Strength And Failure Analyses Of Adhesive Bonded Carbon Fiber Composite Laminate Joints Containing Defects

Carbon fiber reinforced composites(CFRP)have been widely used in the fields of aerospace,marine vessels,wind power,automobiles,and so on due to its high specific strength and specific modulus,excellent fatigue resistance,good shock absorption and corrosion resistance.Adhesive bonding technology has the advantages of maintaining the structural integrity,reducing weight,and less stress concentration w:ithin the joint region.Nevertheless,some defects will inevitably be formed from the improper manufacture process,which will shorten adhesive bonded structure's operation life,and more seriously,will trigger potential safety danger for composite components that are used in major application.Although numerous studies on the analysis of adhesive bonded joints containing defects,a lack of accurate strength prediction and reliable failure criteria still exists limiting a more widespread application of adhesive bonded composite joints in structural applications.Therefore,investigation on the influence of typical defects on the strength and failure progress of adhesive bonded joints is essential to deeply study the strength prediction and failure criteria and to improve the damage tolerance design of adhesive bonded composite structures.In this papery a systematical study on carbon fiber-reinforced epoxy-based composite single-lap joints containing debonding defect or wake bond introduced by improper surface prepare and inaccurate control of the curing process respectively,is conducted.The main tasks of this research are listed below:(1)Quantitative characterization has been carried out for defects in adhesive bonded CFRP laminates joints.1)Debonding defect:The irregular debonding defect in practice was standardized,and according to its geometric characteristics,ultra-thin aluminum foil is used to prefabricate debonding defects with different specifications in adhesive bonded carbon fiber composite joints.Then ultrasonic phased-array technology was used to detect the defective adhesive bonded joints.2)Curing process defects:Considering poor cure in the adhesive layer,quantitatively control of the curing temperature and pressure parameters in the curing process has been done to prepare adhesive joints with different curing process defects.(2)The influence of debonding and weak bond on the bearing capacity and failure mode of adhesive joints was studied experimentally.Tensile tests at room temperature with a constant displace rate were conducted in order to obtain the carrying capacity and load-displacement curve of the adhesive joints with defects,and then the effect of debonding parameters and curing conditions on the carrying capacity and failure mode of adhesive joints was obtained.(3)The influencing mechanism of the debonding defect on the bearing capacity and failure mode of single-lap joints of composite laminates was investigated.The deformation and failure progress of adhesive joints with defects during tensile tests were recorded by two-dimensional Digital Image Correlation(DIC)technology,and strain distributions of adhesive joints with defects were calculated by the record images.Based on the results,the effect of the debonding defect parameters and curing conditions on the stress and strain properties and failure process of adhesive joints,as well as the relationship between strain fields and failure modes were investigated in detail.In addition,finite element models were developed by using Cohesive Zone Model(CZM)in ABAQUS to analysis the stress and strain distributions as well as damage evolution of adhesive bonded composite single lap joints containing debonding defects,and the results were compared with the experimental results.