Kinetics of crack growth in polymethylmethacrylate in various static tension regimes

It has been established that at medium stresses and temperatures crack development in PMMA takes place in three stages: in the first stage the crack grows with progressive deceleration; in the second stage, which determines the life of the specimen, there is almost no development; and only in the final stage does the rate of growth of the crack rapidly increase. Damage accumulation in the interior of the polymer remote from the main crack is shown to play an important part. Experimental stress and temperature dependences have been obtained for the starting velocity and the incubation period of crack development together with a universal relation between these characteristics. The processes determining the crack growth kinetics in the various phases of long-term static tension are given a physical basis.All-Union Correspondence Structural Engineering Institute. Translated from Mekhanika Polimerov, No. 5, pp. 904–911, September–October, 1971.     

Lifetime and relaxation processes in solid polymers

The relationship between relaxation processes and the fracture of solid polymers is examined with reference to the example of repeat loading with recovery. An investigation of polymethyl methacrylate, KAST-V glass laminate, and a Finnish polyester glass-reinforced plastic has shown that this lifetime may be considerably (several orders) shorter than that at the same level of constant stress. This is attributed to the time dependence of the structure-sensitive coefficient in the lifetime equation and is illustrated by means of a model that includes a Regel' fracture element.Moscow Lenin State Pedagogical Institute, Problem Laboratory of Polymer Physics. Translated from Mekhanika Polimerov, No. 4, pp. 629–635, July–August, 1969.     

Variation of the instantaneous modulus of elasticity of certain types of plastics under long-time static loads

The variation of the elastic characteristics of polymeric materials tested to destruction under long-time static loads has been investigated. Experiments on polymethyl methacrylate, KAST-V glass laminate, and Soviet and Finnish polyester glass-reinforced plastics under constant and intermittent (with "recovery") static tensile loads have shown that their elastic characteristics vary with the loading regime, the type of material, and the stress level. In a number of cases the value of the modulus of elasticity falls by 25–35%. This is attributed to the reduction of the effective cross section of the specimen as a result of damage accumulation.All-Union Correspondence Structural Engineering Institute, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 430–435, May–June, 1971.     

Some characteristics of the use of the acoustic emission method in the study of the fragmentation of single fibers in a polymer matrix

Conclusions The energy spectra of acoustic signals during stretching of an epoxy specimen reinforced with carbon fiber and of a pure epoxy matrix differ substantially. Results of a comparison of these spectra make it possible to distinguish acoustic emission signals due to failure of the fiber during stretching of a reinforced composite and to plot curves of the average length of failing fiber fragments as a function of strain.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 734–740, November–December, 1993.     

Critical length and distribution of fibrous fillers and composites

The adhesion of UKN-01 carbon fibers to a PA-12 polymeric matrix is investigated by the method of testing single-fiber model composites. The distribution of critical fiber length is constructed from measurements of fragment lengths formed in the final stage of testing. Variation in the distribution of critical length is established as a result of surface treatment of the reinforcing fiber. A bimodal distribution corresponds to the initial carbon fiber, and a monomodal distribution to the treated fiber. This is explained by replacement of a physicomechanical type of interaction of the phase interface by a physicochemical interaction owing to electrochemical treatment of the fiber surface. Analysis of the results indicated that each type of interphase interaction has its own characteristic critical length. The selection of critical length has been confirmed for calculation of the interphase shear strength by the Kelly-Tyson formula.Uvikom, Moscow Oblast, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 1, 98–103, January–February, 1997.