Short-time strength of reinforced plastics in uniaxial compression

The short-time compressive strength of one-way and two-way reinforced plastics compressed in the direction of the axes of elastic symmetry has been theoretically and experimentally investigated with allowance for the mechanical properties of the components and the orientation of the fracture (shear) plane.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 621–628, July–August, 1969.     

Deformation criterion of the strength of plastics in biaxial compression

The deformation at break under uniaxial loading is taken as a criterion of the strength of an anisotropic glass-reinforced plastic in biaxial compression. Formulas are obtained for determining the breaking stresses and their limits of applicability are investigated. The calculated values of the breaking stresses are in agreement with the experimental values for both instantaneous and long-term loading.Mekhanika Polimerov, Vol. 4, No. 2, pp. 276–281, 1968     

Deformation and strength properties of carbon-reinforced plastics in compression

The deformation and strength properties of unidirectionally reinforced carbon plastics have been experimentally investigated for uniaxial compression in the longitudinal and transverse directions and at 45° to the direction of reinforcement in both short-time and long-time tests. On the basis of the deformation properties of the components an attempt is made to describe the creep curve of the plastic in all three loading directions. The Mohr theory is used to predict the compressive strengths in the direction of reinforcement and at right angles to the reinforcement.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 29–35, January–February, 1973.     

Creep and long-time strength of unidirectional reinforced plastics in compression

An attempt is made to predict the creep and long-time strength of unidirectional reinforced plastics in compression in the direction of the reinforcement from the properties of the components. The reinforcement is assumed to be elastic, while the resin is described by a Boltzmann-Volterraintegral equation with fractional-exponential Rabotnov kernel. Experimentally obtained creep and long-time strength curves are presented for unidirectional reinforced plastics.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 830–835, September–October, 1970.     

Effect of technological factors on the strength of unidirectional fiberglass plastics in compression and shear

The effect of variables in the technological process on the strength properties of fiberglass plastics has been studied. An investigation is made by the methods of regression analysis.     

Experimental investigation of the strength of glass-reinforced plastics in biaxial compression in three planes of symmetry

Glass-reinforced plastics (GRP) with fiber (wound) and fabric (hot-molded textolites) reinforcement have been investigated in biaxial compression in the three planes of symmetry. The high strength in biaxial compression in the transverse plane, observed for all the GRP investigated, is explained. A method of investigating the tensile strength of the fiber components of the GRP from the results of testing a unidirectional composite in biaxial compression in the transverse plane is proposed. The possibility of a nondestructive estimation of the strength of GRP in biaxial compression at an arbitrary stress ratio is demonstrated.Translated from Mekhanika Polimerov, No. 1, pp. 63–72, January–February, 1976.     

Possibilities of a nondestructive one-parameter method of checking the strength of anisotropic glass-reinforced plastics in uniaxial compression

A nondestructive method of checking the strength of glass-reinforced plastics (GRP) in finished products is proposed. This method is based on the correlation, investigated by the authors, between the modulus of elasticity and the compressive strength determined by a standard method. Various orientations in the plane of reinforcement of glass-reinforced plastics with different ratios of the orthogonally arranged fibers are investigated. It is proposed to determine the modulus of elasticity from the propagation velocity of an ultrasonic pulse measured under conditions of one-sided access to the surface of the product."Ritm" Research-Production Association, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 909–919, September–October, 1974.     

Estimating the impact strength of plastics

A method of estimating the impact strength of plastics in transverse two-support bending is proposed. It is shown that if specimens of different size are tested under certain conditions, the ratio of the work done in breaking the specimen to the volume of the specimen between the supports will be the same.Novosibirsk Kuibyshev Structural Engineering Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1109–1112, November–December, 1971.     

Statistical strength of glass-reinforced plastics

The failure of glass-reinforced plastics is treated as an aggregate of successive failures of the individual fibers. A method of estimating the statistical strength from the distribution curve is proposed.Mekhanika Polimerov, Vol. 3, No. 3, pp. 498–502, 1967     

Structural theory of the strength of reinforced plastics

Conclusions In the present study, we developed structural criteria that make it possible to predict at the component level (polymer binder, fibers) and interface level the long-term strength of laminated reinforced plastics in a plane stress state. The proposed relations make it possible to evaluate the effect of the rheological properties of the components, their volume fractions, and the geometry of the structure of the laminated packet on the long-term strength of reinforced plastics. The relations also permit resolution of the inverse problem: efficiently design the structure of such materials for specific loading conditions.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 833–839, September–October, 1989.     

Bending strength of oriented glass-reinforced plastics

The authors consider the effect of the low shear strength and shear stiffness of oriented glass-reinforced plastics (GRP) on the stress distribution and type of failure in bending. On the basis of relations obtained in [1] it is shown that the effect of shears on the magnitude and law of distribution of the normal and shear stresses is important only for very short beams made of materials with a low shear stiffness. An experimental study of the nature of failure in bending has revealed that the chief cause of extension of the region of shear failure of oriented GRP is the low shear strength of the material, and has made it possible to establish the limits of this region for three typical materials. Anisotropy of the elastic properties has little effect on the type of failure in bending.Mekhanika Polimerov, Vol. 2, No. 4, pp. 535–542, 1966     

Improving the strength of plastics by vacuum molding

An account is given of a completely new method of processing thermosets by molding them under vacuum. The authors' vacuum-molding equipment is briefly described. Data on the compressive, tensile, static bending and impact strength of vacuum-molded specimens are given. These indicate that in every respect the strength of vacuum-molded materials is considerably superior to that of plastics molded in the usual way (in the atmosphere).Mekhanika Polimerov, Vol. 2, No. 5, pp. 722–727, 1966     

Testing the interlaminar shear strength of laminated reinforced plastics

An improved method of determining the interlaminar shear strength of reinforced plastics from the results of mechanical bending tests on beams of different lengths is described and the results of an experimental verification of the method on glass-reinforced textolite and longitudinal-transverse-wound (LTW) glass-reinforced plastic are presented.     

Micromechanical strength analysis of fiber reinforced plastics

Strength of an unidirectional lamina is computed with a representative volume element. An approximative “voxel” meshing method is used in conjunction with continuum damage mechanics to simulate crack growth in the RVE. Two material models for the nonlinear material behaviour of the epoxy resin are compared. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Concerning the mechanism of fracture of oriented glass-reinforced plastics in uniaxial compression

The mechanism of fracture of an oriented glass-reinforced plastic in uniaxial compression in various directions in the plane of the sheet is considered on the basis of experimental observations of the microstructure and data on the variation of the linear and volume strains with increasing load. It is shown that increases in load are accompanied by a steady increase in crack development and damage accumulation.Leningrad Structural Engineering Institute. Translated from Mekhanika Polimerov, No. 2, pp. 238–242, March–April, 1971.