CREATION AND VALIDATION OF A FEM STRUCTURAL CALCULATION PROCEDURE FOR GAS TURBINE DESIGN, PROVIDING AN ELASTO-VISCO-PLASTIC MATERIAL MODEL IMPLEMENTING NON-LINEAR INTERACTION BETWEEN FATIGUE AND CREEP

The request to obtain refined simulations of a real behaviour, in structural analysis, is one of the most important goals that actually researchers are attempting to reach. Actually, the automated calculation procedures that structural analysts use through Finite Element Modelling (FEM), allow reaching a very high level of refinement if we refer to the prediction of the structural behaviour of a component/machine under a very complex load system. In this field, the capability to be able to reproduce material behaviours is one of the most intriguing points because the ability to manage the material matrix in FEM software is the necessary starting point to have a satisfying result. Traditionally the possibility to not implement such a complex model has been faced through the use of factors of safety, which are developed and refined on the basis of experience and historical evidence. For systems where efficient design is of the utmost importance (for example the minimum weight design of an aircraft structure) it is possible that the traditional factors of safety may be overly conservative, so that optimal efficiency cannot be achieved. Furthermore, historical factors of safety are unlikely to be appropriate for new design concepts or new complex metal super-alloys. These materials, for instance, have very different behaviours if we consider that depending mainly on the type of load and the temperature. They can present hardening, softening, cyclic stabilization, stress relaxation, creep, etc. The main scope of this work is to provide a procedure for the implementation of an elastovisco-plastic material model that is able to take in account of non-linear interaction of creep and fatigue for structural analysis and life prediction. This is done creating and validating a procedure that, using dedicated software, provides to the FEM software a "real time" updated material model, providing significant improvements in industrial software for life predictions and fracture mechanics. Significant sponsorship and support of this work have been provided to the author by Department of Aerospace Engineering of the University of Naples "Federico II",Avio Areospace Propulsion S.p.A. and General Electric – Oil&Gas.