Study On Component Parameters Identification And Structural Optimization Of Fiber Reinforced Composites

Composite structures have been widely applied in the shipping,aeronautical and aerospace industries due to their excellent mechanical properties.In order to make full use of the superior properties of fiber reinforced composite structures,high-precision structural modeling and design have become an important link in composite engineering application.The accurate constituent performance is the basic information for material design and structural design,while the micro-properties of composite change significantly during the manufacturing process of composite materials.It is of great theoretical significance and application value to identify the micro-parameters of composites after shaping.In this paper,the sensitivity analysis method and the genetic algorithm method are respectively adopted to identify constituent elastic and strength parameters based on the macro-micro model of fiber reinforced composites.Based on the structural dynamic characteristics and strength optimization requirements,research on the structural optimal design of stiffened thin-walled structures is conducted,to optimize the volume fraction of fiber bundles on micro level and the stiffening patterns,the number and direction of layers,etc.on macro level.The specific research work includes:Firstly,an approach on elastic parameter identification of composite components is proposed based on sensitivity analysis method.Based on the finite element model of fiber reinforced composite on micro level,the sensitivity matrix of static displacements with respect to elastic parameters of composite components is formulated and the objective function is defined as the 2-norm of differences between the measured and calculated data on displacements.The relative sensitivity and condition number are introduced to the algorithm to deal with the ill-posed problem during the identification process.The fiber reinforced composite and the 2.5D woven composite are employed respectively to verify the validity and accuracy of the components elastic parameter identification method.The influence of sensitivity analysis method,measurement points selection and measuring errors on identified results are discussed respectively.Secondly,an approach on strength parameter identification of composite components is proposed based on the genetic algorithm.The direct analysis is completed based on the Chamis strength analysis model to obtain the macro-equivalent parameters from the components parameters and the Tasi-Wu failure criterion to determine the macro-scale strength failure of elements.The strength parameters of macro-laminates are identified by global search function of genetic algorithm.The component strength parameters of composite are deduced from the Chamis strength model formula combining with the identified component elastic parameters.The unidirectional composite laminates and multidirectional composite laminates are employed respectively to verify the component strength parameters identification method.Finally,an approach on optimal design method of composite stiffened thin-walled structures is proposed.Combining the requirements of static strength and structural frequency response,the objective function is set to minimize the mass of stiffened thin-walled structures.The optimal design of structural parameters,such as the volume fraction of fiber bundles,the stiffening methods,number and direction of layers and so on,are conducted,which provides a design method for composite reinforced structures in engineering.