Effect of temperature on the fracture surfaces of filled systems based on SKS-85 butadiene-styrene copolymer

The tear fracture surfaces of mixtures of SKS-85 butadiene — styrene copolymer (85% styrene) with ordinary (carbon black, chalk) and polymeric (Kapron and cellophane powder) fillers have been investigated on the interval from –60 to +40°C. As the temperature varies within the limits of the glassy state (T_g SKS-85=+24°C) of the filled polymer, the nature of the fracture surface of specimens of filled mixtures, like that of the unfilled polymer, changes; in the region of the temperature transition of the copolymer associated with the mobility of the phenyl groups (–10±5°C) there is a slowing of the fracture process. At temperatures below the T_g of the copolymer the tear fracture surfaces of specimens of mixtures containing ordinary and polymeric fillers differ sharply. The introduction of fillers (20 vol. %) with a coefficient of thermal expansion different from that of the filled polymer considerably reduces the resistance of the material to fracture and leads to a sharp increase in the rate of crack propagation; the introduction of polymeric fillers with coefficients of thermal expansion similar to that of the filled polymer leads to an increase in the resistance of the material to fracture and to a decrease in the rate of crack propagation.Moscow Technological Institute of the Meat and Dairy Industry; State Institute of Polymer Adhesives, Kirovakan. Translated from Mekhanika Polimerov, No. 5, pp. 819–826, September–October, 1969.     

Rubber strength as a function of time and temperature

Static fatigue in rubbers is examined as a process of crack development at subcritical loads, with and without changes in the structure of the material. It is shown that the service life depends on the conditions of deformation preceding failure and on the susceptibility of the rubber to strain hardening (crystallization).Mekhanika polimerov, Vol. 1, No. 1, pp. 111–116, 1965     

Experimental study of fracture toughness and energy in composite materials

The paper presents an experimental investigation of fracture characteristics of composite materials. The post-peak response of the load-crack opening displacement of notched specimens is used to evaluate the fracture energy associated with progressive matrix damage and crack growth. Effects of fiber orientation and other geometric characteristics on fracture parameters are studied. The load versus crack opening displacement as well as crack length, fracture toughness, and energy versus the number of loading cycles are obtained for different specimens. Based on the experimental results of this study, concepts of the fracture mechanics are applied to evaluate the evolution of fracture toughness and energy.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Department of Mechanical & Industrial Engineering, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 323–332, May–June, 1998.     

Fracture toughness characteristics of laminated composites

Parameters characterizing the resistance of laminated composites to interlaminar fracture are discussed. The properties of the specific interlaminar fracture work, i.e., the amount of work spent on the formation of a unit of new surface of interlaminar crack, were examined. Taking account of the anisotropy of the material, this work may be characterized using a matrix. Upon change in the direction of crack growth, the matrix elements are transformed similarly to the components of a symmetrical second rank tensor. An interpretation is offered for the matrix elements. The proposed theoretical model was in accord with our experimental results.Moscow Engineering Institute. Technical University, Russia. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 21–31, January–February, 1996.     

Analysis of fracture surfaces in polymethyl methacrylate tested in bending with rotation

Typical fracture surfaces are examined for polymethyl methacrylate specimens subjected to multicycle fatigue testing in circular cantilever bending at T=20, 40, and 60°C. It is established that the fatigue life of smooth specimens is very closely correlated with the size of the diffuse fracture zone. The kinetics of damage accumulation with increase in the number of cycles are investigated by rapidly fracturing prefatigued specimens. The decisive role of diffuse fracture in the fatigue-fracture process is demonstrated. A method of estimating the mean main crack propagation velocity in circular bending is described.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 984–990, November–December, 1973.     

Conditions of the ductile-brittle transition in failure of polymer materials

Conclusions The polymer materials are characterized by the transition from ductile to brittle fracture with increasing loading rate and decreasing temperature. The brittle fracture susceptibility of the material can be determined on the basis of the critical size of the defect/ crack. The measure of the cracking resistance of plastics can often be represented by the material scale of the crack length. The quality of the critical size of the defect/crack to the material scale of the crack length can be used as a criterion determining the conditions of transition from ductile to brittle fracture.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 779–785, September–October, 1988.     

Role of the supermolecular structure of PMM in the morphology of fracture and features introduced by the type of loading

The spherulitic supermolecular structure of PMM, expressed in the fracture surface, determines the fracture pattern and kinetics. The effect of the type of loading on the morphology of the fracture surface is described. Banding of the fracture surface is attributed to periodic energy pulses leading to quasi-brittle fracture at the moving crack front and selective local crack development at the band edges.Riga Lenin Komsomol Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 776–782, September–October, 1968.     

The role of diffusion of aggressive media in the fracture of rubber under stress

Formulas expressing the time to rupture of rubbers in aggressive media were derived in terms of the rate of diffusion of these media and the rate of displacement of the leading boundary of the cracking zone. The effect of increasing stress (due to a reduction in the load-carrying capacity of the specimen cross section) on the long-time strength (according to the Bailey principle) was taken into account in these calculations. The calculated and experimental data are in satisfactory agreement when there is a destructive action of working media in the absence of overstressing due to crack formation and swelling.Mekhanika Polimerov, Vol. 3, No. 4, pp. 708–712, 1967     

Effect of the structure of stereospecific rubbers on their rheological properties

The authors discuss the viscosity properties of stereospecific rubbers and the relationship of these properties to structure. The dynamic characteristics of rubbers have been mearured on a board frequency interval, and it is shown that the moduli of elasticity and loss tangents vary considerably with frequency. The relationship between the rheological characteristics and structure of these rubbers and certain of their technological properties is examined.Mekhanika Polimerov, Vol. 4, No. 3, pp. 387–393, 1968     

Fractographic study of macrocrack propagation in oriented Kapron

The fracture surface of an oriented Kapron monofilament has been studied at electron-microscope and optical magnifications with the object of establishing the details of the micromechanism of crack propagation associated with the fracture of polymeric materials. Microparabolic figures can be observed in the specular zone of the fracture surface. This relief may be assumed to originate in the interaction of the main crack and the submicroscopic cracks present in loaded polymers. In the region of high main-crack velocities it is possible to observe a self-oscillatory motion of the tip of the main crack leading to the formation on the fracture surface of a system of bands parallel to the main crack front.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 645–648, July–August, 1971.     

Stability of cylindrical casings of fiberglass plastic having an elastic filler under the action of axial compression,external pressure,and twisting

The stability of orthotropic cylindrical casings containing a filler is studied under the action of axial compression, external pressure, or twisting. Analogies with plates are established for sufficiently stiff fillers. Simple formulas are obtained for calculating critical stresses which are convenient for practical application.Translated from Mekhanika Polimerov, No. 3, pp. 484–489, May–June, 1974.     

Supersonic crack propagation in blocks of polymethyl methacrylate

It is shown that a giant laser pulse can cause supersonic crack propagation in PMMA. The results of the experiments and a microstructural analysis of the fracture surface are presented. A study of the microstructure shows that supersonic crack propagation is associated with the propagation of a shock wave in the focal region.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1027–1029, November–December, 1971.     

Influence of temperature on frictional properties of highly elastic materials in vacuum under high normal pressures

Experimental results obtained by the rubbing of cross-linked rubbers against smooth steel surfaces in vacuum under volume compression conditions at high normal pressures are examined. The influence of volume compression on the frictional properties of highly elastic materials at various temperatures is explained. Basic rules of temperature functions of specific frictional force at high normal pressures in vacuum and in atmosphere are established.V. I. Lenin Moscow State Pedagogical Institute, Problem Laboratory for Polymer Physics. Translated from Mekhanika Polimerov, No. 1, pp. 91–97, January–February, 1972.     

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     

Some characteristics of the strength properties of crystallizing rubbers at elevated temperatures

A study has been made of the reasons for the considerable scatter of the strength properties and the failure of specimens based on crystallizing rubbers outside the gauge length when tested in accordance with Soviet standard GOST 270-53 at elevated temperatures. The relation between the strength distribution and degree of vulcanization is clarified. It is shown that the strength properties of the product are affected by the thermal prehistory of the rubbers.Mekhanika Polimerov, Vol. 2, No. 1, pp. 82–86, 1966     

Effect of disperse mineral fillers on the strain-strength properties and crack resistance of cured polyesters

Conclusion The tendency of disperse mineral fillers toward aggregation, with the formation of a continuous framework of particles, when filler content is greater than the SCC is manifest in a sharp increase in the difference between the relative viscosity of polyester binder-pastes in the uncured state and the relative elastic modulus in the cured state. It is also manifest in an increase in the relative modulus and a reduction in crack growth energy in cured composites. In this case, there is an especially large increase in the size of the characteristic defect, which ultimately determines the reduction in the breaking stress. The modification of binder-pastes with surfactants increases filler dispersion and makes it possible to increase the strength of cured composites.Presented at the Sixth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, November, 1986).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 819–824, September–October, 1987.     

Effect of fiber length on the strength and fracture properties of a fiber-filled silicone composite

The mechanism by which fillers strengthen polymers is discussed, and the effect of fiber length on static and impact bending strength and on the area of the fracture surface is studied with reference to the example of a silicone composite. A correlation is established between the strength properties and the area of the fracture surface. On the basis of the data obtained it is shown that, as the fiber length increases, the fracture mechanism changes from extraction of the ends of the fibers along the fracture path to breakage of the fibers.Moscow Lomonosov Institute of Fine Chemical Technology. Ter-Gazaryan State Scientific-Research Planning Institute of Polymer Adhesives, Kirovakan. Translated from Mekhanika Polimerov, No. 3, pp. 445–449, May–June, 1971.     

Effect of a vacuum on the adhesion of rubbers to metal

The effect of a vacuum on the adhesion of rubbers to metals has been investigated both when the joints are formed in the vacuum and when joints formed under normal conditions are transferred to a vacuum. A method of estimating the effect of the vacuum, independently of the duration of contact and the contact temperature and pressure used in forming the joint, is described. The results obtained (a sharp increase in adhesion under vacuum) correspond to the theoretical notions of Bikerman concerning weak boundary layers.Central Scientific-Research Laboratory of Chemical Packaging, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1036–1041, November–December, 1973.     

Electron-microscope investigation of the type of fracture of filled polymers

An electron microscope was used to study the type of fracture of filled compositions based on SKN-40, SKMS-30, and SKS-85 polymers with TeG-10 thermal-decomposition black, DG-100 channel black, and chalk fillers. It is shown that in all the cases investigated the filled systems fracture along the polymer-filler interphase boundary.Mekhanika Polimerov, Vol. 3, No. 2, pp. 291–295, 1967     

Investigation of the fatigue properties and susceptibility to damage of thin-walled polymer shells

The results of a study of the damage suffered by thin-walled polymer shells are evaluated on the basis of an analysis of the process of crack formation and the variation of the modulus of elasticity under cyclic deformation. The process of fatigue failure has been studied in relation to shells made of three groups of polymeric materials. It is shown that for the polymers investigated there are at least two different fatigue fracture mechanisms. Data on the crack growth kinetics are presented.Plastopolimer Research and Production Association, Leningrad; Lensovet Leningrad Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1019–1026, November–December, 1971.