Compensation of thermal stresses in glass-fiber-reinforced plastic articles by the layerwise winding method

The contact pressures which must be created during winding with layerwise hardening in order to compensate radial stresses on the contact surfaces of the layers are determined. The tensions realizing the necessary pressures are calculated. The relations obtained are checked experimentally.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 640–645, July–August, 1972.     

Vibrocreep of polymeric materials

Experimental data on the static and vibrational creep of rigid porous polyurethane are used in an analysis of the time dependence of the vibrocreep coefficient and its dependence on the derivative of the stresses created by the incremental vibrational load and the static stress level. It is shown that at a constant value of the static stresses and the incremental vibrational load the vibrocreep coefficient decreases with time and in long-time vibrocreep tends to unity. As the parameter characterizing the vibrocreep coefficient for a given moment of time it is possible to employ the amplitude of the dynamic stress rate. The dependence proposed for describing the vibrocreep coefficient curves satisfactorily describes the experimental data. It is shown that the value of the vibrocreep coefficient does not depend on the static stress level (up to 0.5 of the short-time strength).For Communication 5, see [9].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 643–647, July–August, 1970.     

Residual stresses in glass-reinforced polyethylene

The variation of the axial and radial components of the residual stresses in fiber-reinforced polyethylene with distance from the fiber has been investigated. It is shown that, irrespective of the agent employed, coupling leads to an increase in stresses. The values obtained for the residual stresses are compared with the adhesion strength determined by the shearing method. The effect of a structure-forming agent on the residual stresses is investigated.Mendeleev Moscow Chemical Engineering Institute. Translated from Mekhanika Polimerov, No. 4, pp. 722–724, July–August, 1971.     

Composite risers for deep-water offshore technology: Problems and prospects. 1. Metal-composite riser

Prospects for the application of advanced composites in the offshore technology of oil production are considered. The use of composites in vertical pipelines-risers seems to be the most efficient. The operating loads are studied and the attendant problems are formulated. A comparative analysis of the characteristics of metal, composite, and metal-composite deep-water risers is presented. A technique is developed for designing multilayered risers, taking into account the action of internal and external pressures, gravity, and the axial tensile force created by tensioners, as well as the residual technological stresses due to the difference in coefficients of thermal expansion, physical-chemical shrinkage, and force winding. Numerical estimations are given for a two-layered riser with an inner metal layer of steel, titanium, or aluminum alloys and a composite layer of glass- or carbon-fiber plastics formed by circumferential winding. It is shown that the technological stresses substantially affect the characteristics of the riser.Institute of Polymer Mechanics, Latvian Academy of Sciences, Riga, LV-1006, Latvia. Trondheim Technical University, Norway. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 5, pp. 577–591, September–October, 1997.     

Results of an experimental investigation of the residual stresses in wound glass-reinforced plastics

The results of an experimental investigation of the residual stresses in wound glass-reinforced plastic rings are presented. The residual stresses were determined by the Davidenkov method. The dependence of the maximum tensile and compressive circumferential stresses on ring thickness and polymerization temperature is investigated. The experimental data are compared with the results of calculations based on the theory proposed in [1, 2].Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1116–1119, November–December, 1970.     

Effect of the conditions of formation of glued joints on their thermophysical properties

A correlation has been experimentally established between the thermal resistance of adhesive films and the internal stresses that develop during the curing process. During cure the thermal resistance varies in parallel with the internal stresses. It is assumed that the development of thermal resistance is determined by the tension produced in the film by the development of the internal stresses.Voronezh Forest Engineering Institute. Translated from Mekhanika Polimerov, No. 4, pp. 754–756, July–August, 1973.     

Experimental study of the effect of technological parameters on the residual stresses in thin-walled coiled parts

The effect of the parameters of heat treatment and programmed winding under tension on the residual stresses in thin-walled coiled parts made from glass plastic by the "dry" winding of a heated glass strip on an unheated mandrel is studied experimentally. The effect of the thickness of the parts on the maximum radial residual stresses is considered. A method is proposed for regulating the residual stresses in parts with very thick walls.Translated from Mekhanika Polimerov, No. 1, pp. 75–80, January–February, 1972.     

Determination of the residual stresses in wound glass-reinforced plastic rings

The stresses that develop during winding in wound glass-reinforced plastic rings change during polymerization, when the modulus of elasticity in the radial direction is reduced by heating. Further changes occur in connection with cooling and removal from the mandrel. The theoretical relations obtained for determining these stresses are found to be confirmed by experiment.Bauman Moscow Higher Technical College. Translated from Mekhanika Polimerov, No. 5, pp. 892–898, September–October, 1969.     

Investigation of the temperature residual stresses and strains in thick-walled wound reinforced plastic products

The kinetics of the temperature residual stresses and strains in thick-walled reinforced-plastic cylinders and rings have been experimentally investigated employing a special procedure for continuously monitoring the internal strains and stresses in the various zones of the semifinished product during the heat treatment stage. The effect of the resin polymerization (polycondensation) temperature and the mandrel material on the magnitude and distribution of the temperature stresses is considered. The total residual stresses have been determined by a nondestructive strain-gauge method with differentiation of the components.Translated from Mekhanika Polimerov, No. 6, pp. 1040–1046, November–December, 1971.     

Residual stresses in plastic rings reinforced with glass and manufactured with consolidation of the various layers

The residual stresses in thin-wall plastic rings reinforced with glass and prepared by the method of consolidating the layers in combination with various winding regimes have been studied experimentally. It is shown that variation of the winding regime from one layer to another can change the distribution of the stresses through the thickness of the ring.Moscow Energy Institute. Translated from Mekhanika Polimerov, No. 1, pp. 174–176, January–February, 1972.     

Shrinkage stresses in bonded plexiglas structures

It is shown by means of photoelasticity that the shrinkage stresses associated with cold polymerization of the adhesive layer in bonded plexiglas structural elements seriously reduce the reliability of the structure. By suitable heat treatment it is possible to reduce the shrinkage stresses by a factor of approximately four without distorting the shape of the element and increase the permissible stresses by a factor of almost three.S. M. Kirov Ural Polytechnical Institute, Sverdlovsk. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 734–736, July–August, 1968.     

Calculation of the residual stresses in wound glass-reinforced plastic parts when the material characteristics vary over the thickness

The thermoelastic residual stresses in anisotropic rings and cylinders with characteristics that vary over the thickness are determined. The calculation of the stresses in wound glass-reinforced plastic parts is illustrated by examples.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga, Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 4, pp. 686–691, July–August, 1971.     

On the Huang Class of Variable Metric Methods

Several authors have created one-parameter families of variable metric methods for function minimization. These families contain the methods known as Davidon–Fletcher–Powell, Broyden–Fletcher–Goldfarb–Shanno, and symmetric rank one. It is shown here that the same one-parameter families of methods are obtained from the Huang update by requiring the update to be symmetric.     

Nonuniform isothermal curing of cylindrical products made of polymeric composites

Conclusion By increasing the curing temperature and reducing the winding rate, it is possible to obtain compressive radial stresses in a cylindrical product during the entire curing stage — which should prevent loss of integrity during the curing operation. When the duration of the curing process is limited, the magnitude of the compressive stresses will depend in an extreme manner on curing temperature. Meanwhile, in the general case, ensuring minimal residual stresses will not ensure the absence of tensile radial stresses during curing.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 873–877, September–October, 1988.     

Residual stresses in glass-reinforced plastics parts

The determination of the residual stresses in glass-reinforced plastics elements is considered. It is shown that these stresses reach appreciable values and should be taken into account in strength calculations. Quantitative data are supplied for a series of materials. At normal operating temperatures the residual stresses are stable.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1117–1119, November–December, 1969.     

Variation of the residual stresses during the fabrication of thick-walled wound glass-reinforced plastic articles

The results of an experimental investigation of the development of the residual stresses in thick-walled glass-reinforced plastic cylinders during the fabrication process are presented. The variation of the stresses from the beginning of winding to removal of the cyclinders from the mandrel is examined.Translated from Mekhanika Polimerov, No. 2, pp. 355–357, March–April, 1974.     

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.     

Reasons for the lowering of the lifetime of polymers under cyclic loading

A model is proposed which explains the lowering of the lifetime of polymers on transition from static to cyclic loading by the interaction of local stresses from an external load with residual stresses which arose after preceding loading cycles. The results predicted on the basis of the model have been checked experimentally on polymethyl methacrylate, and a good agreement has been shown.M. I. Kalinin Leningrad Polytechnic Institute. Translated from Mekhanika Polimerov, No. 2, pp. 279–283, March–April, 1976.     

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.     

Factors in the adhesion strength of polymers toward a solid substrate

The true adhesion is looked upon as the sum of the experimentally determined strength of the glued area, internal stresses, and unaccountable technological losses (unrealized contacts). It has been established that the internal stresses do not depend on the value of the adhesion strength.Translated from Mekhanika Polimerov, No. 2, pp. 356–359, March–April, 1976.