Papers by Keyword: Plasticity

Abstract: The need to develop new methods for predicting the properties of polymeric materials is also justified by the goal of designing new innovative materials with the required functional properties and increased competitiveness. The classical methods for predicting deformation processes of polymeric materials are based on the numerical solution of integral constitutive equations for polymer viscoelasticity of the Boltzmann-Volterra type, which do not consider corrections for the irreversibility of the plastic component of deformation and therefore can lead to significant prediction errors. To improve the accuracy of predicting the deformation processes of polymer materials it is proposed to introduce a physically justified correction with account for the irreversibility of the plastic component of deformation. The introduction of this correction significantly increases the reliability and accuracy of predicting the functional and operational properties of polymer materials. The article suggests demonstrating the methods for predicting deformation processes with the example of the polyester textile yarn made of polyester fibers. Unlike many other synthetic fibers, the polyester ones have such important properties as structural stability, softness along with high strength, elasticity, resilience, tensile strength, crease and pilling resistance, temperature regulation, shape retention, etc. The polyester fiber has a hollow structure and its single components have the form of spiral springs which give the effect of a springy base when intertwined.

Abstract: The work considers the approach determining suboptimal relation of strength and plasticity by the example of low-carbon constructional steel 3 (0.14...0.22 % С), which is widely used in metal structures. As parameters for the research, the elements of chemical composition and properties of ferrite-pearlite structure of steel were taken. For the reliability of the obtained results for the evaluation of structure, its quantitative analysis was carried out either by traditional methods or by fractal approach. Combining operating regions of the values of steel properties depending on the chemical composition and area and fractal dimension of pearlite, we got the diagram of the region of compromise for indices of strength limit σ_В, σ_0,2 and specific elongation δ. Areas with suboptimal relations σ_В/δ and σ_0.2/δ were defined in the region of compromise for quality criteria. The application of the given approach allows (while adhering to steel production process) to predict areas with stable suboptimal relations for strength and plasticity indices by selecting value range for the elements of chemical composition and analysis of structure.

Abstract: The article presents the results of numerical and experimental studies of stress-strain curves of 1D-reinforced polymer composite materials based on hollow porous fibers and epoxy matrix. The two-scale nature of the composite under research was taken into account. A surrogate easily parameterized model based on Bezier curves was developed and used to approximate the stress-strain curve of ductile material. The calculations were performed using reversible homogenization and finite element methods, which were implemented in computational subsystem of DCS GCD. Representative volume elements of the investigated materials were created using the geometry generating subsystem of DCS GCD. Test samples were made using three-axis milling machine and compression tests were carried out. Computational results of effective stress-strain curves determination were obtained and compared with experiments.

Abstract: Based on the results of the static crack resistance tests, the contribution of the strain-induced γ→α-transformation into the fructure toughness of steel N18K9M5T with two-phase (α+γ)-structure has been assessed.

Abstract: In the process of forming solid materials, the plastic instability phenomena often control the appearance and performance of the finished product. The study of these phenomena is therefore of great scientific and technological importance. Polymers materials, for example, polyvinyl chloride (PVC) are frequently used in the plastic pipes in pressure vessels and pipelines, which require details that are more serious, it is therefore essential to understand the mechanisms of plastic instability in polymers in order to know how to control them. In order to determine the plastic behaviour of PVC, the true stress-strain response under large plastic deformation was investigated in different stress triaxiality frameworks. A particular attention was given on the volumetric strain evolution and the damage. The effect of stress triaxiality on the fracture strain was also examined. In the second part of this paper, an elasto-viscoplastic behaviour model is presented, with non associated plasticity, damage and coalescence, which represents the observed behaviours of a PVC material under different triaxialities and for three initial void shapes

Abstract: The calculation procedure for determining the plasticity of pre-deformed metals during their processing by pressure has been developed. The calculation procedure is based on a fracture model, which in turn is based on the tensor description of damage accumulation. With known mechanical characteristics, as well as with known plasticity diagrams, the fracture model makes it possible to evaluate the plasticity of pre-deformed bend for any kind of stress state. When manufacturing steeply curved branches using the pipe extrusion method, the procedure was tested. Verification of the mathematical model has shown a high level of its adequacy, and it can be used in assessing the plasticity of pre-deformed billet.

Abstract: In this study, a through-the-thickness negative Poisson's ratio of an angle-ply carbon fiber-reinforced plastic (CFRP) laminate is experimentally investigated using a 3D digital scanning method. For this, an image-based measurement method using a 3D digital scanner is developed to obtain the thickness change of CFRP laminates. The thickness change is used to calculate the through-the-thickness Poisson's ratio of CFRP laminates. Then, a tensile test of a [±θ°] angle-ply CFRP laminate is performed, and the through-the-thickness Poisson's ratio is measured based on the developed method. The results obtained suggest that the through-the-thickness Poisson's ratio exhibits negative values which become increasingly negative as (visco)plastic deformation progresses in the laminate, as demonstrated in our previous analysis.

Abstract: This paper presents a novel direct method called the stress compensation method (SCM) for structural shakedown analysis. Being different from the popular direct method of mathematical programming, the SCM just carries out some iterative calculations. Making full use of static shakedown theorem, the residual stress field is constructed via solving the modified global equilibrium equations. An effective and robust iteration control technique is adopted to generate a sequence of decreasing load multipliers. The numerical procedure is incorporated into the ABAQUS platform via some user subroutines. The shakedown problems for a cantilever beam, a symmetric continuous beam and a practical shell with nozzles are effectively solved and analyzed. These results are compared to the analytical solutions and those found in literatures. Both the incremental collapse mechanism and the alternating plasticity mechanism are revealed to determine the shakedown boundaries. Numerical examples show that the SCM is of numerical stability, good accuracy, high computational efficiency, and can effectively perform shakedown analysis of large-scale practical engineering structures.

Abstract: Along with design factors, reliability of the work-pieces for machines and mechanisms is a function of the structure and the properties of the implied materials; these properties depend significantly on the kind and the mode of the process treatment. Taking into account hardwares production, along with the increased structural integrity and service reliability, a reduction of costs starts from the rolled metal production to manufacturing of the finished parts of required quality. This is particularly relevant under the conditions of mass-production. The article presents a resource saving process flow for a 40X rolled steel, developed as a result of studying the influence of thermal and plastic treatment modes on its structural and mechanical properties. The purpose of the new process flow is the production of hardened bolts, involving drawing and isothermal treatment, but excluding the volume quenching and tempering. Spheroidizing annealing is substituted with an isothermal operation, patenting, which allows to reduce energy costs and to increase environmental compatibility of production and service reliability of bolted items. This makes it possible to shorten the process chain and to reduce the cost of long-length bolts production. The method prevents any potential quench cracking, eliminates the necessity for work-pieces' straightening, decreases the risk of thread defects.

Abstract: Mechanical, damping and specific properties of new structural high-damping steel have been studied in the present research. Studied high-damping steel was specially produced by the JSC Severstal in order to obtain metallic material with specified level of damping and mechanical properties. Experiments show that the damping properties of industrial high-damping steel are comparable with damping properties of high-purity damping alloys, produced using laboratory equipment. Mechanical properties of the industrial high-damping steel were found to be comparable with the level of properties of well-known structural steels, widely used in the modern industry. Analysis of the combination of mechanical and specific properties of the new steel indicates that this material can be used for the construction of rigid structures requiring high damping. Specific features of practical application of high-damping steels are also discussed.