Procedure for measuring the thermophysical properties of polymers at high hydrostatic pressures

A procedure is suggested for determining the thermophysical properties of solids under hydrostatic pressure conditions by the instantaneous cylindrical heat source method without allowance for heat exchange at the sample-liquid boundary. A calculation performed showed that the temperature field of a cylinder of finite radius is identical to the temperature field of an infinite body up to Fo=0.05–0.07 with an accuracy far better than 0.5%. It is shown that the sample dimensions can be small thereupon at measurement times sufficient for performing the measurements on a standard apparatus of the order of 40–70 sec.Moscow Chemical Engineering Institute. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 568–570, May–June, 1973.     

Reduced strength of polymethyl methacrylate saturated with carbon dioxide at high pressure

The effect of external pressure on the amount of carbon dioxide sorbed by specimens of polymethyl methacrylate and on the strength of the specimens after removal of the pressure during the initial period of desorption has been experimentally investigated. The experiments were conducted at 20°C, the pressure varied from 20 to 56 bar.S. M. Kirov Ural Polytechnic Institute, Sverlovsk. Translated from Mekhanika Polimerov, No. 2, pp. 243–246, March–April, 1971.     

Investigation of the thermophysical properties of polypropylene

The temperature and pressure dependence of the thermophysical properties of isotactic polypropylene has been investigated. The experimental results are presented and discussed.Mekhanika Polimerov, Vol. 2, No. 5, pp. 793–797, 1966     

Notch sensitivity of polymethyl methacrylate

It is shown that acrylics have a notch sensitivity determined by the nature of the state of stress produced by the loading.Lenin Riga Komsomol Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 3, pp. 562–564, May–June, 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.     

Friction properties of highly elastic materials at high contact pressures

A newly designed high-pressure tribometer has been employed to investigate the pressure dependence of the friction force of SKN-40 crosslinked butadiene-nitrile rubber in contact with a steel surface on the pressure range to 1200 kgf/cm² (20°C). Over the entire range of contact pressures the friction process is molecular-kinetic in nature and characterized by a linear dependence of the friction force on the logarithm of the sliding velocity. In the region of normal pressures up to 200 kgf/cm², where the effect of pressure on the friction force reduces to the formation of the actual contact area, the friction constant (proportionality factor relating the friction force and the actual contact area) is practically independent of the pressure. At pressures above 200–300 kgf/cm² the increase in the friction force at fixed actual contact area is attributable to the effect of pressure on the friction constant. The nature of this effect is related not with an increase in the chain-surface interaction energy (the activation energy does not increase), but with an increase in the forces of adhesion owing to the greater number of polymer chain-steel surface contacts on the actual contact area (increase in contact density).Lenin Moscow State Pedagogical Institute, Laboratory for Problems of Polymer Physics. Translated from Mekhanika Polimerov, No. 1, pp. 140–146, January–February, 1971.     

Investigation of the thermophysical and antifriction properties of polyethylene compositions

The coefficient of linear expansion of polyethylene compositions has been determined. Metals, oxides, and silicates were used as fillers. The coefficient depends significantly on the geometry of the filler particles. Powdered fillers reduce the coefficient by 10–20% (an amount somewhat greater than their volume concentration). Fillers consisting of material with a low coefficient of linear expansion and a high modulus of elasticity in chopped-fiber form may reduce the coefficient of linear expansion by one order as compared with pure polyethylene.Mekhanika Polimerov, Vol. 3, No. 5, pp. 873–880, 1967     

Structural characteristics of laser damage in polymethyl methacrylate

Three types of optical defects are present in the starting structure of specimens of PMM: nontransparent inclusions (1 µ and above), small (less than 1 µ) scattering centers, and local elastic-stress fields. The relationship between these defects and the damage centers excited by laser radiation is considered.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 944–945, September–October, 1970.     

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 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     

Supersonic crack propagation in blocks of polymethyl methacrylate

It is shown that a giant laser pulse can cause supersonic crack propagation in PMMA. The results of the experiments and a microstructural analysis of the fracture surface are presented. A study of the microstructure shows that supersonic crack propagation is associated with the propagation of a shock wave in the focal region.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1027–1029, November–December, 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     

Initial stage of laser-induced crack development in polymethyl methacrylate

It is shown that the successive stages of development of the damage caused by a laser beam are the same in technically pure polymethyl methacrylate and the same material containing artificially introduced absorbing particles. The formation of the characteristic flat cracks from gas bubbles in the specimen is observed. The mechanism of fracture development in polymethyl methacrylate is further refined.Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 551–552, May–June, 1971.     

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.     

Nature of the friction deformation of the surface layers of polymethyl methacrylate

The surface deformation of amorphous thermoplastics (polymethyl methacrylate) by a spherical steel indentor has been investigated at various sliding velocities. Small velocities correspond to elastic and forced-elastic deformation of the surface layers and asperities. At temperatures corresponding to the high-elastic state the deformed surface layer completely recovers its shape. As the sliding velocity increases, the forced-elastic deformation is localized in a thinner layer of plastic. Starting from a certain velocity, depending on the temperature and the activation energy for transition of the chain segments from one equilibrium position to another in the process of thermal motion, the deformation of the surface layers and asperities becomes purely elastic. In the event of elastic deformation at pressures above a certain value the surface layer of plastic suffers brittle fracture in the tensile zone behind the indentor.Mekhanika Polimerov, Vol. 4, No. 1, pp. 90–94, 1968.     

Accumulation of fatigue defects in polymethyl methacrylate in rotational bending

The results of tests on polymethyl methacrylate for fatigue during polycyclic rotational bending through an angle under thermostatic conditions are analyzed. A method of calculation is given for the determination of the defects. The observed changes in the mechanical characteristics and the fractography of the fractures are taken into account comprehensively. Possibilities for the simplification of the method of calculation, and the acceptable methods for the indication of defects before the formation of the main crack are discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1038–1045, November–December, 1974.