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Title: Combined stability of conical shells
Author: Ifayefunmi, Olawale Friday
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2011
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This thesis is concerned with the study of the elastic-plastic buckling of short and relatively thick conical shells subjected to combined loading, i.e., axial compression and external pressure acting simultaneously. This is both numerical and experimental study. Within the context of numerical study, a nonlinear finite element calculations were carried out in order to obtain: (i) the failure loads of cones under axial compression only, external pressure only and under combined loading, (ii) the spread of plastic strain and the effect of strain hardening of the material on failure loads, and (iii) the sensitivity of buckling loads to initial geometric imperfections or to structural defects under various loading conditions. The thesis provides results of extensive FE calculations. An experimental programme involved tests on thirteen conical specimens CNC machined with integral top and bottom flanges from 252mm diameter steel billet. The specimens were made from mild steel material with average yield stress of 230.6 MPa, Young's modulus of 21 0490 MPa and Poisson' s ratio of 0.28l. Prior to tests, the existing test rig had to be significantly modified and instrumented in order to accommodate independent/combined loadings. The test procedure has been developed and successfully implemented. Two models were subjected to axial compression, with further two subjected to external pressure. The remaining nine cones were subjected to combined action of axial compression and external pressure. Experimental results were compared with predictions of failure loads obtained from the existing design codes. For the case of axial compression an extension of the design rules is outlined in order to widen the range of applicability. For the case of external pressure, the test data compared well with the theoretical work by Esslinger and Van Impe, [40]. At the same time the test data highlighted how inadequate estimates of the load carrying capacity are given by the design codes. The case of combined loading, i.e., axial compression and external pressure is only covered by ASME code case 2286-2, [157], and experimental data does not exist. The current study provides the first and much needed test data. The thesis also looks into the concept of equivalent cylinder. Numerical results point out to the fact that this approach is unsuitable for combined stability scenario (axial compression and external pressure). Experimental data is also compared with predictions given by the Finite Element calculations. Details about various approaches to modeling material properties, shape, wall thickness distribution, and boundary conditions are discussed. The quality of FE models is assessed by comparing the FE predictions of the load carrying capacity with the test data.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available