Study of crack resistance of plastically anisotropic metal materials

A version of the Hahn and Rosenfield model is used to develop a structural approach to crack-resistance anisotropy evaluation of dispersion-hardening alloys of semi-finished products with initial strength and plastic anisotropy formed by high-temperature deformation and age-hardening processes. Correlations are obtained which describe crack-resistance anisotropy exponents as functions of the deformation and yield point for uniaxial extension of crack-free specimens in the longitudinal, transverse, and vertical directions. The proposed approach is experimentally substantiated for a number of plastically anisotropic aluminum alloys. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 35, No. 4, pp. 87–94, April, 1999.     

Stability of compressed continuously inhomogeneous plate

The action of an external reactive medium on the components of operational structures often changes the physicomechanical properties of the material, which markedly affects its carrying capacity. This means that the real properties of the material, including the formation of such inhomogeneities, must be taken more thoroughly into account. In the present work, the stability of an isotropic plate whose elastic characteristics are continuous functions of the Cartesian coordinate is investigated.L'vov University, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 30, No. 2, pp. 84–89, February, 1994.     

A new reverse analysis to determine the constitutive response of plastically graded case hardened bearing steels

A new reverse analysis is presented that determines the plastic response of both nongraded and plastically graded materials (PGMs) without the need for traditional tension or compression tests. The method utilizes the concepts of expanding cavity model for strain hardening materials, Tabor’s rule of converting Vickers hardness to flow stress, representative plastic strain induced by indentation, and finite element modeling of the macro indentation process. A unique flow curve is determined when the experimentally measured increase in micro Vickers hardness matches that predicted by the proposed method within the plastic zone of a macro Vickers indent. The method is validated for a nongraded stainless steel first and then extended to determine the gradient in flow curves of plastically graded, case-hardened M50 NiL material, a widely used bearing steel. Such knowledge of the plastic response of the case hardened region will help optimize the design of case hardened bearings with longer rolling contact fatigue life and higher thrust load capabilities.     

Buckling modes of a compressed plate on an elastic substrate

The buckling modes of a homogeneously compressed elastic plate on a soft elastic substrate are studied. The critical compression is uniquely determined by the bifurcation equation, but this compression is associated with a wide set of buckling modes. It was proved that any solution of the Helmholtz equation satisfies the bifurcation equation. At the same time, in microelectronics, it is required to know which buckling mode is realized. Experimental and theoretical investigations show that the chessboard-like buckling mode should be expected. In what follows, this problem is discussed theoretically. The expected buckling mode can be found by analyzing the energy of the initial postcritical deformation, and the desired mode is determined from the condition of its minimum. The analytic expression of this energy is obtained. Its minimization results in the chessboard-like buckling mode.     

Indentation of plastically graded substrates by sharp indentors

The present paper investigates the indentation of plastically graded substrates by sharp indentors. Contact analysis of plastically graded surfaces can be particularly useful in the design of load-bearing devices such as gears, rollers and electric contacts found in many macro- and micro-electro-mechanical systems. Substrates made of plastically graded materials are often encountered in nature or are artificially produced as a result of chemical and/or physical surface treatments. The variation of the plastic properties depends on micro-structural or compositional changes of the material with depth. The analysis of indentation of plastically graded substrates by sharp indentors provide the load-penetration response, as well as the strains and stresses inside the substrate, at maximum loading and at complete unloading. The parametric analysis of the solutions enables the direct correlation of the plastic properties and the load-penetration curves obtained from instrumented indentation tests. The variation of the plastic properties can subsequently be related to important micro-structural parameters such as particle composition, dislocation density and grain size. The results of this work show how surface modifications can induce plastic graded properties that strengthen substrates against contact-induced damage.     

Oblique impact by a spherical solid on a metal plate

The results of experimental studies of oblique impact by a spherical solid on a plane metal plate are presented. Plates made of AMTsM (plastic) and D16AT (rigid) alloys were used to determine the influence of the material characteristics on the impact aftereffects. The dependence of the ballistic limit on the angle of the impact velocity vector inclination to the plate plane was determined. The relationship between the ballistic limits of the oblique and normal impacts on the plate is established. The dependence of the ball motion trajectory refraction angles after collision with the plate on the ratio of the initial velocity to the ballistic impact is determined.     

Elastic instability of a uniformly compressed annular plate with axisymmetric initial deflection

This paper presents a theoretical study of the elastic instability of a uniformly compressed, thin, circular annular plate with axisymmetric initial deflection. The dynamic version of the nonlinear Marguerre plate theory is used, and the linear free vibration problems around the axisymmetric finite deformation of the plate are solved by a finite difference method. By examining the frequency spectrum with various asymmetric modes, the critical compressive load under which the axisymmetric additional deformation of the plate becomes unstable due to the bifurcation buckling is determined, which is found to depend severely on the magnitude of the axisymmetric initial deflection.     

Influence of a longitudinally compressed elastic plate on the nonstationary wave motion of a homogeneous liquid

In a linear formulation, a study is made of the influence of a longitudinally compressed elastic isotropic plate on the nonstationary wave motion of a stream of homogeneous liquid of finite depth on which the plate floats. The waves are generated by periodic (in time) normal stresses applied to a restricted region of the plate surface and beginning at a certain initial time.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 68–75, September–October, 1980.     

Stability of a strip compressed by slabs

Dnepropetrovsk Metallurgical Institute, Translated from Prikladnaya Mekhanika, Vol. 30, No. 6, pp. 88–94, June, 1994.     

Modelling and simulation of rigid bodies transportation by means of rotating flexible rollers

The paper deals with a modelling and simulation approach intended to the solution of a problem of rigid bodies transportation using rotating rollers. It is motivated by problematic phenomenon of ceramic tiles transportation inside long kilns during firing. The row of tiles, which is initially straight at the kiln beginning, is coming out curved at the kiln end or after the passage through a certain part of the kiln. The main aim of the work is the development of the modelling and simulation method for the verification of the problems arising from the tile movement through very long kilns and for the understanding of the problem causation. The multibody dynamics approach is chosen for the development of a comprehensive methodology for the numerical simulation of the tiles and rollers movement. Two approaches to the modelling of the system of tiles and rollers using the SIMPACK simulation tool are shown in the paper. The more suitable one is based on the Polygonal Contact Model developed for the fast and efficient contact analysis between complexly shaped rigid bodies. It can be concluded that the problems of the curved row of tiles are influenced by the flexibility of bent rollers and also occur for ideally cylindrical rollers. The presented simulation methodology can be generally used for the investigation of similar transportation systems.     

Numerical study on flanging and spring-back of stamped thick metal plate

A quasi-three-dimensional shell element model, which can be effectively used to simulate the flanging and spring-back deformation, is introduced into the independently developed CAE software, KMAS. In this model, a double surface contact algorithm, which allows the gap between punch and die to change, and a spring-back treatment scheme based on finite element meshing are described. And then the flanging and spring-back deformations of the retractor's kickstand of a railcar made of stamped thick metal plate are numerically simulated. The simulation results of flanging deformation are compared with those of international commercial software, PAM-STAMP, and experimental ones. Finally, a predicting scheme of spring-back quantily for this problem is given. Project supported by the National Natural Science Foundation of China (No. 19832020) and the Ministry of Education of China.     

Stress state in tempered glass plate and determination of heat-transfer rate

Thermal tempering is widely used to manufacture safety glass for economic as well as for certain safety measures. Laboratory investigations of the tempering process and the resultant strengthening effect are generally limited to rectangular specimens. Results are, therefore, appropriate for this particular geometry. This paper describes a simple stress-state model of a tempered flat glass specimen. the model, developed using photoelastic equations to determine the three-dimensional stress components, was used to predict the transient birefringence in a rectangular glass specimen subjected to uniform and symmetrical heat-transfer conditions, at a temperature where glass behaves as a perfect elastic material with no stress relaxation within the experimental time. A method of determining the coefficient of heat-transfer rate was then developed based on the analysis of the transient birefringence. This technique uses the glass specimen as an optical transducer, and does not affect, in any way, the natural flow of heat by forced convection or contact cooling.     

Destabilisation of a compressed vortex by a round jet

This paper presents data and analysis related to the compression and the breakdown of a tumbling motion after radial disruption in a simple geometry of the compression chamber of a model engine with large optical access. The disruption is a round jet injection perpendicular to the vorticity tube. Two configurations of injection are selected. They correspond respectively to a straight jet that competes with the tumble and an inclined jet that adds angular momentum to the large-scale rotating motion. The ratio between the angular momentum brought by the spray and the initial angular momentum of the tumble is of the order of 30% and is representative of the direct-injection engine situation at moderate rotation rate. The injection is performed at bottom dead centre (BDC) in a well-defined and well-known tumbling motion. The data are obtained in the symmetry plane of a square chamber by using particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF). A calibration is made in order to take account of acetone fluorescence yield during compression. The analysis of the injection phase at BDC shows that the mean topology of the flow after both injections differs significantly and that the vorticity tube is significantly distorted only in the vicinity of the injection plane. Strong transverse mean flows are detected by analysing the divergence of the mean velocity field. Although a mean rotation is still observed after injection during the compression phase, the authors show that no strong vortex core is evident. An important consequence of this finding, confirmed by the evolution of the global in-plane mean and fluctuating kinetic energy in the symmetry plane is that no vortex breakdown occurs during the compression after the injection event. Therefore, the global fluctuating kinetic energy at the end of the compression is much lower after an injection. During the first half of the compression, an inhomogeneous distribution of the jet fluid in the chamber is detected by the PLIF measurements. The transport of the jet fluid clearly results from both in-plane and out-of-plane motions triggered by the injection jet. This spatial repartition depends strongly on the injection strategy and can be very difficult to control accurately from cycle to cycle. The mixture is more homogeneous at top dead centre (TDC) with a low value of the spatial variance of the mean concentration field.