Exploiting internal pressurisation to enhance structural properties

• Main Author: Polenta, Valerio
• Published: University of Nottingham 2017
• Subjects: TA 630 Structural engineering (General)
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.728571

The thesis investigates ways to use internal pressure in a favourable way. It focuses on the structural effects of internal pressurisation of mechanical components. The buckling phenomenon of shell structures is analysed in depth and the conducted work confirms the long known beneficial influence of the internal pressure on buckling and suggests how to exploit this to the utmost extent. Changes in failure modes, stiffness and dynamic response due to pressurisation are also considered. Given the nature of the problem, Finite Element Analysis (FEA) is an essential part of the PhD project. The state-of-the-art FEA techniques are described and employed. Geometric imperfections are introduced in the FE models and, to this regard, a novel FEA technique ensuring high-accuracy simulations is developed. Parametric studies on thin-walled structures are carried out. The studies concern both straight and curved cylindrical shells, as well as more complex geometries. These were subjected to different combinations of loads including bending loads, compressive loads and internal pressure. Among the main findings, it is found that internal pressurisation can change the failure mechanism of the structure and, for a given geometry and material, an optimal value of internal pressure exist. This value allows to fully exploit the material capabilities and to maximise the mechanical performance of the structure. Moreover, it is found that internal pressurisation, as well as pipe curvature, modifies the stiffness and this is significant for structures wherein deflections must be kept to a minimum. Exploitation of internal pressurisation is especially attractive in applications wherein weight minimisation is a key objective. Therefore the content of the thesis is particularly relevant to the aerospace sector. A possible application consisting in the use of pressurised members within aircraft wings is here proposed. With regard to the above application, a prototype of a UAV wing with an internal pressurised structure was built. The structure is made of composite material for performance maximisation and its manufacturing process and related considerations are described. Experimental tests were performed with the aim of measuring the effects of internal pressurisation in the component stiff-ness and natural vibrational frequencies. Experimental results were compared to numerical results. Results confirms the potential of internal pressurisation to enhance mechanical properties.