Multi-scale Anayysis And Experimental Research On The Damage And Failure Of The Plain-woven Fabric Composite Structures

Plain-woven fabric(PWF)composites have been widely used in the design and manufacturing of the high-performance light-weight structures in the airplanes owing to the excellent mechanical properties,the advantages in processing formation performance and the lower production cost.PWF composite structures exhibit obvious multi-scale characteristics,and the mechanical properties and the failure mechanisms of the PWF composites are closely related to the properties of the constituents and the fiber tows in the different analyzing scales.The analysis on the practical engineering PWF composite structures urgently calls for the advanced multiscale analysis methods with high efficiency.However,there are few application cases for the existed multi-scale analysis methods on the large-sized practical engineering PWF composite structures.Since there are difficulties for the academic researches in considering the material choice of the practical engineering structures,the engineering application space of the experience and the data accumulated in the existed multi-scale researches is limited.Besides,under the influence of the aging factors and the economic factors,the engineering analyses are generally short of the support from the fundamental experiments,and it is generally difficult to conduct the multi-scale failure analysis on the practical engineering PWF composite structures.The development of the multi-scale failure analysis method for the PWF composite structures which explains the structural failure into the fiber and matrix constituents’ depth is of significant importance for the composites’ academic researches and engineering strength predictions.Corresponding to the backgrouand of the practical engineering requirements,this research takes the PWF composite of T300/Cycom970 which is widely used in the aerospace structures as the study object.Based on the MMF theory,the multiscale method for the failure analysis of the PWF composite structures is proposed,and then experimentally validated and applied in the failure analysis of the practical engineering structure of the composite beam webs under shear loading.In detail,the research work of this dissertation could be summarized as follows:The modelling parameters for the representative unit cells(RUC)of the T300/Cycom970 PWF composites have been achieved,and the corresponding microscale and mesoscale RUC models have been established.The mesoscale RUC of the PWF composite under uniaxial tensile load has been analytically analyzed,and the analytical model in predicting the PWF composite’s longitudinal elastic modulous has been proposed.With the analytical model,the relationship between the modelling parameters of the RUC and composite’s macroscale mechanical property has been established,which makes it more convenient to filtrate the suitable modelling parameters for the RUC models’ establishment.Based on the analytical model,a new method which combines the analytical calculation and the finite element calculation has been proposed in filtrating the modelling parameters and validating the RUC models.Helpful reference has been offered in improving the efficiency for the RUC models’ establishment.The strength studies of the composite of unidirectional tapes(UNI)and PWF with the same constituents of T300 fiber and Cycom970 matrix have been correlated.The method in determining the constituents’ microscale strengths for the PWF composite has been proposed.Based on the MMF theory,the microscale strengths of the T300/Cycom970 UNI composite have been determined with the assistance of the experimental macroscale strengths of the T300/Cycom970 UNI composite laminates.The mesoscale strengths of the fiber tows in the T300/Cycom970 PWF composite are then back-calculated under the microscale strengths invariant hypothesis and revised with the macroscale strengths of the T300/Cycom970 PWF composite laminates.The microscale strengths of the T300/Cycom970 PWF composite which offer reference and support for the following multi-scale failure analysis are then determined with the revised mesoscale strengths of fiber tows.The stresses of the PWF composite structures are classified according to the different analyzing scales.Based on the mesoscale and microscale RUC models and the stress amplification factor method,the stress transformation method for the PWF composite structures has been developed in transferring the macroscale stresses into the mesoscale and microscale stresses.The multi-scale finite-element procedure for the failure analysis of the PWF composite structures is then proposed,on the basis of which the failure of the open-hole T300/Cycom970 PWF composite laminates under compression loading is numerically analyzed.The calculated results are compared with the experimental results in different aspects,and the rationality of the proposed multi-scale failure analysis method for the PWF composite structures is validated.Finally,the proposed multi-scale method is applied in the failure analysis of the practical engineering PWF composite structures of beam webs.The carrying capacity and the failure characteristics of the PWF composite beam webs under shear loading are studied through the multi-scale finite-element analysis together with the experimental methods.With the shear experiments applied on the two different types of PWF composite beam webs,the experimental results of the structural stability,the ultimate failure loads and the failure modes under shear loading have been achieved and compared.The finite-element models corresponding to the two types of specimens are established and the multi-scale finite-element failure analyses are conducted on the buckling and post-buckling of the beam webs.The numerical results are compared with the corresponding experimental results,with the feasibility of the finite-element models validated and the failure mechanisms of the composite beam webs analyzed.Based on the experimentally validated finite-element models,the parametric analyses are then conducted.The effects of the open-hole and the reinforcement on the open-hole region on the structural stability and the carrying capability of the PWF composite beam webs are investigated.