The effect of hydrostatic pressure on the crack resistance of particulate reinforced composite materials

The effect of hydrostatic pressure on the fracture toughness of disperse-reinforced composite materials is investigated. It is shown that increased hydrostatic pressure leads to an increase in the critical value of the stress intensity factor and, as a consequence, to an increase in the crack propagation rate. In this case, the pressure-time analogy method can be used to describe the effect of hydrostatic pressure on the characteristics of the crack resistance. This method enables us to represent the experimental data obtained in the form of a generalized dependence of the fracture toughness on the reduced loading rate. Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 1, pp. 121–126, January–February, 2000.     

Effect of time-dependent material properties on the crack behavior in the interface of two polymeric materials

Crack penetration through the bimaterial interface of two polymers is investigated numerically. Due to the practical importance of the problem, a crack in a three-layer pipe consisting of a main and two, inner and outer, protective layers is analyzed in this paper. The prime aim is to formulate the conditions under which the crack stays arrested at the interface between the protective layer and the main pipe or penetrates into the interface and causes failure of the main pipe and consequently of the entire pipe system. The crack tip stress field is described by using a generalized stress intensity factor for cases where the crack touches the interface and the stress singularity exponent differs from 1/2. In the case of short-term applications, the stress state on the interface is given simply by a combination of the elastic properties of materials of the main pipe and the protective layers. In long-term applications, the time-dependent properties of the materials can significantly influence the stress state of the interface and can lead to considerable changes in failure conditions. The results presented here may contribute to a more accurate estimation of the residual lifetime of multilayer pipes.     

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.     

An experimental and computational investigation of crack initiation and stable crack growth of ductile materials

Crack initiation and stable crack growth under monotonic loading in steels has been studied using an elastic-plastic finite element analysis. The fracture criterion used for crack initiation and stable crack growth was the critical strain energy density. In addition the shift core method for the analysis of crack extension was used. In the shift core modelling method, crack advance is simulated by moving the coordinates of the core region which surrounds the crack tip, to obtain the stiffness reduction. Simultaneously the core itself geometrically undergoes a simple rigid-body motion or translation during the crack extension. The analytically calculated and experimentally measured load for crack initiation and the subsequent stable crack growth agreed well.     

Comparative microbiological resistance of various self-lubricating materials

Conclusions 1. Self-lubricating materials of the existing range mostly have low resistance to microbial attack.2. This applies especially to the basic components — Kapron, Kaprolon, fluoroplastic, resin bases without fillers.3. The introduction of fillers and binders modifies the resistance of the basic ingredients; filling fluoroplastics, Kapron, and resins with graphite, coke, metals, or alloys considerably improves the resistance of the self-lubricating compound, whereas using certain organic resins (phenol-formaldehyde, urea-formaldehyde) as binders leads to a fall in the microbial resistance of the lubricating coating.4. Lubricating coatings with silicone or inorganic (including silicate) binders, graphite-filled fluoroplastics and metal-filled graphites, carboplastics, polyarylates, and Maslyanits display the greatest ability to resist microbial attack; these materials are chemically unassimilable by the microbial cell. They can be recommended for use in the tropics without an antimicrobial additive.5. Materials with low resistance under tropical conditions require protection with antimicrobial additives. However, whether or not it is advisable to develop an additive depends in each case on the technical justifiability of using the material in question, its cost-effectiveness, and many other factors. In our opinion, it is not worthwhile developing additives for basic materials (fluoroplastic, Kapron, Kaprolon, certain resins) since there are resistant substitutes available (metal-filled graphite, Maslyanits, AMAN, etc.). As for such a promising material as MFPL, with its unique combination of properties, the search for antimicrobial additives appears to us to be both technically and economically justified.Paper presented at the Third All-Union Conference on Polymer Mechanics, Riga (1976).Kiev Technological Institute of the Food Industry. Translated from Mekhanika Polimerov, No. 6, pp. 1011–1016, November–December, 1977.     

Effect of shearing forces on the stressed state of a half space with crack

Using the method of boundary integral equations, we study the stressed state in the neighborhood of a plane crack perpendicular to the boundary of a half space. The crack surfaces are subjected to the action of shearing forces. The problem is reduced to two-dimensional hypersingular integral equations, and their regular kernels, taking into account interaction between the crack and boundary of the half space, are written in explicit form. The dependences of stress intensity factors on the angular coordinate are presented for different loads of the crack. Translated from Matematychni Metody ta Fizyko-Mekhanichni Polya, Vol. 51, No. 1, pp. 112–120, January–March, 2008.     

Effect of hydrostatic pressure on the strength properties of polymer materials

On the assumption that the strength characteristics of homogeneous polymer materials depend on the specific volume, equations are derived for the dependence of the strength or high-elastic limit on the hydrostatic component of the stress tensor and temperature. The ultimate strengths in simple tension, compression and shear are considered in relation to brittle and plastic fracture.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 449–454, May–June, 1969.