Effect of fiber tension on the unwinding resistance of hardening layers of glass-reinforced plastic

The shear fracture toughness characteristics of glass-reinforced plastics used for strengthening metal pressure vessels have been determined by testing metal-GRP rings. The shear fracture toughness characteristics are statistically estimated for a unidirectional GRP as a function of the winding tension.K. É. Tsiolkovskii Moscow Aviation Engineering Institute. Translated from Mekhanika Polimerov, No. 5, pp. 935–938, September–October, 1975.     

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.     

Resistance of wound glass-reinforced plastics to failure by unwinding

The debonding of wound glass-reinforced plastics is examined from the statistical standpoint. The statistical stress intensity distribution function characterizing the fracture toughness is obtained. The effect of defect size on the critical nominal stresses is discussed.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 5, pp. 881–885, September–October, 1969.     

An evaluation of the interlaminar fracture toughness of a thermoplastic composite with offset centre flies

Conclusion The offset DCB specimen has been used to characterize the influence of cooling rate and loading rate on the interlaminar fracture properties of carbon fibre reinforced PEEK. By offsetting the mid-plane fibres by several degrees, the amount of fibre bridging occurring during fracture has been reduced considerably. It has been shown that IM6 carbon fibre PEEK is quite sensitive to the cooling conditions employed after consolidation at 380 °C. Low rates of cooling yield a high level of crystallinity and a reduced fracture toughness. The modified DCB specimen has been successfully applied to highlight a distinct interlaminar fracture rate sensitivity. The high rate properties of this material still leave cause for concern and more work is required before these materials will find widespread use.Published in Mekhanika Kompozitnykh Materialov, No. 4, pp. 476–483, July–August, 1992.     

Dynamic loading of layered composite beams with damage of delamination type

Failure of composite beams containing initial delamination is investigated under low-speed impact by a dropping weight. Bolotin's theory of dynamic failure (1992) is used. The start and stop time of growth of a nonsymmetric delamination crack is studied. It is found that the initial extension starts and subsequently continues at the crack tip, which is located closer to the impact point. Then extension is observed on the second crack tip, and finally a synchronous growth of delamination occurs at both crack tips. With constant impact energy, the final size of delamination does not depend on its initial size. The start and stop time of delamination growth increases as the initial defect approaches the beam surface.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Moscow Power Engineering Institute, Technical University, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 787–794, November–December, 1998.     

Interlaminar Crack Propagation Analysis of ENF Specimens Based on the Cohesive Zone Model北大核心CSCD

Based on the classical laminated plate theory and the cohesive zone model, a theoretical model for general delamination cracked laminates was established for crack propagation of pure mode Ⅱ ENF specimens. Compared with the conventional beam theory, the proposed model fully considered the softening process of the cohesive zone and introduced the nonlinear behavior of ENF specimens before failure. The predicted failure load is smaller than that under the beam theory and closer to the experimental data in literatures. Compared with the beam theory with only fracture toughness considered, the proposed model can simultaneously analyze the influences of the interface strength, the fracture toughness and the initial interface stiffness on the load-displacement curves in ENF tests. The results show that, the interface strength mainly affects the mechanical behavior of specimens before failure, but has no influence on crack propagation. The fracture toughness is the main parameter affecting crack propagation, and the initial interface stiffness only affects the linear elastic loading stage. The cohesive zone length increases with the fracture toughness and decreases with the interface strength. The effect of the interface strength on the cohesive zone length is more obvious than that of the fracture toughness. When the adhesive zone tip reaches the half length of the specimen, the adhesive zone length will decrease to a certain extent. Copyright ©2022 Applied Mathematics and Mechanics. All rights reserved.     

Structure of the set of stationary solutions of phase-lock equations in superconductivity

In previous article [M. Zhan, Phase-lock equations and its connections to Ginzburg–Landau equations of superconductivity, J. Nonlinear Anal. 42 (2000) 1063–1075], we introduced a system of equations (phase-lock equations) to model the superconductivity phenomena. We investigated its connection to Ginzburg–Landau equations and proved the existence and uniqueness of both weak and strong solutions. In this article, we study the steady-state problem associated with the phase-lock equations. We prove that the steady-state problem has multiple solutions and show that the solution set enjoys some structural properties as proved by Foias and Teman for the Navier–Stokes equations in [C. Foias, R. Teman, Structure of the set of stationary solutions of the Navier–Stokes equations, Commun. Pure Appl. Math. XXX (1977) 149–164].     

Sterological modeling and micromechanical analysis of rubber particle-reinforced epoxy composite materials

Some brittle epoxies can be said to be toughened significantly by a dispersion of rubber particles. Several models have been proposed to explained the role of the rubber particles in toughening. In the present research, by introducing the stereological concept based upon the statistical geometry to the microstructural modeling of composites and considering the interfacial phenomena between a matrix and a particle, the micromechanical modeling by means of the generalized equivalent inclusion method is made of the rubber particle-reinforced epoxy composite having the crack bridging particles whose radius are various in size. By analyzing the micromechanical model, the critical length a_c of the matrix crack whose propagation will be arrested, which implies the fracture toughness of such a composite, can be calculated. The effects of the volume fraction of the particles and the variance of the radii of the particles on the toughness can be evaluated. The results obtained are consistent with the common experimental findings.Presented at the Ninth International Conference on the Mechanics of Composite Materials. Riga. October, 1995.Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 3, pp. 317–329, May–June, 1996.     

Statistical laws of fracture and statistical estimation of the static strength of structural elements made from polymeric composites

The basis of the statistical estimation of the strength of structural elements made from fibrous composites is considered; the statistical characteristics of the strength of these materials are described and the limit states are formulated. Special attention is given to the resistance to debonding. The conditions of fracture of this class of materials in plane stress are subjected to a statistical analysis.Presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Aviation Engineering Institute, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 466–482, May–June, 1972.     

Delamination of Grain-Interfaces in Silicon Nitride

Intergranular cracking due to delamination of grain interfaces along with the development of bridging grains is the most important mechanism for the high fracture toughness of silicon nitride. In this line, an interface behavior, which is extending the Coulomb friction concept into the tensile domain has been implemented into a thermodynamical consistent frame work of Helmholtz free energy and dissipation. The model is used to describe the fracture process in a simple model geometry with a β-Si₃N₄ grain embedded into a precracked matrix of oxynitride glass. The material model considers the thermoelastic anisotropy of the grain and the thermal residual stresses, which evolve during the cooling of the model from the glass transition temperature to room temperature. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polymer fatigue from the standpoint of the kinetic theory of fracture

A comparison of the static and cyclic lives of various polymers shows that, whatever the loading regime, fracture may be regarded from the standpoint of the thermal-fluctuation theory. Under comparable test conditions the lifetimes in different loading regimes coincide. The experimentally observed cases of a reduced cyclic as compared with static life do not conflict with the kinetic theory of fracture and can be attributed to hysteresis heating effects or to differences in the structural changes that take place in the test material in different loading regimes.From the standpoint of the kinetic theory, fracture is regarded as a certain process that develops in a body under load and not as a critical event that occurs when a critical stress — ultimate strength — is reached.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 70–96, January–February, 1969.     

Effect of biaxial orientation on the fracture kinetics of polymethyl methacrylate

Biaxially oriented PMM is shown to have important advantages as a structural material over unoriented PMM owing to a difference in fracture kinetics. Under identical conditions primary cracks appear later in the oriented PMM, their growth is impeded, and the rate of crack propagation in the avalanche stage of failure is much lower. This accounts for the greater resistance of biaxially oriented PMM to stress raisers and its higher fracture energy under biaxial loading.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 274–281, March–April, 1969.     

Electron-fractographic investigation of the brittle fracture of polyethylene

The results are presented of an electron-microscope investigation of the brittle fracture of linear polyethylene at the temperature of liquid nitrogen. It is shown that the physical nature of the structural details of the microrelief of the fracture surface is conditioned by local plastic deformation of the stratified lamellar structures in a thin layer adjacent to the fracture surface preceding and accompanying fracture. The possibility of local self-heating is discussed and a possible mechanism of plastic deformation of the crystal platelets at low temperatures is proposed.Mekhanika Polimerov, Vol. 3, No. 2, pp. 286–290, 1967     

Delamination of composite plates under tensile load

Conclusions Among the two configurations discussed, the beam has a rather theoretical importance, as an extension and generalization of the cracked beam problem. Unlike this, embedded delaminations can be found often in real constructions. The fact that the maximum value of SERR vs. fibre orientation angle curve for the circular embedded delamination is surpassed by that for the split beam only by three times and by that for the split beam under mode II loading approximately six times means that an embedded delamination can lead to difficulties when the plate is tensed (or compressed — even in an underbuckled state — within the linear approach the non-opening modes of stress concentration will just change their signs when the load changes its sign), especially under a cyclic loading. Of course, the shell model used is fairly rough and does not take in account several features or real delaminations extension and does not allow one to evaluate properly the stress field near the crack front; thus, more analytical and experimental studies would be needed, to establish the crack development process. The 3D analysis is necessary when initiating delaminations are studied, for the beam/plate assumptions can no longer be regarded as necessary since the delamination linear dimensions are comparable to or less than the thickness of the sublaminate.Published in Mekhanika Kompozitnykh Materialov, Vol. 31, No. 1, pp. 45–50, January–February, 1995.     

Compressive stability of multilayered delaminations in composites

The behavior of defects of the near-surface crack type was investigated in laminated composites. Multilayered delaminations in compressed elements were examined on the assumption that cylindrical bending of the delamination is accompanied by shear within the framework of a model similar to the Timoshenko model. The effect of the mechanical properties and thickness and number of layers in the delaminated section on the critical buckling strain and strain corresponding to the beginning of growth of the delamination was investigated. It was shown that when the delaminated section contains several bearing layers and the rigidity of the composite with respect to interlaminar shear is small, consideration of the shear in the delaminated section can lead to a significant change in the critical compressive strains and/or critical size of the delamination.Translated from Mekhanika Kompozitnykh Materialov. Vol. 33, No. 3, pp. 312–320, May–June, 1997.     

Investigations of interlaminar fracture toughness of laminated polymeric composites

The behavior of interlaminar fracture of fiber reinforced laminated polymeric composites has been investigated in modes I, II, and different mixed mode I/II ratios. The experimental investigations were carried out by using conventional beam specimens and the compound version of the CTS (compact tension shear) specimen. In this study, a compound version of the CTS specimen is used for the first time to determine the interlaminar fracture toughness of composites. In order to verify the results obtained by the CTS tests, conventional beam tests were also carried out. In the beam tests, specimens of double cantilever beam (DCB) and end notched flexure (ENF) were used to obtain the critical rates of the energy release for failure modes I and II. The CTS specimen is used to obtain different mixed mode ratios, from pure mode I to pure mode II, by varying the loading conditions. The highest mixed mode ratio obtained in the experiment was G _I /G _II =60. The data obtained from these tests were analyzed by the finite element method. The separated critical rates G _I and G _II of the energy release were calculated by using the modified virtual crack closure integral (MVCCI) method. The experimental investigations were performed on a unidirectional glass/epoxy composite. The results obtained by the beam and CTS tests were compared. It was found that the interlaminar fracture toughness G _IC ^init of mode I at crack initiation and the corresponding value G _II ^Cinit of mode II obtained by the conventional beam and the CTS tests were in rather good agreement. The experimental results of interlaminar fracture of mixed mode were used to obtain the parameters required for the failure criterion. The two different failure criteria were compared. The best correlation with the experimental data was obtained by using the failure criterion proposed by Wu in 1967 containing linear and quadratic terms of the rates of the energy release.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 307–322, May–June, 1998.     

Structural susceptibility of strength characteristics of polystyrene under uniaxial stretching

The structural susceptibility of the strength characteristics of polystyrene under uniaxial stretching and under test conditions with = const and v_elong = const was studied at 20–100°C. The low structural susceptibility of the durability and durability-equation parameters is due to a change in the elementary fracture volume at different test conditions. It was proposed to characterize the degree of participation of chemical and intermolecular forces by the value U₀/.Moscow Technological Institute of Meat and Milk Industry. Translated from Mekhanika Polimerov, No. 6, pp. 979–984, November–December, 1974.     

Resistance of three-layered structures to static and cyclic bending

Conclusions The above studies of two types of three-layer structural elements showed that the types have different resistances to static deformation in bending. Regardless of the materials, the use of structures which are symmetrical in regard to stiffness makes it possible to obtain a stiffness and strength for the structure which are 10–15% lower than the stiffness and strength of the external plates if the thickness of the latter does not account for more than 25% of the thickness of the structure. This finding, in turn, permits a substantial reduction in the weight of the structure by the use of a lower-density material for the internal layer. Resistance to static bending is determined mainly by the resistance of the structure to shear stresses. The mechanism of fatigue fracture differs appreciably from the fracture mechanism in static deformation. Regardless of the thickness of the structural elements, fatigue fracture for both types of structure occurs as a result of the acting normal compressive stresses. The endurance limit of the hybrid structure is determined by the fatigue resistance of the external layers, and its value is nearly equal to the resistance of the pure materials.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. 878–882, September–October, 1986.     

Structural changes and defect development in epoxy adhesive compounds during thermal aging

The structural characteristics of epoxy adhesive compounds and the development of surface defects during thermal aging have been investigated. Profilograms of the fracture surfaces of bonded joints have been obtained and certain causes of the increased dispersion of the bond strength characteristics explored.Mekhanika Polimerov, Vol. 4, No. 2, pp. 293–295, 1968     

Lifetime levels and fracture of polyethylene terephthalate exposed to γ radiation and an aqueous medium

Conclusion 1. An analysis of the lifetime distribution curves obtained by varying the test conditions has revealed discrete lifetime levels in PETP due to the presence in the material of structural defects with different degrees of dangerousness. These defects are found at the edges, at the surface and in the interior of the specimens.2. Water affects irradiated and unirradiated PETP by reducing the probability of failure, rendering the structural defects less dangerous and, as a result, increasing the lifetime and impeding the fracture process.3. On the dose range investigated, rays affect PETP specimens by causing defects that reduce the lifetime and facilitate the fracture process, the defects produced becoming more dangerous as the dose increases.V. I. Lenin Tadzhik State University, Dushanbe. Translated from Mekhanika Polimerov, No. 6, pp. 1060–1064, November–December, 1978.