Study On Stress Field Interaction Effect And Removal Mechanism Of Glass-ceramics By Multi-scratch

Glass-ceramics find wide applications in aerospace,biomedical and optical fields due to its low expansion coefficient,stable physicochemical properties and good mechanical properties.Grinding is a main processing approach to obtain high precision and surface quality of glass-ceramics parts.The material removal is at micro-scale.The mechanism of material removal directly affects the quality of the glass-ceramics components.At present,the material removal mechanism in the grinding process is studied by the single nanoscratch method.However,grinding is a microscopic removal process of materials by multiple grits randomly distributed on the grinding wheel surface.Existing studies are lack of the consideration of the grits interaction which is the essential feature of the grinding process.It is significant to clarify the removal mechanism of glass-ceramics under the grits interaction for forming a mature and complete grinding mechanism system of glass-ceramics.Therefore,this thesis adopts the method of theoretical analysis combined with the multi-scratch experiments by comprehensive consideration of the composition complexity of glass-ceramics.An interactional stress field model of multi-scratch is established to analyse the distribution of the characteristic stress,and further used to clarify the influence mechanism of the interaction on material deformation,crack propagation and material flow.Detailed contents of this work are summarized as follows:(1)By analysing the characteristics of multiple scratch interaction caused by the grits distributed randomly on the grinding wheel surface during the grinding process,the types of interaction between scratches caused by the distribution of grits in different directions are defined.The interactional stress field model of multi-scratch for glassceramics based on the strain rate effect is established after in-depth analysis of the micromechanical properties of glass-ceramics under the effect of strain rate introduced in the grit loading process.This model provides a theoretical basis for clarifying the removal mechanism of glass-ceramics under multi-scratch interaction and strain rate effect.(2)Nano-indentation technique is used to measure the micro-mechanical properties of glass-ceramics.Using the interactional stress field model,characteristic stress distribution which affects the crack propagation is analysed to reveal the influence mechanism of multi-scratch interaction and strain rate on the crack propagation of glass-ceramics.This analysis provides the understanding and method of suppressing crack propagation and the theoretical explanation for the brittle removal mechanism of glass-ceramics in the grinding process.(3)By clarifying the influence of grit relative sharpness introduced by the grit tip radius in the process of grit loading on the material behaviour of glass-ceramics,the characteristic stress determining the flow behaviour of glass-ceramics are analysed.This analysis contributes to reveal the material flow behaviour and chip formation of glass-ceramics.Moreover,the ductile removal mechanism of glass-ceramics under the multi-scratch interaction and grit tip radius effect during grinding process is clarified.(4)Multi-scratch experiments were carried out on glass-ceramics to analyse material removal mode,subsurface damage and material deformation under multiscratch interaction by measuring the surface morphology,crack propagation and chip removal area.The results show that non-successive sequence and larger scratch distance promote the ductile removal of glass-ceramics;non-successive sequence deepens the depth of the stagnation region,which is beneficial to the chip formation;increasing strain rate promotes the ductile removal of glass-ceramics.Experimental results are consistent with the model results,and verify the effectiveness of the interactional stress field of multi-scratch based on strain rate effect for glass-ceramics.