Research On Drilling Damage Mechanism And Open Hole Tensile Performance Of Plain Carbon/Glass Hybrid Composite Plate

As a representative new material,fiber-reinforced composites have become the preferred material for high-end equipment manufacturing in our country,due to their lightweight,high specific strength and excellent designability.Hybrid is an import concept of composite design,and its components exhibit great application potential,especially carbon/glass hybrid composites have been used in the fields of aviation,transportation and military,etc.Composite components are often manufactured in an integrated way by near-net forming,but in order to meet the demands of connection and assembly,a large number of connecting holes need to be processed with extremely strict damage tolerances.Serious defects involving tearing,delamination and others are easy to occur due to their heterogeneous structures and anisotropic characteristics induced by cutting force and heat.However,carbon/glass hybrid composites are confronted with more complex damages and failure mechanisms during drilling due to the difference of the inherent properties of the two materials.In addition,the promotion and application of fabric structural composites also attracted the attention of the industry on its drilling processing and performance.Stress concentration around the open hole will significantly reduce the ultimate strength and service life of the composite,thus bringing challenges to the bearing capacity of the open-hole hybrid composite.Therefore,this master’s dissertation has studied on the drilling damage mechanism and tensile behavior of woven plain carbon/glass hybrid composites,and characterized the dynamic drilling temperature field of hybrid composites,and established the relationship between cutting force,heat and damage,and investigated the failure modes of perforated parts under tensile loads.The specific research contents are summarized as follows:(1)Investigation on damage mechanism of plain carbon/glass hybrid composites under cutting force and heat.In this work,the drilling experiments of pure carbon fiber composites,pure glass fiber composites and hybrid composite plates were carried out.Based on the damage factor,the drilling damage of each sample was compared and analyzed.The results show that drill-out material reaches highest temperature and which exceeds the glass transition temperature of the resin during the whole drilling process.The glass fiber layers of the hybrid sample accumulate a large amount of heat and dissipate slowly,leading to debonding and fiber pull out.The carbon fiber layers can form a rigid support as a hybrid composite to effectively prevent the out-plane deformation and reduce the delamination at the exit.(2)The influence of fabric reinforced phase structure and process parameters on the quality of hole making.In this work,the drilling characteristics of woven plain woven and two-dimensional triaxial braided carbon fiber composites were compared and analyzed.It is found that the triaxial braided carbon fiber composites have slight tear damage,but their burr defects are obvious.Orthogonal drilling experiments with different spindle speeds and feed rates were designed and carried out,and the thrust force and temperature under different process parameters and their influence on drilling quality were analyzed.The results show that the high feed produces a large thrust force,resulting in significant tearing and delamination defects when drilling materials.At high spindle speed,the burr defect decreases,but the burr increases significantly as the feed rate decreases.(3)Tensile properties of carbon/glass hybrid composites with an open hole.On-axis and off-axis tensile tests were carried out for the samples with low damage holes,and the crack propagation of the samples during tensile was captured using infrared thermography.In addition to damage morphologies and mechanical curves,the numerical model based on continuum damage mechanics was also established through the finite element software ABAQUS,and the strength prediction and failure analysis were obtained.The results show that damage originates from the hole edge due to the stress concentration effect.Failure strain and toughness of hybrid composites are significantly improved compared with pure carbon fiber composite,and its rapid crack growth is effectively restrained.The hybrid specimen with carbon fiber inside has higher tensile strength and failure strain,and performance and failure mode are more sensitive in offaxis load.