Load Path Visualization in Aero-engine Structures Using U* Index Method

Abstract

In the aerospace industry, there exists an extensive demand for improving the performance of mechanical structures in the aircraft components. Such performance can be improved by various measures such as reducing the weight and improving the stiffness of the existing structures. To achieve this, it is important to study how the mechanical load is distributed in the structure which can be done by analyzing so called load paths. The load paths are the trajectories that represent the flow of load within the structure. Existing stress-based concepts generally suffer from stress concentrations due to geometrical features, such as joints and curved sections. Hence, stress concentrations can provide misleading information when applied to study load paths. The load transfer index U* is a relatively modern concept, proposed by previous researchers to study the load distribution in the structures. It expresses the internal stiffness between loading and arbitrary points within the structure. Unlike many other approaches, U* index is unaffected by the presence of geometrical features.The load paths based on U* can provide useful insights that would help in stiffness modification and design evaluation. Thus, this method has the potential to play a key role in structural mechanics. However, the U* index concept-based analysis is not widely used in engineering problems since the calculation and visualization routines are not widely incorporated in finite element software. The purpose of this thesis is to visualize load paths based on U* and enhance design on existing aero-engine structures. This thesis focuses on developing computational methods to calculate the U* index and routines to visualize load paths for structural engineering problems. Different software were used to develop the methodology in this thesis. The necessary finite element method calculations were performed by using ANSYS APDL and the results are post-processed in ParaView to visualize the load paths. The load paths are visualized for 2D and 3D structural problems. The influence of boundary conditions, types of loading, mesh elements and mesh sensitivity analysis were studied. This thesis sets the platform for wider application of the load path visualization concept in structural engineering problems which is of particular importance at GKN Aerospace Sweden AB, Trollhättan where the thesis work was carried out.