Finite Element Analysis Of Laminated Composite Plates Subjected To Thermal-Mechanical Loads Based On Refined Global-Local Higher-Order Theory

Nowadays, laminated composite structures have been widely used in aerospace, architectural engineering, vehicle engineering and many other military and civilian areas for their high strength ratio, high modulus ratio, good corrosion resistance and excellent designability. Compared with other traditional materials, due to the mismatch in material properties between adjacent layers, laminate composite structures also have many shortcomings, such as heterogeneity, anisotropy and environmental sensitivity which will make the deformation and failure mechanisms more complicated under the effect of external loads. Especially, in the process of manufacturing and practical engineering, rapid changes in temperature are often occurred coupled with huge mechanical loads. Under the combined influence of both thermal and mechanical loads, severe interlaminal stresses will be easily produced and may induce large deformation which will cause the failure of the entire structure. Therefore, in order to ensure the safety and reliability of the laminated composite structures, how to predict the accurate distributions of the interlaminal stresses under thermo-mechanical loads has become a key problem in academic and engineering circles.To begin with, the theories of laminated composite plates and research methods of interlaminal stresses are reviewed and concluded in detail. Compared with other theories, the refined global-local higher-order theory can not only satisfy the continuity conditions of transverse shear stresses and in-plane displacements along the thickness of the plate, but also predict the in-plane stresses and transverse shear stressed accurately without any post processing. In addition, it can achieve a good balance between computational efficiency and accuracy. Moreover, in comparison with other methods, finite element method which is based on computer technique has shown more superiority, because it is not only unlimited to the experimental environments, the form of loads and boundary conditions, but also flexible to geometrical shape of the object. In other words, it can solve the problem that all shapes subjected to all loads. Therefore, this method is adopted in this paper. The main work of this thesis are as follows:1) Firstly, the refined global-local higher-order shear deformation theory is deduced detailedly. By means of employing displacement continuity conditions at interfaces, transverse shear stress continuity conditions and transverse shear free conditions of upper and lower surfaces, the total number of displacement variables in final displacement fields is reduced to 19 which are independent to the layers of laminated plates. Subsequently, based on the idea of the DKQ element, transverse displacement functions which can satisfy C0 and C1 continuity conditions between elements are constructed and a four-node quadrilateral laminated plate element which has 19 degrees of freedom per node is also established. Lastly, the strain matrix and the shape function matrix are provided explicitly.2) When it comes to the problem that laminated composite plates subjected to thermal loads, three-dimensional elastic solutions and temperature fields are summarized firstly. Two kinds of temperature fields which include a uniform distribution and a linear distribution in the thickness direction are chosen in numerical examples. In addition, a number of aspects including number of layers, mesh densities and the ratio of width and thickness are taken into consideration to verify the accuracy of the theory and plate element. Numerical result reveals:the theory and plate element can provide a exact prediction of the response of laminated composite plates under thermal loads.3) Likewise, on the basis of existing literatures, three-dimensional elastic solutions of laminated composite plates under mechanical loads and thermo-mechanical loads are summarized. By compared with published results of other researchers and the computational results of ABAQUS, three-layer [0/90/0]s simply supported laminated composite plates are analyzed to verify the accuracy of the theory and plate element under thermo-mechanical loads.4) Last but not least, by the results of different ratios of width and thickness, the changing laws between the interlaminar stresses and the ratios of width and thickness are concluded. Futhermore, the explicit expressions between these two variables are provided. Besides, according to the commom design principles of laminated composite structures, six kinds of typical paving methods are analyzed to study the relations between the interlaminar stresses and fiber orientations. Beside,suggestions concerning the reduction of the transverse shear stresses are provided.