Research On Multi-Scale Characterization Method And Evaluation System Of CFRP Machining Quality

Carbon Fiber Reinforced Plastic(CFRP)has been widely used in the aerospace industry due to its high specific strength,good corrosion and fatigue resistance,and excellent designability.CFRP still needs secondary processing according to design requirements in material and structural performance testing and research,component or structural part trimming and assembly,etc.Its processing quality directly affects the mechanical properties,assembly quality and long-term service performance of structural parts.In actual engineering applications,the quality of CFRP secondary processing is characterized by vernier calipers,coin striking,contact surface roughness measurement devices,etc.,and there are problems such as processing accuracy of microstructure,processing defects and surface microstructure,etc.,which are difficult to obtain real feedback.At present,there is a lack of research on the characterization of processing quality and influencing factors of plain woven CFRP in practical engineering applications at home and abroad,and the correlation between molding pressure and processing factors,processing quality and mechanical properties has not been further shown.Therefore,it is important to carry out research on the characterization of CFRP processing quality and its influencing factors,as well as mechanical properties,to improve the processing quality assessment system.The paper takes plain weave CFRP as the research object,firstly,a multi-scale characterization method of CFRP processing quality is established,secondly,based on the orthogonal test of milling processing,open-hole tensile and in-plane shear performance test research,the intrinsic connection between processing parameters and material forming pressure,processing quality evaluation index and mechanical properties is revealed,finally,the quantitative evaluation index of processing quality is established,and a CFRP A comprehensive evaluation system of processing quality was formed.The research results show that:A combined qualitative-quantitative multi-scale characterization method of CFRP processing quality is established based on the macro-mesoscopic-microscopic multi-scale perspective.The multi-scale characterization method of CFRP processing quality based on macro-mesoscopic-microscopic scale further explores the detailed information of microstructure processing quality,enriches the evaluation basis,improves the accuracy and objectivity of the characterization results,and can more objectively reflect the microstructure of processing surface,processing surface quality,as well as fiber fracture,burr and pore defects.The influence law of milling processing parameters on the processing quality of CFRP is revealed.Among them,there is no obvious correlation between CFRP machining accuracy and machining parameters;while the machining surface quality evaluation parameters Sa value,skewness Ssk and cliffness Sku,and machining defects evaluation parameters burr height and damage density are mainly influenced by spindle speed and feed rate,all independent of cutting depth.Under the same milling machining parameters,the machining surface quality deviation of CFRP specimens with higher forming pressure is more likely to lead to machining defects,while machining accuracy is not affected.The intrinsic correlation between CFRP machining quality,forming pressure and openhole tensile strength and in-plane shear strength was elucidated.The evaluation parameter Sa quantifies the machined surface quality at the chamfer of V-shaped shear specimens to a certain extent,and the in-plane shear performance decreases with increasing Sa,while the burr height and damage density are not significantly correlated with the in-plane shear performance.In addition,the evaluation parameters Sa value,burr height and damage density were not significantly correlated with the tensile properties of CFRP openings.As the forming pressure of CFRP increased,the in-plane shear performance and open-hole tensile performance also showed an increasing trend.The open-hole tensile strength of the specimens with molding pressure of 600 k Pa increased by 4.23% and the in-plane shear strength increased by 7.91%compared with that of the specimens with molding pressure of 300 k Pa.A comprehensive evaluation system of CFRP machining quality with dimensional deviation,three-dimensional surface roughness Sa,burr height and damage intensity as quantitative evaluation indexes was developed.Based on the analysis of variance(ANOVA)method,the degree of influence and contribution of milling parameters on the evaluation indexes were studied,in which the machining quality evaluation indexes were influenced by the "negative" spindle speed and the "positive" feed rate.In order to improve the machining quality of plain weave CFRP,the spindle speed should be increased and the feed rate should be reduced.The research results have important reference value for improving the quality evaluation standard of CFRP machining and improving the quality and accuracy of CFRP milling.