On the use of the criterion of maximum reduced stresses in temperature problems of plane deformation

Работа посвящена решению задачи температурного деформирования тонкой пластины конечной ширины, выполненной из упруго-пластичного материала. В качестве условий наступления пластического течения используется условие максимальных приведенных напряжений, с зависимостью предела текучести от температуры. Именно использование зависимости предела текучести от температуры делает невозможным получение решения с условием пластического течения Треска - Сен-Венана. Показывается, что в зависимости от скорости нагрева распределение остаточных напряжений может быть разным. Rabat is devoted to solving the problem of temperature deformation of a thin plate of finite width made of an elastic plastic material. As conditions for the onset of plastic flow, the condition of maximum reduced stresses is used, with the dependence of the yield strength on temperature. It is the use of the dependence of the yield strength on temperature that makes it impossible to obtain a solution with the condition of the plastic flow of Treska - Saint-Venant. It is shown that, depending on the heating rate, the distribution of residual stresses can be different.

Design Synthesis through a Markov Decision Process and Reinforcement Learning Framework

This paper presents a framework that mathematically models optimal design synthesis as a Markov Decision Process that is solved with reinforcement learning. In this context, the states correspond to specific design configurations, the actions correspond to the available alterations modeled after generative design grammars, and the immediate rewards are constructed to be related to the improvement in the altered configuration's performance with respect to the design objective. Since in the context of optimal design synthesis the immediate rewards are in general not known at the onset of the process, reinforcement learning is employed to efficiently solve the MDP. The goal of the reinforcement learning agent is to maximize the cumulative rewards and hence synthesize the best performing or optimal design. The framework is demonstrated for the optimization of planar trusses with binary cross-sectional areas, and its utility is investigated with four numerical examples, each with a unique combination of domain, constraint, and external force(s) considering both linear-elastic and elastic-plastic material behaviors. The design solutions obtained with the framework are also compared with other methods in order to demonstrate its efficiency and accuracy.

THE INVESTIGATION OF STIFFNESS OF HYBRID BISTEEL I-SECTION BEAMS

The stiffness analysis of the simple supported hybrid bisteel I-section beam subjected by uniformly distributed load is considered in this paper. The hybrid bisteel I-section beam presents a composition of high-strength steel inclusions for the flanges in the region of maximum stresses and of low-strength steel for remaining volume of the beam. The explicit analytical model for evaluation of stiffness of the beams mentioned is presented. The geometrical linear approach and elastic plastic material model have been assumed. The application of high-strength steel inclusion in case perfectly elastic state of the hybrid bisteel I-section beam, increase the deflection insignificantly (up to 10%). While strain hardening effect reduces the deflection by about 4 times compared to the perfect plasticity. The verification of the theoretical analysis has been performed by the FEM. After simple transformations, the proposed model can be easily applied to the evaluation of stiffness of otherwise loaded and supported hybrid bisteel I-section beams.

Influence of the elastic and elastic-plastic material parameters on the mechanical properties of slewing bearings

Slewing bearings are critical components of rotating equipment. Large structure sizes and heavy working load conditions require an extremely high load-bearing capacity and reliability. Overall and local contact finite element models of slewing bearings are verified by the empirical formula and Hertz contact theory. Validated finite element models are used to analyse the influence of the elastic material (E 1) and elastoplastic material parameters (EP 1, EP 2 and EP 3) on the load carrying capacity. The following conclusions are obtained by comparing the maximum contact load, the contact stress, the load distribution and the full-circle deformation. The influence of the material parameters on the slewing bearing is investigated to improve the analysis accuracy of the carrying capacity of the slewing bearings.

Plane waves in anisotropic elastic–plastic material with voids

Dispersion equation is derived for the propagation of one-dimensional plane waves in a general linear anisotropic isothermal elastic–plastic material with voids. The plasticity of the considered material is defined through the dislocation of a single slip plane and direction. The derived dispersion equation is then reduced for the relevant wave propagation in particular media, namely, monoclinic, orthotropic, transversely isotropic, and isotropic elastic–plastic material with voids. In general, it is found that there exist four basic waves traveling with distinct speeds in these specific anisotropic elastic–plastic materials with voids. A new wave is found to appear because of the presence of plasticity in the material. Out of the four basic waves traveling in an orthotropic/transversely isotropic material with voids, a wave travels independent of plasticity and void parameters, whereas the remaining three waves depend on plasticity as well as on the presence of voids. The one which is traveling independent of plasticity and voids is nondispersive and nonattenuating, whereas the other waves are dispersive in nature. The speeds of all the existing waves are computed numerically for a specific model, displayed graphically, and discussed.

CRACK PROPAGATION UNDER INITIAL MODE II CONDITIONS

Series of tests for compact tension shear specimens under mode II and following mixed mode was carried out. Compact tension shear specimens made of steels 34X and P2M, Ti-6Al-4V titanium and 7050 aluminum alloys. During experiments the behavior of the inclined crack angles, kinked crack angles and crack propagation angles, as a function of dimensionless crack length for the curvilinear paths was obtained. The influence of elastic-plastic material properties on the form the curvilinear crack path is established.

Numerical and Theoretical Analysis of the Inertia Effects and Interfacial Friction in SHPB Test Systems

The dynamic properties of materials should be analyzed for the material selection and safety design of robots used in the army and other protective structural applications. Split Hopkinson pressure bars (SHPB) is a widely used system for measuring the dynamic behavior of materials between 102 and 104 s−1 strain rates. In order to obtain accurate dynamic parameters of materials, the influences of friction and inertia should be considered in the SHPB tests. In this study, the effects of the friction conditions, specimen shape, and specimen configuration on the SHPB results are numerically investigated for rate-independent material, rate-dependent elastic-plastic material, and rate-dependent visco-elastic material. High-strength steel DP500 and polymethylmethacrylate are the representative materials for the latter two materials. The rate-independent material used the same elastic modulus and hardening modulus as the rate-dependent visco-elastic material but without strain rate effects for comparison. The impact velocities were 3 and 10 m/s. The results show that friction and inertia can produce a significant increase in the flow stress, and their effects are affected by impact velocities. Rate-dependent visco-elasticity material specimen is the most sensitive material to friction and inertia effects among these three materials (rate-independent material, rate-dependent elastic-plastic material, and rate-dependent visco-elastic material). A theoretical analysis based on the conservation of energy is conducted to quantitatively analyze the relationship between the stress measured in the specimen and friction as well as inertia effects. Furthermore, the methods to reduce the influence of friction and inertia effects on the experimental results are further analyzed.