Studying the stress-strain state of composite cylindrical shells with variable mechanical properties under mechanical and thermal loads based on the Quasi-3D high-order shear deformation theory

1. In this study, the PhD candidate has built a model, established the basic relationships and equilibrium equations in orthogonal curvature coordinate systems for FGM cylindrical structures subjected to combined mechanical, thermal, and mechanical-thermal loads with different boundary conditions based on the Quasi-3D high-order shear deformation theory; provided a solving scheme for the problem of determining the stress-strain state of shells, in which the shear stress components are determined through the equilibrium equation of the spatial elastic theory to satisfy the requirement for the accuracy of the intrinsic equilibrium condition.
2. The PhD candidate has proposed the use of a single trigonometric series, combined the variable separation method and the Laplace transform to solve the problem of closed cylinder shells under the axial symmetry load. The system of partial differential equations has been converted into systems of ordinary differential equations by separating variables, which is more convenient for the solving process.
3. Analysis results regarding the influence of the geometry and the material of the FGM composite cylinder shell, the type of the mechanical/thermal loads, and the boundary condition on the stress-deformation state of the shell; the evaluation of the concentration-stress phenomenon at locations with a strong “boundary effect”. The quantitative comments are of scientific and practical significance for FGM-shell-structure studies, especially thick and/or short shells.