Papers by Keyword: Plastic Deformation

Abstract: This work aims at investigating the stages and irregularity of plastic strain in austenitic stainless steel 12Kh18N9T within a temperature range of 143 < T < 420 K. The localized plastic strain fronts at different stages of strain hardening have been visualized and monitored via digital speckle photography (DSP). This method consists in the high-accuracy recording of the displacement field via tracking any material surface changes and the subsequent comparison of speckle images acquired under uniaxial tension. The stress-strain diagrams were found to strongly vary with a decrease in temperature due to strain-induced-phase transition. The analysis of localized strain distributions revealed the emergence of a mobile system of equidistant strain localization foci at the strain hardening stage. The temperature dependence of plastic strain localization parameters at the linear strain hardening stage was established as well.

Abstract: In this work, the features of plastic deformation of titanium and aluminum plates under high-speed impact conditions were studied. The structure and phase composition of the explosively welded bimetal were analyzed using both scanning and transmission electron microscopy. The deformation and heating of titanium and aluminum under high-velocity impact were simulated using the smoothed particle hydrodynamics method. The features of shockwave and deformation-thermal processes during the collision of plates were described. The phase composition of the weld and heat-affected zone have been studied. The contribution of the welded plates to the jet formation is estimated.

Abstract: Model research tests of plastic deformation, fragmentation and flow of aluminum alloy material of Al-Mg-Sc-Zr system under high loaded friction in pair with a steel counterbody of a complex shape and comparison of the obtained result with the structure formed by friction stir welding have been carried out. The conducted studies show that the structure formed by extrusion of the material from the friction zone and its compaction in the channel of the counterbody is, in general, close in structure to the structure formed by friction stir welding of similar material. The distinguishing features of the structure formed in the model experiments on friction include the introduction into the stirring zone of material with deformed large-crystal structure, increased grain size of the stirring zone, the presence of defects and differences in the geometry of the stirring zone.

Abstract: Surface mechanical attrition treatment enhances the mechanical properties of metallic materials by inducing high strength layer on the top surface. In this study, multiple-shot impact behavior was modeled for the 7075-T6 aluminum alloy to achieve maximum magnitudes of equivalent stress, plastic strain, residual stress depth, and residual stress. Finite element simulations have been carried out to investigate the effect of selected framework on stress and strains in constituent. The plastic deformation process during SMAT was analyzed using ANSYS/AUTODYN explicit dynamic solver according to shot velocity and diameter with a dynamic explicit finite element method (FEM). Deformation behavior was evaluated after multiple-shot impact.

Abstract: The paper reviews and develops the mathematical model of plastic flow during the hot-forming processes. A flat non-stationary temperature problem for a cross-section of a long solid (rolled product) of arbitrary shape with different heat transfer conditions along the perimeter of the cross-section was considered. Equations for calculation of the thermal conductivity coefficient and heat capacity of tungsten billets were obtained in the temperature range of 700 - 1500°C, based on the literature data. Analytical dependences in form of regression equations were obtained, allowing for computer calculations of physical specifications of 11x11 mm VA grade tungsten billets in form of temperature functions with accuracy sufficient for practical calculations.

Abstract: There are results of studying the parameters of the indenter contact interaction with the surface when processing cylindrical parts made of 45 steel of different hardness by surface plastic deformation (SPD) methods with single-indenter elastic tools (diamond burnishing, ball burnishing). There were considered such characteristics as the resistance force when the indenter starts and in the steady state of SDP, the range of force fluctuations during processing, friction factor when the indenter starts and in the steady state, as well as some derivative coefficients. Adequate physical-statistical models for the quantitative estimation of the contact interaction parameters from SPD processing factors are obtained.

Abstract: The burst failure of a high frequency welded (HFW) pipe used for nature gas pipeline in an oilfield was analyzed systematically by macro analysis, physical and chemical property test, scanning electron microscope (SEM), etc., and the limit internal pressure of the pipeline under operation condition was predicted based on finite element method (FEM). The results showed that the chemical composition and mechanical properties of the pipe meet the requirements of relevant standards. The failure results showed that the dent damage of the straight pipe section was at 12 o'clock. In the service of the pipeline, the stress in the dent area exceeds the yield strength, which leads to the plastic deformation of the pipeline, resulting in necking and thinning, and the reduction of wall thickness further leads to the decrease of ultimate internal pressure, until the ultimate bearing capacity of the dent area is less than the internal pressure of pipeline operation, resulting in burst. It is suggested to strengthen the supervision of pipeline construction to avoid the pipeline dent damage. Meanwhile, the operation monitoring of the pipeline with dent damage should be strengthened, and timely repair or depressurization operation should be carried out if necessary.

Abstract: The threshold of optical breakdown of the nickel alloy ChS57 (Inconel) was measured at a wavelength of 0.355 μm with a laser pulse duration of 10 ns. Heat treatment of ChS57 above pulse energy density threshold (1 - 2.5 J/cm²) occurred mainly in the ablative mode with almost no melting. The elemental composition of the surface layer did not change at an irradiation in a fixed spot. When a laser beam moves along the surface of the sample at a speed of 1 mm / s and at pulse energy density of about 0.02 J/cm², oxygen was detected in the elemental composition (3 – 4 wt. %). However, the proportions of the elemental composition of the alloy remained virtually unchanged. Heat treatment under threshold at pulse energy density ≥ 0.25 J/cm² revealed a rise of the surface layer with traces of high-temperature plastic deformation in the form of slippage on grain boundaries and crystallographic slip.

Abstract: Surface mechanical attrition treatment is a pre-stressing process that enhances the lifespan of mechanical parts. The experimental evaluation of SMAT parameters is not only very complex but also costly. In this study, the single impact behavior of commercially pure titanium and Ti6Al4V alloys is analyzed using the finite element method. For simulating the single-shot impact process, a rigid sphere on a rectangular component is modeled using ANSYS/AUTODYN explicit dynamic solver. The effects of single-shot impact on the induced compressive residual stress and plastic deformation were investigated. Besides, the change in shot velocity after a single shot was revealed by calculating the restitution coefficient, and its relation to plastic deformation was investigated.

Abstract: The paper deals with the problems and prospects of forming thin-sheet blanks, using ABS plastic dies, made by 3D printing. This technology combines the positive properties of plastic material and 3D-printing. The mechanical characteristics of the plastic were determined experimentally. On the basis of computer modeling, the dependence between the angle of bending the blank and the stresses arising in the dies is established. As a result of computer simulation and physical experiment, the value of the maximum thickness 0.5 mm for the aluminum 3003 blank is obtained. In this case, there is no plastic deformation of the plastic tool. The use of plastic dies does not require lubrication. The technology of sheet bending, using a plastic tool, can be implemented with the greatest efficiency in single and small-scale production.