Buckling And Post-Buckling Analysis Of Thin-Walled Composite Structures

Reducing the weight of the structures plays an important role in energy savings and optimum design of aircrafts. Because composite materials have many excellent characteristics, ultilization of composite materials in aircraft construction can reduce the weight of structures by 25~30% when compared to those of traditional metal ones, and they can improve the aeroelastic property of the airplane and flight performance obviously. Where and how much amount of the advanced composite materals are used in aircrafts have been an important criterion to measure whether aircraft structures are advanced or not. While the composite aircrafts are usually made of thin-walled laminated composite panels, they are vulnerable or suspectable to instability and nonlinear large deformation under combined loading. Though there are many studies in the literature on the buckling and post-buckling of composite structures, many pending issues, such as post-buckling of composite structures under combined shear and compression, simplified tools for buckling analysis, etc., are still not well addressed. Thus, there are needs to develop advanced methods to analyze the post-buckling behavior of thin-walled composite structures under combined loading and develop simple yet relatively accurate analytical prediction tool for buckling analysis.In Chaper 2, a semi-analytical solution for the shear buckling of symmetric laminated plates with all four edges elastically-restrained against rotation is presented based on the Galerkin method. The considered laminated plates are loaded in pure shear or combined shear and compression. The deformation shape function is constructed through a unique weighting combination of vibration eigenfunctions of simply-supported and clamped conditions, and it is an effective method for solving the considered eigenvalue problem. A parametric study is conducted to evaluate the effect of the rotational restraint stiffness, aspect ratio, material orthotropy and anisotropy on the buckling behavior of the rotationally-restrained symmetric laminated plates under pure shear or combined shear and compression action.In Chapter 3, the nonlinear governing equations of rotationally-restrained symmetric laminated plates with imperfection are presented by the Galerkin method, and they are solved by employing the Newton-Raphson method for the post-buckling analysis. The considered laminates are loaded in pure in-plane shear or combined in-plane shear and compression. The deformation shape function of the restrained plates is obtained through a linear combination of vibration eigenfunctions of simply supported and clamped beams along either the longitudinal or transverse direction of plates. It shows that the presented method is accurate and effective for performing the nonlinear analysis of laminates with all four edges elastically-restrained against rotation by the comparisons with the results of finite element analysis. A parametric study is conducted to evaluate the effect of rotational spring stiffness, material properties, and fiber orientation under pure shear as well as the loading ratio under combined shear and compression on the post-buckling behavior of rotationally-restrained symmetric laminates.In Chapter 4, the post-buckling analysis of laminated plates under combined shear and compression is presented using the nonlinear finite strip method. Similar to the end shortening strain for compression, the skewed angle strain is uniquely proposed for in-plane shear action. The nonlinear governing equations under the skewed angle and end shortening are solved numerically using the Newton-Raphson method. The numerical finite element analysis is conducted to validate the proposed method, and a parametric study is performed to show the post-buckling behavior of composite plates. It is noted that the resulting average longitudinal and transverse section forces induced by the out-of-plane deflection or so called the non-linear strain cannot be ignored when compared to the average shear section force for the case of shear action.In Chapter 5, shear post-buckling of composite laminated plates controlled by skewed angle strain is studied using the First-order Shear Deformation Plate Theory- based spline finite strip method, and then post-buckling of rectangular composite plates rotationally restrained at the longitudinal unload edges and subjected to end shortening strain at the simply supported loaded edges is analyzed using the spline finite strip method, two cases of elastically- and rotationally-restrained plates are analyzed: rotationally-restrained along both the unloaded boundary edges(RR) and one rotationally-restrained and the other free along the unloaded edges(RF). Post-local-buckling of fiber-reinforced plastic(FRP) composite structural shapes is further investigated by employing the spline finite strip method with the discrete plate analysis technique, the two cases of rotationally-restrained plates(i.e., the RR and RF plates) are further treated as discrete plates of closed and open section FRP shapes, and by considering the effect of elastic restraints at the joint connections of flanges and webs, post-local-buckling of various FRP shapes under end shortening is studied. The numerical comparisons with the finite element modeling demonstrate that the proposed discrete plate analysis technique and spline finite strip method can be used as an efficient and valid tool for post-local-buckling analysis of FRP shapes.In summary, both the buckling and postbuckling behavior of composite structures are studied using either the Galerkin method or finite strip method. In particular, the composite plates or panels under in-plane shear or combined in-plane shear and compression action are considered, and analysis of the restrained composite plates as well as the thin-walled FRP shapes by the discrete plate is presented. The research presented in this dissertation provides improved and effective analysis methods for composite structures, such as shear postbuckling analysis.