Temperature-time dependence of strength of organic fibers based on p-polyamides

Conclusions An experimental investigation of the temperature-time dependence of the strength of organic fibers based on p-polyamides has been performed. The possibility has been established of using the temperature-time analogy method to predict the lifetime of fibers from the results of rapid tests at elevated temperatures. A generalized curve of long-term strength has been constructed, and the coefficient of temperature shear has been determined. An approximation of the experimental long-term strength data has been carried out by a formula which satisfies the temperature-time analogy principle.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 470–473, May–June, 1978.     

Effect of the cellular structure on thermal conductivity of rigid closed-cell foam polymers during long-term aging

The thermal conductivity of rigid closed-cell polyurethane foams during long-term aging has been studied. The similarity between the kinetics of changes in the physical and mechanical characteristics of PU foams on progressive aging is established, which is attributed to the effect of matrix destruction. It is found that rigid foams have cell walls of various strength, whose impact on the kinetics of changes in the physical characteristics of the foams during long-term aging is ascertained. The results of predicting the thermal conductivity of PU foams by the method of temperature-time analogy and establishing the limits of its application are discussed. The research presented is of interest both in determining the foam durability and in replacing freons by alternative, ecologically less harmful blowing agents.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 2, pp. 187–198, March–April, 1999.     

Effect of the cellular structure on thermal conductivity of rigid closed-cell foam polymers during long-term aging

The thermal conductivity of rigid closed-cell polyurethane foams during long-term aging has been studied. The similarity between the kinetics of changes in the physical and mechanical characteristics of PU foams on progressive aging is established, which is attributed to the effect of matrix destruction. It is found that rigid foams have cell walls of various strength, whose impact on the kinetics of changes in the physical characteristics of the foams during long-term aging is ascertained. The results of predicting the thermal conductivity of PU foams by the method of temperature-time analogy and establishing the limits of its application are discussed. The research presented is of interest both in determining the foam durability and in replacing freons by alternative, ecologically less harmful blowing agents.     

The conditions for the existence of a temperature - time analogy

The conditions are formulated for the existence of a temperature-time analogy in stationary temperature fields for hereditary viscoelastic media which are described by Volterra equations of the second kind with a singular relaxation kernel. A time transformation has been found for a nonstationary temperature field which results in the heredity equation becoming invariant with respect to temperature.The M. V. Lomonosov State University. Translated from Mekhanika Polimerov, No. 2, pp. 217–222, March–April, 1970.     

Effect of neutron irradiation on the lifetime of polycaprolactam

On the basis of a study of the temperature-time dependence of polycaprolactam irradiated with thermal neutrons, it has been shown that strength and lifetime and the parameters which determine lifetime vary as functions of the radiation dose.     

A study of the lifetime of impact-resistant polystyrene as a function of the action of external factors

The effect of temperature, oils, and domestic washing agents on the lifetime of type 475-K high-impact polystyrene has been studied. An intermittent character of the temperature-time dependence of strength has been observed. It has been discovered that household fats and cleaning media significantly affect the strength characteristics of high-impact polystyrene; the greatest action is exterted by the simultaneous action of an oily medium, temperature, and stress.V. I. Lenin Tadzhik State University, Dushanbe. Translated from Mekhanika Polimerov, No. 6, pp. 1121–1123, November–December, 1972.     

泥质盐岩单轴蠕变寿命研究

岩石流变力学的研究中，蠕变寿命是一个重要问题.由于长期蠕变试验资料的缺乏，难以估计蠕变破坏时间.该文进行了泥质盐岩单轴全应力 应变压缩试验，并采用陈氏加载法进行了单轴蠕变试验.对蠕变曲线进行了处理，获得了不同应力水平下的蠕变曲线簇，进而得到了等时应力-应变曲线簇.通过拟合分析，建立了等时应力-应变曲线割线模量随时间变化关系模型和等时应力 应变曲线的数学模型.对等时应力 应变曲线与全应力-应变曲线之间的关系进行了分析，获得了蠕变破坏强度和破坏应变分别与蠕变寿命之间的数学表达式.该文研究成果可以估计泥质盐岩的蠕变寿命、长期强度、长期模量、蠕变破坏线和蠕变终止线，对相关岩石流变寿命的估计具有借鉴意义.     

Computer approximation of families of curves of physically nonlinear creep of polymer materials

The determination of confidence intervals of deformations was studied for an individual measurement and arithmetical mean common for all points of an experimental family of curves. From the experimental data on the creep of polyamide resin and five different analytical equations of physically nonlinear creep, the problems of the computer approximation of families of creep curves and the determination of the material parameters are discussed. A method is proposed for a quantitative evaluation of the degree of correspondence of the initial data to the similarity of isochronous creep curves and the similarity of the creep curves.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 220–229, March–April, 1976.     

Problem associated with the efficiency of parametric methods used in evaluating the long-term strength of fiberglasses

Conclusions 1. The feasibility of using the Larson-Miller parameter for accelerated evaluation of the long-term bending strength of fiberglasses is analyzed. The inadequate effectiveness of this parameter for predicting _lt ^T is demonstrated by statistical processing of test results.2. The possibility of using the Goldfein parametric method to extrapolate long-term strength is studied. Values of the quantities T₀, c, andlog _st, which enter into the Goldfein parameter, are evaluated and defined more precisely.3. The efficiency of the Goldfein parametric method in predicting the long-term strength of various fiberglasses subjected to both bending and compression is demonstrated; this will make it possible to consider this method effective for accelerated evaluation of _lt ^T in cases where the binder plays an active role in supporting a load.All-Union Scientific-Research Institute of Fiberglasses and Glass Fiber, Moscow Region. Translated from Mekhanika Polimerov, No. 4, pp. 645–652, July–August, 1978.     

Polymer fractography and fracture kinetics

The fractographic method makes it possible to determine the test temperature and time at which anomalies appear in the temperature-time dependence of the strength of polymethyl methacrylate and polycaprolactam by finding the conditions of disappearance of specular zones from the fracture surfaces of these polymers. For PMMA these values are –40°C and 10^–2 sec, for PCL –120°C and 10^–7 sec, respectively.For communication 1 see [2].Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 232–237, March–April, 1971.     

Equilong-term strength surfaces of organic textolite in the plane stressed state

Conclusion Long-term strength tests of textolite were conducted for seven different particular cases of the plane stressed state. Maximum times to failure for which experimental data were obtained reach 2500 h. It is established from analysis of the test results that the experimental long-term strength curves for the types of stressed state under consideration are closely similar. The condition of long-term strength in the general case of the plane stressed state for constant levels of stresses is taken as the equation of the short-term strength surface in which the time factor is introduced parametrically; in this case, the apparent observance of similarity between equilong-term strength surfaces makes it possible to express the tensor components characterizing the long-term strength by tensor components of the short-term strength surface and a certain monotonically decreasing time function, which is independent of the form of stressed state.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 51–56, January–February, 1979.     

Integrable Equations Arising from Motions of Plane Curves. II

Integrable equations satisfied by the curvature of plane curves or curves on the real line under inextensible motions in some Klein geometries are identified. These include the Euclidean, similarity, and projective geometries on the real line, and restricted conformal, conformal, and projective geometries in the plane. Together with Chou and Qu [Physica D 162 (2002), 9–33], we determine inextensible motions and their associated integrable equations in all Klein geometries in the plane. The relations between several pairs of these geometries provide a natural geometric explanation of the existence of transformations of Miura and Cole-Hopf type.     

An evaluation of the activators of static polymer fatigue

In conformity with the kinetic theory [1, 2] a generalized temperature-time dependence of the brittle strength of isotropic polymers is obtained on the basis of a phenomenological model [7]. A quantitative relation between mechanical and thermal degradation is established.Special Design Office for Automation in Petroleum Refining and Petrochemistry, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 654–667, July–August, 1970.     

Prediction of long-term creep of low-density polyethylene

The time-temperature superposition principle is used to obtain generalized compliance curves for predicting the long-term isothermal creep of low-density polyethylene. It is established that the long-term creep is predicted with an accuracy at least 16% (P=0.99) with a reduction in test duration by a factor of more than 50. An attempt is made to extend the time-temperature superposition principle to include estimates of the nonisothermal compliances associated with thermal cycling based on the isothermal curves. It is shown that this method is not accurate enough to predict the long-term nonisothermal creep, the discrepancy being statistically significant and increasing with time.Mekhanika Polimerov, Vol. 4, No. 1, pp. 24–33, 1968     

One model of a nonlinear viscoelastic medium,taking into account the influence of accumulated damage

We have proposed extremely simple equations for the state of a nonlinear viscoelastic medium of the inherent type, containing the scalar function of the accumulated damage as one of the decisive parameters. The equations take into account the influence of the type of stress pattern; they also contain the long-term strength condition. Equations of this type permit determination of the stress and deformation patterns developing immediately before failure, which is very important for experimental verification of the theory of long-term strength. The proposed model also takes into account the aging of the material.M. V. Lomonosov Moscow State University. Translated from Mekhanika Polimerov, Vol. 8, No. 2, pp. 241–246, March–April, 1972.     

Prediction of changes in the strength of filled thermoplastics upon aging in an oxidizing atmosphere

Problems related to analyzing specimens with damaged surface layers have been examined using polyamide, trioxane—dioxolane copolymer, and polycarbonate as source materials. A model was developed for the brittle fracture of block specimens with damaged surface layers, which provides an estimate of the restraints to plastic deformation in these layers. Three segments are seen in the strength—time curves featuring 1) increasing strength, 2) decreased strength with brittle fracture, and 3) constant low strength. The strength of filled specimens of a specific period permits us to evaluate the effect of the filler on the fracture resistance of the matrix. A method was proposed for predicting the strength of filled samples using the matrix aging data.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 3, pp. 375–380, May–June, 1993.     

Multifibre polymer composites: Prediction of deformation and thermophysical properties

Conclusions A theoretical and experimental investigation was carried out to examine the possibilities of a structural approach for prediction of elastic constants, creep functions and thermophysical characteristics of hybrid polymer composites reinforced with anisotropic fibres of several types. The theoretical solutions were obtained by generalizing the self-consistent method for the case of a three phase model. The effects of brittle fibre breakdown under tension in the direction of reinforcement of a unidirectional hybrid composite were studied under conditions of a short-term loading and a long-term creep. It has been shown that a creep of viscoelastic fibres plays a principal role in creep of the hybrid composite. It is just this creep that significantly increases the fibre damage during creep of the composite.A variant of the solution has been proposed for predicting the thermorheologically complex behavior of hybrid composites containing not only elastic but also viscoelastic thermorheologically simple components with different temperature-time shift factors. The peculiarities of thermal expansion of hybrid composites and the possibilities for a purposeful control of thermal expansion coefficients by hybridization were studied. The considered thermal interval included a region of transition of the polymer matrix from a glass state into a viscoelastic one.The control tests were performed for specimens of organic/glass, organic/carbon, glass/carbon and organic/boron polymer composites with different ratios of fibre volume contents. On the whole, the obtained accuracy of predicting the characteristics of the examined hybrid composites may be considered as acceptable for engineering applications.Published in Mekhanika Kompozitnykh Materialov, Vol. 30, No. 3, pp. 299–313, May–June, 1994.     

Viscous properties of amorphous polymers at longitudinal flow under constant rates of tensioning and deformation conditions

The lowest Troutonian viscosities and Troutonian branches of the longitudinal flow curves of polystyrene were determined at various kinematic and temperature conditions of the tensioning process. The temperature dependence of the longitudinal viscosity was examined, and a generalized temperature-time characteristic of the tensioning was obtained.     

Temperature-time analogy applied to thermorheologically complex polymer materials. 2. Mixtures of thermoplastic and thermosetting polymers (polymer-oligomer composites)

Conclusions 1. Stress-relaxation curves have been obtained for polymer-oligomer composites over a wide temperature range, and the temperature-time characteristics of properties of mixtures have been analyzed. The effect of each component on the mechanical characteristics of a mixture has also been examined.2. We have studied the temperature depenence of viscoelastic properties of mixtures of tetrafluoroethylene and vinylidene fluoride copolymer with epoxide-diphenylene propane resin. We have demonstrated that polymer-oligomer composites do not conform to the concept of thermorheologically simple behavior.3. The parameters of the temperature-time analogy were calculated with the aid of a computer for polymer-oligomer composites, examples of thermorheologically complex materials. It has been established, as a result, that the reduction factor depends strongly on time and the relaxation function depends strongly on the ratio of components.For communication 1, see [7].Okhtinsk Scientific-Industrial Combine, Plastpolimer, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 430–434, May–June, 1978.     

Symplectic invariants for curves and integrable systems in similarity symplectic geometry

In this paper, similarity symplectic geometry for curves is proposed and studied. Explicit expressions of the symplectic invariants, Frenet frame and Frenet formulae for curves in similarity symplectic geometry are obtained by using the equivariant moving frame method. The relationships between the Euclidean symplectic invariants, Frenet frame, Frenet formulae and the similarity symplectic invariants, Frenet frame, Frenet formulae for curves are established. Invariant curve flows in four-dimensional similarity symplectic geometry are also studied. It is shown that certain intrinsic invariant curve flows in four-dimensional similarity symplectic geometry are related to the integrable Burgers and matrix Burgers equations.