The mechanism of fatigue failure of plastics

Based on the study of the kinetics of deformation or rigidity, of the rise in temperature, and of the fracture surfaces, the article describes the mechanism of failure of plastics. It as found that in a cyclically loaded solid there occur two processes: strengthening and loss of strength. The main factors affecting strengthening in fatigue were discovered. Among them are the structure of the material, the degree of crystallinity, the load level, conditions of deformation, etc. The kinetics of rigidity can yield the most accurate information providing an idea of the process of fatigue failure of plastics.Paper read at the 9th International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Kaunas Technological University, Lithuania. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 2, pp. 279–285, March–April, 1996.     

Correlation between static and fatigue strength of reinforced plastics

The conventional estimation of the fatigue strength of glass-fiber-reinforced plastics from the static strength in tension is shown to be inefficient by analysis of experimental data. It was found that a more reliable correlation is observed between their static and fatigue strengths as a result of referring _–1 to *, where * is the smaller of the stresses in tension or compression, determined from the inflection points on the static deformation curves. Views are expressed on the use of the correlation found for reducing the amount of fatigue tests.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 468–474, May–June, 1973.     

Glass-reinforced plastics based on matrices combining thermoplastics and thermosetting plastics

The conditions of fabrication and the physicomechanical properties of glass-reinforced plastics based on polysulfone combined in different ratios with epoxy resin and Rolivsan were investigated. It was found that realization of the strength of the fibers in glass-reinforced plastics based on three types of binders and mixtures of them at room temperature is approximately the same. The lower strength of glass-reinforced plastics based on polysulfone is determined by the lower concentration of fibers. Modification of thermosetting plastics with polysulfone significantly increases (by 5–8 times) the specific energy of delamination of the glass-reinforced plastics G_1c, which should be manifested by an increase in their crack resistance and other operating characteristics. Modification of ED-20 with polysulfone and polysulfone with Rolivsan significantly increases the glass transition temperature of the polymer and affects the character of the temperature curves of the strength of the glass-reinforced plastics.Institute of Chemical Physics, Russian Academy of Sciences, Moscow. D. I. Mendeleev Russian Chemical Technological University, Moscow. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 111–117, January–February, 1996.     

Mechanical characteristics of oriented glass-reinforced plastics in shear

The mechanical characteristics of oriented glass-reinforced plastics stressed in shear are considered. Various methods of determining them are compared. The dispersion of the shear strength is characterized and the possibility of glass-reinforced plastics elements failing as a result of low interlaminar shear strength is discussed.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1008–1013, November–December, 1969.     

Strength of honeycomb plastics in a flat stressed state

The strength of textile and paper honeycomb plastics in the flat stressed state is discussed, under the simultaneous action of compressing and shearing stresses. The application of a generalized strength criterion for anisotropic materials to honeycomb plastics is investigated.V. A. Kucherenko Central Scientific-Research Institute of Building Constructions, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 936–938, September–October, 1972.     

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.     

Strength of reinforced plastics under static loading

The question of the static fatigue of reinforced plastics is considered for plane stress. Relations that predict the static fatigue are given for very simple types of loading. Experimental data are presented for thin-walled tubes of SVAM (5:1) glass-reinforced plastic subjected to long-time tests at constant internal pressure.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 265–273, March–April, 1969.     

Measurement of the strength of plastics in high-speed compression

A previously developed [1] method of determining the strength of plastics in high-speed compression is extended to the temperature range –196° to +150°C. Dynamic strength data have been obtained for epoxy-polyester and polyvinyl butyral resins and glass-fabric reinforced plastics based on these resins in the indicated temperature range.Mekhanika Polimerov, Vol. 1, No. 5, pp. 34–38, 1965     

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.     

Correlation between the strength and thermal conductivity of glass-reinforced plastics

The effect of changes in the component ratio and porosity of glass-reinforced plastics on their strength and thermal conductivity is considered. A correlation is shown to exist between the bending strength and thermal conductivity of a glass laminate.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 749–751, July–August, 1969.     

Effect of relaxation phenomena on the strength of plastics exposed to harmonic loads and impacts

It is shown that if the frequency of cyclic loading is varied, the total heat-up is small, and relaxation processes do not play a role (proceed too fast or too slowly), the loading times are additive. It is shown that deviations from this additivity rule manifest themselves in a disproportionally slow increase or even in a decrease of the strength with rising frequency; these deviations may be caused by relaxation factors, i.e., by structural changes and local warming up. It is established that the degree of deviation depends on various factors determining the rate of relaxation, i.e., on the temperature, plastification, and orientation, which is in accordance with ideas on the role of relaxation phenomena in fatigue rupturing but conflicts with the view that the number of load cycles should be the decisive factor. The phenomenon of fatigue rupturing of plastics exposed to repeated impacts is discussed; specific features of impacts are the high loading rate and the rest between the impacts. It is shown that, in spite of the much shorter action time of the load, the strength under repeated impacts is lower than that under harmonic loading, owing to the stronger effect of local excess stresses and disorientation during unloading.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 165–168, January–February, 1972.     

Mechanical characteristics of radiation-cured glass-reinforced plastics

Data are presented on the mechanical characteristics of oligoester maleates copolymerized with styrene and the corresponding glass-reinforced plastics crosslinked by the thermochemical and radiation methods. It is established that the radiation-cured glass-reinforced plastics have improved strength and stiffness as compared with similar specimens obtained by thermochemical curing.Institute of Mechanics, Institute of High Molecular Compounds, Institute of Physical Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 4, pp. 704–710, July–August, 1969.     

Investigation of the adhesion strength of carbamide resins

The adhesion of carbamide resin to clean or treated fiber glass surfaces has been determined. The effect of this adhesion on the strength of glass-reinforced plastics is examined.Moscow Mendeleev Chemical Engineering Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1119–1121, November–December, 1968.     

Choice of optimal structure of glass laminates with random reinforcement. I

The effect of structural parameters — length, diameter, and distribution of the reinforcing elements — on the mechanical characteristics of glass-reinforced plastics is investigated with reference to the case of glass laminates with randomly distributed, straight, uncut glass fibers in parallel planes. It is shown that the reduced strength of these laminates as compared with unidirectional material is associated with the redistribution of the load between the fibers and the resin and the relative reduction in the number of fibers in the cross section. A formula is proposed for estimating the strength of glass-reinforced plastics with a random distribution of the fibers in parallel planes.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fiber, Moscow Region. Moscow Bauman Higher Technical College. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1043–1050, November–December, 1968.     

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.     

Determination of the shear strength of the metal-plastic adhesion bond and its response to lubrication

A new method of determining the shear strength of the metal-plastic adhesion bond is considered. Experimental data on its dependence on load and indenter dimensions are presented for various types of plastics under different conditions.State Scientific Research Institute of Machine Science, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 854–858, September–October, 1970.     

Shear strength of composites based on whiskerized fibers

The elastic and strength characteristics of unidirectional carbon plastics have been studied, based on carbon fibers, whiskerized with fiber crystals of silicon nitride prepared from the gaseous phase and titanium dioxide from an aerosol. The advantages of these composites and glass textolites based on satin-type fabrics whiskerized with fiber crystals of aluminum nitride and titanium dioxide over the usual carbon and glass plastics are demonstrated.All-Union Scientific-Research Institute of Aviation Materials. Institute of Polymers Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 492–501, May–June, 1973.     

The ultimate state of polymeric materials and laminated and fibrous composites under asymmetric high-cycle loading

The prediction of the high-cycle fatigue strength of polymeric and composite materials in asymmetric loading is considered. The problem is solved on the basis of a nonlinear model of ultimate state allowing us to describe all typical forms of the diagrams of ultimate stresses. The material constants of the model are determined from the results of fatigue tests in symmetric reversed cycling, in a single fatigue test with the minimum stress equal to zero, and in a short-term strength test. The fatigue strength characteristics of some polymers, glass-fiber laminates, glass-fiber-reinforced plastics, organic-fiber-reinforced plastics, and wood laminates in asymmetric tension-compression, bending, and torsion have been calculated and approved experimentally. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 1, pp. 87–102, January–February, 2008.     

Effect of temperature on the mechanical characteristics of carbon plastics reinforced with metal mesh

The behavior of carbon plastics based on FN resin and FN plus rubber and reinforced with metal mesh is investigated over a broad range of temperatures in tension, compression, and pure bending. The presence of a rubbery component considerably reduces the strength of the plastic while improving its deformation properties.Dnepropetrovsk State University. Translated from Mekhanika Polimerov, No. 2, pp. 358–361, March–April, 1971.     

Determination of adhesive strength in a thermoplastic-resin-thin-fiber system

Conclusion A method was developed for determining adhesive strength in thermoplastic-material—thin-fiber systems formed from a melt. Values of _o were determined for joints between PSF and PC On the one hand and high-modulus organic fibers on the other hand. We studied the dependence of the bond strength on the temperature at which the contact is formed, the area of the contact, and the condition of the surface. The adhesion of PC and PSF to organic polyamide fibers is good enough to make it unnecessary to develop adhesives or specially modify the fiber surfaces for the production of organic-fiber-reinforced plastics. The low shear strength of laminated plastics based on thermoplastic resins is evidently due to the small area of actual contact, which is in turn a consequence of the poor wetting and impregnation of the fiber filler by the melt.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 9–12, January–February, 1990.