Deformation and failure of angle-plied organic fiber-reinforced plastics in the 3D stress state

Tubular specimens of organic fiber-reinforced plastic (OFRP) are tested in tension under a high hydrostatic pressure of up to 300 MPa. The specimens are made by winding at an angle of ±60° to the generatrix. The experimental equipment and technique are described. The tests show the insignificant effect of hydrostatic pressure on the elastic properties and the failure mode of the OFRP. The hydrostatic pressure considerably affects the strength properties of the OFRP. The material strength increases almost twofold under a pressure of 300 MPa. The failure strains of the material increase significantly as well.N. E. Bauman Moscow Higher Technical School, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 5, pp. 592–602, September–October, 1997.     

Effect of gaseous oxygen pressure on the kinetics of accumulation of residual deformation in resins

The authors studied changes in the properties of resins in the static deformed state under the effect of gaseous oxygen pressures of up to 200 atm at 25, 50, and 70° C for 20–500 days, depending on the experimental conditions. It was shown that an increase in gaseous oxygen pressure significantly affects the process of accumulation of residual deformation up to 30–40 atm while a further pressure rise has practically no effect on changes in the accumulation rate of residual deformation.Scientific-Research Institute of the Resin Industry, Moscow. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 552–554, May–June, 1973.     

Plane-stress creep of a glass-reinforced plastic

The creep behavior of an orthotropic glass-reinforced plastic based on Polimal'-109 resin and 19-S4 glass fabric is described. A special device for testing tubular specimens in plane-stress creep has been designed. The loading conditions include combined torsion and tension, internal pressure, and loading along the principal directions of anisotropy. Constitutive equations describing creep and recovery are proposed for the two-dimensional case.Warsaw. Translated from Mekhanika Polimerov, No. 3, pp. 398–410, May–June, 1971.     

Impact strength of high-density polyethylene with various molecular weight distributions

The Charpy impact strength of high-density polyethylene specimens prepared under low pressure with average molecular weight from 60·10³ to 1.5·10⁶ and differing substantially in molecular weight distributions has been studied at room temperature and at –190°C. It is shown that, both at room temperature and at temperature considerably below the glass-formation temperature, the impact strength of polyethylene in the range of molecular weights mentioned is determined mainly by the content of fractions with molecular weights about 10⁵ and more and does not depend on the width of the molecular weight distribution."Plastpolimer" Scientific-Research Association, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 919–921, September–October, 1973.     

Thermal deformation of unidirectional hybrid composites. 2

Conclusions A variant of the solution of the problem of the thermorheologically complex temperature strain of a hybrid composite containing viscoelastic thermorheologically simple components with differing functions for temperature-time reduction in addition to elastic components, is proposed. An experimental study is conducted on unidirectional specimens of organic- and glass-fiber-reinforced plastic, organic- and carbon-fiber-reinforced plastic, and carbon- and glass-fiber-reinforced plastic at a constant rate of temperature change in the 20–150 °C range. Satisfactory correspondence is obtained between predicted and experimental data.For previous communication, see [1].Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 969–979, November–December, 1989.     

Analysis of fracture surfaces in polymethyl methacrylate tested in bending with rotation

Typical fracture surfaces are examined for polymethyl methacrylate specimens subjected to multicycle fatigue testing in circular cantilever bending at T=20, 40, and 60°C. It is established that the fatigue life of smooth specimens is very closely correlated with the size of the diffuse fracture zone. The kinetics of damage accumulation with increase in the number of cycles are investigated by rapidly fracturing prefatigued specimens. The decisive role of diffuse fracture in the fatigue-fracture process is demonstrated. A method of estimating the mean main crack propagation velocity in circular bending is described.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 984–990, November–December, 1973.     

Apparatus for fatigue testing glass-reinforced plastic specimens in symmetrical tension-compression at acoustic frequencies

The characteristics of an electromechanical apparatus for fatigue testing glass-reinforced plastic specimens in symmetrical tension-compression at loads up to 10–40 kN and acoustic frequencies on the interval 300–5000 Hz are described.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 525–528, May–June, 1972.     

Experimental study of fracture toughness and energy in composite materials

The paper presents an experimental investigation of fracture characteristics of composite materials. The post-peak response of the load-crack opening displacement of notched specimens is used to evaluate the fracture energy associated with progressive matrix damage and crack growth. Effects of fiber orientation and other geometric characteristics on fracture parameters are studied. The load versus crack opening displacement as well as crack length, fracture toughness, and energy versus the number of loading cycles are obtained for different specimens. Based on the experimental results of this study, concepts of the fracture mechanics are applied to evaluate the evolution of fracture toughness and energy.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Department of Mechanical & Industrial Engineering, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 323–332, May–June, 1998.     

Investigation of the temperature change associated with the adiabatic compression of high-density polyethylene

The changes in the temperature of high-density polyethylene specimens during adiabatic compression and unloading have been experimentally investigated at various initial temperatures and at pressures up to 2500 kgf/cm². It is shown that the temperature rise depends nonmonotonically on the initial temperature, which is due to the temperature and pressure dependence of the volume expansion coefficient and thermal stability.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 416–419, May–June, 1976.     

Thermal effects in a glass laminate in tension

The results of a calorimetric investigation of a glass-reinforced textolite in uniaxial tension are presented. The specimens were deformed on the interval of strain rates from 0.3 to 10.5 mm/min at test temperatures from –30 to 80°C. The thermal effects are shown to depend on strain rate and test temperature.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 599–604, July–August, 1971.     

Behavior of Adhesively Bonded Concrete-CFRP Joints at Low and High Temperatures

This paper presents an evaluation of the results obtained from an initial study carried out at the IBMB, Technical University of Braunschweig, on the influence of temperature on adhesively bonded plate-concrete joint systems. The results of a theoretical model are also presented. The type of specimen used in this study is a three-point bending beam. The concrete specimens were prismatic in form, 100 × 100 × 700 mm without an internal steel reinforcement, strengthened at the intradoss with two types of UD CFRP lamina 20 mm wide and 590 mm long of thickness 1.4 mm for the E = 300 GPa type and 1.24 mm for the E = 175 GPa type. The plate-bonded specimens were designed to produce bending failure under a load, by not bonding the lamina and the concrete around the midspan of the specimens. The specimens were tested to failure at –100°, –30°, and +40°C after an approximately homogeneous temperature distribution within the concrete specimen has been reached. For comparison only, specimens of the same type were tested to failure at room temperature. The results obtained showed varying behavior of the bonded plate-concrete joint depending on variations in temperature. Furthermore, they showed different failure mechanisms. Greater reductions in the ultimate bond force were recorded for the test specimens strengthened with lamina having a high elastic modulus. A reasonable correlation was found between the experimental and theoretical results.     

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.     

Experimental study of the contribution of interfacial friction to the deformation resistance of particle-reinforced polymers

A study has been made of the dissipative properties of heavily filled elastomers as influenced by friction of the elastic matrix on the surface of the solid filler particles. In order to model the frictional surface, specimens were predamaged by cyclic deformation, with strain amplitudes sufficient to cause separation of the matrix from the filler. The predeformation operation was performed by means of a mechanical system having individual particle-matrix bonds, so that it was possible to evaluate the contribution of interfacial friction to the resistance of the polymer. When external pressure was applied to the specimens, the width of the hysteresis loop increased with increasing pressure, obviously reflecting an increase of the surface friction in the matrix. It was established that for a given volumetric fill, the dissipation of mechanical energy increased with decreasing particle size (with increasing frictional surface area). The significant influence of interfacial friction on the level and rate of strain relaxation was demonstrated experimentally.Paper presented at the 9th International Conference on the Mechanics of Composite Materials (Riga, October 1995).Translated from Mekhanika Kompositnykh Materialov, Vol. 31, No. 5, pp. 579–583, September–October, 1995.     

Effect of temperature on the fracture surfaces of filled systems based on SKS-85 butadiene-styrene copolymer

The tear fracture surfaces of mixtures of SKS-85 butadiene — styrene copolymer (85% styrene) with ordinary (carbon black, chalk) and polymeric (Kapron and cellophane powder) fillers have been investigated on the interval from –60 to +40°C. As the temperature varies within the limits of the glassy state (T_g SKS-85=+24°C) of the filled polymer, the nature of the fracture surface of specimens of filled mixtures, like that of the unfilled polymer, changes; in the region of the temperature transition of the copolymer associated with the mobility of the phenyl groups (–10±5°C) there is a slowing of the fracture process. At temperatures below the T_g of the copolymer the tear fracture surfaces of specimens of mixtures containing ordinary and polymeric fillers differ sharply. The introduction of fillers (20 vol. %) with a coefficient of thermal expansion different from that of the filled polymer considerably reduces the resistance of the material to fracture and leads to a sharp increase in the rate of crack propagation; the introduction of polymeric fillers with coefficients of thermal expansion similar to that of the filled polymer leads to an increase in the resistance of the material to fracture and to a decrease in the rate of crack propagation.Moscow Technological Institute of the Meat and Dairy Industry; State Institute of Polymer Adhesives, Kirovakan. Translated from Mekhanika Polimerov, No. 5, pp. 819–826, September–October, 1969.     

Effect of hydrostatic pressure on the tensile strength of polymer materials

The effect of hydrostatic pressure on the tensile strength of amorphous, crystalline, and thermosetting polymers has been investigated. The maximum hydrostatic pressure was 2000 kgf/cm². The surfaces of some specimens were protected from the ambient medium (oil). The tests showed that hydrostatic pressure improves the strength or high-elastic limit and Young's modulus of all the materials investigated. In the case of brittle materials, the increase in strength is greater if the surface is protected, whereupon the plasticity is also improved. Hydrostatic pressure produces important changes in the deformation behavior of crystalline polymers.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1043–1047, 1967     

Effect of external pressure on the physicochemical and mechanical properties of polymers

The behavior of crystalline polymers obtained by molding at high pressures has been investigated. External pressure can promote or retard polymer crystallization processes, depending on its intensity. Comparison of various physicochemical and mechanical properties of specimens obtained at different external pressures shows that the corresponding curves have two maxima: one at 200–800 kgf/cm² and another on the narrower interval between 1300 and 1500 kgf/cm². The position of the first maximum is associated with the molecular weight distribution and the flexibility of the polymer chain, and position of the second is determined by the chemical nature of the polymer. The data obtained help to make possible a rational choice of polymer processing methods in which pressure is involved.Mekhanika Polimerov, Vol. 4, No. 2, pp. 200–204, 1968     

Effect of supermolecular structure on deformation and strength properties of low-pressure polyethylene

The effect of the supermolecular structure on the mechanical properties of polyethylene was studied. A change in the structure of films was achieved by varying the isothermal crystallization conditions. Films have been prepared from low-pressure polyethylene (LPPE) which have fine spherulitic and lamellar structures. It has been demonstrated that the strength of unorientated films with a fine spherulitic structure is twice that of unorientated lamellar specimens. This difference in the strengths was also retained after orientational elongation to 20 times the length at a high temperature (102°C). The conclusion was reached that the casting of LPPE plays an important part in preparing high-strength orientated polyethylene films.A. F. Ioffe Physicotechnic Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 963–966, November–December, 1972.     

Optimization of cylindrical composite shells with regard to their critical mode of imperfections

This study deals with the optimum design of composite shells under external pressure with material strength and loss of stability according to the critical mode of imperfections taken as the failure criterion. The problem of optimum design is solved and the critical mode is obtained by nonlinear optimum programming for which the geometric and initial imperfection parameters are treated as variables. Numerical results are obtained for a cylindrical composite shell supported freely at its ends. The effect of shear forces between layers on the load-carrying capacity of the shell is also investigated.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 613–620, September–October, 1998.     

Study of the prefracture states of rigid polymers 1. Forced high-elastic deformation

It is shown that in the process of extension specimens of a rigid unoriented polymer — polyethylene terephthalate — go over into the oriented state before failure. Various cases of transition to the oriented state are considered: with the formation of a neck and deformation bands, with and without loss of continuity. The degree of molecular orientation of the specimens and their fracture conditions are estimated.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 8–14, January–February, 1976.     

Experimental testing of the applicability of a fourth degree polynomial in describing surfaces of equicritical planar stress distributions in glass-reinforced plastics

The possibility of using a fourth degree polynomial for calculating the anisotropy of glass-reinforced plastics in the planar stress state is evaluated experimentally. The experiments were carried out on industrial specimens of glass-reinforced plastic tubes loaded with an internal pressure, and subjected to an axial tensile force and a torque. Surfaces of equicritical planar stress distribution were constructed for the material of the glass-reinforced plastic tubes. The experimental and theoretical values of the breaking stresses were compared statistically. Most of the experimental values of the breaking stresses were found to lie within the confidence intervals of their theoretical values.S. M. Kirov Timber Technology Academy, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 284–294, March–April, 1970.