Optimizing selection of a model of the viscoelasticity of synthetic fibres

A method was obtained for numerical solution of the problem concerning the resolvent of the determining integral relaxation and creep equations for the case of nonlinearity of the viscoelastic properties of synthetic fibres. Numerical rotation of the integral relaxation and creep kernels and the corresponding normalized functions in the form of the normalized arctangent of the logarithm of the reduced time allows drawing a conclusion concerning the validity of the choice of a given function as the basis for the model of the viscoelastic properties. The optimality criteria for selection of the mathematical model of the viscoelasticity of synthetic fibres are reported. __________ Translated from Khimicheskie Volokna, No. 6, pp. 58–60, November–December, 2006.     

Modell zur beschreibung der viskoelastischen eigenschaften von synthetischen fasern

The evaluation of the viscoelastic response of synthetic fibres from stress-relaxation data over a wide range of time at different strain rates is very time-consuming. Therefore, mathematical models are used to describe the viscoelastic response. The characteristic of synthetic fibres is that already at very low deformation rates like an elongation < 1% a nonlinear viscoelasticity has to be considered. Based on the analytical representation of isothermal viscoelastic behaviour by Boltzmann a new model making an assertion to the nonlinear viscoelasticity is proposed. Applying this model, the calculated values of moduli and relaxation tensions of the fibres Nomex® and PEEK are in good agreement with the experimental values.     

Systems analysis of the viscoelasticity of polyester fibres

A comprehensive study of the mechanical properties of polyester fibres and other polymeric materials and prediction of deformation processes are only possible with systems analysis of the viscoelasticity of polymers. In determining the mechanical characteristics of polymeric materials and predicting the deformation processes that take place in them, selection of the mathematical model plays a role of no little importance. Although the deformation processes of one group of materials are more accurately predicted with one mathematical model, another mathematical model can be better for another group of materials. The broader the set of mathematical models and corresponding methods, the more accurately the mechanical characteristics of polymers can be determined and the more accurate the prediction of deformation processes will be. Both in selecting the mathematical model and in predicting the mechanical properties of polymeric materials, computerization of the calculations, which ensures reaching a higher level of investigation of the properties of the materials, plays a role of no little importance. __________ Translated from Khimicheskie Volokna, No. 1, pp. 62–65, January–February, 2007.     

Computer study of the viscoelasticity of polymeric materials

The use of mathematical modeling of viscoelasticity combined with computerized methods of predicting viscoelastic processes in synthetic materials increases the accuracy of calculating deformation processes, including deformation-recovery and reverse-relaxation processes, close to the conditions of use of the articles. Computerization of methods of separating the mechanical work of deformation into elastic and scattering components will allow solving problems of calculating the resistance of synthetic materials to impact loads. A computer-integral criterion of the reliability of the prediction is suggested for increasing the reliability of calculating deformation processes in synthetic materials in selecting a variant of normalized relaxation and lag functions. __________ Translated from Khimicheskie Volokna, No. 5, pp. 53–56, September–October, 2006.     

Study of the elastic,viscoelastic, and plastic characteristics of chemical fibres

Methods were developed for dividing the total mechanical work of deformation and the deformation corresponding to it into elastic-reversible and viscoelastic-plastic components which suggests use in both calculation of the resistance of chemical fibres in the dynamic deformation regime and for assessing the ability of materials to resist a mechanical effect and recover the initial shape during use. Incorporation of a coefficient for the irreversibility of deformation allows separating the viscoelastic and plastic components of deformation after the total deformation of chemical fibres is broken down into the constituent components. __________ Translated from Khimicheskie Volokna, No. 6, pp. 52–55, November–December, 2007.     

Automatic control system for spinning and winding of synthetic fibres

An automatic control system for spinning and winding of synthetic fibres that provides for operation of the electric drive of the metering pumps in conditions of stabilization of the melt pressure and rotation rate of the winder drive was proposed. A laboratory bench that simulates operation of the device for controlling spinning and winding of synthetic fibres based on software provided in a microcomputer was created. A parametric, adjustable, asynchronous electric drive from the KPE series which provides for energy-saving conditions was used for the extruder drive. __________ Translated from Khimicheskie Volokna, No. 3, pp. 56–57, May–June, 2007.     

Flow of polymer systems in the viscoelastic state through round capillaries. A rheological analysis

Steady-state flow ofpolymer systems (polymer melts and solutions) in the viscoelastic state is considered the superposition of two processes — flow of a viscous fluid and extrusion of an elastic fluid (elastic state). The dynamic elasticity is proposed for characterizing the elastic properties of polymer systems, and the complex viscosity, which is the total value of the dynamic elasticity and the dynamic viscosity, widely used for assessing viscous properties, is proposed for characterizing the generalized properties, by analogy with periodic deformation. __________ Translated from Khimicheskie Volokna, No. 1, pp. 3–6, January–February, 2006.     

High-strength synthetic fibres for reinforcement of thermoplastic organoplastics for construction. A review

An analysis of the published data shows that the expansion of the areas of application of high-strength synthetic fibres for creating promising thermoplastic organoplastics is due to the use of both new technologies (fibre, maximum reinforcement) and new materials (LC polyesters and fibres based on them, blended fibres of the molecular composite type or composite fibres with a predominant content of a rigid-chain polymer). Almost all of these directions are probably promising for further development and use in production of CM. The maximum tensile strength of organoplastics fabricated by the described methods is approximately the same: 1.1–1.8 GPa, that is, it is close to the indexes for traditional CM, and the advantages are obvious: simplicity of manufacturing technology, high fatigue characteristics, etc. Limiting reinforcement using high-strength thermoplastic synthetic fibres containing flexible-chain thermoplastics produced on the industrial scale to make them inexpensive and give them thermoplasticity without decreasing the strength properties is probably the most attractive. This is a mechanism of creating a fibre having the properties of CM on the molecular level. Translated from Khimicheskie Volokna, No. 3, pp. 44–53, May–June, 1997.     

Determination of the deformation characteristics of polycaproamide fabrics

The applicability of a previously developed fast method of determining the viscoelastic characteristics of synthetic thread with the measured relaxation curve to polycaproamide fabrics was demonstrated. This fast method can be used to model the physicomechanical properties of cloth for goal-oriented solution of problems of the mechanical technology of these fabrics and the study of their properties in use. Translated from Khimicheskie Volokna, No. 1, pp. 37–40, January–February, 1998.     

Experimental study of the thermophysical properties of carbon fibres

A number of thermophysical properties of carbon fibres was investigated. The measurement method, experimental setup, and experimental data obtained at 300–400 K are described. The temperature dependence of the thermal conductivity of carbon fibres is explained based on the phonon model of heat transfer. __________ Translated from Khimicheskie Volokna, No. 4, pp. 16–19, July–August, 2007.     

Effect of preliminary loading on the deformation and strength properties of high-strength fibres

High-strength, high-modulus polyethylene fibres fabricated with gel technology is similar to low-modulus fibres of the olefin and amide series (Capron, polypropylene) with respect to the character of the correlation of the stress—strain diagrams and curve of accumulation of the residual component of deformation. The residual deformation component is relatively large both for high-strength PE fibre and for p-polyamide fibres. The differences in the character of accumulation of the plastic component in these fibres are due to the fact that the residual strains arising in high-strength PE fibre, as in other flexible-chain polymer fibres (polypropylene, Capron) is initiated by breaking of bonds in the main chain. In p-polyamide fibres (Armos, SVM, Terlon, Kevlar), plastic strains arise due to highly elastic deformation “frozen≓ by hydrogen bonds and orientation of molecular chains. Preliminary deformation affects the strength properties of high-modulus fibres differently: in PE fibres, the strength decreases, it increases for Armos and SVM fibres, and remains unchanged for Terlon fibre. This difference is to a great degree due to the difference in the types of intermolecular interaction in fibres of the olefin and amide series. For all fibres investigated, the character of accumulation of the residual deformation component can be correlated with the type of stress—strain diagram, which will allow creating simpler methods of evaluating residual strains. Translated from Khimicheskie Volokna, No. 3, pp. 30–33, May–June, 1998.     

Development of an Automated Design Method for Manufacture of Fabrics of Defined Structure

An automated method of designing technology for manufacturing fabrics of defined structure was developed. An algorithm was developed for calculation of fabrics of defined structure in designing the technology, consisting of determining the properties of the fibres used (tensile and compressive viscoelastic parameters, durability parameters, resistance to wear and repeated loads, hemicyclic characteristics); determination of the coarse fabric structure phase; calculation of warp and weft tension during frontal battening based on use of the linear theory of warp thread fibre tension in the “warp roller—dropper” zone and the weft thread pinch tension based on the linear theory of viscoelasticity; estimation of the loom threading tension using long-term strength criteria; determination of the maximum possible rotation rate of the main loom shaft; calculation of breakage of warp and weft threads based on the assigned properties of the fibres. Software was created for designing loom manufacture. The manufacturing process for production of an important number of fabrics was designed. The basic process parameters for manufacturing fabrics were determined. __________ Translated from Khimicheskie Volokna, No. 5, pp. 35–40, September–October, 2005.     

Effect of the temperature on the structure and mechanical properties of poly(ethylene terephthalate) fibres and yarns

The load—elongation diagrams were obtained for PETP yarns and monofilaments at different deformation temperatures, demonstrating the dependence of the σ(ε) curves on the testing temperature and the thermomechanical history of the samples. The dependences of the basic strain characteristics determined from the σ(ε) curves on the temperature can be used to predict the change in the mechanical properties of PETP yarns and fibres at high temperatures. In addition to the fundamental relaxation transition, the σ(ε) curves can be used to find a new transition in the 180°C region which controls the behavior of PETP yarns and fibres above the transition temperature. The thermomechanical tests and structural studies of the fibres at different temperatures allow correlating the transition found with crystallites and assigning it to an α_c transition based on the characteristic set of properties. St. Petersburg State University of Technology and Design. Translated fromKhimicheskie Volokna, No. 1, pp. 32–35, January–February, 2000.     

Dynamic Relaxation of Synthetic Fibres

The stress regions where amplitude-modulated oscillations (AMO) appear, intensify, weaken, and disappear were determined for PET, Armos, SVM, Terlon synthetic fibres and monofilament PET fibres. The reappearance of AMO caused by the structure of the random copolymer was also found in Armos synthetic fibre. It was found for all fibres investigated that AMO do not appear at temperatures close to the glass transition temperature or any other “softening” point. A method is proposed for determining the temperature after which AMO do not appear. AMO were also not observed in many synthetic fibres (for example, polypropylene, polyethylene) in the devitrified state. The various explanations of AMO with respect to the structural and kinetic features of oriented polymers, related to the inhomogeneity of the supramolecular structure of oriented polymers, combined with the activating effect of an external load on the relaxation spectrum are examined. __________ Translated from Khimicheskie Volokna, No. 4, pp. 44–46, July–August, 2005.     

Simulation of the dynamic compression of polycrystalline Al2O3

A model for the behavior of Al₂O₃ ceramics under dynamic and shock-wave loading is developed on the basis of the model of a Maxwell-type viscoelastic body, which is used here for ceramics for the first time. An equation for the variation in the internal energy for a nonspherical strain tensor and the relation between the time of relaxation of tangential stresses and the state parameters of the medium are derived. The time of relaxation serves to describe the microstructural mechanisms of irreversible deformation. The applicability of the model is validated by comparing the results of solving a number of problems of dynamic and shock-wave deformation with experimental data. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 6, pp. 85–94, November–December 1998.     

Creep and recovery of polypropylene nonwoven material

An increase in both the irreversible component of deformation and the deformation rigidity as the load increases was experimentally established. In modeling the nonlinear viscoelasticity, the increase in rigidity is accounted for by the increasing character of the mean statistical lag time. Due to its small values, only the positive part of the Gaussian distribution (spectrum) of relaxing particles in the material on the relative dimensionless time logarithmic scale is effective in static mechanical effects. The convenience of the proposed version of modeling of nonlinear viscoelasticity consists of the minimum number of parameters in the mathematical model. __________ Translated from Khimicheskie Volokna, No. 1, pp. 65–68, January–February, 2007.     

Computer study of the dynamics of heavy electric spindles

Algorithm and program software for studying the dynamics of heavy electric spindles with the computer developed with a mathematical model is described. The results of a study of the dynamic characteristics of the EVV-04-PTsV-8 electric spindle (dependence of movements and accelerations of the top of the pack on time, winding mass, buffer rigidity, and spindle rotation rate) are reported. The article can be of use to developers of equipment for manufacturing chemical fibres and textile machines, since use of the models and software in the article will cut equipment costs and time in developing designs for winding mechanisms based on heavy electric spindles. __________ Translated from Khimicheskie Volokna, No. 5, pp. 62–65, September–October, 2006.     

Effect of molecular mobility on the deformation characteristics of polycaproamide fibres

The deformation characteristics of PCA fibres are a function of the deformation temperature to a significant degree. The character of the curves of E(ε), E_max(t), σ_b(t), and ε_b(t) indicate a pronounced change in the mechanical properties of PCA fibres not only in “thawing” of segmental mobility in amorphous regions of the polymer, but also in passage of crystallites into the mesomorphic state, which is characterized by pronounced weakening of interchain interactions in the crystallites. The first segment of σ(ε) is only observed in the curves for PCA fibres in the glassy state. In activation of segmental mobility, the σ(ε) curves only contain the second and third segments. St. Petersburg State University of Technology and Design. Translated fromKhimicheskie Volokna, No. 6, pp. 30–31, November–December, 1999.     

Acoustic emission in investigation of the characteristics of fracture of complex viscose fibres and textile materials based on them

Acoustic emission methods were used to study deformation and fracture of viscose fibres, fabrics, and tricots. The effect of twisting and the frictional effect of the filaments in the complex fibre on the character of their fracture and acoustic spectrogram was demonstrated. The study of fracture of fabrics (in stretching and tearing) and tricots based on the character of the acoustic spectrograms revealed a significant difference in them determined by the characteristics of stretching and failure of individual fibres. The method of recording acoustic emission signals in deformation and failure of fibres, fabrics, and tricots combined with the strain diagram before break provides new information on the process of their fracture and the existence of defective structural elements — correspondingly filaments in the complex fibre or complex fibres in textile materials. Translated from Khimicheskie Volokna, No. 6, pp. 43–46, November–December, 1997