Theoretical Study Of The Generalized Thermoelasticity Problem Of Composite Barrels

Non-Fourier heat conduction theories are used in the dissertation to investigate the heat conduction problem of carbon fiber reinforced resin matrix composite barrels under the powder gas temperature loading,and the effect of liner material on the temperature field is discussed.Then,the transiently coupled temperature and stress fields are obtained based on the generalized thermoelasticity theories.Focusing on the composite barrel with an inner-edge circumferential crack,the thermal stress intensity factors are calculated and the crack propagation mode is analyzed.At last,the effect of cylindrical interface crack between the liner material and the composite material on the disturbance of the temperature field is studied.The classical Fourier heat conduction theory has been used for a long time in practical engineering.However,its unphysical inherent drawback,infinitely thermal propagation speed,has prompted scientists to propose new heat conduction theories.Up to now,by introducingthe thermal phase-lag parameters,the common C-V and DPL models could predict the wave nature of thermal propagation in media.With simply mathematical form and straightforward physical meaning,the models are easy to use.Focusing on composite barrels,the non-Fourier heat conduction theories are first used in this dissertation to obtain the temperature field of the barrel when firing.The effect of three kinds of liner material,namely,steel,SiC ceramic,and refractory tantalum,is discussed as well.Based on the different kinds of non-Fourier heatconduction models,the thermal-elastic models are proposed accordingly,and they are named as generalized thermoelasticity theory.L-S and C-T thermoelasticity theories correspond to C-V and DPL heat conduction models,respectively,and the L-S model serves as a special case of the C-T model.Furthermore,the C-T thermoelastic model is adopted to get the transient temperature,displacement,and stress fields in the continuous firing condition.The fiber reinforced composite is assumed to be a macroscopically homogeneous,transversely isotropic material with effective properties which are obtained using the micromechanical method.In order to manage the transient problem easily,the Laplace integral transform is used thoroughly to eliminate the time variable in the governing equations and boundary conditions.After having the results in the Laplace domain,the numerical Laplace inversion technique is used to transform the results to the time domain.The effects of heat conduction model,phase-lags,liner material,liner depth,convective heat transfer coefficient of the barrel inner surface,and fiber volume fraction on the temperature and stress fields are analyzed.The results show that,compared to the results obtained from the diffusive Fourier model,non-Fourier heat conduction theory could predict significantly thermal wave propagation in a whole composite barrel,and the maximum temperature is pretty high.Luckily,the usage of a liner material decreases the temperatures remarkably.Among the three kinds of liner material,steel liner composite barrel has best responses,and the temperature value could be decreased if the liner is thickened.However,the barrel with thicker liner becomes heavier.Thus,a trade-off between the thermal response and lightweight demand is observed.The analysis of the effect of thermal-mechanical coupling and inertial terms shows that the former effect is much more significant than the later one.Thus,the coupling effect should be incorporated while neglecting the inertial effect when the generalized thermoelasticity theory is employed,which could give more accurate results while decreasing the complexity of the problem.Similar to the thermal responses,the usage of liner material weakens the mechanical responses.The convective heat transfer coefficient of the inner surface represents the ability of the inner surface temperature being affected by the temperature change of inner environment.A larger value of the coefficient means more thermal energy is transported into the barrel,thus,the magnitude of the temperature,displacement,and stresses increases.Temperature increases of the inner bore will cause a compressive axial stress near the inner surface of the barrel.If this stress is higher than the compressive yield limit of the composite material,the part of barrel near the inner surface will be in the yield state.Then,the compressive axial stress will release from the yield stress when the inner bore temperature decreases,and finally the residual tensile stress comes.This tensile stress stretches the barrel and might cause a circumferential crack at its inner surface.On the focus of a circumferential precrack with a particular length in the composite barrel,the generalized thermoelasticity theory is used in this dissertation to solve the thermal fracture problem,and the transient thermal stress intensity factor is obtained.Due to the manufacturing technique of the liner composite barrel and considering the high hoop stress of the barrel in service,the interface is prone to debonding.The non-Fourier theory is employed to investigate the heat conduction problem of a liner composite barrel with an interface cylindrical crack,and the two-dimensionally disturbed temperature field and the heat flux intensity factor is achieved.The mode I crack problem in cylindrical coordinate systems is formed when the circumferential crack is subjected to the axial thermal stress.With the help of standard Fourier and Hankel integral transform techniques and the singular integral equation method;the fracture problem could be solved.As a fundamental concept,stress intensity factor quantitatively represents the stress concentration degree near the crack tip.The effect of heat conduction model,convective heat transfer coefficient,crack length,and fiber volume fraction on the thermal stress intensity factor is analyzed.The results show that once a shallow circumferential surface crack starts to propagate,it will grow to a deeper crack,and its growth will be retarded when the crack becomes longer.The heat is impeded by the interface crack when it flows from the barrel inner surface to the outer one in a composite barrel,which results in the concentration of thermal energy at the crack tip.By assuming a partially conducting crack surface,the singular integral equation method is adopted to get the temperature field and heat flux intensity factor.The effects of liner material,liner depth,and heat transfer coefficients of the crack surface and barrel inner surface on the results are analyzed.One can conclude that the steel liner composite barrel has the best thermal responses with smallest temperature and heat flux intensity factor values.The crack has no disturbance on the temperature field when is crack is fully conductive,while the temperature jump across the crack surfaces is highest when the crack is fully insulated.