Dynamic adhesive strength of fiber-polymer systems

A new device for studying the dynamic adhesive strength is created. A procedure for determining the dynamic adhesive strength in fiber—polymer systems under impact loading (pull-out technique) is developed. The adhesive strength of the interface of polymer—steel wire joints formed by polymers of different chemical nature (epoxy resin, polysulfone, and polypropylene) is examined. It is shown that the dynamic adhesive strength grows as the loading rate increases for all the systems under investigation and that the relationship between the adhesive strength and the loading rate, , over a wide range of rates can be described by two straight lines corresponding to the quasi-static and impact loading, respectively. When passing from the quasi-static to dynamic loading, the character of scale relations of the adhesive strength does not change.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 6, pp. 689–700, November–December, 1999.     

Analysis of the adhesive strength variance in expoxy matrix-boron fiber joints

A new approach to the problem of adhesive joint failure based on the study of the scale effect of the adhesive strength variance is applied to an epoxy matrix-boron fiber system. The shear adhesive strengh is measured using the pull-out technique. It is found that the variance D practically does not depend on the joint area S, whereas the adhesive strength markedly decreases with increase in S. It is noted that the scatter of the values of by far exceeds the experimental errors. The –S and D–S curves obtained behave similarly to the corresponding curves for EDT-10-steel wire joints. The independence of D from S confirms the concept that the failure of fiber-polymer joints in pull-out tests starts near the end of the joint at which the external force is applied. An analysis of the adhesive strength distribution curves within sufficiently narrow (S=0.1 mm²) intervals of S values also confirms this concept.Presented at the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000).Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 4, pp. 435–444, 2000.     

Temperature dependence of the strength of adhesive joints based on crystalline polymer adhesives

The temperature dependence of the stripping strength of adhesive joints between steel and dural plates using crystalline polymers as adhesive (mixed polyamide-4, 5, 8 and guttapercha, both unfilled and filled with an inert filler) has been investigated. The temperature-strength curves pass through two local maxima, near the glass transition temperature of the crystalline adhesive and near its melting point. It is shown that the presence of a high-temperature maximum is determined by recrystallization of the polymer in the overstressed zone at the tip of the developing crack. The relationship between temperature and strength in adhesive joints based on crystalline polymer adhesives is very pronounced in both cohesive and adhesive failure. It is shown that the addition of filler reduces the recrystallization stress of guttapercha.Mekhanika Polimerov, Vol. 1, No. 3, pp. 63–67, 1965     

Global existence for a highly nonlinear temperature-dependent system modeling nonlocal adhesive contact

In this paper we analyze a new temperature-dependent model for adhesive contact that encompasses nonlocal adhesive forces and damage effects, as well as nonlocal heat flux contributions on the contact surface. The related PDE system combines heat equations, in the bulk domain and on the contact surface, with mechanical force balances, including micro-forces, that result in the equation for the displacements and in the flow rule for the damage-type internal variable describing the state of the adhesive bonds. Nonlocal effects are accounted for by terms featuring integral operators on the contact surface.The analysis of this system poses several difficulties due to its overall highly nonlinear character, and in particular to the presence of quadratic terms, in the rates of the strain tensor and of the internal variable, that appear in the bulk and surface heat equations. Another major challenge is related to proving strict positivity for the bulk and surface temperatures.We tackle these issues by very careful estimates that enable us to prove the existence of global-in-time solutions and could be useful in other contexts. All calculations are rigorously rendered on an accurately devised time discretization scheme in which the limit passage is carried out via variational techniques.     

Determination of long-term strength characteristics from crack-growth-kinetics data

The basic concepts of the quasi-stationary approximation of the kinetic theory of long cracks and a model of thermal-fluctuation crack growth are examined. The known experimental results on crack kinetics are discussed and it is shown that these results can be interpreted within the framework of the above-mentioned theory. Certain questions of methodology are considered.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Scientific-Research Institute of Mechanics, M. V. Lomonosov Moscow State University. Translated from Mekhanika Polimerov, No. 4, pp. 634–640, July–August, 1973.     

Effect of cyclic cooling to low temperatures on the adhesive strength of fiber-thermoplastic matrix joints

The adhesive strength of the interface between the polyarylene sulfone PSK-1 and a steel wire 150 mm in diameter was measured using a pull-out technique after cyclic cooling of the joints from room temperature down to liquid nitrogen temperature. All specimens were prepared under isothermal conditions (300 °C, 30 min) without applying pressure. The number of cycles N of plunging in liquid nitrogen reached 900. All measurements were taken at room temperature with constant loading rate. The joint areas S were varied within a wide range. It was found that ten cooling cycles do not cause any appreciable change in the values of (Figs. 1–3). After 100 cooling cycles, the adhesive strength losses reached 30–45% (Figs. 1–3). After 810 cycles, the fiber-matrix interface is almost totally destroyed (Fig. 1). As the number of cycles N increases, the character of the dependence of the adhesive strength on the joint area changes: when N < 100, the values of are reduced as the interfacial surface area increases; when N = 810, the adhesive strength does not depend on S. The main factor that governs the reduction in adhesive strength is assumed to be residual thermal stresses. Analysis of the data obtained here and earlier shows that the behavior of polymer-fiber systems after cyclic cooling down to low temperatures is the same for both network and linear polymer matrices. The origin of this behavior also seems to be the same for all polymer-fiber adhesive joints.Report presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October 1995).Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 2, pp. 156–162, March–April, 1995.This work was done with the support of the International Science Foundation (the G. Soros Foundation), grant NED000.     

Determination of the non-linear reaction term in a coupled reaction-diffusion system

In a reaction-diffusion model, the problem of determination of the reaction term is of immense importance. Sometimes the form of the reaction is assumed with certain unknown parameters which are later determined from experimental data. The aim of the present study is to propose an iterative method of determination of the reaction term in a general form without involving parameters and analyze the basic problem of convergence of the iterative process. The equations considered are coupled one dimensional react ion-diffusion system with nonlinear interactive terms along with initial conditions and boundarydata. The overspecified Dirichlet data are used for the determination of the reaction term.     

Determination of economic packaging frequency in a multi-brand joint replenishment inventory system

The search procedure developed in this paper is typically applicable in those inventory systems where a product is packaged immediately after manufacture into a number of container sizes and the packaged items of similar sizes are sold under more than one brand name. The most common example of such items can be seen in supermarkets where grocery items of identical characteristics (produced by the same manufacture) are available under the supermarket's own brand and under the manufacturer's nationally advertised brand. An example has been solved to illustrate the method.     

Determination of residual stresses in a layered system during two-sided high-temperature spray-coating

In order to describe the process of high-temperature spray-coating of covering layers, we prescribe boundary conditions determining the effect of the covering layers on the heat-exchange of the sublayer with the medium, and generalize to the case in which the quantity of heat introduced by the jet of plasma-forming gas is taken into account. Analytic expressions for the thermal stress state in a sheet with covering layers on each side are obtained. Computations of residual stresses in a steel sheet and the forces in the spray-coating on its surface are conducted for the cases of nichrome and aluminum alloys.Translated from Matematicheskie Metody i Fiziko-Mekhanicheskie, Polya, No. 29, pp. 8–12, 1989.     

Determination of the strength of the bonds between the fibers in cellulose compositions

It has been shown that the magnitude of the tensile strength of the bonds between the fibers in cellulose compositions can be determined from data obtained by measuring the tensile strength of a specimen at standard and zero length. The influence of the thickness of the material on some of its strength and optical characteristics has been studied. It has been confirmed experimentally that there is a functional relationship between the tensile strength of the bonds between the fibers and the magnitude of the light-scattering coefficient in the cellulose compositions studied.