Three-dimensional Thermodynamic Analysis Of Fiber Metal Laminates

Fiber metal laminates are increasingly used in aircraft,automotive,aerospace and other fields,the safety of their using is a problem that must be considered.The study of thermodynamic response in complex operating environments becomes very necessary.Therefore,the heat transfer model,mechanical behavior constitutive model and thermal response of fiber metal laminates in hot and humid environment have important research significance.The main research work of this thesis includes the following aspects:（1）Based on the theory of heat conduction,the three-dimensional transient heat conduction partial differential equations were analyzed in detail.Firstly,the temperature evolution caused by the moving heat source in the finite field was modeled by reasonable assumptions,and then the temperature evolution of the finite thin plate was analyzed by the plane heat source with uniform distribution and Gaussian distribution.Finally,the temperature response of the thin plate was explored from multiple angles such as laser speed and sheet length to width ratio.The results showed that the highest temperature of the Gaussian distribution heat source is higher than the uniform distribution heat source under the condition of the same heat input and no phase change;the highest temperatures of the two laser heat sources occur behind the laser center and are strongly dependent on the laser scanning speed,and the highest temperature of the Gaussian distribution laser lags behind that of the uniformly distributed heat source;the laser operation is actually limited to the heating area,there is less diffusion in the cross-sectional area as well as in the thickness direction.（2）Based on the principle of energy conservation,the three-dimensional transient heat conduction differential equation of Fiber Metal Laminates（FMLs）was firstly established to obtain the corresponding temperature field.Then based on the elastic theory of laminated plates,the nonlinear motion control equations of fiber-metal laminates were established.Finally,based on the laser processing model proposed in this paper,the effects of laser power and related calculation parameters of the model（laminates material,fiber laying angle,etc.）on the thermal response of FMLs were studied by numerical examples.The results showed that the magnitude of the dimensionless deflection w*of the FMLs increases with the increase of laser powerq₀.The influence of fiber orientation on the dimensionless displacement u*,v*and w*of the midpoint of FMLs is different.The fiber orientation greatly affects the mechanical properties of the laminates,but the fiber orientation does not affect the vibration frequency of the FMLs.（3）For the three-dimensional transient temperature field and humidity field in a given hot and humid environment,firstly derived the constitutive equation corresponding to the FMLs structure and established its equation of motion,then used the finite difference method and the Newmark method to solve the dynamic equilibrium differential equation.Finally,the effects of fiber type,fiber arrangement angle and humidity coefficient on the deflection,normal stress and shear stress of FMLs were analyzed.The results showed that the amplitude of the dimensionless deflection w*of the FMLs decreases with the increase of the in-plane size ratio a/b of the FMLs.As a whole,the amplitude of the normal stress?_x of the laminates increases with the increase of the humidity coefficient,but the top of the FMLs the amplitude of the normal stress of the Al plate decreases with the increase of the humidity coefficient;the magnitude of the dimensionless deflection w*increases with the increase of the humidity coefficient.（4）Based on the separation variable method and the equivalent temperature method,first,a three-dimensional transient temperature field of coated fiber-reinforced metal laminates（CFMLs）during laser surface treatment was obtained.Then,the finite difference method and Newmark method were applied in the spatial and temporal domains respectively to solve the three-dimensional transient thermodynamic control equation of CFMLs under laser processing conditions.Based on the first two work,the effects of the number of fiber types and the number of FMLs on the deflection,normal stress,shear stress and vibration frequency of CFMLs were analyzed.The results showed that the number of fibers types affects the quality of the laminated structure,which affects the vibration frequency.The stiffness and mass of CFMLs decrease with the increase of the number of FMLs.The dimensionless deflection decreases as the number of FMLs increases,and the variation of the vibration frequency is opposite.The innovations of this paper mainly include:1.Based on the theory of heat conduction,the temperature evolution model of the thin plate caused by the constant velocity moving Gaussian distributed planar heat source in the finite field was established;2.Based on the elastic theory of laminated plates,the nonlinear motion control equations of FMLs in humid heat environment were established;3.Based on the separation variable method and the equivalent temperature method,the three-dimensional transient temperature field of CFMLs during laser surface treatment was obtained.In this thesis,the transient three-dimensional heat conduction problem of thin plates under laser action,the three-dimensional transient heat conduction problem of CFMLs during laser surface treatment,and the thermodynamic behavior of FMLs in hot and humid environment were studied,and the three-dimensional heat conduction and nonlinear dynamic behavior of the laminated structure were revealed,which lays a solid foundation for the theoretical research and practical application of the laminated plate.