Numerical Analysis And Experimental Study On Propagation Behavior Of Laminated Composite Plates With Embedded Delamination

Fiber reinforced composite laminates have become one of the most importantstructural materials in modern airplane industry because of the excellent mechanicalproperties. However, during the manufacture process, the delamination in laminatedcomposites is unavoidable, which will lower the loading capacity and the fatigue life.Therefore, the delamination existed in laminated composites is a key factor to thestructure security and must be payed full attention. In this paper, aimed at the typicaldelamination existed in actual structures in airplane, theoretical analysis, numericalresearch and experimental study have been put forward to predict the delaminationstatus of carbon fiber reinforced resin composite laminate under both compressiveload and compressive fatigue load, in order to investigate the effect of delaminationon the mechanical property of the composite structure quantificationally and providethe evaluation theory and the experiment foundation ulteriorly.Through collecting statistics of the actual delamination existed in compositesduring the airplane manufacturing, we establish the typical delamination parameters,based on which the investigation has practical value in engineering application.Furthermore, we build the numerical model based on the cohesive element theoryand the delamination buckling and growth behavior in laminated composites hasbeen predicted. And by implementing experiments of interfacial mechanicalproperties and delamination buckling, the validation of numerical model has beenproofed. Besides, the effect of specimen length-width ratio, delamination size anddepth position on the delamination behavior has been investigated quantificationallyin order to build evaluation standard of the sensitivity parameters on delaminations.Otherwise, during the fabrication of laminated structures, the uneventemperature field and the corresponding residual stress and the uneven distributingresin are always unavoidable which results in several delaminations appearing thesame time in a certain scope of the laminated composites. At present, there is noreference introducing the coupling behavior between those coexisting delaminations.Therefore, based on the research of single delamination, chapter three focuses on themultiple delaminations and the corresponding delamination growth behavior, in orderto build the allowance for multi-delaminations. For the first time, we investigate thedelamination behavior of double delaminations both in depth position and in plane.Using the cohesive element method, we ascertain the buckling mode and thecoupling behavior between the existing delaminations; we put forward a three stagetheory of the coupling scope; and we investigate the effect of delamination size anddepth position on the coupling behavior between coexisting delaminations in detail.As the delaminated plate undergoes repeated buckling and unloading, aprogressive accumulation of damage at the delamination front occurs. As a consequence, an existing delamination may grow, even if the static growth criterionis not satisfied. Therefore, in chapter four we implement the compressive fatigueexperiments based on the static experiment and study the delamination fatiguegrowth behavior including the delamination growth rate and the delaminationstabilized length. Otherwise, the components of energy release rate have beencomputed and fully considered by finite element method using VCCT technology.The effect of loading level, delamination size and depth position on delaminationfatigue growth behavior has been analyzed quantificationally. And a SEMfractographic analysis has been performed to investigate the micro mechanics ofdelamination growth behavior.In chapter five, we put forward a simplified model on delamination fatigue.Based on the compressive fatigue experiment, the empirical parameters for numericalanalysis have been obtained by curve fit of experimental data, and there exists highsimilarity between numerical results and experimental results proving the validationof this numerical model. Otherwise, using this simplified model we haveaccomplished the prediction of fatigue delamination growth for central delaminationsuccessfully, proofing that the mentioned model is highly computable and applicable.