Investigation On Buckling And Thermal Buckling Behavior Of Composite Thin-walled Structure

The application of composite materials represents the scientific and technological level of advanced manufacturing industry in a country,and guides the development direction of modern industry.And thin-walled structure is the main utilization form of composite materials due to its outstanding advantages such as convenient design,easy manufacturing and processing,wide application scenarios and good working performance.However,because of the anisotropy and inhomogeneity and the complex mechanical response characteristics of laminated thin-walled structures,there are various research difficulties in its development of mechanics theories and engineering applications.It also results in the focus of simply supported,symmetrical and orthogonal laminated structures in existing literature rather than the research on general laminated structures.Buckling and thermal buckling are the important evaluation indexes of the stability of thin-walled structures,and composite laminated structures are sensitive to the buckling.The complexity of constitutive relationship increases the difficulty of stability research.However,the stability of thin-walled structures such as composite pressure vessels and pipes is very important for the safe operation of the system.Therefore,it is of important to detailed study the buckling and thermal buckling behavior of the composite thin-walled structure in this work.Firstly,the buckling problem of composite thin plate structure is studied theoretically.Based on the classical theory of shell,using the mode function of two end fixed beam as the approximate function of displacement,the theoretical calculation formula of critical buckling load is derived successfully.It is in good agreement with the numerical solution of ANSYS using FEM(Finite Element Method),and the maximum relative error is less than 7%.The critical buckling load increases with the increasing of the aspect ratio and the number of plies,while the stiffness coupling effect decreases with the increasing of the number of plies.Deducing the formula of critical buckling load reversely,the design formula of the number of plies is obtained.Calculation of the example with the actual mechanical parameters and literature parameters of 3D printed PLA material prove the reliability of the calculation formula.Then,the buckling of composite cylindrical shell under external pressure is studied in details.Taking the transverse shear force into account,and using the shape function of the two end fixed beam bearing the transverse shear force as the displacement approximate function,the theoretical critical buckling external load calculation formula is deduced successfully.The theoretical solution and the FEM solution are in good agreement,with the maximum error of 7.48%.Comparing with the theoretical solution in the existing literature,the theoretical method considering shear force can further improve the accuracy of result.The critical pressure load increases with the increasing of the thickness to diameter ratio,and the coupling effect between stretching and bending gradually was weaken with the increasing of the number of layers.The difference of the instability wave number is caused by the difference of the numerical method adopted by the theoretical solution and ANSYS solution as well as the influence of boundary conditions.Finally,the thermal stability of composite thin-walled shell structure is studied theoretically.The shape function of multi-modal two end fixed beam is used to simulate the buckling waveform of the two end fixed cylindrical shell.The critical temperature rise under the uniform temperature field is theoretically derived,and the accurate calculation formula is obtained successfully.The relative error between the theoretical and the numerical solution is small,which meets the engineering requirements.The critical buckling temperature rise of composite cylindrical shell increases with the increasing of the thickness-diameter ratio and the number of plies,while the length-diameter ratio has little effect on the critical temperature rise.The theoretical formula of critical load in this work can be used to guide the design of related composite thin-walled components.