Properties of polyurethanes SKU-10 under pulsed and static loads

Conclusion The investigations of the optical and mechanical properties of modifications of polyurethane SKU-10 under static and pulsed loads and the results of solving the model problem of the nonstationary stressed state permit concluding the possibility of using these materials for solving by the photoelasticity method engineering problems of the stressed state of structural elements and structures under static and pulsed loads?Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 121–128, January–February, 1981.     

Analysis of critical strains and loads in layered composites

The present work is devoted to investigation of the compressive fracture for piecewise homogeneous materials with specific kinds of delaminations (defects with connected edges). The critical buckling strains and loads at which ply instability in laminated composites occurs under uniaxial and biaxial compression were evaluated. Different types of layers (linear elastic, elastic-plastic, hyper-elastic incompressible) were investigated. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of technological factors on the mechanical reliability of structures made from composites

Research on the effect of technological factors on the strength of reinforced-plastics structures is reviewed. Attention is concentrated on structures in the form of bodies of revolution fabricated by the winding technique. The influence of the winding parameters and the curing regime on the residual stresses is discussed. Data on the variation of the mechanical properties of the resin in the course of the curing process are examined. The contributions of chemical and thermal shrinkage to residual stress formation are compared. Methods of reducing the residual stresses are considered.Presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 3, pp. 529–540, May–June, 1972.     

Deformation of shell structures under local loads

The article presents a method of calculating the characteristics of elastic deformation of sectional shell structures modeling transported vessels. It explains the results of calculations in which excess pressure, the liquid-weight load, and local reactions of the supports are taken into account. The calculation procedure also makes it possible to obtain information on the effect of widely spaced stringers and to choose advantageous values of their parameters.Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 19, pp. 72–77, 1988.     

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     

Elasticity solution of multi-span beams with variable thickness under static loads

This paper studies the stress and displacement distributions of continuously varying thickness multi-span beams simply supported at two ends and under static loads. The intermediate supports of the beam may be elastic and/or rigid in one or two directions. On the basis of the two-dimensional plane elasticity theory, the general solution of stress function, which exactly satisfies the governing differential equations and the simply supported boundary conditions, is deduced. In the present analysis, the reaction forces of the intermediate supports are regarded as the unknown external forces acting on the lower surface of the beam under consideration. The unknown coefficients in the solutions are determined by using the Fourier sinusoidal series expansions to the boundary conditions on the upper and lower surfaces of the beam and using the linear relations between reaction forces and displacements of the beam at intermediate supports. The solution obtained is exact and excellent convergence has been confirmed. Comparing the numerical results obtained from the proposed method to those obtained from the Euler beam theory, the Timoshenko beam theory and those obtained from the commercial finite element software ANSYS, high accuracy of the present method is demonstrated.     

Resistance of three-layered structures to static and cyclic bending

Conclusions The above studies of two types of three-layer structural elements showed that the types have different resistances to static deformation in bending. Regardless of the materials, the use of structures which are symmetrical in regard to stiffness makes it possible to obtain a stiffness and strength for the structure which are 10–15% lower than the stiffness and strength of the external plates if the thickness of the latter does not account for more than 25% of the thickness of the structure. This finding, in turn, permits a substantial reduction in the weight of the structure by the use of a lower-density material for the internal layer. Resistance to static bending is determined mainly by the resistance of the structure to shear stresses. The mechanism of fatigue fracture differs appreciably from the fracture mechanism in static deformation. Regardless of the thickness of the structural elements, fatigue fracture for both types of structure occurs as a result of the acting normal compressive stresses. The endurance limit of the hybrid structure is determined by the fatigue resistance of the external layers, and its value is nearly equal to the resistance of the pure materials.Presented at the Sixth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, November, 1986).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 878–882, September–October, 1986.     

An evaluation of the activators of static polymer fatigue

In conformity with the kinetic theory [1, 2] a generalized temperature-time dependence of the brittle strength of isotropic polymers is obtained on the basis of a phenomenological model [7]. A quantitative relation between mechanical and thermal degradation is established.Special Design Office for Automation in Petroleum Refining and Petrochemistry, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 654–667, July–August, 1970.     

Relaxation effects and the nature of damage accumulation in polymethyl methacrylate under static loads

The relation between the size of the specular zone on the fracture surfaces of PMMA specimens and the loading rate is investigated at various temperatures. It is shown that the rate and time dependences of the size of the specular zone have certain common characteristics determined by the kinetic nature of damage accumulation in the material. It is proposed to employ the Robertson method [8] for studying the crack growth kinetics in polymers. This makes it unnecessary to observe the growth of cracks in the specimen during testing.All-Union Correspondence Structural Engineering Institute, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 663–669, July–August, 1971.     

Assessment of the static and fatigue strength of a precession driven dynamo under thermomechanical loads

At the Helmholtz-Zentrum Dresden-Rossendorf an experimental plant is developed to investigate the formation of magnetic fields in flows of liquid metals. Because of the enormous hazard potential of the used liquid sodium it is essential to avoid any damages during operation and so a detailed analysis using the finite element method is necessary considering the various mechanical and thermal loads. Therefore several tens of thousands load cases have to be taken into account. Hence an algorithm is developed to identify the relevant stresses referring to FKM guideline which are used for the static and fatigue strength assessment. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of the reliability of glass structures with steady and alternating loads

A method is developed for determining the reliability (nonfailure probability) of glass structures for a prescribed loading duration by alternating loads; an equation is obtained for calculating the reliability of glass structures from material (glass) strength parameters. It is shown that reliability with steady loads is a particular case of reliability with alternating loads. The method developed is based on a correlation established between long-term strength of the material and glass structure, and use of a new criterion of equal reliabilities for alternating loads.Lvov. Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 21, pp. 90–97, 1990.     

Multifibre polymer composites: Prediction of deformation and thermophysical properties

Conclusions A theoretical and experimental investigation was carried out to examine the possibilities of a structural approach for prediction of elastic constants, creep functions and thermophysical characteristics of hybrid polymer composites reinforced with anisotropic fibres of several types. The theoretical solutions were obtained by generalizing the self-consistent method for the case of a three phase model. The effects of brittle fibre breakdown under tension in the direction of reinforcement of a unidirectional hybrid composite were studied under conditions of a short-term loading and a long-term creep. It has been shown that a creep of viscoelastic fibres plays a principal role in creep of the hybrid composite. It is just this creep that significantly increases the fibre damage during creep of the composite.A variant of the solution has been proposed for predicting the thermorheologically complex behavior of hybrid composites containing not only elastic but also viscoelastic thermorheologically simple components with different temperature-time shift factors. The peculiarities of thermal expansion of hybrid composites and the possibilities for a purposeful control of thermal expansion coefficients by hybridization were studied. The considered thermal interval included a region of transition of the polymer matrix from a glass state into a viscoelastic one.The control tests were performed for specimens of organic/glass, organic/carbon, glass/carbon and organic/boron polymer composites with different ratios of fibre volume contents. On the whole, the obtained accuracy of predicting the characteristics of the examined hybrid composites may be considered as acceptable for engineering applications.Published in Mekhanika Kompozitnykh Materialov, Vol. 30, No. 3, pp. 299–313, May–June, 1994.     

On the simulation of textile reinforced composites and structures

This paper presents experimental and numerical methods to perform simulations of the mechanical behavior of textile reinforced composites and structures. The first aspect considered refers to the meso-to-macro transition in the framework of the finite element (FE) method. Regarding an effective modelling strategy the Binary Model is used to represent the discretized complex architecture of the composite. To simulate the local response and to compute the macroscopic stress and stiffness undergoing small strain a user routine is developed. The results are transfered to the macroscopic model during the solution process. The second aspect concerns the configuration of the fiber orientation and textile shear deformation in complex structural components. To take these deformations which affect the macroscopic material properties into account they are regarded in a macroscopic FE model. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)