Acoustic-optical criteria of analysis of orientation ordering in some fiber forming polymers

Conclusions A correlation was established between the scalar field describing the ordering of the structure and the tensor field characterizing the elastic constants of a material. It was proved that it is possible to use the acoustic and optical criteria for the analysis of the structure of some oriented fiber forming polymers. It was shown that the correlation between the suggested acoustic criteria can be used for optimizing the process of orienting drawing.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 771–775, September–October, 1986.     

Rationalization of the shape of wound membrane shells of revolution composed of high-modulus material

A method of designing composite membrane shells of revolution under axisymmetric loading is described. The properties of the shell material are analyzed. It is shown that for shells of high-modulus material in the presence of tensile membrane stresses the fibers fail in the matrix. A fiber arrangement and shell geometry ensuring isotensoid properties are proposed for this case. A technological and weight analysis is presented.S. Ordzhonikidze Moscow Aviation Institute. Translated from Mekhanika Polimerov, No. 5, pp. 822–828, September–October, 1975.     

Some characteristics of the use of the acoustic emission method in the study of the fragmentation of single fibers in a polymer matrix

Conclusions The energy spectra of acoustic signals during stretching of an epoxy specimen reinforced with carbon fiber and of a pure epoxy matrix differ substantially. Results of a comparison of these spectra make it possible to distinguish acoustic emission signals due to failure of the fiber during stretching of a reinforced composite and to plot curves of the average length of failing fiber fragments as a function of strain.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 734–740, November–December, 1993.     

Effect of hot-drawing conditions on the orientation characteristics of carbon-chain fibers determined by the acoustic method

The orientation characteristics of polypropylene, polyacrylonitrile, and chlorinated PVC fibers, determined by the acoustic method, have been investigated in relation to the fiber drawing conditions (draw ratio, speed, and temperature). It is shown that there is a correlation between the mechanical characteristics and the degree of acoustic anisotropy.Tashkent Institute of the Textile and Light Industries. Translated from Mekhanika Polimerov, No. 3, pp. 552–554, May–June, 1971.     

Investigation of the fiber packing density in a unidirectional composite

Recommendations are made for designing a unidirectional composite with an optimal arrangement of the fibers. The effect of the fiber diameter distribution law on the packing density is investigated.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fiber, Moscow. Moscow Institute of Electronic Machine-Building. Translated from Mekhanika Polimerov, No. 3, pp. 538–541, May–June, 1976.     

Discriminantal Arrangements, Fiber Polytopes and Formality

Manin and Schechtman defined the discriminantal arrangement of a generic hyperplane arrangement as a generalization of the braid arrangement. This paper shows their construction is dual to the fiber zonotope construction of Billera and Sturmfels, and thus makes sense even when the base arrangement is not generic. The hyperplanes, face lattices and intersection lattices of discriminantal arrangements are studied. The discriminantal arrangement over a generic arrangement is shown to be formal (and in some cases 3–formal), though it is in general not free. An example of a free discriminantal arrangement over a generic arrangement is given.     

Scale effect of Young's modulus of highly oriented polymers

The scale effect of the acoustic Young's modulus E of oriented polymer fibers has been experimentally revealed. If the fiber length L is smaller than its critical value L₀, the modulus decreases proportionally to the logarithm of the fiber length. An increasing temperature causes a proportional increase in the slope dE/d(In L). The scale effect is explained by the influence of the specimen volume on the probability of initiation of intense thermal fluctuations, which cause a decline in the Young's modulus.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 839–846, November–December, 1998.     

Analysis of elastomeric composites based on fiber-reinforced systems 3. Two-directional composites

Results of investigation of deformation of elastomeric composite materials with a two-directional reinforcement scheme are presented. The study is performed on the basis of a structural macroscopic theory. The matrix of the composites analyzed is of a poorly compressible material. The fibers of both reinforcing systems are simulated as compressible bodies. Dependences of the parameters of tensile and shear strains on the strain values for different geometries of fiber arrangement are obtained.State Metallurgical Academy of Ukraine, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 4, pp. 479–492, May–June, 1999.     

Modern trends in the development of fibrous composites

The two main trends in the development of high-modulus composites are considered. Improved methods of calculation sensitive to the effects associated with the weak shear and transverse characteristics are reviewed. It is shown that the disadvantages of composites with a traditional arrangement of the reinforcement can be overcome. The properties of boron- and carbon-reinforced plastics with a traditional reinforcement structure are described and compared with those of three-dimensionally structured materials with two- or three-strand reinforcing. Whiskerized fiber reinforcement is also considered. A program of further research on high-modulus composites is outlined.Presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 541–552, May–June, 1972.     

Relation between molecular orientation characteristics determined from birefringence and acoustic data and the effect of orientation on the strength of polycaprolactam fibers

The mean molecular orientation calculated from birefringence and acoustic data has been investigated in relation to the degree of stretching for polycaprolactam fiber. A correlation has been found between the characteristics calculated by these two independent methods. It is shown that the molecular orientation factor calculated from the speed of sound does not depend on crystallinity if the measurements are made below the glass transition temperature. It is confirmed that the strength of the fiber depends importantly on the degree of orientation of the molecular segments in the amorphous zones.Mekhanika Polimerov, Vol. 3, No. 1, pp. 3–7, 1967     

Winding trajectories of noncircular composite shells

An approach has been proposed for determination of the trajectory parameters of a layer formed by winding of continuous ribbons on a complicated surface. An algorithm has been developed for determining the geodesic trajectories of the reinforcement fiber arrangement, reinforcement angles, and geodesic deviation angles. Conditions have been formulated for positional stability of the ribbons on the surface and avoidance of gaps and overlapping between the ribbons along with restrictions to the surface form. Results are given for a calculation of the geodesic turn parameters on a fuselage surface, which is not a surface of revolution, of a light airplane.Translated from Mekhanika Kompozitnikh Materialov, Vol. 30, No. 4, pp. 546–551, July–August, 1994.     

Composites reinforced with a system of three straight mutually orthogonal fibers

The effectiveness of reinforcement in direction 3 has been estimated by investigating the mechanical characteristics of two types of three-dimensionally reinforced materials differing with respect to the arrangement of the reinforcement and the fiber content in each direction. The superior transverse stiffness, shear strength, and transverse tensile strength of three-dimensionally reinforced composites based on a system of three mutually orthogonal fibers, as compared with laminated materials, is demonstrated. The theoretical values of the elastic constants, calculated from the relations of [5], are compared with the experimental data.For communication 1 see [5].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1011–1018, November–December, 1973.     

Optimal reinforcement of a glass-reinforced plastic plate

Relations are derived for the optimal arrangement of the reinforcement in a rectangular glass-reinforced plastic plate supported at the edges and stressed in uniaxial compression by a short-term or long-term, uniformly distributed load. (The optimal arrangement is understood to be that which maximizes the critical load.)All-Union Scientific-Research Institute of Railroad Transport, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 741–744, July–August, 1969.     

Predicting rupture processes in glass plastics by a seismoacoustic method

Experimental curves of acoustic emission (seismoacoustic radiation) are presented for woven glass plastics subjected to brief uniaxial extension along the weft and also along the warp of the reinforcing fiber. Plotted on a logarithmic scale, the acoustic-emission curves exhibit a sharp break. The break in the acoustic-emission curves slightly precedes the break in the – curves.For communication 1 see ref. [6].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 455–459, May–June, 1973.     

Relationship between acoustic emission and development of the damage zone in the interlaminar fracture of fiber composites

A study is made of unidirectional carbon-fiber-reinforced composites with both thermosetting and thermoplastic matrices. Experimental data on acoustic emission for unidirectional fiber composites with a crack is presented in the form of an exponential dependence of the number of AE signals on the stress-intensity factor. The increase in the size of the damage zone across the layers of the composite turns out to be linearly dependent on loading time (and, thus, on K_lc), in contrast to the usual quadratic dependence along the layers.Presented at the IX International Conference on the Mechanics of Composite Materials (Riga, October 1995).Institute of High-Molecular-Weight Compounds of the Russian Academy of Sciences (St. Petersburg).Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 6, pp. 792–796, November–December, 1995.     

Theoretical and experimental investigation of anisotropic damage in textile-reinforced composite structures

In the present work, a phenomenological plane-stress damage-mechanics-based model for textile-reinforced composites is presented and its predictive capability is evaluated by carrying out a series of experimental tests. Damage variables are introduced to describe the evolution of the damage state and, as a subsequence, the degradation of material stiffness. For calculating the nonlinear stress and strain distribution of complexly loaded composites with a textile reinforcement, a special emphasis has to be placed on the interaction between the fiber failure due to the stress in the fiber direction and the matrix failure due to the transverse and shear stresses. This demands the formulation of realistic failure criteria taking into account the microstructural material behavior and different fracture modes. The new failure criteria, like the fracture mode concepts, consider these fracture modes, as well as further fracture types, in the reinforcement plane. The failure criteria are based on equations for failure surfaces in the stress space and damage thresholds in determining the stiffness degradation of the composite. The model proposed was used to characterize the strength and the failure behavior of carbon-fiber-reinforced composites. For this purpose, several unidirectional and bidirectional tests were performed to determine the specific properties of the material. The specimens were investigated by using acoustic emission techniques and strain-controlled tension and torsion tests.Russian translated published in Mekhanika Kompozitnykh Materialov, Vol. 40, No. 6, pp. 791–810, November–December, 2004.     

Dependence of the acoustic and mechanical properties of polyethylene on temperature and cyclic cooling and heating

The low-temperature stability of polyethylene is confirmed by acoustic and mechanical investigations. Data are given on the dependence of the acoustic and mechanical properties of polyethylene on temperature and repeated cyclic cooling to –50° and heating to +60°C, together with information on the change in Poisson's ratio and volume during deformation.Mekhanika Polimerov, Vol. 1, No. 3, pp. 145–150, 1965     

Gauss–Man i n Conne ction s for Arrangements, I E igenvalues

We construct a formal connection on the Aomoto complex of an arrangement of hyperplanes, and use it to study the Gauss–Manin connection for the moduli space of the arrangement in the cohomology of a complex rank one local system. We prove that the eigenvalues of the Gauss–Manin connection are integral linear combinations of the weights which define the local system.     

Evaluation of layered composites by laser optoacoustic transducers

An ultrasonic method for evaluation of composite structures by laser-excited wide-band acoustic pulses is proposed. Two types of laser optoacoustic transducers, in transmission and reflection modes, are used in the spectral range of 0.1–10 MHz. In the first case, the frequency dependence of the attenuation factor of ultrasound is measured. In the reflection mode, the optoacoustic transducer allows us to obtain the time-dependent shape and spectrum of the backscattered acoustic signal with one-sided access to a specimen or product. Specimens of a layered graphite-epoxy composite of different porosity (up to 1.2%) are studied. In the frequency range of 1–5 MHz, the attenuation factor of ultrasound measured in the transmission mode is the greater the higher the porosity of the specimen. The noise part of the backscattered acoustic pulse is found to increase with increasing porosity of the specimens. A 1% growth in porosity causes a threefold increase in the noise power. The results obtained confirm the advantages of the laser optoacoustic method for evaluation of composite materials and products during their manufacturing and operation.International Laser Center, Lomonosov Moscow State University, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 1, pp. 125–134, January–February, 1999.     

Apparatus for fatigue testing glass-reinforced plastic specimens in symmetrical tension-compression at acoustic frequencies

The characteristics of an electromechanical apparatus for fatigue testing glass-reinforced plastic specimens in symmetrical tension-compression at loads up to 10–40 kN and acoustic frequencies on the interval 300–5000 Hz are described.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 525–528, May–June, 1972.