Research On Damage Model And Reliability Of Double-layer Composite Shell Subjected To Multi-field Coupling

Double-layer composite shell is a kind of shell that the bonding interface between inner and outer layer is with metallurgical bond, whose material needs to be selected according to technical requirements. Its material structure is the same as the composite board, which belongs to composite materials. The double-layer composite shell has many incomparable advantages that the single-layer shell does not possess, which has been widely applied in aviation, nuclear power and petrochemical fields etc. Due to the specialty of industries process, raw materials and products, once the damage failure occurs, it is easy to cause significant casualties. Therefore, it is necessary to analyze the damage model as well as the reliability design and evaluation of such equipment.Double-layer composite shell is widely used in high temperature and corrosive environment, so its coupled environment is very complex, including the fluid - solid coupling with thermal elastic vibration and other factors, which makes the reliability design and evaluation extremely difficult. Through the literatures, so far there have been many studies on the structural integrity of high temperature components at home and abroad, but the studies on the reliability evaluation of high temperature components subjected to multi-field coupling are rare, moreover, the studies on the reliability evaluation of double-layer composite shell under high temperature is less. In this paper, the studies on the damage model and reliability of double-layer composite shell subjected to multi-field coupling will be conducted as follows:(1) Damage model of double-layer composite shellThrough analyzing the composite form and selection principles of shell, the performance characteristics of study object is clear. On the basis of analyzing the damage forms and internal stress of double-layer composite shell, the thermal stress damage model of double composite shell was established and the dynamic response was analyzed. Moreover, the fatigue damage model of double-layer composite shell subjected to multi-field coupling was established.(2) Material damage characteristics parametric test of double-layer composite shell Under complex coupling environment, the double-layer composite shell has clear local damage features. The degradation of macro and micro damage characterization were studied through micro-optical, X-ray and macroscopic strength, toughness and so on, which can infer the main damage causes. In addition, through statistical analysis of the experimental data from different parts of the double-layer composite shell structure, random parameters of reliability analysis model was obtained, thus the reliability of the shell can be evaluated.(3) Theory analysis of dynamic response of double-layer composite shell subjected to thermal - liquid - solid multi-field couplingThe mathematical model of dynamic response of composite cylindrical shell subjected to multi-field coupling was established, in which the multi-field coupling partial differential equation contains fluid impact load and thermal load. The solution of partial differential equation, including the double Laplace operator and the dynamic response with the changes of velocity, shell radius and length, and elastic modulus as well as the deflection function were obtained.(4) Finite element analysis of the dynamic response of double-layer composite shell subjected to thermal - liquid - solid couplingAccording to a typical double-layer composite shell structure, the finite element model of asymmetric double-layer composite shell was established, and then a comprehensive analysis on the dynamic response double-layer composite shell subjected to multi-field coupling was conducted, which includes modal, harmonic response and vibration analysis. The impact of material and structural parameters on structural response, as well as the dynamic response of double-layer composite shell was discussed. (5) Reliability assessment method of double-layer composite shell The reliability calculation method with statistical Von Mises stresses of 3D solid element nodes was proposed, and the secondary development technology of ANSYS and MATLAB was used to achieve 3D modeling, solving stochastic finite element and Von Mises stresses statistics. The proposed method was applied to the dynamic reliability assessment of cyclone. Moreover, based on Rice J integral theory, the J C integral approach was applied to solve the reliability of double high temperature components. The numerical and engineering examples were presented to verify the implementation effect of the J Cintegration approach. The J C integral can be used as the fracture parameters to evaluate the reliability of high temperature components with defects, which provides a useful expansion for the traditional stress - strength interference model.(6) Reliability sensitivity analysis of double-layer composite shellReliability sensitivity analysis reflects the importance order of the basic variables with the failure probability, which is the necessary step of robust optimization design of structure reliability. The correlated non-normal distribution random variables do exist in engineering, so the reliability sensitivity analysis model of correlated non-normal was studied. The three reliability sensitivity analysis methods, named orthogonal transformation method (OT), decomposition method (CF) and JC method respectively, were given, and their application advantages were analyzed. In addition, the mixed programming technology of Visual Basic and MATLAB was employed to develop the reliability sensitivity analysis system. The proposed methods were verified by numerical example and the correlated non-normal problem can be solved with computer, which can be used as a useful extension for the reliability sensitivity analysis methods.The study provides a theoretical basis for reliability design and evaluation of double-layer composite shell as well as the scientific basis for the work safety and equipment maintenance.