Reologiczne, mechaniczne i optyczne własności polimetakrylanu metylu w warunkach złożonej historii obciążenia

The paper delas with the experimental investigations of the influence of the history of loading on the mechanical and optical properties of polymethyl-metacrylate under uni-axial tension. The investigations were carried out for various loading programmes at room temperature and embraced active creep at various load levels, recovery creep after unloading and additional creep. Test results have been analyzed from the point of view of linearity of observed effects in the sense of fulfilment of the Boltzmann superposition principle. Analysis of the test results proves that the material under consideration is strongly non-linear both with respect to the optical and the mechanical properties, the degree of non-linearity being greater for higher load values and longer duration of the load application. Comparison of the functions of optical and mechanical creep seems to indicate that a proportional relationship exists between the function of optical crecp and the function of mechanical creep. This means that the optical effects depend on the deformation only. The second part of the paper includes the mathematical description of the non-linear properties of material based on the application of the Green-Rivlin integral representation. An approximate description has been suggested consisting in the selection of such form of the integral kernels that they could be completely determined from several basic investigations. An additional approximation has also been used consisting in the separation of the behaviour of material into linear and non-linear region. Numerical values of the material functions have been calculated.