Equilong-term strength surfaces of organic textolite in the plane stressed state

Conclusion Long-term strength tests of textolite were conducted for seven different particular cases of the plane stressed state. Maximum times to failure for which experimental data were obtained reach 2500 h. It is established from analysis of the test results that the experimental long-term strength curves for the types of stressed state under consideration are closely similar. The condition of long-term strength in the general case of the plane stressed state for constant levels of stresses is taken as the equation of the short-term strength surface in which the time factor is introduced parametrically; in this case, the apparent observance of similarity between equilong-term strength surfaces makes it possible to express the tensor components characterizing the long-term strength by tensor components of the short-term strength surface and a certain monotonically decreasing time function, which is independent of the form of stressed state.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 51–56, January–February, 1979.     

Effect of interlaminar stiffness and strength of fiber-reinforced materials in plane stress

The distortion of the strains associated with a difference in the influence coefficients of the reinforcing layers is considered. The effect of the compliance of the intermediate resin layers on the average stiffness of composites is estimated. An attempt is made to explain in these terms the experimentally established deformation characteristics of three-dimensionally reinforced materials [12, 13] and laminated plastics loaded at an angle to the direction of reinforcement [11].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 876–883, September–October, 1970.     

Relation between the structural and strength characteristics of textolite glass laminates

The authors derive approximate relations between the microstructure parameters of densely reinforced textolite glass laminates and the static strength and fatigue life of the material. The relations obtained are compared with the results of experiments performed on materials with varying degrees of crimping of the filaments and varying densities of the cloth reinforcement.Mekhanika Polimerov, Vol. 3, No. 2, pp. 302–308, 1967     

Deformation and failure of angle-plied organic fiber-reinforced plastics in the 3D stress state

Tubular specimens of organic fiber-reinforced plastic (OFRP) are tested in tension under a high hydrostatic pressure of up to 300 MPa. The specimens are made by winding at an angle of ±60° to the generatrix. The experimental equipment and technique are described. The tests show the insignificant effect of hydrostatic pressure on the elastic properties and the failure mode of the OFRP. The hydrostatic pressure considerably affects the strength properties of the OFRP. The material strength increases almost twofold under a pressure of 300 MPa. The failure strains of the material increase significantly as well.N. E. Bauman Moscow Higher Technical School, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 5, pp. 592–602, September–October, 1997.     

Approximation of strength surfaces in plane stress

Approximation of strength surfaces in plane stress is considered with the use of the method of expansion of the function on a sphere by means of tensors. Examples of the approximation are given for certain composite materials.     

Singular stress concentrations in plane Cosserat elasticity

Zusammenfassung Auf Grund der Cossertschen Elastizitätstheorie werden exakte Lösungen gegeben für den singularen Teil des Spannungsfeldes in der Halbebene unter konzentrierten Normal-und Tangentiallasten und unter diskontinuierlichen normalen und tangentialen Oberflächenbelastungen.     

Strong influence of a small fiber on shear stress in fiber-reinforced composites

In stiff fiber-reinforced composites, it has been known that the shear stress increases at the rate of as the distance ? between adjacent fibers approaches 0. This paper reveals a strong influence of a combination of a triple fiber, as well as the distance between a pair of fibers, on the blow-up so that the stress concentration can be significantly accelerated by adding a small fiber in-between fibers. Specifically, if a fiber F₂ with a small diameter δ is located in-between fibers F₁ and F₃, ?₁=dist(F₁,F₂) and ?₂=dist(F₂,F₃), then the stress blows up at the exact rates of and between F₁ and F₂ and between F₂ and F₃, respectively. This estimate still holds even when a part of F₂ overlaps with F₃. The magnification factor yields the enormous increase in the stress that greatly surpasses the expectancy by previous methods.     

The plane stress problem of Ghizzetti in elasto-plasticity

The theory of variational inequalities is applied to some special problems of elastic-plastic deformation.     

Experimental evaluation of the strength anisotropy of a unidirectionally reinforced organic fiber-reinforced plastic

Conclusions The strength of a unidirectional organic fiber-reinforced plastic has been experimentally determined in various special cases of plane stress. An analysis of the data obtained shows that it is possible to describe the strength of the material in plane stress by means of a second-order surface equation containing linear and quadratic terms. The dependence of the strength in tension and compression on the angle between the directions of loading and reinforcement has been predicted and experimentally confirmed using the values found for the components of the strength surface tensors. The results of the study can be used to estimate the strength of multilayer organic fiber-reinforced plastics in cases where a unidirectionally reinforced layer can be taken as the basic structural element of the material.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 799–803, September–October, 1979.     

Long-time strength of isotropic polymers in plane stress state

A criterion of strength of isotropic polymers in the form of the critical work done by stress was postulated and shown, by statistical analysis, to be independent of the time and form of loading. The introduction of the time factor in the existing theories of strength of isotropic materials was postulated and experimentally verified with the aid of this criterion.Mekhanika Polimerov, Vol. 2, No. 6, pp. 837–844, 1966     

Deformation of teflon in linear and plane states of stress

Teflon specimens have been deformed in accordance with various laws of variation of stress and strain with time under plane stress conditions. Fairly simple expressions describing the relation between the stresses and large (up to 60% relative to the initial dimensions) strains are constructed for a broad class of loading regimes.Scientific-Research Institute of Mathematics and Mechanics, A. A. Zhdanov Leningrad State University. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 742–746, July–August.     

Strength of glass-reinforced plastics in the complex stress state

A new criterion of strength is proposed for anisotropic materials of the glass-reinforced plastic type. This criterion takes into account not only the different ultimate strengths in tension and compression in each direction but also the dependence of the ultimate shear strengths on the sign (direction) of the shear stresses. The criterion is given in tensor invariant form, so that it can be rewritten for any direction of the glass fibers. The criteria proposed by other authors, in particular, R. Hill's condition of plasticity [1], follow from the new generalized criterion as special cases. The results of experiments conducted both by the authors of the present article and by other investigators provide good confirmation of the proposed criterion.Mekhanika Polimerov, Vol. 1, No. 2, pp. 70–78, 1965     

Diffraction of a plane wave by a step discontinuity in an impedance plane

In the present paper, the high-frequency diffraction of a plane wave by a right-angle step discontinuity in an impedance plane is analyzed with the help of the uniform geometric theory of diffraction, beginning with the Maluzhenets solution. The principal term of an asymptotic solution of the problem, which is uniform with respect to the angle of incidence of the plane wave and the angle of observation, is derived. The excitation of primary and multiply diffracted fields radiated from the upper edge, as well as surface waves, is considered (the lower edge does not radiate cylindrical or surface waves owing to a right-angle step). For simplicity, the details of computation are given here for a right-angle step discontinuity. A similar procedure is applied to other examples with more complicated geometry. Bibliography: 7 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 250, 1998, pp. 97–108. Translated by V. V. Zalipaev.