Analysis of the zonal winding pattern of thin spherical shells

Conclusions 1. A method has been proposed for calculating the zonal pattern of winding thin spherical shells.2. The tested strength of shells wound by the calculated pattern correlates with the theoretical.3. The proposed calculation apparatus makes it possible to calculate winding patterns with any variants of angles and number of zones.4. A zonal pattern in a spherical shell having a connecting pipe of small diameter can give a mean constructional strength which does not exceed 0.39 times the strength of the unidirectional plastic (as against 0.5 in the ideal case for a sphere of bidirectional material), i.e., not more than 78% of the strength of the plastic is realized.5. The bearing ability of a sphere wound by the zonal method is 22% less than that of a long cylinder (with no bottom) made by the same winding method.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 625–631, July–August, 1978.     

Statistical analysis of the bearing capacity of rim-spoke flywheels made of reinforced plastics

Conclusion The suggested numerical method makes it possible to plot the distribution functions of the bearing capacity of RSF at the structural level of their design elements (rim, spokes) with a view to the scatter of the strength and strain properties of the used materials and the geometry of arrangement of the structure. This involves taking into account the random nature of the radial distribution in the rim material of both strain and strength properties, which makes it possible to investigate more fully the processes of failure really occurring in RSF. The suggested method is the basis for stipulating a scientifically substantiated safety factor (the theoretical bearing capacity) in dependence on the required reliability; this makes it possible to use a differentiated approach to problems of devising RSF for actual purposes. Our investigations may serve as the basis for solving problems of optimal planning of RSF according to the conditions of the required reliability.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 1041–1047, November–December, 1987.     

Investigation of the principal dense-winding conditions for wound glass-reinforced plastic pipe

The dense-winding conditions have been found for glass-reinforced plastic pipe wound simultaneously with a large number of strands [conditions (15), (17), and (18)] and relations have been obtained for calculating the winding mechanism kinematics. Kinematic equations have been derived for dense winding by displacement of the strands in the pipe cross section, along the pipe axis, and in both directions at once.Glass-Reinforced Plastics Division of the All-Union Lenin Electrical Engineering Institute, Khar'kov. Translated from Mekhanika Polimerov, No. 6, pp. 1057–1064, November–December, 1970.     

Mathematical modeling of processes of devising fibrous composite materials and thin-walled structural elements by forced winding

Conclusions With the aid of the method of averaging processes in regular media, on the assumption that the temperature field in the semiproduct of PM is homogeneous at all stages of the production of thin-walled articles of CM, we suggested averaged equations of equilibrium, and also constructive algorithms for calculating the effective moduli and defining relations of the material of the semiproduct of CM. On the basis of these equations and the boundary conditions corresponding to them, we showed that it is possible to determine the RTS in a finished product of CM, and also to predict the change of its shape after removal from the mandrel and cutting it up into separate elements. To determine the above-mentioned technological characteristics of thin-walled elements made of fibrous CM, it is necessary to know the physicomechanical characteristics of the fibers and of the PM before and after polymerization; the volume fraction of the reinforcing filler and of the PM during winding, and also the orientation of the reinforcement; the relative change of volume of the PM after heat treatment and cooling; the prestresses in the fibers in the process of winding. It should be noted that the obtained averaged equations make it possible to calculate only the components of the averaged RTS in products of CM. To determine the local stresses in PM and fibers at all stages of making the product, it would be necessary to investigate in detail the rheology of PM at different temperatures.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 513–527, May–June, 1990.     

Initial stresses in filament-wound reinforced-plastic rings

Methods of experimentally determining the initial stresses in filament-wound GRP rings are examined and the effect of winding tension is investigated. It is shown that by varying the winding tension it is possible to exercise a considerable degree of control over the magnitude and distribution of the initial stresses.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 505–511, May–June, 1969.     

Dispersed failure of an anisotropic flywheel

Based on a hereditary damage model of solids, the strength of a cylindrically anisotropic flywheel is calculated. By using a failure criterion, the location and time of initial failure is determined in relation to an anisotropy parameter, for which the ratio of rigidities in the tangential and radial directions is taken. The process of dispersed failure depends on the expansion intensity of the damaged zone. The boundary of the zone is the failure front, whose equations of motion are obtained in the cases of absence and presence of a residual strength for the material behind the failure front. In the second case, the damaged material is modeled by an isotropic elastic medium with considerably reduced values of strength and rigidity characteristics, and variations in the pressure on the failure front are also determined. Graphs of the radial coordinate of failure front as a function of time are constructed and analyzed for different values of the anisotropy parameter, the degree of residual strength and density behind the failure front, and proportions of geometrical sizes of the flywheel. The critical failure times are found. A system of restrictions on the values of mechanical and geometrical parameters is revealed which makes possible the realization of the process of dispersed failure investigated.Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 1, pp. 93–108, January–February, 2005.     

Evaluation of the physicochemical properties of boron-aluminum composite by the method of acoustic emission

Conclusion With the aid of the described method processes occurring in composites at the early stages of loading can be judged. The method yields a comparative characteristic of the strength of the bond at interfaces and makes it possible to judge initial defectiveness of the composite and residual thermal stress due to different production technologies of the composite. Moreover, the method makes it possible to differentiate between the kinds of defect of the composite. For a more detailed study of the properties of composites it is necessary to carry out experiments with composites obtained by different technologies. For a better understanding of the physics of the process it is necessary to obtain the spectral components of the signals, the amplitude distribution in time, and also to use additional research methods.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 1106–1109, November–December, 1988.     

Formation of the structure and effective properties of composite material in the manufacture of shells with cross-ply reinforcement

Conclusion The proposed model of formation of the reinforcing framework in the manufacture of an axisymmetric shell by the CPW method makes it possible to numerically determine the thicknesses and rates of filling the layers, reinforcement angles as a function of the main parameters of the technological process, geometry of the mandrel, and characteristics of the reinforcing filament. It was established that the thicknesses of the layers, reinforcement rates and angles, and, as a consequence, the effective stiffness characteristics of the composite are substantially variable both along the meridian and over the thickness of the shell.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 609–617, September–October, 1992.The authors thank V. A. Frolov for the experimental results.     

Equilong-term strength surfaces of organic textolite in the plane stressed state

Conclusion Long-term strength tests of textolite were conducted for seven different particular cases of the plane stressed state. Maximum times to failure for which experimental data were obtained reach 2500 h. It is established from analysis of the test results that the experimental long-term strength curves for the types of stressed state under consideration are closely similar. The condition of long-term strength in the general case of the plane stressed state for constant levels of stresses is taken as the equation of the short-term strength surface in which the time factor is introduced parametrically; in this case, the apparent observance of similarity between equilong-term strength surfaces makes it possible to express the tensor components characterizing the long-term strength by tensor components of the short-term strength surface and a certain monotonically decreasing time function, which is independent of the form of stressed state.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 51–56, January–February, 1979.     

Effect of structural and processing parameters of the reinforcement on the strength of unidirectional metalfiber composites under different types of loading

Conclusion The above studies show that the strength of unidirectional FCP's in uniaxial and biaxial tension is largely determined by the strength of the bond between the fibers and matrix and the internal geometry of the reinforcement. This dependence is particularly significant when the FCP product is loaded across as well as along the fibers. Impulsive loading as a method of making FCP's makes it possible to broadly vary the strength of the fiber-matrix interfaces. The unidirectional FCP's and tubular products of FCP's obtained by this method have a high strength under different types of loading, and this strength can be predicted by calculation.Presented at the Sixth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, November, 1986).Translated from Mekhanika Kompozitnykh Materiaiov, No. 6, pp. 1033–1038, November–December, 1986.     

Evolution of structural damage and macrofailure of inhomogeneous media at the supercritical stage of deformation

The article deals with the evolution of structural damage of an inhomogeneous body as a function of the properties of the loading system whose characteristics are taken into account by supplementing the boundaryvalue problem (1), (2) with the boundary conditions of the third kind (3) and (4). With the numerical solution by the finite-element method these boundary conditions are satisfied in accordance with the Eqs. (6) and (7) by changing the rigidity matrix of the discretized body (8). The material loses its load-bearing capacity at some point of the descending branch of the stress-strain diagram (Fig. 1a) at the instant the conditions of stability (9) are infringed. Normalized correlation functions of a damaged structure plotted for different equilibrium states of a granular composite (Fig. 2) make it possible to identify characteristic stages of failure. Macroscopic failure of material is regarded as the concluding stage of the processes of the onset, localization of structural disruptions, and formation of a macrodefect. Increased rigidity of the loading system makes it possible to stabilize the process of damage calculation, and this leads to an increase of limit deformations. The realization of the supercritical stage of deformation, together with energy dissipation upon structural destruction is the mechanism of adaptation of an inhomogeneous body to the loading conditions.Perm State Technical University, Russia. Translated from Mekhanika Komozitnykh Materialov, Vol. 33, No. 3, pp. 329–339, May–June, 1997.     

Winding glass-reinforced plastic rings under programmed tension

The strength, stiffness, and initial stresses of glass-reinforced plastic rings wound under variable tension in accordance with five different programs are considered. The relative thickness of the rings was 0.15–0.20. It is shown that the law of variation of the tension on the tape during winding has an important effect on the investigated parameter.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 361–364, March–April, 1971.     

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.     

Organization of pseudoarrays in REFAL

A pseudoarray in REFAL is described that makes it possible to speed up filing and the introduction of elements in an array. The corresponding programs are presented.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 48, pp. 18–22, 1974.     

Evaluating the strength of plates of composite laminates in the region of a bolted joint

Conclusions The proposed efficient method of calculation of the SSS and the strength of CLM plates in the region of a loaded hole makes it possible, comparing with the FEM, to reduce the computing time, the amount of initial data, and the amount of memory that is necessary. The shown calculated and experimental data indicate that the proposed method can be used for calculation of the strength and type of failure on the stage of designing mechanical joints made of the CLM.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 877–883, September–October, 1990.We thank V. V. Dolin for his assistance in performing the experiment.     

Winding trajectories of noncircular composite shells

An approach has been proposed for determination of the trajectory parameters of a layer formed by winding of continuous ribbons on a complicated surface. An algorithm has been developed for determining the geodesic trajectories of the reinforcement fiber arrangement, reinforcement angles, and geodesic deviation angles. Conditions have been formulated for positional stability of the ribbons on the surface and avoidance of gaps and overlapping between the ribbons along with restrictions to the surface form. Results are given for a calculation of the geodesic turn parameters on a fuselage surface, which is not a surface of revolution, of a light airplane.Translated from Mekhanika Kompozitnikh Materialov, Vol. 30, No. 4, pp. 546–551, July–August, 1994.     

Effect of the geometry of the structure on the strength distribution of multilaminate tridirectional reinforced plastics

Conclusion The proposed analytical method makes it possible to predict the strength distribution of an LRP of the type [0/±]_s from its structure (the geometry of the packet, the number of layers, and the strength properties of the layers) in a plane stress state. Allowance is made for the random character of the strength properties of the layers, which makes it possible to evaluate the reliability of the LRP for both determinate and random loading. A criterion was formulated for the optimum design of the structure of an LRP with respect to ensuring maximum reliability for specific loading conditions. We also evaluated the effect of the parameters of the structure and the characteristics of the plane stress state on reliability. According to the results of a numerical analysis performed with the above-developed structural model of the failure of an LRP — with allowance for the random character of the strength properties of the layers — the imbalance of the laminated packet which occurs during failure can be ignored. The method used to predict the strength distribution of the LRP, involving determination of the strength distribution law of an RSE and subsequent examination of the loading of parallel-connected RSEs, is promising for other reinforcement schemes as well.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 805–812, September–October, 1988.     

Elastoplastic deformations of metal pressure vessels reinforced with unidirectional glass-reinforced plastic

The design of cylindrical shells reinforced in the circumferential direction with high-strength elastic fibers is considered. The problem is solved on the basis of the deformation and flow theories. Relations are derived for the layer thickness required to obtain a structure of uniform strength and for the tension that must be applied to the glass tape during winding.Moscow Ordzhonikidze Aviation Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1069–1074, November–December, 1969.     

Residual technological stresses in the winding of the stator of large electrical machines

Conclusions Equations were derived for calculating RTS in the gap part and the zone of bending the coils and bars of the stator winding; it was shown that in calculating the RTS in the bending zones, it is necessary to take into account the presence of residual stresses in the copper of the bar. The calculated and experimental results indicate the high concentration of the stresses _X in the bending zones, These regions are most critical from the view-point of possible disruption of the monolithic nature and reduction in the electrical strength of the housing insulation.Paper presented at the Fifth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, October, 1983).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 868–872, September–October, 1983.     

An analysis of the thermal stresses in glass elements of electrovacuum devices in the neighborhood of metallic inclusions

On the basis of the improved theory of plates, which makes it possible to determine all the components of the stress tensor, we study the thermally stressed state of a finite round plate with a concentric inclusion of a different material. We obtain the exact analytic solution of the corresponding boundary-value problem for the system of singularly perturbed equations, valid for any ratios between the diameters of the plate and the inclusion. In the contact zones the stresses differ significantly (both quantitatively and qualitatively) from those predicted by the classical plate theories. The results obtained make it possible to draw a number of conclusions that are useful for estimating the strength of electrovacuum devices.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 28, 1988, pp. 1–6.