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     

Analysis of fracture surfaces in polymethyl methacrylate tested in bending with rotation

Typical fracture surfaces are examined for polymethyl methacrylate specimens subjected to multicycle fatigue testing in circular cantilever bending at T=20, 40, and 60°C. It is established that the fatigue life of smooth specimens is very closely correlated with the size of the diffuse fracture zone. The kinetics of damage accumulation with increase in the number of cycles are investigated by rapidly fracturing prefatigued specimens. The decisive role of diffuse fracture in the fatigue-fracture process is demonstrated. A method of estimating the mean main crack propagation velocity in circular bending is described.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 984–990, November–December, 1973.     

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.     

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 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 small vibrations on cracking kinetics in polymethyl methacrylate. Concept of a rate-dependent cracking resistance. Possible thermal mechanism

Conclusions 1. Small vibrations superposed on the main static component of an external load cause the cracking rate in polymethyl methacrylate to increase appreciably. Within the range of low cracking rates (<10^–4 cm/sec), evidently most important from the practical standpoint, the cracking resistance of this material is also found to decrease.2. The concept of a rate-dependent cracking resistance applies to conditions under a vibration load, over a wide range of vibrations at low or intermediate cracking rates.3. The effect of small vibrations is local in nature. It may have to be taken into account, if cracks or similar defects already exist in a structure or appear in it during service.4. The thermal mechanism is not adequate for quantitatively describing the experimentally observed effect of vibration.Paper presented at the Third All-Union of Conference on Polymer Mechanics in Riga, 1976.M. V. Lomonosov Moscow State University. Translated from Mekhanika Polimerov, No. 5, pp. 846–853, September–October, 1977.     

Comparison of the activation energies of the processes of thermal degradation and mechanical fracture of polymethyl methacrylate

On the basis of a comparison of the activation energies of the processes of thermal degradation and mechanical fracture of PMM with various additives it is concluded that in the presence of a "pole shift effect" it is more correct to calculate the activation energy U₂ of the mechanical fracture process on the assumption that ₀ = const and =f(, T). The energy U₀₂ is then correlated with the weak-bond rupture energy. In the general case, the activation energy U₀₁, calculated on the assumption that ₀=f(, T) const, i. e., from the slopes of the lg -1/T graphs, cannot be identified with the interatomic-bond rupture energy.Mekhanika Polimerov, Vol. 4, No. 3, pp. 467–473, 1968     

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     

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.     

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.     

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.     

Two-stage biaxial orientation of polypropylene film

The microstructure of polypropylene film at various points of the two-stage orientation process is described. It is shown that the supermolecular structures and film properties vary with the method of orientation. A proposed mechanism of two-stage biaxial film orientation is based on the experimental results.Moscow M. V. Lomonosov Institute of Fine Chemical Technology. Translated from Mekhanika Polimerov, No. 4, pp. 735–737, July–August, 1969.     

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.     

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.