Mechanical properties of boron fibers

The distribution of the strength of boron fibers is examined on the basis of a large amount of experimental material. The typical defects are isolated and described. The dependence of the average strength on the length of the test fiber is investigated.State Scientific-Research Institute of Chemistry and Technology of Heteroorganic Compounds, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 641–647, July–August, 1973.     

Effect of temperature on the mechanical properties of boron fibers

The effect of exposure to temperatures on the interval 20–600°C for up to 1000 h on the physicomechanical properties of boron fibers at room temperature has been investigated. Prolonged exposure to temperatures up to 200°C does not have much effect on the mechanical characteristics of the fibers, whereas heating for one hour at 300–350°C increases the strength of the fibers by 10–12%.All-Union Scientific Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 329–332, March–April, 1971.     

Strength and fracture properties of advanced SiC-based fibers

The tensile strength and the fracture properties of advanced SiC-based fibers were characterized, and an extensive fractographic analysis was conducted to correlate their mechanical behavior and microstructure. Tensile tests re vealed that the strength of Hi-Nicalon™ and Hi-Nicalon™ Type S fibers was sensitive to a critical flaw. The inspection of fracture surfaces revealed that the fracture of these fibers originated mainly at the critical flaw, which was surrounded by an obvious mirror zone. The Tyranno™-SA fiber showed a transcrystalline fracture behavior. The different fracture behavior observed in this work could be related to different fabrication processes and compositions at the grain boundary. For the Hi-Nicalon™ and Hi-Nicalon™ Type S fibers, the critical flaw size was linearly related to the mirror size. By using the linear fracture mechanics, the fracture toughness and the critical fracture energy of the fibers were estimated. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 759–770, November–December, 2006.     

Strength and deformability of reinforced polymers in tension normal to the fibers

The strength and deformability of reinforced polymers in tension across the fibers is investigated. It is assumed that the polymer deforms as an ideal elastoplastic body. Relations are obtained for the nature of the deformation of the polymer between the fibers and the strength and deformability of the composite with allowance for the structural distribution of the components. Theoretical stress-strain diagrams are presented for composites with different reinforcement densities and resin elasticities. The theoretical values of the strength and deformation of reinforced polymers with the load applied across the fibers are compared with the results of experiments on model specimens of epoxy-Thiokol polymers.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 682–687, July–August, 1970.     

Strength of adhesion of epoxy polymer to carbon,glass, and steel fibers

A study has been made of the strength of adhesion of epoxy polymer to fibers of various chemical natures, and it has been shown that the magnitude of the adhesion depends not only on the nature of the fiber but also on its surface geometry. Questions are discussed on the effect of residual (internal) stresses arising during the process of heat-treating or cooling samples of bonded articles on the strength of the adhesive bond.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 37–42, January–February, 1974.     

Ramsey degrees of boron tree structures

We investigate the combinatorial properties of the Fraïssé class of structures induced by the leaf sets of boron trees — graph-theoretic binary trees without an assigned root — and compute their Ramsey degrees. The Ramsey degree of a boron tree structure is shown to equal the number of its possible orientations, which are herein defined to depend on the embedding of the said structure. One direction of this computation involves an asymmetric version of the Graham-Rothschild theorem. By expanding these structures to oriented ones, we arrive at a Fraïssé class which possesses the Ramsey property. Consequently, the automorphism group of its Fraïssé limit is extremely amenable, i.e., it possesses a very strong fixed point property. Furthermore, we construct the universal minimal flow of the automorphism group of this limit.     

Morphological characteristics of carbon fibers

Scanning electron microscopy has been used to study the surface, before and after thermochemical treatment, and the fracture sites of PAN carbon fibers heat-treated at 2100°C. The fractographs are analyzed in an attempt to estimate the effect of various defects on the strength of PAN carbon fibers.All-Union Scientific-Research and Design-Technological Institute of Electro-Carbon Products, Moscow Region. Translated from Mekhanika Polimerov, No. 1, pp. 158–160, January–February, 1976.     

Transverse compression of PPTA fibers

Results of single transverse compression testing of PPTA and PIPD fibers, using a novel test device, are presented and discussed. In the tests, short lengths of single fibers are compressed between two parallel, stiff platens. The fiber elastic deformation is analyzed as a Hertzian contact problem. The inelastic deformation is analyzed by elastic-plastic FE simulation and by laser-scanning confocal microscopy of the compressed fibers ex post facto. The results obtained are compared to those in the literature and to the theoretical predictions of PPTA fiber transverse elasticity based on PPTA crystal elasticity.Presented at the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000).3TEX, Inc. 109, MacKenan Drive, Cary, North Carolina 27511, USA. Published in Mekhanika Kompozitnykh Materialov, Vol. 36, No. 4, pp. 533–544, March–April, 2000.     

Experimental identification of chaotic fibers

In a 2D parameter space, by using nine experimental time series of a Chua’s circuit, we characterized three codimension-1 chaotic fibers parallel to a period-3 window. To show the local preservation of the properties of the chaotic attractors in each fiber, we applied the closed return technique and two distinct topological methods. With the first topological method we calculated the linking numbers in the sets of unstable periodic orbits, and with the second one we obtained the symbolic planes and the topological entropies by applying symbolic dynamic analysis.