ANALYSIS OF STRESS-STRAIN CURVES
ПОД- СЕКЦИЯ 8. Современные строительные технологии и материалы.
Artamonova E.N.
Doktor of Technikal Sciense Professor of the Department of Mechanics Deformable Solids of the Saratov State Technical University. Russia
ANALYSIS OF STRESS-STRAIN CURVES
Analysis of experimental data suggests characteristics of the temperature dependence of relaxation processes and fracture for viscoelastic polymers with the same energy value activation for each material [1, p.295]. Both aspects of the strength of polymers (short-term and long-term loading) depend on the local structural changes that primarily can be linked with the process of accumulation of damage, education grid hairline cracks. Combining different approaches to describing these processes, ie formulation of a general theory of deformation and fracture of polymers depends on the study of the relationship of deformation, destruction and action voltage, temperature, aggressive factors in the whole time interval of operation of the element. Relaxation properties influence the process of destruction, enhancing the growth of microdamage. This is explained by the fact that in the process of development forced highly elastic deformation near the damage is mechanical energy into heat. An examination of these experimental data one can draw conclusions that should be taken into account when constructing the conditions of fracture: 1. Mechanical properties and the process of destruction of polymer materials substantially depend on time and operating conditions.
2. Destruction is a two-stage process. At the first stage of degradation of the properties of the material, the accumulation of damage, microcracks occur. The stage ends at a time when the merger of microdamage formed macroscopic crack. This moment is short-lived and by their physical nature is a loss of stability of equilibrium microdefects. 3. At failure, the material from corrosion or silent creep value of the first stage is so large that the evaluation time of destruction the destruction process can be generally described as the accumulation of damage and degradation properties of plastic.
4. Given the irreversibility of the process of destruction is determined not only the current values of parameters characterizing it, but the entire prior history of these parameters. A survey of literary sources, to analyze the long-term durability of materials and elements of them, there are basically two alternative approaches: mechanical (benchmarking) and kinetic. Under the first approach, we introduce a generalized condition of destroyed material: where some combination of the components of the stress or strain; (objective indicator of strength; invariants of the stress-strain state).The function f depends on the accepted theory
strength or given empirically, and then the function contains parameters, determined experimentally.
According to the second (kinetic) approach, the destruction seems like gradually developing in time change the microstructure of particles of the body under a load. Such an approach takes on special significance in connection with the growing use of structures of composite materials based on polymers that have the task of forecasting performance is complicated because of the irreversible and reversible process changes the molecular and supramolecular structures during operation. In this paper we propose a model of destruction (the relations connecting parameters of efficiency at the time of fracture characteristics
material), based on the relationship of both these approaches to allow for the dependence of the limiting critical conditions at which the destruction, the time of stress, temperature environmental exposure, exposure, etc. This is especially typical for polymers . To build a relationship of the proposed mathematical model of fracture consider a number of hypotheses.
1. The strain tensor can be represented as a sum of tensors of elastic deformation of inelastic deformation.
2. To describe the strain state and fracture in the framework of a generalized model of inelasticity is necessary to consider the history of deformation of the sample depends on the loading path and on time. For different loading paths for the processes of varying duration results will be different.
References:
1. Suvorova J.V., Ohlson N.G., Alexeeva S.I. An approach to the description of time-dependent materials //Materials and Design, Vol.24. Issue 4, June 2003.- P.293-297.
