| Carbon Fiber Reinforced Composites(CFRCs)has excellent physical and chemical properties and are widely used in defense and military.These fields put forward higher requirements for the machining of CFRCs,and require more advanced technology to meet the needs of high-quality and high-precision.The problems of material machining difficulties and poor surface quality in ordinary grinding can be solved by ultrasonic grinding technology.However,there is no systematic study on material removal mechanism in ultrasonic grinding of CFRCs,which needs to be further revealed.The mechanical model of ultrasonic grinding of CFRCs was established in this research,and the finite element analysis of ultrasonic grinding of CFRCs in different fiber directions was carried out from macro and micro perspectives.The mechanism of ultrasonic grinding was studied.The main contents and results of this research are as follows:(1)According to the relationship between cutting depth,protruding height of abrasive grains and radius of transition fillet,three different machining conditions were discussed.The interaction between abrasive grains and workpiece was analyzed based on the brittle material fracture theory and the kinematic relationship between abrasive grains and workpiece.The mechanical models of end grinding,side grinding,transition corner grinding and overall grinding force were established respectively.The total grinding force model was also be tested by experiment.The results show that the maximum error between calculated value and experimental value of the axial force model is 9.5%,while the maximum error between calculated value and experimental value of the feed force model is 9.6%.The effects of process parameters on the grinding force were studied based on this model.It is found that the grinding force decreases with the increase of abrasive grain size,ultrasonic amplitude and ultrasonic frequency,and increases with the rise of grinding depth.(2)Through the analysis of the macro-mechanical properties of CFRCs,the engineering mechanical parameters and failure criteria of CFRCs were obtained.Macro-ultrasonic grinding simulation analysis of CFRCs was carried out and the cutting performance of materials in different fiber directions was studied based on the finite element theory.The results show that the maximum stress is 751.7 MPa in the fiber direction of 45°,and the minimum stress is 267 MPa in the fiber direction of 135°.The chip morphology of CFRCs with fiber direction of 0°,45°,900 and 135° are small bundle,strip,a smaller block and block,respectively.There are few pits on the surface with fiber direction of 0°,and surface quality is the best.There are many burrs and pits on the surface with fiber direction of 45°,and the surface quality is the worst.(3)The failure modes of carbon fiber,resin matrix and bonding layer materials were considered,based on the analysis of mechanical properties of each material.A micro-finite element model of ultrasonic grinding of CFRCs was established.The stress,cutting damage and surface quality in different fiber directions were studied and compared with results in ordinary grinding.It is found that the stress in ultrasonic grinding is smaller than that of ordinary grinding.The propagation of cracks propagates along the feeding direction in the fiber direction of 0°,90° and 135°,while the propagation of cracks propagates parallel to the fiber direction in the fiber direction of 45°.The ultrasonic vibration makes the cracks propagate more easily and the materials can be removed easily.The surface quality with fiber direction of 0° and 90° is relatively good,and the high-frequency vibration makes surface quality further enhanced.The surface quality with fiber direction of 45° and 135°is relatively poor,and the machined surface quality is improved by ultrasonic impact. |
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