Characterisation of a simplified aeroengine casing subjected to a radial loading condition using FE and approximate methods

In general, aeroegine casings may experience an axial force, a bending-moment and radial loading. Under these loads, the high stress regions of these complex aerongine casings will experience local stress and strain concentrations, with various load combinations. The stiffness will also depend on the loading mode. Hence, careful design is required to avoid the various types of failure such as buckling, crack initiation and propagation must be taken into account when designing an aeroengine casing structure. In addition, aerongine casings require extremely high reliability in service and adequate strength under extreme load conditions, i.e. Fan-Blade-Off (FBO) condition, must be demonstrated. Under radial loading of aeroengine casings, which have spoke to shell connections, these are the most likely sites for plastic deformation to occur and cracks to initiate. Also, the load path for each spoke to shell connection within the casing structure changes during loading. Based on these observations, this paper concentrates on the behavior which occurs in spoke to shell connections, referred to as local joints. The intention is first to characterize the local joint behavior and then to incorporate this into a global casing model. The work reported in this paper includes studies of mesh sensitivity, predictions of load path at each local joint under radial load, FE failure loci, upper bound techniques for predicting limit loads and stresses-strains predictions at local casing notches under elastic-plastic and creep situations using approximate notch methods. Hence, the global responses of a casing structure were predicted by utilizing a "repeated local joint" technique in conjunction with simplified global models.