Calculation of Pipes under Multiaxial Mechanical Strain

The mechanical properties of thermoplastics are determined by strong. non-linear structures which are primarily functions of time,-temperature and degree of multiaxial loading. With the help of simple approximation-functions an exact description of this non-linear relationship between stress and strain is possible for uniaxial stresses. The coefficients of the approximation-functions are dependent upon time and temperature. Because of the validity of the time-temperature shifting principle, the long-time behaviour can be calculated from material data, measured during short term tests under constant strain rates and elevated temperatures. To calculate the influence of multiaxial loadings on the modulus. the volume-specific work of deformation is used.