Mechanical Behavior And Characterization Of Short Fiber Thermoplastic Composites

The continuous demand for ultra-high capability and lightweight in aerospace equipment has promoted the rapid development and widespread application of fiber thermoplastic composites.Non-uniformity and anisotropy of mechanical properties are the important characteristics of fiber composites.Especially,intricate microstructure of short-fiber composites is a huge challenge for the prediction of macroscopic equivalent properties of short fiber composites.The microstructure parameters such as fiber length,orientation and distribution have a great influence on the mechanical properties of short-fiber composites.This paper focuses on the microstructural characterization and the prediction of macroscopic properties of short fiber thermoplastic composites and the design of short fiber microstructure parameters.The main research content includes:(1)Random Sequential Adsorption method(RSA)is improved.Based on the spatial geometry concept,a rapid method to determine the intersection of two fibers is established.A parallel homogenization method for efficient calculation of equivalent properties is established.The results show that the proposed method guarantees the accurate prediction of equivalent properties and significantly improves the computational efficiency.The influence of microstructure parameters of short-fiber thermoplastic composites on macroscopic equivalent properties is analyzed.The equivalent modulus is related to fiber length,fiber mass fraction,and fiber elasticity.The equivalent modulus is positively related to fiber length,fiber volume fraction,fiber elastic modulus and matrix elastic modulus,while negatively related to fiber diameter.(2)Based on the orientation distribution function,the RSA method is improved.A mathematical model is established based on the orientation tensor to reconstruct the fiber orientation distribution function.The simulation of the length distribution of the traditional RSA method is inconsistent with the preset length distribution function.The random sequential adsorption method is improved and a reconstruction method for the microstructure of short fiber composites considering the fiber length distribution is established.The results of the example show that as the RVE size increases,the fiber length distribution is more consistent with the preset distribution function;(3)Updating approach considering discrete-variable and surrogate model optimization framework is proposed.The maximum value of EI function is optimized by using discrete-variable genetic algorithm to avoid the rounding error.It is verified by mathematical function examples and compared with the literature method.The optimal solution has a small phase difference and the number of running objective functions is less than half the literature method.An optimization model of microstructure parameters of short-fiber thermoplastic composites is proposed.The maximum equivalent modulus obtained by the discrete variable surrogate model optimization method is 62.4% higher than the initial value.