Effect of extension on the structure and thermophysical properties of kapron (nylon 6)

The effect of extension on the structure and thermal conductivity of kapron has been investigated experimentally in the temperature range +20–130° C. The thermophysical characteristics were determined via a method based on the principle of the regular regime. The structure of the kapron was investigated by infrared spectroscopy and x-ray and microstructural analysis. The mechanical loads produced important structural changes that affected the thermophysical parameters of the kapron.Mekhanika Polimerov, Vol. 4, No. 1, pp. 180–182, 1968     

Effect of cycle asymmetry on the cyclic strength of polymers

Cyclic strength diagrams have been obtained for polymethyl methacrylate and kaprolon at different degrees of loading asymmetry (from a pure compression to a pure tension cycle) on the interval from –100 to +80° C at 2·10³ and 3·10⁵ cycles.M. I. Kalinin Leningrad Polytechnic Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 948–951, September–October, 1968.     

The scale effect and the statistical theory of strength of polymer coatings

As a result of normal tensile tests on coatings based on ED-6 epoxy resin and kapron applied to a metal surface it has been established that the fracture is brittle in character and accompanied by a scale effect and a regular distribution of the strength values for specimens of the same type. It is shown that the data obtained are all in good agreement with the statistical theory of strength.State All-Union Scientific-Research Technological Institute for the Repair and Maintenance of Tractors and Agricultural Machinery, Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 839–843, September–October, 1968.     

Effect of hydrostatic pressure on the density of various plastics

It is shown that application of hydrostatic pressure causes an increase in the density of ebonite but practically no change in the density of polyethylene, kapron (nylon-6), PVC, plexiglas, and FKP-1. Uniaxial compression of some materials first increases their mean density, then, at fairly high strain, causes the density to decrease. For the majority of the materials examined, the rate of this reduction in density decreases in the simultaneous presence of hydrostatic pressure.Mekhanika Polimerov, Vol. 2, No. 3, pp. 355–358, 1966     

Study of the deformation properties of certain elastic reinforced plastics films

The author describes the results of an experimental study of the stress-strain relationship in elastic plastics films reinforced with kapron (nylon 6) mesh and tested in uniaxial and biaxial tension.Mekhanika Polimerov, Vol. 2, No. 1, pp. 43–51, 1966     

The relationship between stress and deformation of polymers in the linear stress state

The relation between stress, strain and strain rate is proposed as a means of describing the deformation properties of polymers. The equation describes the stress-strain curve, aftereffect, and stress relaxation in polymers. The theoretical conclusions are in good agreement with the results of creep tests on kapron (nylon-6).Mekhanika Polimerov, Vol. 1, No. 5, pp. 25–29, 1965     

Temperature dependence of the mechanical properties of oriented kapron fibers crosslinked with formaldehyde

Comparative regions of effective performance of oriented kapron fibers crosslinked with various amounts of formaldehyde are obtained on the basis of tensile test data in a broad temperature interval. As the degree of crosslinking increases, the region of softening of the crosslinked fibers is displaced in the direction of higher temperatures.Mekhanika Polimerov, Vol. 4, No. 2, pp. 304–308, 1968     

On the difference in the moduli of elasticity of polyamides subjected to different kinds of deformation

Experiments to determine the moduli of elasticity of polyamides (kapron) in tension and compression are described. A substantial difference in these characteristics was detected. The modulus of elasticity in tension is 0.75–0.80 of the value of the modulus in compresion. This difference is explained by the textural characteristics of the polyamides. The use of values of the modulus of elasticity obtained by testing specimens in tension to determine the stiffness of parts working in compression give overestimated strain values.Mekhanika Polimerov, Vol. 1, No. 4, pp. 47–51, 1965     

Markov model of connection between the distribution of static strength and fatigue life of a fibrous composite

Within the framework of a unified mathematical model based on the Markov chain theory, an attempt is made to describe the distribution of static strength, the fatigue curve, and the accumulation of fatigue damages. It is assumed that the fatigue failure of a test specimen occurs after the destruction of some its critical microvolume consisting of two — elastic (brittle fibers) and plastic (matrix) — parts. In the second part, plastic strains accumulate as soon as the cyclic load exceeds some level. Numerical examples are presented. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 615–630, September–October, 2006.     

Effect of orientation and molecular weight on the modulus of elasticity of polymer materials

The modulus of elasticity of a perfectly crystalline polymer is calculated as a function of the orientation of the crystallites. The calculations are based on the mechanics of a micro-inhomogeneous continuum. The dependence of the modulus of elasticity on crystallite orientation and molecular weight is calculated with reference to the example of crystalline kapron.Moscow-Lenin Pedagogical Institute. Problem Laboratory of Polymer Physics. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1002–1007, November–December, 1968.     

Behavior of the supermolecular structure of oriented amorphous-crystalline polymers under cyclic loading

Equipment has been developed for investigating small-angle X-ray diffraction in various phases of the loading period in cyclically extended polymers. The behavior of the large-period structure of oriented polycaprolactam (kapron) films in cyclic extension has been studied. The results are compared with the data on the behavior of the same structure in static tests.Mekhanika Polimerov, Vol. 4, No. 2, pp. 195–199, 1968     

Effect of liquid media on fatigue strength of polyamides

The results of an experimental study of polyamide fatigue strength are presented. Multiple flexing tests were performed on specimens rotating at 3000 cycles/min with a symmetrical load cycle in various media, including air (with and without blowing), volatile liquids (petroleum ether, ethanol, water), glycerin, and transformer oil. Fatigue strength is determined from (N — log N) curves for 10⁶ cycles. Dissipation of heat is found to be the main factor determining the effect of slightly aggressive media on fatigue strength. Values of the ratio fatigue strength/static strength (coefficient K) are presented.Mekhanika polimerov, Vol. 1, No. 1, pp. 124–127, 1965     

Fatigue strength of glass fiber/epoxy angle-ply laminates with different matrix ductility

Conclusion Angle ply laminates made up of glass fiber/epoxy plies have a good static strength for laminate angles up to about 45 °. This is due to the limitation of transverse strain in the plies due to constraints exerted by neighboring plies. At laminate angles of 50 ° and above the transverse and shear strains in the plies are not sufficiently constrained and cause failure in the matrix material. The constraint effect is present in fatigue but since the polymeric matrix material is sensitive to fatigue loading fatigue failure will occur at much lower strain levels than in static loading. This effect cannot be offset by increasing the ductility of the matrix material. Thus, strain to failure under fatigue loading will be only a small fraction of the static strain to failure for angle ply laminates with ply angles up to around 45 ° where the static strength is due to the constraint effect.Published in Mekhanika Kompozitnykh Materialov, No. 5, pp. 632–638, September–October, 1992.     

Progressive necking and orientation effects in the deformation of kapron

The stretching of kapron has been investigated by x-ray structural analysis using an estimate of the degree of orientation based on development of the Debye ring. It is established that with the progressive development of a first, second and third neck there is a decrease in the width of the texture maxima (increase in the degree of preferred orientation). The width of the texture maxima varies with the relative reduction of the cross section approximately in accordance with a linear law.Mekhanika Polimerov, Vol. 1, No. 4, pp. 7–11, 1965     

Comparison of the lifetimes of polymers tested in a vacuum and in air

The temperature-time dependence of the strength of kapron (nylon 6) fibers has been studied in a vacuum and in air. In the vacuum tests a pole shift effect is observed, whereas in air no such effect is present. It is shown that the pole shift observed under vacuum conditions can be attributed to the inconstancy of the coefficient in the Zhurkov equation. In this case the activation energy of the fracture process U₀, calculated from the slopes of the log vs 1/T graphs, cannot be assigned the significance of a unit bond rupture energy.Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, Voo. 5, No. 2, pp. 250–256, March–April, 1969.     

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.     

Isotropic softening model for high-cycle fatigue

As known the high cycle loading of structural elements above the fatigue limit results in catastrophic propagation of macroscopic fatigue crack(s). Therefore it is in demand to find a method, which would allow for early prediction of the fatigue life-time of particular structural element. The series of force-driven tests carried on 30CrNiMo8 steel have shown that, although the stresses by high-cycle fatigue do not reach the tensile stress, the material strength (measured indirectly from the strain-stress loop) decreases from the begin of the test, hence the damage nucleates and propagates from the very begin of the loading history. In this study we propose a thermodynamically consistent, strain driven constitutive model for isotropic damage accumulation by high-cycle fatigue of a homogeneous isotropic material, which should be capable to account for the above-mentioned experimental results. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of loading history on the free vibrations of an elastic-hereditary oscillator

The effect of the dynamic loading history on the free vibrations of an elastic-hereditary oscillator is examined. The response of the material is described by an integral relation of the heriditary type with an exponential-fractional relaxation kernel. An integrooperator representation of the starting equation makes it possible to obtain a closed solution to the problem of free vibrations of an elastic-heriditary oscillator for certain specific loading histories. The results are illustrated with reference to polyamide (kapron).Mekhanika Polimerov, Vol. 4, No. 2, pp. 222–226, 1968     

Resistance of three-layered structures to static and cyclic bending

Conclusions The above studies of two types of three-layer structural elements showed that the types have different resistances to static deformation in bending. Regardless of the materials, the use of structures which are symmetrical in regard to stiffness makes it possible to obtain a stiffness and strength for the structure which are 10–15% lower than the stiffness and strength of the external plates if the thickness of the latter does not account for more than 25% of the thickness of the structure. This finding, in turn, permits a substantial reduction in the weight of the structure by the use of a lower-density material for the internal layer. Resistance to static bending is determined mainly by the resistance of the structure to shear stresses. The mechanism of fatigue fracture differs appreciably from the fracture mechanism in static deformation. Regardless of the thickness of the structural elements, fatigue fracture for both types of structure occurs as a result of the acting normal compressive stresses. The endurance limit of the hybrid structure is determined by the fatigue resistance of the external layers, and its value is nearly equal to the resistance of the pure materials.Presented at the Sixth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, November, 1986).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 878–882, September–October, 1986.     

Dynamic properties of some polymer materials in loading and unloading

A series of quasi-static tests have been carried out on kapron fiber, vinyl plastic, and fluoroplastic specimens with small cross sections. Stress-strain diagrams have been obtained at strain rates from 1 · 10^–3 to 1 · 10² sec^–1. In the experiments the strain rate changed sign, which corresponded to loading and unloading. In each regime the strain rate remained constant. The experimental data are analyzed using the model of a standard linear viscoelastic solid.Mekhanika Polimerov, Vol. 3, No. 1, pp. 118–122, 1967