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.     

Effect of continuous gas-laser radiation on polymethyl methacrylate

The effect of continuous powerful (up to 20 W) 10.6- radiation on PMM is described. The relationship between crater growth and time is established. A region of softened polymer with a clearly defined boundary, an isotherm with temperature equal to the softening point, has been detected. Theoretical estimates of the propagation velocity and depth of the crater are obtained starting from the heat balance equation. The agreement with experiment is good.Mekhanika Polimerov, Vol. 4, No. 2, pp. 282–287, 1968     

Profile of a laser crack in polymethyl methacrylate

The profile of a laser crack in a transparent dielectric, polymethyl methacrylate (in the free-generation procedure), has been studied by the equal-thickness interference band method. It has been established that zones of changed material, a zone of slow change of profile, and a zone of rapidly changing profile (center of the crack) exist in the cross section of the crack. Values of thickness of the crack are given. Suggestions are expressed as to a possible mechanism of laser damage.Institute of Problems in Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 921–923, September–October, 1973.     

Effect of laser radiation on the mechanical strength of a block of polymethyl methacrylate

The effect of pre-existing microcavities, created by laser radiation, on the mechanical strength of polymethyl methacrylate is investigated. It is established that "seeding" with microcavities does not affect the breaking stress and relative elongation, but does shorten the lifetime.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 247–250, March–April, 1971.     

Effect of notches of different length on the properties of sheet polymethyl methacrylate

It is shown that increasing the length of a vee notch in polymethyl methacrylate sheet specimens does not significantly intensify the effectiveness of the notch as stress raiser. Over a broad interval of variation of its length the notch has a constant quantitative effect on the mechanical properties.Lenin Riga Komsomol Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 4, pp. 745–747, July–August, 1971.     

Effect of fibrous filler on the mechanical properties of polystyrene and polymethyl methacrylate in the glassy state

The authors have investigated the effect of introducing fiberglas into polystyrene and polymethyl methacrylate films on the transition temperatures and on the intervening glassy-state temperature intervals within which the polymers possess different physicomechanical properties. The variation in a number of the mechanical characteristics of these polymers has been studied as a function of filler concentration within all the subregions of the glassy state bounded by the transition temperatures obtained. Temperature inversion of the reinforcing action of the fibrous filler within the glassy state has been detected. Attention is drawn to the existence at a given temperature of a large number of filled polymer systems with the same reinforcing effect and the same strength at different contents of the same filler in the same polymer.Mekhanika Polimerov, Vol. 3, No. 3, pp. 517–523, 1967     

Effect of strain rate on the mechanical properties and transition temperatures of glass-reinforced polystyrene and polymethyl methacrylate

The effect of strain rate on the mechanical properties and transition temperatures and the subregions of the glassy state that the latter define has been investigated for polystyrene and polymethyl methacrylate films containing various amounts of fiberglas. An inversion of the reinforcing effect of the filler is observed as the strain rate is varied at fixed temperature. Varying the temperature can also lead to an inversion of the nature of the strain-rate dependence of the strength of the reinforced polymer within the glassy state. In the low-temperature region the strength increases with decrease, and in the high-temperature region with increase in strain rate. The transition temperatures of the reinforced polymers are more sensitive than those of the unreinforced polymers to changes of strain rate. The subregions of the glassy state are almost independent of the strain rate, except that as the latter increases they are shifted into the high-temperature region.Mekhanika Polimerov, Vol. 4, No. 3, pp. 462–466, 1968     

Buildup of defects in polymethyl methacrylate in service and their effect on its notch sensitivity

This study deals with the effect which defects built up in polymethyl methacrylate during 0–16,000 h of service have on its physicomechanical properties, fracture topography, and notch sensitivity. The trend of strength and plasticity characteristics is established as well as that of the coefficients of notch sensitivity as functions of the notch depth.Lenin Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 2, pp. 256–262, March–April, 1976.     

Fluctuations of forced vibrations in a medium with resistance

For a differential oscillation equation with coefficients perturbed by Gaussian delta-correlated random processes with a random external force, we obtain closed moment equations. In a special case, the mathematical expectation and the covariance function are found.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 45, No. 1, pp. 132–135, January, 1993.     

Effect of porosity on the thermal resistance of adhesive bonds

The relation between the thermal resistance R of an adhesive bond and the relative porosity of the adhesive layer r was investigated. It was shown to be possible to predict r from the measured values of R.Voronezh Wood Technology Institute. Translated from Mekhanika Polimerov, No. 2, pp. 369–372, March–April, 1972.     

Effects of a small length scale on vibrations of an embedded double-walled carbon nanotube

Extensive continuum analyses are carried out to estimate the influence of matrix stiffness, a small length scale, and intertubular radial displacements on free vibrations of an individual double-walled carbon nanotybe. The analyses are based on both local and classical Euler–Bernoulli and Timoshenko elasticity theories with concentricity and nonconcentricity assumptions. The effect of a small length scale is incorporated in the formulations. New intertubular resonant frequencies are calculated based on these theories. Detailed results are demonstrated for the resonant frequencies as functions of matrix stiffness and the small length scale. The results indicate that the internal radial displacement and the stiffness of the surrounding matrix can greatly affect the resonant frequencies, especially at higher frequencies, and thus the latter does not keep the otherwise concentric structure at ultrahigh frequencies. More over, at high frequencies and small aspect ratios, the effect of the small length scale be comes more significant.     

Effect of vertical vibrations on a two-layer system with a deformable interface

The effect of single- and two-frequency vibrations on the behavior of a system consisting of two homogeneous viscous fluids bounded by rigid walls is analyzed. It is assumed that the system as a whole is under vertical vibrations obeying a certain law. An eigenvalue problem is obtained in order to analyze the stability of the relative equilibrium. The case of finite frequencies and arbitrary modulation amplitudes is treated along with the case of high frequencies and small modulation amplitudes. In the former case, the parametric resonance domains are examined depending on the parameters of the system. In the latter case, the high-frequency vibration is shown to create effective surface tension, thus flattening the interface, and can suppress instability when the heavy fluid is over the light one.     

Effect of ultrasonic vibrations on the flow of a viscoelastic liquid

The rheological characteristics of a viscoelastic liquid flow, on which finite-amplitude ultrasonic shear vibrations have been superimposed, are investigated. It is shown that at periodic deformation amplitudes of 5 µ or more there is a thixotropic reduction of the viscosity and elasticity of the system owing to the destruction of certain types of structural bonds. The experimental apparatus is described.Moscow Institute of Chemical Machine Building. Translated from Mekhanika Polimerov, No. 6, pp. 1097–1099, November–December, 1971.