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Thus, by constructing polymeric composites it is possible to alter the damping properties of metal structures reinforced with composites over a wide range, and to make it possible to obtain the required material properties for the structure.

The results of an investigation of the dispersion (standard deviation s and coefficient of variation V) of the static and dynamic strengths of plastics are described. The effect of temperature, state of stress, and type of plastic on the dispersion characteristics is considered.

Experimental values of the strength and deformation are presented for SO-95, SO-120, and SO-140 acrylic plastics (polymethyl methacrylate: plasticized, unplasticized, and copolymer) stressed in unaxial tension at v=10 mm/min, stationary temperature gradients of from 2.5 to 17.5 deg/mm over the thickness of the material, and a constant cold-face temperature of 25°C. The deformation properties under these conditions are described: in the presence of a temperature gradient the ultimate strains are higher than for a uniform temperature field at a temperature equal to the cold-face temperature, and the elongation at break falls as the hot-face temperature rises. The tensile strength of plastics with a temperature drop over the cross section can be approximately calculated from the mechanical characteristics obtained for a uniform temperature field.

The effect of fast-electron bombardment (2MeV) on the mechanical properties of glass-reinforced plastics (EDT-10 and SGM) and epoxy EDT-bonded textolite with a lavsan fabric filter was studied. Electron paramagnetic resonance (EPR) and infrared spectroscopy (IRS) methods were used to investigate structural changes in these materials. A comparison of EPR spectra with the yield of free radicals made it possible to establish the existence of a chemical interaction between the glass fiber and the bonding material in EDT-10 glass-reinforced plastic.

The tensile strengths of glass laminates of various compositions under standard, high-speed and impact loading have been experimentally investigated in relation to the effect of low-temperature and stress raisers. As the loading rate increases (from 0.7 to 253 · 103 kgf/cm2. · sec) and the temperature falls to −196° C, the effective stress concentration coefficient decreases, which indicates that the glass laminates will perform adequately under these conditions.

A method is proposed for constructing the creep curves of a material whose nonlinear memory properties are described by Rozovskii's nonlinear integral equation [2] (with allowance for the stress dependence of the relaxation time) under given periodic loading from known creep curves recorded at constant stress. In deriving the theoretical relation certain simplifying assumptions are made (the creep strain accumulated in 1–2 cycles is small, no vibration [4–6]). An experimental check shows that the proposed method can be used to predict the behavior of a material under periodic loading with an accuracy sufficient for practical purposes.

The effect of the type of state of stress on the activation energy and relaxation time is investigated with reference to the mechanical glass transition (softening) process in polymers. An expression relating the mechanical glass transition temperature with the structural glass transition temperature, the mean stress, and the stress intensity is obtained for isotropic homogeneous polymers. Experimental data obtained for polymethyl methacrylate in uniaxial tension and compression, pure bending, and shear are presented.

The relaxation properties of polyethylene are analyzed. The nonlinear time-dependent stress-strain relations and the creep and relaxation equations are obtained from the experimental creep data. The analysis is based on an appropriate variant of the nonlinear memory theory with singular functions whose parameters, together with the modulus of elasticity, are determined by the method described in [1].

The local overheating at the tips of growing cracks in cyclically loaded plastics is examined on the assumption that there is almost no change in overheating up to failure (relatively small load amplitudes). A method is proposed for estimating the fatigue life of solids and polymers with allowance for local overheating or local aging of the material. A comparison of the formulas obtained with the experimental data confirms the importance of overheating in cyclic loading as compared with other manifestations of the local relaxation processes.

The dynamic characteristics E and G and the damping capacity δ* of polymeric resins and composites based on glass, carbon, and boron fibers have been investigated. It is shown that the mechanical losses are correlated with the modulus of elasticity and the shear modulus of the resin and composites with different types of reinforcement. The vibrational strength of various structural materials is estimated.

A six-parameter model of a viscoelastic medium with nonlinear properties is examined in the region of the time-temperature analogy. Formulas are given for determining the parameters from the data of simple quasi-static tests.