Electron-microscope study of cellulose and Capron fibers with different strenghts

Oriented polymer fibers whose strengths differ by a factor of two have been subjected to an electron-microscope study. Both cellulose (=40 and 75 kgf/mm²) and Capron (=80 and 170 kgf/mm²) fiber were investigated. Specimens were obtained by ultrasonic dispersion followed by negative contrasting of the dispersion products with FVK solution. It is shown that there is no correlation between the transverse dimensions of the microfibrils and the strength of the investigated fibers.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 364–366, March–April, 1971.     

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.     

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.     

Stress on the interatomic bonds near the surface of a polymer

The stresses on the interatomic bonds in the interior and at the surface of polyethylene terephthalate film in uniaxial tension have been determined by means of infrared transmission and reflection spectroscopy. The stresses are found using the shift in the frequency of the atomic vibrations produced by the application of a mechanical load. It is shown that the stresses on some bonds in the specimen reach 700 kgf/mm², i.e., approach their theoretical strength. The concentration of these bonds in a surface layer 1 µ thick is approximately an order greater than the concentration in the interior of the specimen.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 512–514, May–June, 1976.     

Adhesion of polysulfone—Liquid crystalline polymer blends to fibers

The effect of modifying a thermostable thermoplastic matrix with a liquid-crystalline (LC) polymer on its adhesion to fibers was investigated. Poly(arylene sulfone), LC polyether, and blends of them of varying composition were used as the matrices, and high-strength steel wire 150 m in diameter and alkali-free glass fibers 150–300 m in diameter were the substrates. The adhesive shear strength , measured by the pull-out method, was used as the measure of adhesion. The samples were formed at a temperature of T_f=300°C, and the heat treatment time t_f varied from 15 min to 2 h. It was found that when the values of t_f increased, the dependence –t_f was described by a curve with a maximum. The maximum was observed for t_f=30 min. The adhesive strength at the bonds of the poly(arylene sulfone) with the steel wire was sufficiently high (comparable to the adhesive strength of epoxy—4,4-isopropylidenediphenol matrices). The adhesive strength of the LC polyether with the steel wire was much lower. The strength of the interface of poly(arylene sulfone), LC polyether, and blends in bonds with the steel wire was much higher than in bonds with the glass fiber. The adhesive strength of the blends as a function of the concentration of LC polyether was described by a curve with a maximum. The maximum adhesive strength with fibers was provided by matrices containing 2–7% LC polyether.Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 4, pp. 433–442, July–August, 1997.     

Structure and properties of ceramic composites based on ZrO2

Monodisperse fine powders of high purity obtained by sol-gel method are used for production of high technical data ceramics. The fiber reinforcement is used for hardening of composite materials. It was of interest to study production possibility of reinforced composite material based on ZrO₂ obtained by sol-gel method with filler from fibers of partially stabilized zirconia. ZrO₂ powders were obtained by precipitation of its hydrated gel from aqueous zirconium oxychloride solution by ammonium hydroxide followed by thermal treatment. For composite reinforcement ceramic partially stabilized (8 mole Y₂O₃) ZrO₂ fibers 0.16–0.67 mm in length and 5–7 m in diameter were used. Content of the fibers in composite was 20 wt.%. From powders and their mixtures with fibers, the samples were pressed as disks, beams and cylinders, and anneal in air at 1100–1600°C temperature range. The investigation has shown that the fibers of partially stabilized zirconia change the composite structure, increase the content of tetragonal modification that promotes its hardening. Treatment temperature of precursor determines physical chemical properties of compositions with fibers. Their high specific surface and reaction ability provides a workability of forming and sintering processes into strong composite material. The ceramics was increased by 2.5–3 times as strength after fibrous filler introduction into ZrO₂ hydrogel matrix.Presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October 1995).Presented at the Ninth International conference on the Mechanics of Composite Materials (Riga, October 1995). Institute of General and Inorganic Chemistry of the Academy Sciences of the Belarus. Minsk. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 3, pp. 418–427, May–June. 1996.     

On the positivity of certain Cotes numbers

It is shown that the Cotes numbers are nonnegative for some interpolatory quadratic rules with nodes at the zeros of the ultraspherical polynomialsC _n , when integrating with respect to the weight functions w_µ(x)=(1–x²)^µ–1/2.     

Structural characteristics of materials reinforced with high-modulus fibers

Research on the mechanics of boron and carbon-reinforced plastics is briefly reviewed. The design and testing characteristics of these materials associated with the high degree of anisotropy of their elastic properties, as compared with those of glass-reinforced plastics, are discussed. Problems relating to testing at an angle to the direction of the reinforcement, the effect of misorientation and distortion of the fibers, and the consequences of the low shear strength are considered. Experimental confirmation has been obtained by testing unidirectional (1 : 0), orthogonally reinforced (1 : 1 and 2 : 1), and tridirectional (1 : 1 : 1 in the 0°, +60°, and –60° directions) boron and carbon-reinforced plastics.DeceasedInstitute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 676–685, July–August, 1971.     

Dynamic compressive strength of epoxy composites

The strength of laminated and unidirectionally reinforced composite materials was investigated in conditions of dynamic uniaxial compression with a strain rate of 50–1000 sec^–1 using the split Hopkinson pressure bar method. It was shown that in conditions of dynamic compression, glass/epoxy, aramid/epoxy, and carbon/epoxy composites exhibit elastic-brittle behavior with anisotropy of the strength and elastic properties. The effect of the strain rate on the strength characteristics of fiberglass-reinforced plastics was demonstrated.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 6, pp. 776–782, November–December, 1995.Presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October, 1995).     

Failure of water-filled cylindrical glass-reinforced epoxy shells under internal impulsive loading

Conclusions 1. The explosive failure of water-filled, geometrically similar glass-reinforced epoxy shells, whose dimensions increase by a factor of 1.5–4.4, is not associated with an energetic scale effect. This is attributable to the imperfect similarity of the shells, since although their dimensions changed, the diameter of the glass reinforcing fibers remained the same.2. The relative mass of explosive required to fracture the shells is approximately 0.4%. With respect to this index, glass-reinforced epoxy is comparable to structural steels 20 and 17Mn1Si at R₀160 mm.3. The circumferential deformation of the shells at failure is about 4% and does not depend on the thickness of the shell wall, the dimensions of geometrically similar shells, or the initial strain rate on the interval 0.21 · 10³–1.2 · 10³ sec^–1. Thin-walled shells begin to fail from the outside surface, thick-walled shells from the inside surface.4. The modulus of elasticity of the GRE is 2.4 · 10⁵ kgf/cm² and does not depend on the strain rate on the interval 10^–3–1.5 · 10³ sec^–1. The material deforms elastically up to failure.Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 283–289, March–April, 1978.     

Effect of thermal treatment temperature on the structure and properties of carbon fibers

Conclusions 1. It has been shown that the presence of a maximum in the dependence of strength on Young's modulus for carbon fibers made from PAN fiber may be explained by an effect of the process of temperature stress accumulation which takes place under the conditions of isometric heating. The start of this process, which causes a rearrangement of the internal structure of the high-modulus fiber, coincides with the start of the anomalous rise in fiber density.2. The interconnection between surface and internal defects and the elastic-strength properties of carbon fibers made in the temperature treatment range 600–3000°C has been studied.3. Original data on the elastic-strength properties of borided carbon fibers have been obtained; the structure of these is marked by a high degree of perfection. It has been shown that in boriding, which facilitates graphitization of the carbon, the process of regular reduction in fiber strength which is reached in the precrystallization stage is somewhat retarded.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1036–1042, November–December, 1976.     

Changes in the mechanical properties of polyimides induced by electron bombardment

The change in the tensile strength and relative elongation of PM polyimide with absorbed dose has been investigated. It is shown that after irradiation with very large doses (5 · 10¹⁰ rad) the mechanical properties are still satisfactory.Scientific Research Institute of Electrophysical Apparatus, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 1111–1112, November–December, 1969.     

Effect of temperature and strain rate on the adhesion of polyvinyl butyral to glass

The shear strength of silicate glass bonded with polyvinyl butyral has been investigated over a broad temperature interval together with the effect of plasticization of the polymer on the strength of the bond. The _adh ^–t curves have intervals corresponding to adhesion failure, cohesion failure of the substrate, and cohesion failure of the adhesive, respectively. The dependence of adhesion on strain rate has been investigated and a maximum observed at 20 mm/min.Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1104–1107, November–December, 1970.     

Alkali-silica reaction expansions in high-performance and normal-strength cement grouts reinforced with steel and synthetic fibers

The role of brass-coated steel (BCS), hooked steel (HS), and polypropylene fibers in controlling the expansion and cracking in high-performance and normal-strength cement grouts is investigated. The grouts were prepared using the BCS, HS (from 0 to 2.0 vol.%), or polypropylene (from 0 to 0.30 vol.%) fibers. Standard prisms (25 × 25 × 300 mm³) were cast and cured for 40 days before subjecting to a special treatment to accelerate the alkali-silica reaction (ASR). Expansion measurements were taken for these prisms over an immersion period of up to 98 days, during which the extent of cracking was monitored. The results indicated a significant role of brass-coated and hooked steel fibers at volume fractions of 1.0 and 2.0% and polypropylene fibers at a volume fraction of 0.15% in reducing the expansion due to the ASR. The reduction in expansion of high-performance and normal-strength grouts was also dependent, in addition to the fiber type and content, on the duration of immersion of the grouts in a NaOH solution.Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 1, pp. 121– 130, January–February, 2005.     

Choice of optimal structure of glass laminates with random reinforcement. I

The effect of structural parameters — length, diameter, and distribution of the reinforcing elements — on the mechanical characteristics of glass-reinforced plastics is investigated with reference to the case of glass laminates with randomly distributed, straight, uncut glass fibers in parallel planes. It is shown that the reduced strength of these laminates as compared with unidirectional material is associated with the redistribution of the load between the fibers and the resin and the relative reduction in the number of fibers in the cross section. A formula is proposed for estimating the strength of glass-reinforced plastics with a random distribution of the fibers in parallel planes.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fiber, Moscow Region. Moscow Bauman Higher Technical College. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1043–1050, November–December, 1968.     

Scanning electron microscope study of the structure of carbonized polyacrylonitrile fibers

The morphology and physicomechanical properties of carbonized PAN fibers (oxidized and heat-treated to 1500, 2000, and 2750°C) have been studied. It is shown that surface and internal structural defects sharply reduce the values of the physicomechanical characteristics of the carbonized fibers. The scanning electron microscope reveals the nonuniformities of the fiber over the fracture surface and makes it possible to take into account the effect of macro- and microdefects in studying fiber strength.Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Institute of Fossil Fuels, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1122–1124, November–December, 1971.     

Concerning the strength and fracture of thermally aged polycarbonate

The change in the strength, fractography, and supermolecular structure of polycarbonate after thermal aging has been experimentally investigated. It is shown that the fall in the strength of the polycarbonate after aging (T 160°C) is chiefly related with the formation of dangerous defects as a result of the destruction of the supermolecular structure at the surface of the block. It is noted that under the same conditions there is some ordering of the supermolecular structure of the polycarbonate at depths of 150 µ or more, but this has practically no effect on the strength characteristics.Institute of Physicotechnical Problems of Energetics, Academy of Sciences of the Lithuanian SSR, Kaunas. Translated from Mekhanika Polimerov, No. 5, pp. 951–952, September–October, 1971.     

The dynamic properties of polyethylene and an acrylonitrile — Butadiene — Styrene material in a broad range of temperature and strain-rate variation

Conclusions The mechanical properties of an acrylonitrile-butadiene-styrene material and polyethylenes of densities =0.92 and 0.96 g/cm³ are studied within the temperature range of from 100 to –196°C and at strain rates of from 10^–3 to 1.3 · 10³ sec^–1. It is observed that under low-temperature and high-strain-rate conditions, the laws governing the mechanical properties of the acrylonitrile-butadiene-styrene material and polyethylenes are similar. Regions of strain rates and temperatures are found for which the behavior of the test materials is in good agreement with the Ree-Eyring equation, and, consequently, conforms to a temperature-time analogy. No embrittlement of the polyethylene is observed during tests at strain rates to 1.3 · 10³ sec^–1 and temperatures down to –196°C. In approximating these values of and T, the mechanical properties of polyethylenes will cease to be dependent on initial density.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, 1027–1033, November–December, 1978.     

Study of the role of intermolecular interactions (hydrogen bonds) in the initial stage of orientation of polyvinyl alcohol and vinyl alcohol copolymers

The effect of hydrogen bond rupture on the process of destruction of the starting crystallite structure of polyvinyl alcohol and copolymers of vinyl alcohol and N-vinylpyrrolidone and -vinylcaprolactam has been investigated. The differential spectrum method is used to establish the frequency (3200 cm^–1) of the band corresponding to the vibrations of the bound hydroxyl groups; the temperature dependence of the optical density of the 3200 cm^–1 band has been recorded. The strength of the starting structure is calculated from the stress-strain diagram and its temperature dependence is plotted. It is concluded that the strength of the starting structure is chiefly determined by the presence of hydrogen bonds between the polymer macromolecules.Leningrad Kirov Institute of Textile and Light Industry. Translated from Mekhanika Polimerov, No. 2, pp. 327–329, March–April, 1971.     

Properties of multicomponent polymers systems

In order to design materials having different mechanical properties combined with a permittivity of 2.2–2.6 and tg =2·10^–4-4.10^–4 at 20±1° C and 10⁶ Hz, it is possible to use compositions consisting of polystyrene, polyisobutylene and polyethylene. Projections of the three-dimensional triangular composition-property diagrams are presented for selecting the composition corresponding to spcified properties (hardness at 20 and 50° C and breaking stress and elongation).Central Scientific-Research Institute of Communications, Moscow. Moscow Krupskaya Regional Pedagogical Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 133–1135, November–December, 1968.