Rusinov A. Long-term fracture of thin-walled cylindrical tubes under creep conditions with biaxial static loading.

The Thesis is devoted to the solution of the life time calculation problem of thin-walled elements of cylindrical tubes in creep under biaxial load using the equivalent stress concept.Long-term fracture of thin-walled tubular specimens of isotropic metallic and polymer materials in creep under combined action of internal pressure, torsion and tension is considered. The method of long-term fracture criteria creation under plane stress state has been obtained. It allows to use all functions of the second invariant of the stress diviator when the criterion components are being given. The mixed long-term fracture criterion of isotropic materials has been built. The criterions stucture depends on signses of principal stresses and takes kinds of loading into account by using Nadai-Lode parameter. The problem of life time calculation of thin-walled tubes under different kinds of biaxial loading has been solved. Calculation results are compared with experimental data and good agreement is obtained.