on mechanical properties of welded joints of aluminum alloy 2219 for different types of heat treatment (T62, T81, and T851), types of rolled products (plate with thickness of 40 mm and sheet with thickness of 5 mm) depending on the direction of the weld. In a wide interval of operating temperatures the temperature limits of strength and fluidity, relative elongation after rupture and modulus of elasticity were obtained. It is shown that heat treatment to the thermal state T62 – in comparison with T81 and T851 – is the most effective for strength of material. In this case there is a rather small decrease of strength characteristics with increasing temperature up to 200°C. It is noted that the alloy under study is characterized by significant anisotropy of mechanical properties in the entire temperature range, and the location of the welded seam of the sheet material along the rolling direction relative to the direction across the rolling allows to increase to 5% of the ultimate strength. [ABSTRACT FROM AUTHOR]

The results of an experimental study of the mechanical properties of carbon fiber-reinforced plastics (CFRP) made by the "wet" winding method in the temperature range of room temperature to −196°C with different reinforcement schemes are presented. The temperature dependences of strength, plasticity and elasticity characteristics of these materials in tensile and three-point bending tests are obtained. The elastic modulus of CFRP with a longitudinal scheme of reinforcement in a given temperature range is at the level of 160 GPa. The ultimate stress of the material at room temperature is 1370 MPa. The temperature dependence of this characteristic is close to linear and practically coincides with that of bending. The low-temperature hardening, estimated by the change in the value of the ultimate stress due to cooling, reaches 39%. The mechanical characteristics of CFRP with a transverse reinforcement scheme both in tension and in bending in the considered temperature range have rather low values and are determined mainly by the matrix properties. When cooling from 20 to −196°C, the elastic modulus of CFRP with a ±45° reinforcement scheme increases by 55%, and its low-temperature hardening is 40%. At the same time, the elastic modulus and ultimate stress are six to eight and ten times, respectively, lower than the similar characteristics of CFRP with the longitudinal reinforcement scheme. Fracture of such a composite at all investigated temperatures occurs locally by shifting at an angle of 45° because of delamination of the material. [ABSTRACT FROM AUTHOR]

In this paper, a method is proposed for specifying the parameters of the exponential hereditary function kernels of the endochronic theory of plasticity to describe the ratcheting (cyclic creep) effect of metallic materials under stress-controlled complex non-proportional loading. The method involves the dependence of the difference of plastic moduli on the ratcheting rate on the steady-state portion of the cyclic stress-strain curve. The plastic moduli are determined at the points where the maximum stresses act in different half-cycles of asymmetric loading. It is believed that the greater the difference of plastic moduli towards the mean stress in the cycle, the greater the strain increment in each cycle of loading. The statements of our previously proposed approach were used to determine the rate of plastic strain accumulation at the steady-state stage of deformation under biaxial loading. This approach, based on the data of uniaxial experiments under cyclic asymmetric loading in tension-compression and reversed torsion with the known value of the cycle nonproportionality parameter, is developed to analyze the cyclic loading paths with equal mean and amplitude von Mises stress values. With some simplifications, the expression is proposed to determine the parameters of the exponential kernel of the hereditary function depending on the cyclic path geometry and the known ratcheting rate for the basic loading path. Similar values for the exponential kernel parameters of the hereditary function are obtained in terms of the difference of plastic moduli by using a simpler bilinear model of elastoplastic deformation. The obtained values of the hereditary function parameters were used to simulate the ratcheting effect under uniaxial and biaxial cyclic loading. The loading programs and data of experiments were taken from the literature. The results of simulation have shown that the parameters of the constitutive equations for cyclic plasticity obtained with this method allow one to describe satisfactorily the kinetics of the stress-strain state of metallic materials subjected to biaxial non-proportional loading under cyclic creep. [ABSTRACT FROM AUTHOR]

The paper analyzes the technical state of the hydrogen sulfide absorber of the catalytic reforming unit and hydraulic cleaning containing hydrogen and hydrogen sulfide with its operation time of 168,200 h (21 yr). 17G1S manganese-silicon steel is used in the absorber structure. In operation, in the vessel shell, a cone-shaped region of subsurface metal lamination is developed across the entire periphery. The region is under constant observation using the methods of nondestructive testing. In case the region of the damaged metal intersects the longitudinal welded joint, the vessel shell is being repaired. A low-temperature (to the boiling point) hydrogen-related fracture of metal in the petroleum refining due to hydrogen saturation and its accompanying cracking are considered to be the most critical types of corrosion of oilfield equipment. In view of this, a set of laboratory tests using specimens of metal templates cut out of the damaged shell region has been performed to evaluate the serviceability of the absorber, as well as to determine the effect of hydrogen sulfide on the structure and mechanical characteristics of the metal. It is found that the process of lamination is detected inside the metal intersection and is caused by the macroinhomogeneity of rolled metal, i.e., the axial segregation zone, which is the most critical region of the deformed metal. X-ray phase analysis lends credence to the metallurgical nature of lamination of the shell plate. The results of metallographic examination imply that the subsurface hydrogen-induced cracking is caused by aggregation of brittle refined nonmetallic inclusions, mainly of MnS, and it propagates chiefly over sulfide films along the rolled metal direction. The results of experimental investigations on the specimens are provided. From the fractographic investigations on the fractured surface of specimens after mechanical testing it is established that the process of fracture is ductile occurring via microvoids coalescence in the fracture of bridges between them. The key mechanism of microvoids formation is the inhomogeneity of the plastic strain in the micro-volumes around the nonmetallic inclusions. [ABSTRACT FROM AUTHOR]

The paper describes an experimental setup for studying a contact interaction between fragments of real wheels and rails under conditions that correspond to the electric railroad operating conditions. [ABSTRACT FROM AUTHOR]

A version of the endochronic theory of plasticity is developed to describe the stress-strain state under stress-controlled, asymmetric biaxial non-proportional cyclic loading. In order to solve the obtained non-linear system of differential equations, the numerical procedure is proposed and the relevant computational program is developed. The model validity is verified by satisfactory agreement between the calculated and experimental data. [ABSTRACT FROM AUTHOR]

The paper addresses the mechanical behavior of carbon steel 20 in asymmetric loading under the conditions of plane stress state that occurs in a thin-walled specimen in tension-compression and alternating torsion. The asymmetric cyclic loading of specimens was carried out in a stress-controlled mode along three paths with a frequency of 0.1 Hz with a base up to 1200 cycles. Cyclic stress-strain diagrams have been constructed for the specimens under tension-compression, alternating torsion, and proportional loading. The curves of von Mises equivalent ratcheting strains have been plotted. The highest ratcheting rate is shown to take place in the tension-compression loading case. [ABSTRACT FROM AUTHOR]

For a series of steels and alloys, we have studied energy transformations and thermal effects arising in the course of low-temperature discontinuous yield using the results of tensile tests of specimens at T = 4.2 K. Our calculations, carried out in the adiabatic approximation, demonstrate that the transformation of the work of deformation into heat leads to a very significant heating of the yield zone, the upper bounds of which reach 70–190 K for various materials. We show that the coefficient of energy transformation grows in the course of deformation and is a function of strain, which is represented in analytical form. We have established that the degree of heating correlates with the ultimate strength of the material and have proposed the corresponding empirical relation. We have also evaluated the level of abrupt deformations and inertial effects. [ABSTRACT FROM AUTHOR]