| In dental prosthodontics,zirconia ceramics have become the preferred material for dental prostheses due to its good mechanical properties and excellent aesthetic effects.Grinding is one of the most commonly used processing methods for ceramic materials,but in the grinding zone,a large amount of heat is easily accumulated,which makes the temperature rise,and poor lubrication conditions will increase friction and cause crack damage.Completely nondestructive processing is inefficient and difficult to control.When the crack exceeds the damage tolerance,the material breaks,which can not meet the performance requirements of the prosthesis.This technical bottleneck limits the clinical application of zirconia materials.Therefore,how to enlarge the removal range of ductile zone while reducing or avoiding crack damage has become a key problem in dental prosthesis processing.In the traditional processing condition,a large amount of cutting fluid is used in flood grinding,which causes cost increase and environmental pollution,which is not in line with the current theme of green processing.The nanofluids minimum quantity lubrication(NMQL)technology has solved the bottleneck problems such as high cost of flooding and insufficient heat transfer capacity of minimum quantity lubrication(MQL),effectively improved the surface integrity of the workpiece and improved the processing efficiency.Based on the above problems,the removal mechanism and tribological properties of dental zirconia materials under NMQL grinding are studied in this paper.The stress state and crack growth mechanism of ceramic materials under the action of abrasive particles are studied,and the influence of friction coefficient on the crack growth mechanism is analyzed.The mechanism of lubrication conditions and crack damage on the ductile zone removal of materials is revealed,and the crack depth is studied.The law of influence on Tribological Properties of materials.The main contents of this paper are as follows:1.The mechanism of NMQL grinding ceramics is studied,and the evaluation parameters of specific grinding force,friction coefficient and surface morphology of the workpiece are analyzed.2.The stress field model of the indentation and scratch process is established.The stress state of indentation and scratch state is studied.The influence of directional load and tangential load on principal stress and shear stress is analyzed.The mechanism of crack generation and propagation under abrasive action is revealed.The relationship between friction coefficient and crack length is analyzed.3.The material removal methods of ceramic materials are studied,and the effect of ductile domain removal on material properties is analyzed.A subsurface damage model is established in the grinding process,and the influence rule of grinding parameters on subsurface damage depth is obtained.The critical condition of ductile-brittle transition of dental ceramics is proposed.The critical undeformed cutting thickness model considering the damage depth is established.The influence of friction coefficient and subsurface damage depth on the critical undeformed cutting thickness is analyzed.4.The mechanical behavior of crack propagation under different lubrication conditions(dry,MQL and NMQL grinding)is studied.The lubrication performances of different lubrication conditions are compared by specific grinding force and friction coefficient.The average grinding force of a single abrasive particle is used to determine the material removal grinding behavior,and the removal threshold of dental zirconia ductile domain under different lubrication conditions is determined.The model error of critical undistorted cutting thickness for the ductile-brittle transition is analyzed.The influence mechanism of NMQL grinding on the removal of the dental zirconia ductile domain is studied.5.The influence mechanism of different lubrication conditions on the tribological properties of dental zirconia is studied.The tribological properties of dental zirconia under MQL and NMQL grinding are analyzed by simulating oral environment.The mechanism of the effect of crack growth depth on the tribological properties of dental zirconia was studied,and the effect of nanoparticles on the tribological properties of dental zirconia ceramics was revealed. |
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