Fatigue and fracture of plasticized and stabilized polyamides

Polyamides have been tested in cyclic bending to determine the effect of certain plasticizers, plasticizing conditions, diffusion stabilization, and aging on the mechanism and energy of fatigue fracture. The fracture surfaces of the most typical plasticized specimens are analyzed. The optimal conditions of diffusion stabilization of polyamides with quinhydrone, giving a considerable improvement in antifatigue properties, are selected.Institute of the Physicotechnical Problems of Power Engineering, Academy of Sciences of the Lithuanian SSR, Kaunas. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 693–697, July–August, 1968.     

Fatigue of glass laminates subjected to repetitive impact loading

Fatigue characteristics obtained for repetitive impact tensile loading in a DSO impact tester are presented for a glass-reinforced Textolite. There are differences in the fatigue life, temperature rise, and the variation of the elastic properties as compared with the case of repetitive sinusoidal stress cycles. The effect of the geometry of the test piece gage length on the measured parameters is examined and methods of predicting fatigue life are discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 751–754, July–August, 1969.     

Relationship between the molecular structure and certain mechanical properties of oriented polymers

The correlations between the molecular structure and intermolecular energy and the fatigue and elastic properties of fibers are considered. It is shown that the maximum of these properties corresponds to an optimal value of the intermolecular energy.Leningrad Branch of the All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 4, pp. 734–735, July–August, 1969.     

Change in the properties of the membrane of the left ventricle of an artificial heart after operating in an animal

Conclusion After 53-day operation of a biomer membrane of an AH in a calf its physical and mechanical properties changed little. The membrane retained the greater part of its fatigue life and a high surface quality; as a consequence of insignificant creep, its functional properties also changed little.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 533–536, May–June, 1985.     

Determination of the fatigue life of plastics from the self-heating temperature

The nondependence of the critical self-heating temperature of plastics on the variable load level and the linearity of polymer self-heating have been used to devise an accelerated method of determining fatigue life, which makes it possible to shorten testing times by a factor of up to 10 with satisfactory agreement between the calculated and actual fatigue lives.Mekhanika Polimerov, Vol. 3, No. 1, pp. 111–117, 1967     

Fatigue performance of glass/polyester laminates and the monitoring of material degradation

Experiments are performed on glass/polyester composites under fatigue loading. The stiffness degradation is recorded as an indirect measure of material damage. The stiffness decrease rate is described by a power dependence on stress; this relationship allows the fatigue law to be derived. Stiffness-controlled fatigue curves are generated and presented in an S-N-diagram based on normalized stress (equivalent to strain). Such stiffness controlled fatigue curves can be used as a basis for design criteria for components.Presented at the 9th International Conference on Mechanics of Composite Materials, 17–20 October 1995, Riga, Latvia.Materials Department, Risø National Laboratory, Roskilde, Denmark. Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 1, pp. 32–41, January–February, 1996.     

Endurance limit of polyethylene during cyclic loading under conditions of a plane stressed state

Conclusions The effect of the asymmetry of the loading cycle on the fatigue strength of HDPE subjected to biaxial tension has been studied. An increase in the acuteness of the cycle leads to an increase in the durability of the material. Under conditions of cyclic loading, the material became embrittled as the duration of the experiment was extended. The effect of various different ratios between the principal stresses on the fatigue strength of HDPE has been investigated. It has been shown that the form of the isochronous boundary curves depends on the duration of the experiment. It was established that the mechanism of HDPE fracture changes depended on the duration of the loading. The accumulation of defects, when an experiment was of average or longer duration, built up at a greater rate than would have been predicted by a linear rule for summation.M. I. Kalinin Leningrad Polytechnic Institute. The "Plastpolimer" Okhtinsk Scientific Manufacturing Association, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 35–40, January–February, 1977.     

Acoustic fatigue of polymer materials

Methods are proposed for experimentally estimating the temperature-time aging of a filled rubber and the degree of damage accumulation in high-frequency fatigue tests. A procedure for experimentally determining the energy dissipation function of a material from the specimen temperature kinetics is described. The results of an investigation of the fatigue properties of two series of filled rubbers at a vibration frequency of 20 kHz are presented. It is shown that the fatigue failure of the materials tested is thermal in character. No accumulation of mechanical damage in the material in the course of intense vibration could be detected.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 662–668, July–August, 1969.     

Effect of anisotropy on the cyclic deformation and heating of SVAM-type glass-reinforced plastics

The effect of anisotropy of the mechanical properties on the cyclic deformation and heating of 1:1 and 5:1 SVAM-type glass laminates has been investigated for symmetrical tension-compression and pulsating tension and compression. It is shown that on the main part of the fatigue curve, depending on the anisotropy and the cyclic stress level, the temperature may be stabilized. At the same time, fracture is invariably accompanied, under fixed experimental conditions, by a rise in temperature to a certain value that depends only on the anisotropy property of the glass-reinforced plastic, the strain also reaching critical values that are determined by the cycle asymmetry and the anisotropy property of the material.Institute of Mathematics and Mechanics, Academy of Sciences of the Armenian SSR, Erevan. Translated from Mekhanika Polimerov, No. 5, pp. 898–903, September–October, 1971.     

Strength of boron fibers

The tensile and flexural strength and elastic properties of continuous boron fibers 95–105 µ in diameter obtained by depositing boron on a tungsten filament 10–12 µ in diameter have been investigated. The strength properties are primarily determined by the defects present at the boron sheath-core interface and for the fibers investigated have a limit of approximately 400 kgf/mm². Coarse surface or internal defects are capable of reducing the strength of the fibers to 200–250 kfg/mm².All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1126–1127, November–December, 1970.     

Properties of fiberglass-plastics reinforced with high-modulus fibers

The question of reinforcement of unidirectional fiberglass-plastic with boron or carbon fibers is considered. Static fatigue curves for the Poisson coefficient and the elastic modulus as functions of the volume content of the glass and the high-modulus fibers have been constructed. The theoretical dependences are compared with the experimental data.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Moscow. Translated from Mekhabika Polimerov, No. 1, pp. 68–74, January–February, 1972.     

Fatigue strength of certain materials used in airframe construction

Conclusions The completed tests show that the fatigue strength of carbon-plastic is 2.5 times greater than that of glass-plastic. Consequently, it is best to use carbon-plastic with ED-20 epoxy resin filled with 4–5m glass microspheres for adhesive purposes in load-bearing components. This makes it possible to significantly reduce the weight of airframes and improve their service properties. It was established that, for the composite materials investigated, stiffness is lost during cyclic loading mainly as a result of damage accumulation; the loss in stiffness may serve as a criterion for evaluating the progress of fatigue fracture.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 451–455, May–June, 1980.     

Investigation of the fatigue properties and susceptibility to damage of thin-walled polymer shells

The results of a study of the damage suffered by thin-walled polymer shells are evaluated on the basis of an analysis of the process of crack formation and the variation of the modulus of elasticity under cyclic deformation. The process of fatigue failure has been studied in relation to shells made of three groups of polymeric materials. It is shown that for the polymers investigated there are at least two different fatigue fracture mechanisms. Data on the crack growth kinetics are presented.Plastopolimer Research and Production Association, Leningrad; Lensovet Leningrad Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1019–1026, November–December, 1971.     

Acoustic fatigue of polymer materials

An experimental investigation of the fatigue properties of filled rubber under acoustic loading is briefly discussed. It is shown that two processes take place in the material—hardening and softening. A corresponding mathematical model is proposed. The form of the Wöhler fatigue curve in logarithmic coordinates is almost linear for high-frequency cyclic loading and may be assumed linear in the calculations with a risk of not more than 1%.Mekhanika Polimerov, Vol. 3, No. 3, pp. 467–475, 1967     

Self-heating and failure of plastics under cyclic loading

It has been shown that plastics heated by cyclic deformation have two characteristic temperatures—a critical temperature T_hc, at which the most heavily stressed part of the test piece is intensely heated, and a temperature T_h, at which the test piece fails. The values T_hc and T_h are determined not only by the physicomechanical properties of the material, but also by the state of stress and strain, by the scale factor, and by the heat transfer conditions. It has likewise been shown that the form of the fatigue fracture surface of plastics is determined by the type of deformation and the temperature T_h.Mekhanika Polimerov, Vol. 3, No. 3, pp. 483–492, 1967     

Fatigue of a glass-fiber-reinforced plastic under sonic-frequency vibrations

A procedure is described for fatigue tests of glass-fiber-reinforced plastics specimens under conditions of symmetrical extension and compression with a steady peak of dynamic stress at a vibration frequency of approximately 500 Hz. As a test for fatigue failure we chose the steep increase in the mechanical loss angle of the vibrating system which occurs when a macrocrack is formed in the specimen. The time dependence has been plotted for the mechanical loss angle, the resonance frequency of the vibrations system, a parameter proportional to the peak deformation of the specimen, and the temperature of vibrational heating-up in its cross section where there is the greatest stress. The progress of these dependences has been analyzed in the build-up of fatigue damage in the material. An experimental relation has been obtained between the resultant dissipative function of the material and the peak dynamic stress. Results are given of fatigue tests on specimens of a glass-reinforced plastic winding cut in the weft direction of the reinforcing fabric.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1039–1043, November–December, 1972.     

Influence of technological factors on the supramolecular structure and frictional properties of the surface layers of thermoplastics

X-ray and optical diffraction methods have been used to study the changes in supramolecular structure, degree of orientation, and drawratio of the material in the 0–650-µm range for polypropylene samples obtained by molding. Using a microtribometric technique, the influence of these factors on the frictional properties of the polymer have been elucidated.Institute of Mechanics of Metal-Polymer Systems, Academy of Sciences of the Belorussian SSR, Gomel'. Translated from Mekhanika Polimerov, No. 2, pp. 202–206, March–April, 1976.     

Effect of temperature on the mechanical properties of boron fibers

The effect of exposure to temperatures on the interval 20–600°C for up to 1000 h on the physicomechanical properties of boron fibers at room temperature has been investigated. Prolonged exposure to temperatures up to 200°C does not have much effect on the mechanical characteristics of the fibers, whereas heating for one hour at 300–350°C increases the strength of the fibers by 10–12%.All-Union Scientific Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 329–332, March–April, 1971.     

Behavior of rigid plastics under cyclic loading

Research progress on the dynamic fatigue of plastics is briefly reviewed. Attention is concentrated on the problems of damage accumulation and self-heating. The effect of various factors on the fatigue of plastics is considered. The possibility of predicting the cyclic life-time from the results of long-time static strength tests is examined. The prospects for the construction of a theory of fatigue strength in complex states of stress are weighed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 1, pp. 97–107, January–February, 1969.     

Structural approach to calculation of the effect of moisture on elastic characteristics of organoplastics

Data have been obtained for the structural calculation of the effect of moisture on the elastic characteristics of organoplastics from the properties of components. The distribution of moisture between the fiber and matrix — the components of a unidirectional composite — is considered. The elastic properties of the fiber are determined by an inverse calculation using the experimental dependences of the composite and matrix on moisture. The moisture effect on the properties of the materials is taken into account with influence functions, which differ by more than 25% for various characteristics. The results can be used for calculating the elastic properties of composites with various reinforcement schemes and at the nonequilibrium distribution of the moisture concentration in an actual environment.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Polymer Mechanics, Riga, LV-1006, Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 525–530, July–August, 1998.