Experimental determination of the transverse shear modulus of a wound glass-reinforced plastic in creep

It is proposed to determine the interlayer shear modulus in creep starting from the results of bending tests on simply supported beams with a concentrated load. It is assumed that the increase in deflection with time is caused by interlayer creep. The data of creep tests on wound glass-reinforced plastic beams are presented and used to determine the long-time interlayer shear modulus.Leningrad. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 370–372, March–April, 1969.     

Effect of the sign of the shear stresses on the shear strength of reinforced plastics

The effect of the sign of the shear stresses on the shear strength has been investigated for a glass-reinforced plastic of the SVAM type with various ratios of the longitudinal and transverse reinforcement in shear in the plane of reinforcement in axes turned through 45° relative to the direction of reinforcement. More than 80 tubularspecimens were tested. The shear strengths T ₄₅ ⁺ and T ₄₅ ^– corresponding to shear stresses of different signs can be found from uniaxial tests in tension and compression in the direction of the reinforcement.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 262–268, March–April, 1971.     

Stability loss of reinforced cylindrical shells under isotropic external pressure

Conclusions 1. Upon the loading of a composite shell having a metallic matrix the shear effects are insignificant even in the case of comparatively large volume reinforcement contents and wall thicknesses.2. The principal modulus of a material which determines the stability of a reinforced shell upon isotropic external pressure is the secant modulus in the circumferential direction.3. In the case of complex reinforcement schemes some decrease in the stability of the shell is possible, probably due to an imperfection in reinforcement technology.Institute of Solid State Physics, Academy of Sciences of the USSR, Moscow Region. Translated from Mekhanika Polimerov, No. 1, pp. 90–95, January–February, 1977.     

Elastic characteristics of ferrocement reinforced by hexagonal grids

The methods of the structural mechanics of composite materials are used to develop a method for predicting the elastic modulus and shear modulus of ferrocement reinforced with hexagonal woven and stamped grids. The method takes into account the elastic properties of the components and the geometry of the reinforcement.Riga Technical University, LV-1047 Latvia. Translated from Mekhanika Kompozitnykh Materialov, No. 2, pp. 182–186, March–April, 1997.     

Method of determining the volume and shear characteristics of elastico-viscous hereditary media from uniaxial-tension (compression) experiments

A method is proposed for determining the elastic constants — instantaneous modulus of elasticity, Poisson's ratio, shear modulus, bulk modulus, and the shear and volume influence functions — the shear creep kernel, the shear creep rate kernel, and the corresponding relaxation kernels from the data of creep or relaxation tests.Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 754–758, July–August, 1969.     

Elastic characteristics of ferrocement reinforced with woven meshes

Applying structural mechanics methods for composite materials, we have worked out a procedure for predicting the elasticity modulus, the shear modulus, and Poisson's ratio for ferrocement taking into account the elastic properties of the components, the wire diameter, the mesh size, and the distance between the meshes. The results make it possible to exploit the potential of such reinforcement to the fullest.Translated from Mekhanika Kompozitnykh Materialov, Vol. 30, No. 4, pp. 526–530, July–August, 1994.     

Effect of shear stiffness and concrete wedge cone failure on fracture of a fiber-reinforced plastic rod at an intersection with a concrete crack

Experimental results of model speciments in which FRP rods fractured due to local deformation at a crack intersection in a concrete member were analyzed by a 3D nonlinear finite element method in which orthogonal anisotropy of the FRP rod was considered. The analytical results indicated that accurate prediction of shear modulus of the FRP rod and size of concrete wedge cone failure around the FRP rod was significant to predict deformation and fracture of the FRP rod. FRP rods as reinforcement in concrete members, the small shear modulus, because of the orthogonal anisotropy and the wedge cone failure, may prevent the FRP rod from fracturing at a very low tensile stress due to the local deformation at the crack intersection.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Published in Mekhanika Kompozitnykh Materialov, Vol. 21, No. 2, pp. 158–166, March–April, 1996.     

Bending of prestressed glass-reinforced plastic beams

Initial waviness of the fibers and prestressing are investigated in relation to their effect on flexural stiffness and strength for beams with low shear strength. It is shown that prestressing the reinforcement increases the flexural stiffness but at the same time adds to the shear correction as a result of an increase in the modulus of elasticity E_x in the direction of reinforcement and the insensitivity of the shear modulus G_xz to prestress. It is established that prestressing increases the shear strength and the degree of anisotropy . Materials of two types are investigated: unidirectional (AG-4S) and cloth-reinforced (SKT-11).Mekhanika Polimerov, Vol. 3, No. 5, pp. 888–893, 1967     

Deformative characteristics of plastics reinforced with high-modulus anisotropic fibers

The independent elastic constants of plastics unidirectionally reinforced with transversely isotropic fibers have been determined. It has been assumed that the distribution of reinforcement in a transverse section of the plastic is regularly rectangular or hexagonal. To determine the transverse elastic modulus and the shear modulus in the plane of reinforcement, a constancy-of-plane-sections hypothesis was used. Values of deformative characteristics determined by the assumed calculational dependences have been compared with the experimental ones for plastics reinforced with graphite fibers.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 631–639, July–August, 1972.     

Evaluating the effect of whiskerization of the fibers of composites on the fundamental frequency of a laminated cylindrical shell

Conclusion The calculations showed that whiskerization of the reinforcement of the structural material of multilaminate shells makes it possible in some cases to increase the fundamental vibration frequency of the structure up to 15–20%. In combination with the well-known [1] effect of improved strength characteristics for a whiskerized composite in the transverse and shear directions, this finding allows us to conclude that whiskerized structural materials are more efficient than ordinary laminated composites in shell-type load-bearing structures. Here, the greatest benefit can be expected in the case of whiskers which have higher elastic moduli than the main reinforcement. Since considerably higher reinforcement intensities can be achieved in whiskerized laminated composites than in composites with a reinforcement characterized by an arbitrary three-dimensional structure, it can be concluded on the basis of the results obtained here that, at least for shells of moderate thickness (10 < R/h 50), whiskerized composites are the optimum structural material for load-bearing shells.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 1022–1027, November–December, 1987.     

Influence of vibration on creep in glass-fiber-reinforced plastic in a complex state of stress

The author describes the method and results of tests on tubular specimens of glass-fiber-reinforced plastic for creep under simultaneous torsion (shear in the plane of reinforcement), compression, and vibration in the longitudinal direction. He finds that vibratory creep is not manifested if the amplitudes of the alternating component of the stress are up to 0.1 times the limit of short-term strength and the frequency is 20 kHz.Institute of Mechanics of Polymers, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 358–360, March–April, 1974.     

Determination of the elastic characteristics of compact bone tissue by investigation of the natural vibration frequency

The dynamic elastic H and shear G_dyn moduli of compact bone tissue have been determined by investigating the natural vibration frequency of specimens obtained from long tubular human bones. The modulus of elasticity E has also been determined by conducting mechanical bending tests. The value of the H modulus is found to change in the course of storage.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 167–172, January–February, 1971.     

Ultrasonic method of determining the elastic characteristics of anisotropic materials

An ultrasonic method of determining the elastic characteristics, developed for isotropic materials and based on the measurement of the angles of total internal reflection of ultrasound at a liquid-solid interface, is applied to an anisotropic Compreg of the DSPA type. The results obtained for the shear modulus using the ultrasonic method at 2.5 MHz and an independent method based on measuring the frequency of the damped torsional vibrations of a prismatic bar at 10–30 Hz are compared. It is shown that the shear modulus varies only slightly (10–12%) on the frequency interval investigated.Leningrad Kirov Forest Engineering Academy. Translated from Mekhanika Polimerov, No. 4, pp. 728–731, July–August, 1969.     

State of stress of reinforced cylindrical shells with zones of slip

Conclusion Shells with angular reinforcement are more sensitive to delamination in the sense of an increase of the coefficient k_xz which characterizes the concentration of shear stresses. The magnitude of the ratio of the moduli of elasticity of the reinforcement and of the binder has a substantial influence on the concentration of shear stresses: when the values of E increase, the coefficient k_xz decreases (see Table 1).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 896–901, September–October, 1989.The authors express their profound gratitude to Professor Yu. V. Nemirovskii for his constant attention and useful review of the work.     

Structural characteristics of materials reinforced with high-modulus fibers

Research on the mechanics of boron and carbon-reinforced plastics is briefly reviewed. The design and testing characteristics of these materials associated with the high degree of anisotropy of their elastic properties, as compared with those of glass-reinforced plastics, are discussed. Problems relating to testing at an angle to the direction of the reinforcement, the effect of misorientation and distortion of the fibers, and the consequences of the low shear strength are considered. Experimental confirmation has been obtained by testing unidirectional (1 : 0), orthogonally reinforced (1 : 1 and 2 : 1), and tridirectional (1 : 1 : 1 in the 0°, +60°, and –60° directions) boron and carbon-reinforced plastics.DeceasedInstitute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 676–685, July–August, 1971.     

Stability of a transversely isotropic spherical shell coupled with an elastic foundation

The stability "in the small" of a flat spherical shell with elastic reinforcement is investigated. It is assumed that the shell is made of material (glass-reinforced plastic) with low shear resistance [7, 8], which determines the choice of calculation procedure: generalized applied shell theories of the Timoshenko and Ambartsumyan types [1, 3]. The results obtained are compared with the corresponding results of the Kirchhoff-Love theory.L'vov Polytechnic Institute. Translated from Mekhanika Polimerov, No. 1, pp. 129–131, January–February, 1970.     

Tensile testing of high-strength unidirectional composites

Conclusions 1. In order to obtain stable values of the tensile strength of high-strength unidirectional composites it is necessary to use bar specimens with pressboard end reinforcement 90–110 mm in length.2. In determining the strength on specimens without end reinforcement it is necessary to select their size and shape with allowance for the transverse compressive strength, the shear strength and the taper of the grip jaws.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 717–723, July–August, 1978.     

Determination of in-plane shear characteristics of composite materials with [±45°] layup

The shear characteristics of a composite with a [±45°] layer layup are measured experimentally by different methods. Investigations were conducted on flat and tubular specimens. The strength and shear modulus were determined by the rail method, the losipescu method, and by applying torsion to thin-wall tubes; only the shear modulus was determined by applying torsion to square plates. Determination of the shear modulus yields quantitatively comparable results, and, at the same time, the scatter of the shear-strength values of the specimens is significant. Maximum strength is achieved on the tubular specimens. The cause of the lower strength values of the flat specimens can be explained by secondary stresses and strains in their effective sections. The influence exerted by the geometry of the specimens on their strength is investigated for specimens tested by the rail and losipescu methods. It is shown that it is possible to increase the strength appreciably by varying the specimen's geometry.Institute of Polymer Mechanics. Latvian Academy of Sciences, Riga, Latvia. AERPAC Company. Netherlands. Translated from Mekhanika Kompozitmykh Materialov, Vol. 32, No. 2, pp. 256–264, March–April, 1996.     

Nonlinear shear response of fluid polymers during periodic deformation. Basic harmonics

Conclusions 1. A model with a relaxation spectrum independent of accumulated elastic strains describes the combination of data on the amplitude and frequency dependences of the components of the shear modulus in terms of basic harmonics for low-molecular-weight polyisobutylene and a filled-polyethylene melt.2. The greater the amplitude of the shear strain, the broader the region of invariance of the relaxation functions relative to the amplitude of the rate of oscillatory shear.3. The kinetic (s) function affects the amplitude dependences of the modulus in terms of basic harmonics. Its effect is significantly greater on the real component of the modulus than on the imaginary one.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1093–1100, November–December, 1977.     

Limiting stresses in spatially reinforced composites with components-having different structural geometries nd elastic properties

A model which is proposed for calculating structural stresses in spatially reinforced composites and an invariant-polynomial criterion for evaluating their limiting values are used to predict the effect of the elastic and strength properties of the components and their relative content on the limiting stress-strain state of composites of different structures. Emphasis is given to tri-orthogonal and 4D cubic structures, in addition to structures with hexagonal and angle-ply fiber reinforcement schemes in the plane and perpendicular to it. The types of composite loading typical of standard tests are examined in separate numerical experiments for shear, tension, compression, and their proportional combination. A computational variant of a criterional estimate of the limiting stresses is substantiated for an anisotropic composite of variable strength. The limiting-stress surface is obtained along with contour maps showing stress isolines as a function of the properties of the components and the geometry of the structure. The maps are suitable for practical use. The cases of maximum resistance to shear, tension, compression, and combination loading of 3D and 4D composites are compared to the analogous cases for two-dimensional structures.Presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October, 1995).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 616–639, September–October, 1995.