Spectroscopic method of measuring the stresses at stress raisers in polymers

A method of measuring the mechanical stresses near stress raisers from the frequency shift of the IR absorption bands is proposed. The stresses at the edge of an ellipse as determined by IR spectroscopy, from the birefringence, and by theoretical calculation are compared. It is shown that the results coincide. The stress near the tip of a crack has been measured by the IR spectroscopy technique. It is shown that these stresses may be ten or more times greater than the external tensile stress.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 167–170, January–February, 1970.     

Effect of biaxial orientation on the fracture kinetics of polymethyl methacrylate

Biaxially oriented PMM is shown to have important advantages as a structural material over unoriented PMM owing to a difference in fracture kinetics. Under identical conditions primary cracks appear later in the oriented PMM, their growth is impeded, and the rate of crack propagation in the avalanche stage of failure is much lower. This accounts for the greater resistance of biaxially oriented PMM to stress raisers and its higher fracture energy under biaxial loading.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 274–281, March–April, 1969.     

Creep of polymer materials under periodically varying loads

A method is proposed for constructing the creep curves of a material whose nonlinear memory properties are described by Rozovskii's nonlinear integral equation [2] (with allowance for the stress dependence of the relaxation time) under given periodic loading from known creep curves recorded at constant stress. In deriving the theoretical relation certain simplifying assumptions are made (the creep strain accumulated in 1–2 cycles is small, no vibration [4–6]). An experimental check shows that the proposed method can be used to predict the behavior of a material under periodic loading with an accuracy sufficient for practical purposes.Mekhanika Polimerov, Vol. 2, No. 3, pp. 330–336, 1966     

Strength of glass laminates at low temperatures and high strain rates

The tensile strengths of glass laminates of various compositions under standard, high-speed and impact loading have been experimentally investigated in relation to the effect of low-temperature and stress raisers. As the loading rate increases (from 0.7 to 253 · 10³ kgf/cm². · sec) and the temperature falls to –196° C, the effective stress concentration coefficient decreases, which indicates that the glass laminates will perform adequately under these conditions.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 836–841, September–October, 1970.     

Creep of a multilayer cylinder under nonisothermal loading

A method is proposed for calculating the creep of a multilayer cylinder under nonisothermal loading with allowance for the temperature dependence of the physico-mechanical characteristics of the material. Numerical examples are considered. The states of stress and strain of the viscoelastic and elastic components of a two-layer cylinder are compared.Baranov Central Institute of Aviation Engine Construction, Moscow. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 321–327, March–April, 1969.     

State of stress of flexible plastic shells with an opening

The state of stress of flat flexible shells with an opening is investigated with allowance for the viscoelastic properties of the material. The equilibrium equations and boundary conditions are written in finite-difference form. A nonlinear system of algebraic equations is solved by successive approximations. A method of accelerating the convergence of slowly converging iteration processes is proposed. The effect of the viscoelastic properties of the shell material on its state of stress is investigated with reference to the example of a polymethyl methacrylate shell. The variations of the ring moment and ring forces at the free edge of the shell are plotted for various moments of time, load values, and flatness parameters. It is shown that as soon as the viscosity factor begins to take effect, the state of stress and strain of the shell changes sharply; the concentration of forces and moments increases in the flexible viscoelastic (as compared with the elastic) shell.Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 6, pp. 1071–1075, November–December, 1973.     

Cracks in fiber composites: Determination of the stress intensity factor by the polarization-optical method

Composite plates with cracks coinciding with one of the principal axes of anisotropy of the material were examined. The mechanical behavior of the composite is described by the model of a homogeneous orthotropic body. A method was proposed for determining the stress intensity factor K₁ with the known values of the fringe orders m in the vicinity of the tip of the crack. It was found that the value of K₁ is a function of the ratio of the length of the plates to their width d/b. The stress intensity factor K₁ increases with a decrease in ratio d/b. Tlie effect of the orthotropy of the material on the value of K₁ is also a function of the ratio of the length of the plate to its width d/b.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 6, pp. 769–775, November–December, 1996.     

Resistance of bony tissue to tensile fracture

The tensile fracture resistance of compact bony tissue is considered. The relation between specific strain energy and stress level is established. A strength criterion characterizing the degree of deformation is proposed on the basis of a model, according to which compact bony tissue may be regarded as a composite material. The mode of variation of the proposed resistance parameter over the various zones of the cross section of the diaphysis of a human tibia has been experimentally established.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1084–1091, November–December, 1971.     

Optimal reinforcement of a material in a known state of stress

The problem of minimizing the total reinforcement of a material in a known state of stress is considered. In the proposed geometric formulation the problem reduces to the determination in normal stress space of the shortest path from a point representing the state of stress to the region of strength. Examples of the determination of the relative area of reinforcement in three-dimensional and plane states of stress are given for characteristic regions of strength: for plane stress and plane strain the calculations lead to expressions that permit the relative areas of reinforcement to be determined directly.Kucherenko Central Scientific-Research Institute of Building Structures, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 922–930, September–October, 1971.     

Determination of the complex modulus of elasticity of soft viscoelastic materials

A method of determining the complex modulus of elasticity of soft viscoelastic materials is proposed. This method is based on the measurement of the dynamic characteristics of a three-layer symmetrical bar, in which the investigated material forms the middle layer, and on the subsequent calculation of the characteristics of the soft material from the experimental data obtained.N. E. Zhukovskii Central Aerohydrodynamics Institute, Moscow Branch. Translated from Mekhanika Polimerov, No. 1, pp. 178–181, January–February, 1976.     

Calculation of the residual stresses in wound glass-reinforced plastics

The effect of the winding and polymerization conditions on the residual stress distribution in wound glass-reinforced plastic cylinders is subjected to a numerical analysis. The calculations are based on the method proposed in [1]. The computer data are examined and the theoretical and experimental results compared.Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1026–1030, November–December, 1970.     

One model of a nonlinear viscoelastic medium,taking into account the influence of accumulated damage

We have proposed extremely simple equations for the state of a nonlinear viscoelastic medium of the inherent type, containing the scalar function of the accumulated damage as one of the decisive parameters. The equations take into account the influence of the type of stress pattern; they also contain the long-term strength condition. Equations of this type permit determination of the stress and deformation patterns developing immediately before failure, which is very important for experimental verification of the theory of long-term strength. The proposed model also takes into account the aging of the material.M. V. Lomonosov Moscow State University. Translated from Mekhanika Polimerov, Vol. 8, No. 2, pp. 241–246, March–April, 1972.     

Analysis of plates of polymeric material subjected to local loads

An approximate method of analyzing plates of polymeric material under local loading is described. The state of stress and strain and the stability of the plate are investigated.Moscow Institute of Electronic Machine Building. Translated from Mekhanika Polimerov, No. 3, pp. 430–434, May–June, 1976.     

Finite-difference method of solving the bending problem for glass-reinforced plastic plates with allowance for creep

A new finite-difference method is proposed for solving the bending problem as it applies to thin rectangular orthotropic plates of linear hereditary material. The proposed method makes it possible to obtain a closed approximate solution in explicit form for a series of finite-difference systems of equations corresponding to the problem of the bending of plates of orthotropic glass-reinforced plastic with allowance for the rheological properties of the material under various boundary conditions.Institute of Cybernetics and Computer Center, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Mekhanika Polimerov, No. 6, pp. 1075–1082, November–December, 1969.     

Resistance of composite flywheel rim to radial tensile stresses from centrifugal forces based on results of pure bending of a rim segment

A method is proposed for evaluating the resistance of a flywheel rim to radial stresses in free rotation. The method is based on loading a rim segment in pure bending and calculating the limiting moment and the corresponding limiting angular velocity. Applicability of the method is substantiated theoretically by investigating the similarity of the radial stress diagrams in rotation and pure bending. The method is verified experimentally for the strained state of a rim segment in pure bending.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 4, pp. 521–526, July–August, 1993.     

Contact creep as the principal source of the losses associated with the rolling of a plastic ball

An engineering method is proposed for calculating the contact creep of plastic balls used in rolling bearings. The method is based on empirical expressions relating the relative creep strain with the specific load and its duration of action. The complex contact-creep characteristics of the material are obtained by means of simple laboratory tests.Moscow Bauman Higher Technical College. Translated from Mekhanika Polimerov, No. 3, pp. 498–504, May–June, 1969.     

Experimental determination of the concentration of stresses and strains around a circular hole in a glass-reinforced plastic specimen

The results of experimental studies on the concentration of stresses and strains at a circular hole in a glass-reinforced plastic specimen, involving the use of the photoelastic coating method, are given. The effects of the anisotropy of the material, of ratio of the hole diameter to the width of the model, and of the load level on the magnitude of the stress and strain concentration factor are indicated.Translated from Mekhanika Polimerov, No. 1, pp. 159–163, January–February, 1972.     

Il'yushin approximation method applied to media with unstable properties

A method is proposed for solving the viscous-elastic integral equation with a singular kernel when the parameters depend on the temperature or some other physical factor. No assumption is made as to the existence of a temperature-time analogy. The results are used to solve boundary problems of heredity theory by the Il'yushin approximation method for time-varying properties of the material.M. V. Lomonosov Moscow State University. Translated from Mekhanika Polimerov, No. 3, pp. 411–419, May–June, 1970.     

A mathematical model of structurally inhomogeneous macroisotropic materials

The proposed mathematical model of microinhomogeneous material statistically distributes mechanical properties and contains mutually uninteresting cracks. The physical interpretation of model parameters is given, and the domain of its applicability is established. Analysis of the stress state in microinhomogeneous material is made and a probable failure criterion is suggested. The obtained results coincide with those known in the literature for partial cases.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Physico-Mechanical Institute, Ukrainian Academy of Sciences, Lviv, Ukraine. Institute for Applied Problems of Mechanics and Mathematics, Ukrainian Academy of Sciences, Lviv, Ukraine. Published in Mekhanika Kompozitmykh Materialov, Vol. 32, No. 4, pp. 480–492, July–August, 1996.     

A type of mechanically anisotropic,optically sensitive material

The technology for obtaining a mechanically anisotropic, optically sensitive material that can be used in photoelastic stress analysis is described. The mechanically anisotropic, photoelastic materials obtained by this method (method 3) are free of initial birefringence, have a sufficiently high degree of mechanical anisotropy, and possess high optical sensitivity. The elastic and piezooptic properties of specimens of orthotropic material have been investigated and it has been found that the isochromatics (lines of equal path differences ) are lines of equal principal strain differences. Experimental results are presented for the stress distribution in an orthotropic disk compressed by a pair of opposing concentrated forces.Translated from Mekhanika Polimerov, No. 5, pp. 835–839, September–October, 1971.