Abstract: The paper reviews several theoretical and experimental methods for the assessment of ductile fracture criteria and for their application to the fracture prediction in metal forming processes. In particular, distinguished features of two widely used ductile fracture criteria are demonstrated in the case of free surface fracture. Conventional empirical ductile fracture criteria are not compatible with behaviour of plastic solutions in the vicinity of maximum friction surfaces. An approach to overcome this difficulty is discussed. Finally, a theoretical/experimental method to reveal a possible effect of geometric singularities on the applicability of ductile fracture criteria is reviewed.
Abstract: Propagation of elastic waves in heterogeneous linear 1-D media is considered. The scalar wave equation is transformed by the Liouville substitution and the Dyson integral equation is applied for a statistically homogeneous field of heterogeneities. The result is the mean wave field which is analysed in detail for the exponential correlation functions. The general case of the random elastic medium with an arbitrary heterogeneity of small scale is considered and simple closed form expressions for the mean field and attenuation are derived.
Abstract: This paper aims to manufacture aluminum alloy metals with gradient micro-structures using hot extrusion process. The extrusion die is designed to have a straight channel part combined with a conical part. Materials pushed through this specially-designed die generate a non-uniform velocity distribution at cross sections inside the die and result in different strain and strain rate distributions. Accordingly, a gradient microstructure product can be obtained. At first, temperature, effective strain, and effective strain rate distributions at the die exit are discussed for different inclination angles in the conical die using the finite element analysis. Then, hot extrusion experiments are conducted to obtain aluminum alloy products with gradient micro-structures. The effects of the inclination angle on the grain size distribution at cross sections of the products are also discussed.
Abstract: Chemical-mechanical polishing (CMP)-a perspective technology in fabrication of micro-and nanoelectronics elements, devices and systems. The development of models of CMP processes remains to be the actual problem. It is pointed out that known CMP models do not account for the features of chemical and mechanical mechanisms of interaction of active fluid and particles with a polished surface as well as an interaction of a viscoelastic pad with the surface. A description of the elementary acts of such interaction are absent in the available models. On the base of the analytical review of the current state of the theory and problems of (CMP) modeling some approaches were suggested to the problem accounting for the complex of the phenomena of different scales determining the polishing rate such as diffusion of slurry into the surface layer and restriction of time of chemical treatment of the surface by a rough pad being under the action of a mechanical load. A model of the CMP process was developed. Within the framework of this model a dependence of the polishing rate on the loading parameters was derived. The dependence generalizes the empirical Preston law.
Abstract: In the present paper, we propose new equations describing the fluid behavior in nanochannels with its molecular structure. We consider the Poiseuille flow and the flow throw the channel with vibrating walls. The obtained results show that it is possible to describe the structural transformations in thin layers by using the continuum mechanics methods. We introduce new degrees of freedom of the material by introducing the second continuum, which plays the role of the arising new phase of state. In the models considered here, the properties of the new phase are determined by the influence of rigid boundaries with a different structure.
Abstract: Buckling modes of a linearly elastic compressed medium are discussed. Stability of a plate lying on a soft elastic foundation is investigated. To the plate surface a membrane with initial stresses is attached. The stresses in the membrane simulate difference of equilibrium distances between atoms of crystal lattices of a surface layer (membrane) and of a plate. Also the influence of force and thermal stresses is studied. The chessboard-like stable buckling mode appears on the membrane surface at the stability loss. The ways of control of the wave length of buckling mode are discussed.
Abstract: Based on the analysis of experimental data on measuring metal density under plastic deformation, an adaptive model of damage accumulation, which takes into account the transient processes of damage variation with changes in loading conditions, has been formulated. The analysis of damage in the process of cold closed-die forging of a lid-type steel blank being taken as an example, the applicability of the model to the prediction of fracture in the optimization of industrial metal forming technologies has been demonstrated.
Abstract: The effect of plastic tensile deformation on changes in density and magnetic behaviour has been studied on low-carbon steel specimens under hydrostatic pressure of 0.1 to 500 MPa in a test chamber. It has been shown that the parameters of minor magnetic hysteresis loops can be used to estimate the amount of plastic strain and the strain-related structural damage of metal.
Abstract: Behavior of isotropic media with stress state dependent plastic properties is studied in this paper. One of the possible general approaches to the formulation of constitutive equations of these materials is demonstrated. The derived equations are applied to the problem of tension of a notched stripe under plane stress conditions. Some general equations of stress state dependence of plastic properties of materials that can be used with large variety of models are derived in the case of hyperbolic constitutive equations. Theoretical results are compared with FEM solution of this problem for the Drucker-Prager material model.