Determination of the modulus of elasticity of the amorphous regions of chemical fibers

A method of calculating the orientation index and modulus of elasticity of the elements of a two-phase fiber model is presented. The effect of orientational drawing on the variation of these characteristics has been investigated for nylon [capron] fibers.Mekhanika Polimerov, Vol. 3, No. 3, pp. 409–412, 1967     

Investigation of the stability of the physicomechanical properties of carbon fibers 1. Dependence of Young's modulus on the cross-sectional area of the fiber

The modulus of elasticity in tension and the density of various carbon fibers (re-inforcement for high-modulus carbon-reinforced plastics) have been studied. There is an experimentally confirmed dependence of the modulus of elasticity on the orientation and density of the monofilament which explains the variation of this characteristic in a fiber bundle. It is shown that the principal factor determining the modulus of elasticity and its stability in a bundle of carbon fibers is the orientation and its variation for the individual fibers.     

Vibration using for the longitudinal elasticity modulus determination

Longitudinal elasticity modulus, E, is a material specific feature, which,. in general, is establish on the pieces by longitudinal stress. This procedure is possible to apply to the compact material but not to the sintered power parts (or porous material test pieces). For sintered parts, the establishing of Young's modulus, in this paper, it is proposed by transmition of mechanical vibrations along to the test pieces. The test pieces of compact or porous material were strained at longitudinal vibrations. It was establish the linkage between vibration and density, respective between the density and the value of the longitudinal elasticity modulus. Using the test pieces of compact material we realized the methodology to obtain the longitudinal elasticity modulus regarding the compact material, and in this way can be establish the possibility to measure with a good result the longitudinal elasticity modulus for the pieces of sintered powders or of porous material. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ultrasonic determination of the modulus of elasticity of heat-treated thermosets

The results of an ultrasonic investigation of the modulus of elasticity of K-18-2-TsS and K-18-22 phenolics, before and after heat treatment, are examined.     

Determination of the complex modulus of elasticity of soft viscoelastic materials

A method of determining the complex modulus of elasticity of soft viscoelastic materials is proposed. This method is based on the measurement of the dynamic characteristics of a three-layer symmetrical bar, in which the investigated material forms the middle layer, and on the subsequent calculation of the characteristics of the soft material from the experimental data obtained.N. E. Zhukovskii Central Aerohydrodynamics Institute, Moscow Branch. Translated from Mekhanika Polimerov, No. 1, pp. 178–181, January–February, 1976.     

Optimization of a member with variable modulus of elasticity

The problem of the optimal (from the weight standpoint) law of longitudinal variation of the modulus of elasticity is considered with reference to a member in axial compression when the limit state is reached as a result of loss of stability. Constraints are imposed on the modulus of elasticity. The problem is solved with the aid of the apparatus of the generalized maximum principle.     

Relation between the temperature and deformation dependences of the modulus of elasticity

An analysis of the temperature and deformation dependences of the modulus of elasticity and the rate of stress relaxation has revealed the existence of a strain-temperature analogy. It is suggested that the physical significance of this analogy is associated with the change of volume. The experimental expression of the temperature and deformation dependences of the modulus in terms of change of volume leads to coincidence of the curves in the region above T_g, which confirms the correctness of the conclusion that the temperature-strain equivalence may be associated with the volume changes in that region.     

Investigation of the structure of carbon fibers by means of the scanning electron microscope

The structure of carbon fibers based on hydrated cellulose and polyacrylonitrile after heat treatment between 800 and 3000°C and of carbonized fibers based on polyacrylonitrile, submitted to oxidation in air, was investigated. It was established that significant changes in the surface structure occur after heat treatment at 2600°C and above. Structural changes in the carbonized fibers after various degrees of oxidation were demonstrated. Additional data were obtained on the change in the surface structure and the formation of a porous structure in carbon materials during oxidation under certain conditions.Translated from Mekhanika Polimerov, No. 5, pp. 925–926, September–October, 1972.     

On the anisotropy of multiwalled nanotubes and high modulus fibers

This paper attempts to explain the significant anisotropy of boron and carbon fibers by the presence of primary sliding planes, microinhomogeneities in the presence of viscous friction at the contacts between the layers composing a fiber. The averaging problem is considered using the Bakhvalov method for a multiwalled carbon nanotube with cylindrical anisotropy.     

Internal friction and shear modulus of carbonized fibers

Results are presented from a study of internal friction and shear mdulus of fibers with-drawn at various stages in preparation — starting fibers, oxidized fibers, and carbonized fibers. A considerable difference in the relaxation spectra of these fibers is noted, which may be useful in choosing optimum regimes for the preparation of carbonized fibers based on polyacrylonitrile.     

Generalized thermoelasticity with temperature dependent modulus of elasticity under three theories

A new model of generalized thermoelasticity equations for isotropic media with temperature-dependent mechanical properties is established. The modulus of elasticity is taken as a linear function of reference temperature. The present model is described both generalizations, Lord-Shulman (L-S) theory with one relaxation time and Green-Lindsay (G-L) with two relaxation times, as well as the coupled theory, instantaneously. The method of the matrix exponential, which constitutes the basis of the state space approach of modern control theory, applied to two-dimensional equations. Laplace and Fourier integral transforms are used. The resulting formulation is applied to a problem of a thick plate subject to heating on parts of the upper and lower surfaces of the plate that varies exponentially with time. Numerical results are given and illustrated graphically for the problem considered. A comparison was made with the results obtained in case of temperature-independent modulus of elasticity in each theory.     

Method of determining the modulus of elasticity of epoxies in the initial stages of cure

A method is proposed for determining the temperature-time dependence of the modulus of elasticity of epoxies in the early stages of cure. The kinetics of the time dependence of the modulus of elasticity during the cure are investigated for four epoxy compounds. It is shown that for the polymers investigated the modulus of elasticity characterizes the degree of cure.Technological Institute of the Refrigeration Industry, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 163–165, January–February, 1970.     

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.     

Correlation of the elastic characteristics of Arimid PM with the elasticity modulus of its crystal lattice

Studies were made of the elastic characteristics (longitudinal elasticity modulus, elastic recovery) of Arimid PM fibers and of the longitudinal elasticity modulus of the crystal lattice of these samples. The elasticity modulus of the crystallites was determined by x-ray diffraction studies of loaded fibers. It is shown that the studied samples practically instanteneously recover their starting length after removing the load; the sample and its crystal lattice have comparatively low elasticity moduli with nearly identical values. Based on this data, reasons are discussed for the high elastic recovery of Arimid fibers and for the low elasticity modulus of its crystal lattice.Leningrad Branch, All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 5, pp. 771–773, September–October, 1972.     

Effect of a dispersed filler on the modulus of elasticity of composites in the glassy state

An expression is proposed for predicting the reinforcement of composites by a dispersed filler in both the rubbery and glassy states with allowance for the internal thermal stresses in the polymer matrix. It is shown that by varying the plasticizer concentration in composites based on polyvinyl chloride it is possible to regulate the thermal stresses in the polymer matrix. The time-stress and time-concentration superposition principles are shown to be applicable to the dependence of the relative modulus of elasticity on filler concentration for glassy composites.     

Effect of fiber curvature on the modulus of elasticity for unidirectional glass-reinforced plastics in tension

The effect of curvature of the fibers on the modulus of elasticity of unidirectional glass-reinforced plastics (GRP) in tension has been investigated on the basis of the theory of layered reinforced media with random initial irregularities [1,2]. It is shown experimentally that relatively minor distortion of the fibers during manufacture may result in important changes in the modulus of elasticity. A model is proposed for determining the effect of fiber curvature on Young's modulus; experiments on specimens with a given regular fiber curvature indicate good agreement with the theory. The effect of prestressing the fibers on the modulus of elasticity has been studied using commercial AG-4S material and the optimum prestress has been established.Mekhanika Polimerov, Vol. 3, No. 2, pp. 243–249, 1967