Effect of the static strength of a metal on long-rod penetration at low velocities

The effect of the static strength (yield stress) of a material on major penetration parameters (specific work of cavity formation and pressure at the contact surface) was examined. The analytical equations and the quantitative evaluation of the specific work spent for the formation of a spherical or cylindrical cavity and of the pressure at the surface of such cavities upon their static expansion were obtained for rigid-plastic and elastoplastic materials. The evaluation of the specific work of deformation upon the formation of the spherical cavity in the plate and the cylindrical one upon the penetration of a rigid rod are shown to be adequate. The influence of strain hardening on maximum radial stresses on the cavity surface was evaluated. The resistance to penetration and the expansion of a cavity are shown to be influenced by the elastic compressibility of a material in the inelastic region. The kinetics of the stress-strain state of the material upon the formation of the cavity was analyzed for the case of considerable deformation of a rod at penetration. Institute of Problems of Strength, National Academy of Sciences of Ukraine, Kiev Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 93–110, January–February, 2000.     

Influence of the dynamic behavior of materials on the penetration of long rods at elevated velocities. Discussion

We present a brief survey of the influence of the dynamic behavior of materials on the stationary penetration of long rods into thick plates at elevated velocities. Our attention is mainly focused on the analysis of the influence of the resistance of the material to plastic flow, strain rate, temperature effects, compressibility, and the boundaries of interacting bodies on the process of penetration. We also formulate basic directions of subsequent investigations. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 39–51, July–August, 1998.     

Analysis of the stress-strain state of a rectangular orthotropic plate under the action of biaxial tension and shear

We propose a method for the analysis of the stress-strain state of rectangular orthotropic plates under the conditions of biaxial tension and shear. According to this method, we specify a field of displacements in the plate in the form of the product of a matrix of differential operators by an unknown vector function or a column of three scalar functions, each of which admits a representation in the form of the sum of the products of an unknown function of one variable by a trigonometric function of the other variable. The number of independent coefficients of each function is determined from the boundary conditions by the method of Fourier series. We also performed calculations of the stressed state in the plate depending on the ratio of its sides and the type of loading. ^aKarpenko Physicomechanical Institute, National Academy of Sciences of Ukraine, Lviv.^bInstitute for Applied Problems in Mathematics and Mechanics, National Academy of Sciences of Ukraine, Lviv.^cLutsk Industrial Institute, Lutsk, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 47 – 55, January – February, 1998.     

Efficiency of the method of spectral vibrodiagnostics for fatigue damage of structural elements. Part 2. Bending vibrations, analytical solution

We discuss the possibility of efficient application of the harmonic analysis of strain cycles formed in an elastic rod in the process of natural or resonance vibrations to the evaluation of the degree of fatigue damage. Fatigue damage is simulated by discontinuities of the material resulting in different values of the modulus of elasticity in the processes of tension and compression. In determining the potential strain energy of a rod in the presence of a crack on the basis of linear fracture mechanics, this model enables us to deduce expressions for relative changes in the stiffness of the rod in the presence of edge and surface cracks. By using the asymptotic method of nonlinear mechanics, we find the second approximation to the solution of the differential equation of vibrations of the rod whose nonlinearity is explained by the effect of “breathing” of the discontinuity formed in the material. It is shown that the discontinuity of the material caused by fatigue damage is responsible both for changes in the natural frequency of vibrations of the rod and for significant contributions of the constant component and even harmonics to the spectrum of strain cycles in the rod. The values of the constant component and the amplitudes of even harmonics (mainly of the second one) may serve as an efficient parameter for the detection of fatigue damage to materials. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 6, pp. 9–22, November–December, 1998.     

Deformation of a rectangular plate under impulsive loading

We report the results of the experimental investigation of the behavior of a rectangular plate in the processes of cutting by linear shaped charges according to the axisymmetric and asymmetric modes of unilateral loading and fracture caused by the explosion of a linear charge. It is shown that the transverse velocities and displacements of the same points of the plate subjected to unilateral explosive cutting by shaped charges are much higher (almost by an order of magnitude) than the corresponding parameters for the other modes of fracture. We also observed that the values of longitudinal mass velocities and displacements in the case of bilateral cutting by shaped charges are 1.5–7.0 times higher than the same parameters for unilateral cutting and explosive fracture without using shaped charges. It is also shown that the longitudinal accelerations attain their maximum values in the case where the shaped charge is placed at a focal distance from the plate. Subbotin Institute for Geophysics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 6, pp. 85–90, November–December, 1998.     

Correlation of a plastic zone length near the tip of a mode I crack in an orthotropic material with anisotropy parameters

We derived equations that relate the length of a plastic zone near a mode I crack tip in a plate made of an orthotropic material with yield strength levels in the direction of the anisotropy axes. The case of crack orientation along one of the anisotropy axes is examined, with the latter being determined by the strain hardening of a material at the stage preceding the crack nucleation. The growth of yield strength along the axes lying in the plane of the plate is shown to result in smaller sizes of the plastic zone. An increase in yield strength in the direction of the normal to the above plane leads to an increase in its length. Ukrainian Regional Research and Design Institute of Civil Engineering, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 32–37, July–August, 1999.     

Conjucate heat transfer and thermostressed state of a plate with radiation and conduction heating

The problem of combined analysis of the parameters of conjugate heat transfer and thermostressed state of a plate with its radiation and conduction heating in an absorbing-medium layer is considered. The effect of the optical characteristics of the medium on the parameters of conjugate heat transfer and the distribution of thermal stresses in a plate is studied. Dnepropetrovsk State University, Dnepropetrovsk, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 1, pp. 79–84, January–February, 1996.     

Comparative estimation of mechanical properties of cemented carbides by the kinetics of penetration of a rigid punch under contact cyclic loading

We suggest a method of contact fatigue testing of cemented carbides. It involves cyclic loading of a specimen (half-space) with a flat circular punch by a pulsating compressive stress. Both the loading punch and the test specimens are made of cemented carbides. It is found that the parameters of contact fatigue of a cemented carbide include the depth of the punch penetration into the specimen, σ, after a given number of cycles, the form of the dependence of the penetration depth on the number of cycles, the number of loading cycles between abrupt changes in the growth of the σ values, and the number of these changes. With these parameters determined by laboratory tests on small specimens, we can predict the durability of large carbide components subjected in operation to contact cyclic loads. V. N. Bakul Institute for Superhard Materials, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 28–37, May–June, 1998.     

A version of the endochronic theory of plasticity to describe the asymmetrical cyclic loading of materials

A version of the endochronic theory of plasticity to predict the asymmetrical alternating cyclic loading of materials is considered. Basic experiments are determined and a calculation and experimental procedure for specifying the proposed functional of plasticity is described. The advantages of this approach are shown in solving certain specific problems. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 21–27, January–February, 1999.     

Bilateral bending of a plate with nonsymmetric through-thickness arc crack with allowance for the contact of its edges

The problem of bending of plates with nonsymmetric through-thickness arc crack with distributed moments at infinity with allowance for the contact of the crack edges has been examined on the basis of the classical theory of plate bending. The conditions for the existence of the solution of the problem in this formulation have been established. A numerical analysis of intensity factors of forces and moments, contact force between the crack edges has been performed, the results of which have been graphically illustrated. __________ Translated from Problemy Prochnosti, No. 5, pp. 135–141, September–October, 2006. Report on International Conference “Dynamics, Strength, and Life of Machines and Structures” (1–4 November 2006, Kiev, Ukraine).     

Elastic characteristics of iron-glass materials at low temperatures

We present the results of an investigation of the influence of low temperatures on the elastic characteristics of iron-glass materials with 3, 5, 12, or 20 wt.% of glass at 77–300 K and show that Young’s modulus exponentially decreases as the glass content of the material increases. We suggest a relation for the evaluation of the Young’s modulus of a composite at various temperatures according to its value at room temperature. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 42 – 46, January – February, 1998.     

Forced stationary vibrations of flexible plates induced by random narrow-band excitations

We consider some problems related to the analysis of the modes of forced vibrations of elastic plates induced by random narrow-band excitations. The investigation of nonlinear vibrations of a plate is performed within the framework of a reduced discrete model constructed by using the Hamilton variational principle, finite-element methods, and generalized coordinates. To study the dynamical state of the analyzed structure, we perform numerical simulation of the vibrations induced by a particular realization of narrow-band excitations. Each realization of random narrow-band excitations is obtained with the help of a shaping filter of the second order and describes harmonic oscillations with slowly varying amplitude and phase. We also consider the scenarios of transitions between different modes of vibrations of the plate and estimate the time of its residence in different dynamical states. Kiev National University of Civil Building and Architecture, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 2, pp. 105–117, March–April, 2000.     

On the procedure of evaluating the damping ability of the materials of specimens subjected to torsional and bending vibrations

We describe a method for the design and numerical analysis of compact mechanical vibrating systems with generators of vibrations on their inertial weights and establish the conditions of damping of unwanted vibrations in these systems aimed at guaranteeing the absence of favorable conditions for the introduction of systematic errors to experimental results. The designed and manufactured vibrating systems are dynamically balanced, and predicted values of the frequencies of their natural vibrations satisfactorily agree with the experimental data. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 145–152, July–August, 1997.     

Influence of the modes of thermomechanical preloading on the resistance of heat-resistant steels to brittle fracture

We describe the methods and results of the experimental investigation of the influence of various modes of thermomechanical preloading on the resistance of nuclear pressure-vessel steels to brittle fracture. We studied specimens of different thickness (25–150 mm) made of the base and weld metals of the vessels of water-moderated, water-cooled nuclear power reactors. The materials under consideration belong to different strength classes. It is shown that the positive effect of thermomechanical preloading is preserved or even strengthened after the subcritical ductile growth of a crack in the process of preloading. We compare the available experimental data with the results of numerical calculations performed by using the Chell model. It is shown that the Chell model fails to explain some experimental data. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 2, pp. 126–138, March–April, 1999.     

Shear effects of the stressed state in transversely isotropic plates. Part 2. Potential effect

We investigate the potential effect of the stressed state in transversely isotropic plates on the basis of an improved theory of the second approximation. The equations of this theory are deduced on the basis of the solution of the variational problem of finding the conditional extremum of the functional of total energy of the plate by the method of undetermined Lagrangian multipliers. The terms responsible for the vortex effect are excluded from these equations. We present the numerical results obtained for one-layer and three-layer hinged plates and show that the contribution of the potential effect to the stressed state is substantial and the results obtained by taking this effect into account are closer to the exact solution. For a plate rigidly fixed at the edges and subjected to cylindrical bending, the potential effect turns into an edge effect and this significantly increases the level of stresses in the restraint. Ukrainian Transport University, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 63 – 71, January – February, 1998.     

Determination of the characteristics of distribution of the fatigue limits of materials on the basis of the energy approach

We propose a method for the determination of the mean value of the fatigue limit of a material and its mean-square deviation according to the results of standard fatigue tests. The interpretation of these results from the viewpoint of energy enables us to establish the relationship between the individual durability of specimens and their potential ability to withstand fatigue fracture in the form of individual fatigue limits. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 28–33, July–August, 1998.     

A new approach to the evaluation of danger of short fatigue cracks

We demonstrate the possibility of using new physically substantiated characteristics of toughness of metals and the embrittling action of stress concentrators proposed by the authors somewhat earlier in the analysis of brittle fracture initiated by short cracks. We describe a procedure for the experimental determination of a parameter characterizing the embrittling action of these defects and obtain an approximate expression for its evaluation in the presence of a short crack. For typical structural steels, we establish the dependence of the toughness margin of steel with a short crack on the level of strength of this material. We also formulate the requirements on the level of toughness of steels guaranteeing that defects of this type are not dangerous. Institute of Physics of Metals, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 106–114, May–June, 2000.     

Thermophysical models for evaluation of the activity of the functioning kidney by means of infrared thermography

Methods of biothermal modeling and analysis are used to determine the possibility of evaluation of the thermophysical parameters of the functioning kidney using infrared thermography. It is shown that the induced local heating from the outside enlarges the information content of medical thermography. It is shown that the man, factor that determines thermographic visualization diagnostics is connected with the bloodflow. An analysis makes it possible to interpret thermographic situations for the kidney in the normal state and in the case of its particular pathology. Institute of Experimental Pathology, Oncology, and Radiation Biology, National Academy of Sciences of Ukraine, Kiev, Ukraine; National Technical University, Kiev, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 4, pp. 633–640, July–August, 1996.     

Endochronic theory of plasticity: Prediction of nonproportional cyclic deformation of materials

The possibilities of the endochronic theory of plasticity to describe the nonproportional cyclic deformation of materials are evaluated. Certain considerations are stated as to the refinement of its equations of state. Institute for Problems of strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 38–45, May–June, 1998.     

Shear effects of the stressed state in transversely isotropic plates. Part 1. Vortex effect

We present the results of an investigation of the Reissner vortex edge effect in transversely isotropic plates on the basis of an improved theory of the second approximation according to which transverse shears obey the fourth-order parabolic law, unlike the first approximation described by ordinary parabolas. We compared the degrees of decay of the edge effect in the first and second approximations and establish the ranges of parameters of the plate characterized by “strong” and “weak” edge effects in the second approximation. It is shown under what conditions one can neglect the vortex effect in the second approximation. Ukrainian Transport University, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 56 – 62, January – February, 1998.