M.Sc Thesis


M.Sc StudentAlexander Broytman
SubjectBuckling and Post Buckling Behavior of Stiffened Composite
Cylindrical Panels under Combined Loading
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Abramovich Haim
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Stiffened cylindrical shells or panels are major components of an airplane. There is an advantage to construct stiffened cylindrical panels from composite materials, mainly because of their lower specific weight. The present study focuses on buckling and post buckling analysis of stiffened cylindrical composite laminated panels using the ANSYS finite element software. Finite element models of a single panel and torsion box (two panels connected by two flat aluminum thin plates) were built. The models simulated structures and their associated boundary conditions, which were tested in buckling tests at the Aerospace Structure Laboratory at the Technion. Linear and non-linear, static and quasi-static (dynamic) numerical methods were used. In order to perform quasi-static analysis, the ANSYS/LS-DYNA module of ANSYS software was used.

The work consists of four phases: studying the buckling solution methods presented in the software by solving a simple structure, buckling and post buckling analyses of a single stiffened cylindrical panel and comparing with test results, sensitivity analysis of the first buckling and collapse loads due to stiffener structure variation, and buckling and post-buckling analysis of torsion boxes under compression and torsion loading.

During the analysis of the flat stiffened rectangular panel, good agreement was found between the different buckling solution methods utilized in ANSYS (especially among the non-linear methods). It was found that only the quasi-static solution method was able to pass the first buckling load into the post-buckling region and to solve the structure behavior until total collapse.

Concerning the analysis of the stiffened cylindrical panel, a good agreement between analysis and tests was found. The quasi-static solution gave the closest results to the test values. In general, the test results were slightly higher than the numerical ones which are in contradiction to common practice.

During the sensitivity analysis, the best stiffener configuration for the first buckling load and the best configuration for the collapse load (a different one) were found. It was found that a buckling load has a maximum when increasing the stiffener height and decreasing the panel thickness.

The results of the analysis of the torsion boxes were higher than the test results in the case of first buckling load while for the collapse load case, the analysis results were usually closer to the test ones. In addition, a convex first buckling interaction curve for combined loading was found - confirming the Papcovich criterion.