| Carbon fiber-reinforced plastics(CFRP)is one of the most advanced composites.Compared with metal materials,it has the advantages of low density,high specific strength,high specific modulus,corrosion resistance,fatigue resistance which has been widely used in aerospace and military and developing more and more in the fields of automobile,fitness equipment,mechanical arm,bridge and chemical containers.In the application of CFRP,it is inevitable to carry out secondary processing.Drilling is the main processing form.However,due to the inherent anisotropy,non-uniformity and low interlaminar bonding strength of CFRP materials,delamination,burrs,poor surface roughness,fiber pullout and tearing are easily encountered in the cutting process of CFRP.Delamination is considered to be the main damage.Ultrasonic-assisted drilling(UAD)technology is widely used in the processing of hard and brittle materials,which can improve the quality of materials.This paper focuses on the delamination damage of CFRP under the condition of UAD.The main contents of this paper are as follows:1)The delamination mechanism of CFRP-UAD was studied.The composition and properties of CFRP were analyzed.According to the inherent characteristics of CFRP and UAD,the material removal process of two most common drilling modes,right angle cutting and abrasive cutting was analyzed.The influencing factors of delamination damage and the role of ultrasonic vibration in reducing delamination damage were revealed theoretically.The experimental platform was built,the experiment of delamination process was designed,and the evaluation method of delamination was introduced.Through the analysis of the experimental results,the layering mechanism under different drilling forms was obtained,and the correctness of the above analysis was proved,which provides a theoretical basis for the delamination control methods.2)The cutting force characteristics of CFRP-UAD were studied.Based on the brittle fracture theory and the classical plate and shell theory,combined with the mechanism of delamination damage,a critical thrust force model for core drill was established.Based on indentation depth theory,the tool blockage of core drill was taken into account,and a semi-empirical cutting force model of core drill under UAD was established.A cutting force measurement platform for UAD was built,and single factor experiments under different processing parameters were designed.The experimental results show that the experimental values were in good agreement with the theoretical values,and the causes of the deviation were analyzed,which provides data support for the delamination damage control methods.3)The delamination control method of CFRP-UAD was studied.Based on the mechanism of delamination damage and the research results of cutting force in this paper,the control methods of delamination were discussed,and the control methods of delamination were put forward from three aspects: material properties,processing tools and processing technology.Emphasis were laid on the analysis of different processing tools(core drill,twist drill,improved twist drill and dagger drill).The delamination damage experiments of different tools under different parameters were designed.The experimental results of delamination damage morphology,cutting force,delamination damage area and delamination damage thickness under different tools were obtained.The processing characteristics of different tools were obtained through the analysis of the results,and the corresponding application scenarios were given.In this paper,through theoretical analysis and experimental research,the delamination mechanism,the effect of ultrasonic vibration on CFRP,the cutting force characteristics of CFRP and the control methods of delamination were deeply studied.The theory of delamination process,the critical thrust force and the axial cutting force model of delamination were obtained.And the characteristics of different tools provide guidance and reference for UAD of CFRP without delamination. |
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