Study on the Fracture Behavior of Ceramics Induced by Microwave Ant the Microwave Induced Thermal Controlled Fracture Method

Author:Wang Hai Long

Supervisor:wang yang zhang hong zhi


Degree Year:2019





Thermal Controlled Fracture Method(TCFM)aim to utilize thermal stress to induce initial crack propagate along with the desired trajectory,which has been used to cut glass and ceramics successfully.The clean cut section has been obtained which drawing much attentions nearly.Laser was used as the mainly heating source of TCFM before.However TCFM can not be used to cut ceramics very effectively because of that laser can not heat internal part of ceramics.The method for evaluating the process-ability of ceramics by using TCFM has not been noticed before,which limited the application of TCFM.The mechanism of deviation between cutting trajectory and heating path has not been established completely,which caused the lower cutting trajectory accuracy.To solve the problems above,this paper formed three kind of microwave heating source to cut classical ceramics based on TCFM(MTCFM)at first.Then the mathematical model for evaluating process-ability of ceramics by using MTCFM was established.At last,the mechanism of deviation between cutting trajectory and heating path was studied thoroughly.Two physical models(rectangular wave guide with shrink short edge and coaxial-rectangular wave guide converter)of focusing microwave in near field excitation of resonant microwave has been established.The electromagnetic field stimulated by two physical model above has been simulated and testified.The simulating results would testify the effectiveness of two physical models above.The power density of heat source formed by two physical models were simulated with the consideration of microwave power,the dimensions of physical models,the dielectric parameters of material and the thickness of work piece.Three microwave spots has been obtained based on the physical model according to the simulating and temperature experiments results,which is single elliptical microwave spot,double elliptical microwave spot and circular microwave spot respectively.The mathematical model of heat sources above were fitted by using Gaussian equation.The Factor of Fracture Ability of Ceramics under the heating of Microwave(FFACM)was presented to evaluate the processing ability of ceramics with microwave.Theoretical analysis indicated that FFACM can be used to evaluate the propagating ability of initial crack induced by same microwave spot and the threshold of input microwave energy to induce initial crack to propagate.Simulating of intensity of thermal stress(Kmax)at the crack tip was carried out.The ratio of Kη=Kmax/KIC(KICC was the fracture toughness of ceramics)was obtained.Simulating results indicate that FFACM is linear related with Kη.Four kinds of ceramics were cut by using two microwave spots.The threshold of input energy of unit crack(Qs=Pin/vs)to induce initial crack to propagate were obtained.Experiment results showed that FFACM has a linear relation with Qs.Theoretical model of inducing crack to propagate with the desired way was established.The reason of non-stable propagation of initial crack and deviation of fracture has been theoretical analyzed based on the theoretical model above.The thermal stress distribution along with the edge of work piece and desired trajectory were obtained.The fracture process of four different ceramics were simulated based on the extended finite element method(XFEM)to testify the effectiveness of theoretical model above.Four different kinds of ceramics plates were cut by using microwave spot.The experiment results were coherent with the simulating results.The influence of processing parameters on the thermal stress distribution and fracture process were obtained by using XFEM method.The main processing parameters were the shape of microwave spot,the power of microwave spot,the velocity of microwave spot,the thickness of work piece and the cold condition.The non-stable propagation of initial crack was predicted.The cutting of glass plates and AL2O3 plates was carried out systematically.The deviation of cutting trajectory were coherent with the simulating results.The cracking controlled method based on long initial prefabricated crack and surface micro discharge was proposed.The experiment results showed that the deviation of the fracture was restricted in a smaller dimension.