Intensity of mechanical action and mechanical degradation of rigid polymers

The authors have investigated the relation between the degradation of rigid carbon-chain polystyrene, polyvinyl acetate, and polymethyl methacrylate polymers with the kinetics of mechanical degradation during vibromilling. They determine the critical value of the intensity necessary for the onset of the degradation process.Moscow Technological Institute of Light Industry. Translated from Mekhanika Polimerov, No. 2, pp. 362–364, March–April, 1974.     

Dynamic modulus of elasticity and resistance to mechanical breakdown of individual polymers and their mixtures

It is shown that when polystyrene, polymethyl methacrylate, polyvinyl acetate, and an ultramicroheterogeneous mixture of polyvinyl acetate and polymethyl methacrylate are vibroground in the brittle state, the resistance of the system to mechanical breakdown is determined by its elastic properties.Moscow Technological Institute of the Wood Industry. Translated from Mekhanika Polimerov, No. 4, pp. 744–745, July–August, 1969.     

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.     

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.     

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.     

Reasons for the lowering of the lifetime of polymers under cyclic loading

A model is proposed which explains the lowering of the lifetime of polymers on transition from static to cyclic loading by the interaction of local stresses from an external load with residual stresses which arose after preceding loading cycles. The results predicted on the basis of the model have been checked experimentally on polymethyl methacrylate, and a good agreement has been shown.M. I. Kalinin Leningrad Polytechnic Institute. Translated from Mekhanika Polimerov, No. 2, pp. 279–283, March–April, 1976.     

Biaxial orientation of amorphous linear polymers

The mechanical properties of biaxially oriented polymethyl methacrylate, obtained on a broad range of stretch ratios and under a variety of orientation conditions, have been investigated. There is a fundamental difference between the variation of the forced elastic limit with increase in stretch ratio, which is monotone increasing, and the variation of such properties as the brittle strength, brittle temperature, true strength and elongation at break, which have an optimum at a certain stretch ratio. It is shown that the presence of an optimum is associated with the transformation of the supermolecular structures in the process of biaxial high-elastic deformation. A relation is established between the mechanical properties of biaxially oriented polymethyl methacrylate (orientation hardening) and the density of the molecular network.For communication 1 see [3].Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 586–593, July–August, 1971.     

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.     

Effect of cyclically changing temperatures on poly(methyl methacrylate) during subsequent loading

The cyclically changing temperature of polymethyl methacrylate in the glassy state increases subsequent decrepitation and shows a strong influence on adsorption, desorption, and change of shape during loading and unloading of the polymer.Lenin Institute of Civil Aviation Engineers, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 339–344, March–April, 1970.     

Removing "silver" type microcracks in polymethyl methacrylate glass by dry friction

"Silver" type microcracks in polymethyl methacrylate are self-removed on aging. Dry friction can assist in their accelerated removal; by intensifying relaxation processes and causing flow in the surface layer of the polymer, it is able to restore both the polymer structure in the zones of "silver" type microcracks and also to age obvious microcracks. The restored polymer quality is stable. Dry friction raises the resistance of polymethyl methacrylate to splitting in failure.Lenin Civil Aviation Engineering Institute. Translated from Mekhanika Polimerov, No. 3, pp. 465–470, May–June, 1970.     

Comparison of the mass spectra of the volatile products liberated from polymers in the course of mechanical destruction and thermal degradation

The compositions of the volatile products liberated from polymers in the course of mechanical destruction and thermal degradation have been studied and compared by means of mass spectrometry. For those polymers in which in both cases breakdown of the macromolecules begins with the basic chain, the volatile products are the same. For polymers in which breakdown of the molecules in thermal degradation begins with the stripping of side groups, the volatile products of thermal and mechanical degradation are different. This confirms and extends the ideas of the kinetic theory of fracture concerning the relationship between the processes of mechanical fracture and thermal degradation of polymers.Mekhanika Polimerov, Vol. 3, No. 1, pp. 80–88, 1967     

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.     

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 surface-active agents on the friction properties of polymers

The effect of surface-active agents on the friction properties of plastics has been investigated in relation to the example of an aqueous solution of alkyl phenol polyethylene glycol ether (OP-10) and polymethyl methacrylate. In the presence of a surface-active agent, as a result of adsorption plasticization, the deformation is localized in a thin plasticized layer without affecting the underlying layers of plastic.Moscow Lenin State Pedagogical Institute, Problem Laboratory of Polymer Physics. Translated from Mekhanika Polimerov, No. 5, pp. 927–929, September–October, 1970.     

Effect of molecular mobility,state of stress,orientation, and plasticization on the temperature dependence of the mechanical properties of linear polymers

The temperature dependence of the breaking stress and ultimate creep strain has been investigated in relation to preorientation, plasticization, and state of stress for polymethyl methacrylate, high-pressure polyethylene, polystyrene, and polyvinyl alcohol. The results of the mechanical tests are compared with the NMR data on the molecular mobility. The causes of the observed effects are discussed.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 30–35, January–February, 1971.     

Mechanism of the increase in strength and heat resistance of oriented polymeric materials modified by graft copolymerization with vinyl monomers

The mechanical properties and structures of oriented films and fibers composed of polyethylene, polymethyl methacrylate, and other amorphous and crystalline polymers modified by the synthesis of uniformly distributed graft and block copolymers of methyl methacrylate, acrylonitrile, vinylidene chloride and other monomers have been the subject of a comparative investigation. The effect of the grafted polymers on the molecular mobility, relaxation processes, and solubility of the materials is explained by reference to a universal physical "crosslinking" mechanism. A theory of the interrelation between the structure and physical properties of the materials, the nature of the polymers, and the grafting conditions is developed and used to analyze the experimental data on a broad range of systems.V. I. Lenin Belorussian State University, Minsk. Translated from Mekhanika Polimerov, No. 6, pp. 968–975, November–December, 1973.     

Direct proofs of self- and mutual diffusion in the formation of adhesion bonds between polymers

The authors discuss experiments aimed at the direct investigation of self- and mutual diffusion in polymers. New electron microscope data are presented for mutual diffusion in the systems polyvinyl chloride — polymethyl methacrylate, polyvinyl chloride — polybutyl methacrylate, and polystyrene — SKS-85. It is shown that with increase in temperature and improvement in compatibility the depth of mutual diffusion increases. The data obtained make it possible to calculate the polymer-polymer diffusion coefficient.Mekhanika Polimerov, Vol. 2, No. 3, pp. 446–452, 1966     

Effect of cycle asymmetry on the cyclic strength of polymers

Cyclic strength diagrams have been obtained for polymethyl methacrylate and kaprolon at different degrees of loading asymmetry (from a pure compression to a pure tension cycle) on the interval from –100 to +80° C at 2·10³ and 3·10⁵ cycles.M. I. Kalinin Leningrad Polytechnic Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 948–951, September–October, 1968.     

Autovibrational development of laser cracks

The authors experimentally investigate the discontinuous ("jumping") character of the development of laser cracks in polymethyl methacrylate. The discontinuities arise in such an order that the crack remains rounded, even if the laser beam is rectangular in cross section. The authors estimate the pressure drop in the crack during a "jump."Institute of Problems in Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 475–481, May–June, 1973.