A study of the causes of the reduced strength of glass-reinforced phenolformaldehyde plastics

A study of the curing kinetics of phenolformaldehyde resin in the presence of glass and quartz has shown that one of the chief causes of the reduced strength of glass-reinforced plastics based on phenol-formal-dehyde resin is the difference in the rate and degree of cure in layers close to the fibers and in the bulk of the resin. This is caused by the presence on the surface of the fibers of a hydrate sheath with increased concentration of hydroxyl ions and by the presence of hydrogen bonds between the oxyphenyl groups of the resin and the silanol groups on the surface of the fibers. Chemical treatment of the glass fibers has the effect of diminishing those factors responsible for the reduced rate and degree of cure, and in spite of the lower surface energy of the fibers, the strength of the glass-reinforced plastic increases.Mekhanika Polimerov, Vol. 1, No. 3. pp. 8–14, 1965     

Stresses in various resins cured on glass films

By using Sanzharovskii's method for determining the stresses in lacquer coatings and employing as a model a layer of resin deposited on a glass film, it is possible to simulate the processes that take place in glass-reinforced plastics and determine the stresses that develop in different resins cured under various conditions. The method proposed makes it possible to estimate the effect on the stresses of the shrinkage of the resin, its elasticity, and the difference in the coefficients of thermal expansion of the resin and the glass. Such an investigation is desirable before selecting the composition of the resin, additional organic or mineral fillers and elasticizers, and the optimal curing regime for glass-reinforced plastics.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 481–486, May–June, 1969.     

Effect of elevated temperatures on the strength of cured resins and resin-based materials

Measurement of the loss of weight and ultimate compressive strength of phenol-formaldehyde resins under the influence of elevated temperatures has shown that during thermal degradation there is an abrupt transition from a first to a second and third structural stage with steadily increasing stabilization of the strength properties. Apart from the dependence on the heat treatment conditions, all the resins investigated were found to give a straight-line relation between the relative change in ultimate compressive strength and the relative change in weight for each structural stage. The investigation was conducted on standard specimens obtained by molding a mixture of hardening resin and the same resin in precured powdered form.     

Reinforcement of epoxy compounds with fillers

The mechanical and physicochemical properties of epoxy compounds containing different amounts of a series of fillers have been investigated. The strength characteristics of compounds with reinforcing fillers improve, starting from very low concentrations, pass through a maximum, and then fall at large concentrations. In the case of nonreinforcing fillers, the strength falls, slowly at first, and then, beyond a certain critical concentration, much more rapidly. Electron microscope studies have shown that reinforcement of the resin is associated with deep-seated changes in supramolecular structure, which passes from globular to partially fibrillar when the resin is cured in the presence of fillers. On the basis of the studied concentration laws a method is proposed for characterizing the reinforcing effect of fillers with respect to the particular property tested and a given production technology.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1060–1065, 1967     

Glass-reinforced plastics based on matrices combining thermoplastics and thermosetting plastics

The conditions of fabrication and the physicomechanical properties of glass-reinforced plastics based on polysulfone combined in different ratios with epoxy resin and Rolivsan were investigated. It was found that realization of the strength of the fibers in glass-reinforced plastics based on three types of binders and mixtures of them at room temperature is approximately the same. The lower strength of glass-reinforced plastics based on polysulfone is determined by the lower concentration of fibers. Modification of thermosetting plastics with polysulfone significantly increases (by 5–8 times) the specific energy of delamination of the glass-reinforced plastics G_1c, which should be manifested by an increase in their crack resistance and other operating characteristics. Modification of ED-20 with polysulfone and polysulfone with Rolivsan significantly increases the glass transition temperature of the polymer and affects the character of the temperature curves of the strength of the glass-reinforced plastics.Institute of Chemical Physics, Russian Academy of Sciences, Moscow. D. I. Mendeleev Russian Chemical Technological University, Moscow. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 111–117, January–February, 1996.     

Effect of boundary-layer processes on the strength of glass-reinforced plastics

It is shown experimentally that the strength of glass-reinforced plastics is determined by the properties of the resin close to the fibers; these depend on the structure and chemical composition of the fiber surface. A study is made of the effect of modification of the glass fiber on curing conditions in the layer next to the fiber for a number of resins (K9 silicone resin, ED-6 epoxy resin, polyacrylate-911, and furfural PF resin).Mekhanika polimerov, Vol. 1, No. 1, pp. 26–35, 1965     

Creep and long-time strength of unidirectional reinforced plastics in compression

An attempt is made to predict the creep and long-time strength of unidirectional reinforced plastics in compression in the direction of the reinforcement from the properties of the components. The reinforcement is assumed to be elastic, while the resin is described by a Boltzmann-Volterraintegral equation with fractional-exponential Rabotnov kernel. Experimentally obtained creep and long-time strength curves are presented for unidirectional reinforced plastics.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 830–835, September–October, 1970.     

Influence of nanofillers on the thermal and mechanical behavior of DGEBA-based adhesives for bonded-in timber connections

Results of an experimental investigation into the thermal behavior and mechanical properties of a room-temperature-cured epoxy adhesive (diglycidyl ether of bisphenol A, DGEBA) cross-linked with polyetheramines and filled with different fillers, namely nanosilica, liquid rubber (CTBN), and clay, are reported. The nanosilica and liquid rubber increased the flexural strength and elastic modulus of the adhesive systems; the addition of clay particles raised the elastic modulus significantly, but embrittled the adhesive. Establishing a correct cure time is very important for bonded-in timber structures, as it will affect the bond strength. A study on the effect of cure time on the flexural strength was carried out, from which it follows that the adhesives should be cured for at least 20 days at room temperature. The damping characteristics and the glass-transition temperature of the adhesives were determined by using a dynamic mechanical thermal analysis. The results showed that the filled adhesives had a higher storage modulus, which was in agreement with the elastic moduli determined from static bending tests. The introduction of the fillers increased its glass-transition temperature considerably. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 599–614, September–October, 2006.     

Effect of certain technical and geometric factors on the properties of glass-reinforced plastics

Experimental data are used as the basis for a discussion of some of the technical factors affecting the strength of filament-wound glass-reinforced plastics (GRP): winding speed, tension on the glass, life of resin. A relationship between the strength of GRP and these factors is demonstrated. The effect of the thickness and diameter of the test piece on the tensile strength of GRP material is examined.Mekhanika Polimerov, Vol. 3, No. 1, pp. 99–103, 1967     

Behavior of antifrictional self-lubricating plastics at elevated temperatures in the friction process

Conclusions 1. The process of friction of antifrictional self-lubricating plastics based on F-1 polyarylate and various fillers has been studied. It has been shown that a distinctive feature of this process is the formation of a film of the same composition as that of the antifrictional plastic on the steel surface.2. It has been shown that during the process of friction of antifrictional self-lubricating plastics both structural changes in the mobybdenum disulfide and also tribochemical transformations of molybdenum disulfide and copper, plus reaction of these with the counterbody material, take place in the surface films.3. It has been found that the nature of the tribochemical transformations depends on the chemical composition of the antifrictional self-lubricating plastic and affects the temperature limits of the friction zones.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 649–657, July–August, 1976.     

Investigation of the adhesion strength of carbamide resins

The adhesion of carbamide resin to clean or treated fiber glass surfaces has been determined. The effect of this adhesion on the strength of glass-reinforced plastics is examined.Moscow Mendeleev Chemical Engineering Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1119–1121, November–December, 1968.     

The effect of fullerene fillers on the mechanical properties of polymer nanocomposites

The effect of fullerene and carbon fillers on the mechanical properties of polymer nanocomposites based on thermoreactive (epoxy resin) and thermoplastic (polyamide-12) matrices was investigated. It was found that the introduction of these fillers did not affect the properties of the thermoreactive blends, but Young’s modulus and the tensile strength of the thermoplastic ones increased by about 30-40% upon addition of 0.02-0.08 wt.% fullerene materials. The best results were obtained for a mixture of C ₆₀/C ₇₀.     

Adhesion between Epoxy-Polysulfone Blends and Fibers

The adhesive strength of a fiber-polymer interface is determined, where epoxy resin blends and linear heat-resistant thermoplastics - polysulfone (PSF) and polyetherimide (Ultem) - are used as matrices. Steel wire and polyamide (nylon-6) fibers are taken as reinforcing fillers. It is shown that the addition of PSF to epoxy resin results in a maximum on the concentration curve corresponding to a 10% PSF content. It is also found that the adhesive strength of the ED-20+Ultem-steel wire interface is practically independent of the modifier content under low (up to 10%) Ultem concentrations.     

Numerical simulation of rheological processes in hardening plastics under stress control

The paper concerns the simulation of rheological processes in hardening plastics (resins) under stress control. It is assumed that the resins work in the glassy state, under normal conditions, and the rheological processes are quasi-static and isothermal. The reduced stress levels do not exceed 30% of the instantaneous tensile strength. A resin is modelled as a homogeneous, isotropic, linearly viscoelastic material. The HWKK/H rheological model, developed recently by the author, is used. Short-term, medium-term, and long-term shear strain components are considered and described by one fractional and two normal exponential functions as the stress history (memory) functions. A novel algorithm for the numerical simulation of rheological processes in resins has been developed, which is unified for all stress history functions in the HWKK/H model. The algorithm employs the Boltzmann superposition principle, a virtual table for the classic creep process, and a high-rank Gaussian quadrature. The stress function is approximated with a stair case function. The constitutive equations governing the HWKK/H model are trans formed into an algebraic form suitable for algorithmization. The problem of quasi-exact calculation of the double-improper integral resulting from the fractional exponential function is solved effectively. The algorithm has been tested successfully on selected loading programs of unidirectional tension of epoxide. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 2, pp. 201–212, March–April, 2007.     

Calculation of shrinkage stresses in fibrous composites with regular structure

The effect of the chemical and thermal shrinkage of the epoxy matrix on the structural residual stresses in plastics reinforced with anisotropic fibers has been investigated. The process of residual stress formation in all stages of a given curing regime is examined with reference to a regular triangular fiber distribution. The model of a hardening hypoviscoelastic medium [8] is used to describe the variation of the rheological properties of the matrix. The effect of the cooling rate on the residual stresses is investigated with reference to a single inclusion.Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 3, pp. 409–415, May–June, 1976.     

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.     

Effect of temperature on the mechanical characteristics of carbon plastics reinforced with metal mesh

The behavior of carbon plastics based on FN resin and FN plus rubber and reinforced with metal mesh is investigated over a broad range of temperatures in tension, compression, and pure bending. The presence of a rubbery component considerably reduces the strength of the plastic while improving its deformation properties.Dnepropetrovsk State University. Translated from Mekhanika Polimerov, No. 2, pp. 358–361, March–April, 1971.     

Effect of a filler on the strength properties of thermosets

The effect of a filler on the strength properties of polymers in tension is investigated. The thermostructural stresses that develop in the composite during cure are taken into account. Relations are given for the strength of the filled polymer as a function of the percentage filler content. In the process of analyzing the thermostructural stresses an analytic expression is obtained for the linear expansion coefficient of the composite with allowance for the structural distribution of the components. Calculated values of the strength and thermostructural stresses are presented for composites with different filler contents. The theoretical determination of the strength of filled polymers is compared with the results of experimental investigations of composites based on epoxy resin filled with quartz dust.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 1, pp. 97–101, January–February, 1973.     

Physicomechanical properties of radiation-cured PN-1 polyglycol maleate resin

The radiation and thermochemical methods of crosslinking polyesters are compared with reference to PN-1 resin, commonly used for glass-reinforced plastics. Certain physicomechanical properties of copolymers obtained by the two methods are examined. It is established that the radiation copolymers have greater rigidity and strength.Mekhanika Polimerov, Vol. 3, No. 3, pp. 395–398, 1967     

Effect of fillers on the structure and properties of cured resins

It is shown for the first time that the increased strength of filled plastics is associated with an increase of the internal pressure in the resin determined by the nature of the filler surface and the curing conditions.For communication 1, see [1].Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 54–58, January–February, 1970.