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.     

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     

Further studies on the strength geometry of anisotropic materials

The connection between the form of the strength surface of an anisotropic material and the procedure of experimentally determining the starting parameters is examined. Strength surfaces which were constructed for a flat sheet of constructional plywood in four octants of stress space and strength surfaces constructed in three planes of symmetry for two fiberglass plastics in the third octant are shown.S. M. Kirov Leningrad Wood Technology Academy. Translated from Mekhanika Polimerov, No. 2, pp. 269–278, March–April, 1976.     

Experimental investigation of compression waves in polyurethane foam

The behavior of porous foam plastics under impact loading has been experimentally investigated with reference to the example of polyurethane foam. The specially designed loading mechanism made it possible to measure the propagation velocity of the compression wave, its dependence on the impact velocity, and the absorption. The impact loading velocities varied from 2.5 to 13 m/sec. The results obtained are discussed from the standpoint of nonlinear acoustics.Leningrad Zhdanov State University. Translated from Mekhanika Polimerov, No. 1, pp. 160–162, January–February, 1970.     

Long-time strength of polyethylene in biaxial tension

The long-time strength of high-density polyethylene (HDPE) in biaxial tension has been experimentally investigated at ratios of the principal stress components =₁/₂=0, 0.5, 1, 4. The maximum duration of the experiments was 2500 h. The limit surface for HDPE has been constructed. It is shown that the limit surface for this material varies with time as the mode of fracture changes from quasibrittle at medium stresses to brittle at low stresses. In the case of quasibrittle fracture the condition of equivalence of simple and plane states of stress is satisfactorily described by the Malmeister and Gol'denblat-Kopnov criteria, and in the case of brittle fracture by the maximum normal stress criterion.All-Union Scientific-Research Institute of Hydromechanization, Sanitary Engineering, and Special Construction, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 401–408, May–June, 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.     

Experimental investigation of the impact strength of Caprolon in linear and plane stress

An apparatus for investigating the impact strength of materials in plane stress is described. The results of testing Caprolon in plane stress and linear tension over a broad range of strain rates are presented.Leningrad Kalinin Polytechnic Institute. Translated from Mekhanika Polimerov, No. 2, pp. 332–334, March–April, 1971.     

Experimental investigation of the strength of structural plastics in multiple pulsed bending

Strip-beams of molded fabric-reinforced plastic, unidirectional wound glass-reinforced plastic, and polystyrene and syntactic foam have been tested in pulse bending in a modified electrodynamic testing device. The main stages of the failure process and the nature of the relation between the peak load and the number of cycles to failure have been established. For all the materials tested these relations are similar to the cyclic strength curves obtained at low loading rates. It is shown that for glass-reinforced plastics there is a correlation between the various stages of the failure process.Translated from Mekhanika Polimerov, No. 2, pp. 337–341, March–April, 1971.     

Inelastic deformation of round concrete columns in triaxial compression

The inelastic strains are used to characterize the deformation of concrete in triaxial compression. The relation between the plastic volumetric strain and the plastic strain deviator in round confined concrete columns is analyzed. This relation is described by the inclination of the incremental plastic strain vector. A relationship for the inclination as a function of the plain concrete strength, confinement properties, and hydrostatic pressure is found.     

Testing the strength of anisotropic rings

A study was made of the distribution of stresses in an anistropic ring under compression or tension with rigid cams, taking into account the final dimensions of the zone of contact.Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 1, pp. 175–177, January–February, 1974.     

“A new approach to formulate the general strength theories for anisotropic discontinuous materials” Part B General form of polynomial to describe the strength of anisotropic discontinuous materials

A new approach to describe the failure hypersurface on the basis of assumptions presented in Part A reveals the new form of failure stress polynomial. In the presented theory new terms such as: unit tensor object, object formed on the basis of unit tensor object, the first, second and third form of the anisotropy failure function, and the first and the second type of object axis, were defined. On the basis of these terms the coefficients of their polynomials were formulated as values of the appropriate objects. The presented theory divides the six dimensional hyperspace of stresses into eight parts in which eight intersected hypersurfaces constitute the failure hypersurface. Six hypersurfaces may be assigned to two of three mutually coupled sets of elements. In general cases the theory may be used to describe the failure hypersurface for anisotropic structures where tensorial relationships do not occur. The obtained polynomial is transformed to tensor polynomial on the assumption that the failure stress tensorial relationships describe the failure hypersurface of anisotropic materials.     

Static strength and failure mechanism of CFRP under biaxial loadings

Tests of cross-ply composite tubes were performed under combined axial and torsional loading up to failure. Strength properties and failure mechanisms were evaluated with reference to the biaxiality ratio of the loading. The scattering of the biaxial strength data was analyzed using the Weibull distribution. The axial contraction of carbon fiber-reinforced plastic (CFRP) tubes under biaxial loading was investigated theoretically and experimentally. Artificial neural networks were introduced to predict the failure strength using the algorithm of the error back-propagation. The prediction was also made by the Tsai-Wu theory using the experimental data and by the combined optimized tensor-polynomial theory. A comparison shows that the artificial neural network has the smallest root-mean square (RMS) error of the three prediction methods. The prediction of the axial contraction of the tubes correlates well with the results of a linear variable differential transformer (LVDT) of the testing machine. From the phenomenological analysis of the failure and the fractographic observations of the fracture surface, three types of failure modes and microscopic failure were investigated, depending on the biaxiality ratio, and the corresponding failure mechanisms are suggested.Submitted to the Tenth International Conference on Mechanics of Composite Materials, Riga, April 20–23, 1998.Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang 790–784, Korea. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 1, pp. 38–56, January–February, 1998.