Research On Laser Processing Of C/C Composites Based On Dic Technology

Carbon fiber reinforced carbon matrix composites(C/C)have low coefficient of thermal expansion,corrosion resistance,thermal shock resistance and wear resistance,and are increasingly used in weapons and equipment,aerospace and automotive manufacturing.It is difficult to achieve high precision processing by conventional processing technology,and laser processing technology has advantages that other processing methods do not have because of its low requirements on material size,shape,high processing accuracy and low thermal damage.Therefore,this paper takes C/C composites as the research object to study the interaction mechanism between nanosecond pulsed laser and C/C composites.Based on the orthogonal test,the main and factor significance of the influence of the process parameters on the test index and the oxidation law of the ablation zone are explored,and the influence law of the process parameters on the material deformation is analyzed by digital image processing technology(DIC).The specific research contents are as follows:(1)The primary and secondary influences,factor significance and mechanism of action of the process parameters of C/C composites processed by nanosecond pulsed laser were investigated by a four-factor,five-level orthogonal test.Repetition frequency,laser power,scanning speed and pulse width were used as the influencing factors,and width of cut,depth of cut and melt height were used as the experimental indicators to compare the ablation thresholds of the materials at different pulse frequencies.The results show that the laser pulse frequency affects the ablation threshold of the material,and the range of the ablation threshold was 1.101.19 J/cm2 for the repetition frequency of 40-70 kHz,and the laser power has the greatest influence on the test indexes among the factors.(2)In order to study the influence of nanosecond pulsed laser parameters on the processing characteristics of C/C composites,the ablation zone cutting width,cutting depth,melt height,heat-affected zone width,as well as the microscopic morphology of the processed surface and material oxidation conditions were compared by single-factor experiments with different process parameters.The results showed that the cutting width,depth and melt height increased and then decreased with the increase of repetition frequency,and the critical repetition frequency was 40 kHz.The increase of laser power and pulse width caused the cutting width,depth and melt height to increase gradually.Increasing the scanning speed can reduce the cutting width,depth and melt height as well as the heat-affected zone width,and increasing the repetition frequency and scanning speed can reduce the oxidation in the ablation zone.(3)To solve the problem of material deformation caused by thermal stress concentration during nanosecond pulsed laser processing,the laser process parameters and the displacement and strain patterns during processing were analyzed using the DIC technique to optimize the processing effect.The results show that the deformation in all directions gradually increases with increasing time,in which the strain in the vertical scanning direction was far greater than the combined strain along the scanning direction and in both directions and the maximum deformation was concentrated at the cutting edge.The higher the repetition frequency,the lower the longitudinal strain of the material.The lower the laser power,the greater the negative strain on the material,and the higher the power,the greater the positive strain on the material.The optimal cutting width parameters were:70kHz,18W,100mm/s,300ns;the optimal cutting depth parameters were:60kHz,36W,80mm/s,400ns;the optimal melt parameters were:70kHz,12W,100mm/s,200ns.The effectiveness of the optimized parameters was verified by the analysis of experimental data.