Study On Drilling Damage Mechanism And Characterization Method Of Plain Weave Composites

With the development of lightweight cars,Carbon Fiber Reinforced Plastics(CFRP)has been widely applied in the automotive industry.Its high specific strength,specific modulus,and good corrosion resistance and anti-fatigue properties enable it to help the lightweight and long life of aviation,vehicles and other products to achieve the goal of high performance and low energy consumption.However,due to the characteristics of multi-scale,heterogeneity,and anisotropy of woven CFRP,the initiation and evolution of damage during the process of assembling and making holes of knitted CFRP is extremely complex,and there are many influencing factors.The evaluation methods of geometric and mechanical properties are not comprehensive enough.Based on the above background,this paper studies the damage mechanism of braided composites during drilling,establishes a mesoscopic model of braided composites,and conducts finite element simulation of dynamic drilling.The damage degree around the hole is quantitatively evaluated,and a new method for characterizing the damage degree around the hole is proposed,which provides a new idea for studying the processing damage of braided composite materials.First of all,in order to simulate accurate simulation results,this paper combined with the micro morphology of the braided composite material,extracted the morphology features through image processing,obtained the geometric size of the micro model through digital fitting,and created the micro model of the braided composite material according to the results..The mesoscopic model.The constitutive relationship,initial damage criterion,interface failure criterion and damage evolution of the material are defined through the VUMAT subroutine.The finite element simulations under different drilling process parameters were performed on the two tool models respectively,and the reasons for the damage and defects around the hole were analyzed,and the damage mechanism during the drilling process of the braided composite material was revealed.Secondly,in order to quantify the degree of damage around the hole,this paper proposes a new damage evaluation method:Equivalent damage impact factor(FEDI).This method introduces the damage area and damage cracks around the hole.The combined effect of damage area and damage cracks on the damage degree around the hole is considered.It can more accurately characterize the degree of damage around the hole.Finally,in plain weave composite drilling hole experiment,on the plate after drilling a post-processing,namely around burr content analysis and around morphology of CT scanning,using electron microscope to collect around burr images,through image processing calculation around burr content proportion,to explore the system of low damage of braided composites hole process parameters.The internal damage around the hole was analyzed by CT scanning method,and the geometric model around the hole was reconstructed in the professional processing software,the slice image of the material internal damage was extracted,the image processing of the damaged area was carried out,and the equivalent damage impact factor around the hole was calculated.The results were compared with the finite element analysis to complete the experimental verification.