Creep behavior anisotropy

Flow properties and slip systems operating at different temperature ranges, including anisotropy of these systems and its effect on creep behavior. 

FEA is applicable in several types of analyses. The most common one is static analysis to solve for deflections, strains, and stresses in a structure that is under a constant set of applied loads. In FEA material is generally assumed to be linear elastic, but nonlinear behavior such as plastic deformation, creep, and large deflections also are capable of being analyzed. The designer must be aware that as the degree of anisotropy increases the number of constants or moduli required to describe the material increases. 

Yet it is noticeable that these behavior laws have been obtained from creep data where the specimen is submitted to longitudinal deformation. To meet demands of the French safety authorities, a creep campaign was launched in the 1980s where the creep specimens were closed tube sections put under internal pressure [18]. This time, the samples were submitted to a load closer to biaxiality, and a potential anisotropy of the tube due to manufacturing would have been detected. This campaign showed scattered results in similar stress and temperature conditions, and some unexpected early ruptures. The creep capsules and the internal pressure values were perhaps not adequately designed. To fuUy clarify this point and validate alloy 800 SPH creep databank, some other multiaxial creep campaigns should probably be carried out. 

---