A moving boundary approach for cylinders subjected to high internal pressure

This dissertation proposes a novel analytical approach for elastic plastic analysis of thick wall cylinders under internal pressure. It involves two parametric functions and piecewise linearization of the stress strain curve. A deformation type of relationship is combined with Hooke's law in such a way that stress strain law has the same form in all linear segments of the material curve, but each segment involves different material parameters. -- This approach incorporates the deformed geometry in elastic plastic analysis of thick wall cylinders. Using an iterative procedure based on the principle of virtual work, this approach accounts for the effect of deformed geometry due to high internal pressure. The resulting analytical formulation is capable of predicting stress, strain, displacement, and energy on a moving boundary basis. -- The analytical formulation for autofrettaged cylinders obeying work hardening material behavior has also been presented. An iterative implementation procedure for shakedown pressure calculation has been developed. Shakedown pressures have been calculated for both undeformed geometry and deformed geometry. The proposed formulation has also been applied to plastic collapse load estimation. Calculations indicate that the moving boundary approach provides conservative plastic collapse load estimation compared with the traditional small deformation theory. -- This moving boundary approach is appropriate for inelastic analysis including autofrettage, shakedown, and limit analysis on thick wall cylinders. The comparison of the analytical formulation with the ANSYS inelastic finite element analysis is favorable. -- The effect of deformed geometry on inelastic analysis has been assessed on thick wall cylinders subject to high internal pressure. The discrepancy of results between the proposed method and small deformation theory has been analyzed. Calculation indicates that the difference of energy is significant for high internal pressures. -- The J integral of thick wall cylinders with circumferential flaw has been evaluated using the ANSYS finite element program. The result indicates a significant difference between the analysis using large deformation and small deformation theories. This difference depends on the magnitudes of the internal pressure, and is dependent on the material behavior. It indicates that neglecting the difference can be unconservative when evaluating the inelastic fracture parameter, J integral. Therefore the proposed approach is appropriate for representing energy of deformation in the energy approach in fracture mechanics, as it incorporates the effect of geometric change due to high internal pressures. -- As the analytical approach can be implemented by MAPLE program, this method represents an alternative assessment tool that can be used for inelastic analysis of thick wall cylinders, which is usually performed by the more expensive and elaborate nonlinear finite element analysis