| Functionally graded materials(FGMs)are composed of two or more discrete constituent phases with continuous and smoothly varying components.Due to the distinctive merit comparing with usual composite materials that they can reduce the stress concentration and optimize the stress distribution to make good use of each component,utilizing of FGMs helps to resolve some problems in composite materials such as low bond strength and inharmonious of properties effectively.Based on the concept of functional gradient,many novel graded materials have been developed and extensively studied.Due to the preparation technology or for the need of special structures,micropores or pores are commonly found in various types of FGM and play an important role in the influenceial factors on mechanical properties of FGMs.In addition,the application conditions of FGMs are usually complex or extreme with multiple physical fields,and the mechanical responses of various FGMs under coupleing melti-fields will be more complex.Based on the mechanics composites,mechanics of elasticity and theory of heat and mass transfer,considering synthetically the porosity type,effect of aggregation,distribution type of reinforcement,properties dependency to heat and moisture and coupling of heat and mass transfer,the mechanical models and calculation methods of multi-field responses of novel FGM rotating disks with variable thicknesses which reinforced by particles(ceramic-metal,piezoelectric-piezomagnetic),long fiber in nanoscale(carbon nanotube)and short fiber in nanoscale(graphene nanoplatelet),are further studied.A rotating FGM circular disk with ceramic-metal contents and variable thickness,considering temperature-dependent property of the material parameters,was investigated.The variation of thickness of disk was represented by the specific geometric parameters.The governing equations of temperature and displacement of disk were established on the basis of steady heat conduction and linear elastic theory,and solved numerically by layered approximation method.The effects of gradient index,variation of thickness,angular speed,and temperature conditions on thermodynamic response of the circular disk were discussed in numerical examples.A formula for pores which is combined linearly with contents itself and interfaces between the contents,for a rotating circular FGM circular disk with metal and ceramic contents and variable thickness,was proposed.Considering temperature-dependent property of contents and fillers in pores,and total humidity diffusivity and humidity-dependent density,the nonlinear steady hygrothermal equation was established.The governing equation of displacement of the circular disks was developed by linear elastic theory,and solved by the differential quadrature method(DQM).The effects of gradient index,the types and parameters of pores,the variation of thickness,hygrothermal conditions,and angular speed on the hygrothermal field and mechanical response of the circular disk were discussed in numerical examples.Taking magnetoelectric effect of contents into consideration,a rotating porous circular FGMEE disk with variable thickness under steady hygrothermal environment was investigated.The hygrothermal equation was established by adopting the theory of steady heat conduction and humidity diffusion.The electromagnetic displacement governing equation was established on the basis of Maxwell's electrodynamic theory,passive electrostatic and magneto-static equations,and linear elastic theory.The differential quadrature method(DQM)was utilized to solve the governing equations.The effects of contents,gradient index,the types and parameters of pores,the variation of thickness,and hygrothermal conditions on the multi-field response of the circular disk were discussed in numerical examples.In the study of rotating circular plates with varying thickness which made of functionally graded carbon nanotube reinforced composite(FG-CRC),the prediction model of properties of functionally graded carbon nanotube reinforced composites(FG-CRC)taking consideration of probability of aggregation of carbon nanotube(CNT)was established;considering coupling effect of heat and mass transfer,the equations of heat and mass transfer in FG-CRC circular plate were established;the equilibrium equation was established based on linear elasticity;the spatial domain and time interval are discretized by DQM,Runge-Kutta and Newmark methods,then the numerical results were obtained.In numerical examples,the effects of heat and mass coupling transfer,aggregation considering probability,porosity,graded parameter,variation of thickness and rotating velocity to the heat and moisture fields and mechanical responses were discussed.In the study of rotating circular plates with varying thickness which made of functionally graded graphene nanoplatelet reinforced composite(FG-GRC),considering effect of aggregation of graphene nanoplatelet(GNP)in matrix,way of aggregation and distribution,prediction model of properties in the way of random or aligned distribution of GNP was proposed;the heat and mass transfer coupling equations and governing equation with respect to displacement were established;DQM,Runge-Kutta and Newmark methods were adopted to solve the equations numerically.In numerical examples,the effects of distribution way of GNP,way of aggregation,size of GNP,porosity,graded index and variation of thickness to the heat,moisture and mechanical responses were discussed.In this dissertation,the mechanical responses of several novel FGM rotating circular plates with varying thickness in heat and moisture environments were obtained by theoretical model and numerical methods.The influences of some factors to the mechanical responses were discussed.The work of this research not only enriched and developed the mechanics of composites and theory of heat and mass transfer,but also provided theoretical basis to the design,manufacture and application of engineering structures made of novel FGM with porosity,which,of course,has important research meaning and great value to engineering applications. |
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