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Study On Materials Removal Mechanism Of Glass-ceramics Based On Nano-mechanical Consecutive Incremental Loading

Posted on:2020-07-09Degree:MasterType:Thesis
Country:ChinaCandidate:X LiFull Text:PDF
GTID:2491306518457874Subject:Instrument Science and Technology
Abstract/Summary:PDF Full Text Request
Glass-ceramics has lots-of excellent properties,such as high mechanical strength and hardness,good abrasion resistance,chemical stability and adjustable thermal expansion coefficient.As a result,it has been widely used in national defense,chemical,architecture and medical treatment.As a typical intractable material with hard and brittle properties,glass-ceramics is prone to generate surface and sub-surface damage in the machining process,which is a new challenge to ultra-precision machining technology presented.At present,ultra-precision grinding is considered to be one of the most effective processing methods of glass-ceramics.Due to the random distribution of abrasive grits on the surface of the grinding wheel,the material is usually removed by multi-grits at the same time in the grinding process.However,previous studies paid more attention to the removal of materials under single-grit,and few could deeply study the removal mechanism of glass-ceramics under multi-grits.This paper aims to study the residual stress of finished surface under multi-grits consecutive incremental loading through finite element simulation.A series of indentation and scratch experiments under multi-grits consecutive incremental loading were designed to study the material removal mechanism of glass-ceramics.The main contents of this paper are as follows:1.The fracture mechanism of glass-ceramics was studied according to the nanoindentation/scratch theory,and the mechanical parameters such as hardness,young’s modulus and yield stress of glass-ceramics were measured.Moreover,the brittle-plastic transition depth and critical load of glass-ceramics were obtained by nano-scratch test.These provided theoretical basis for subsequent ductile regime and brittle regime processing;2.The finite element simulation model of glass-ceramics was established to analyze the influence of the distance between multi-grits on consecutive incremental loading.It could provide a basis for the establishment of the model under consecutive incremental loading.The effect of consecutive incremental loading on scratch morphology and residual stress was analyzed by finite element simulation;3.The simulation results were validated by nano-scratch experiments,which were analyzed from two aspects: ductile regime processing and ductile regime processing,aiming to study the effects of consecutive incremental loading on the surface morphology and crack growth of materials under different processing conditions as well as the effect of scratch speed and indenter shape on the material removal of glass-ceramics under triple-grits consecutive incremental loading.The experimental results show that: when consecutive incremental loading in ductile regime is applied,the residual depth increases with the increase of loading times,and the pile up formed on both sides becomes more obvious.When consecutive incremental loading in brittle regime is applied,the increase of loading times can promote crack propagation and material removal,so as to improve the processing efficiency of glass-ceramics.Based on nano-indentation/scratch theory,the grinding mechanism of glassceramics under consecutive incremental loading was studied by experiment and finite element simulation.It clarifies the material flow phenomenon and crack propagation mechanism of glass-ceramics in the processing of grinding,and offers a theoretical foundation of obtaining glass-ceramics devices with high surface quality.
Keywords/Search Tags:Glass-ceramics, Material removal mechanism, Consecutive incremental loading, Crack propagation, Residual stress
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