反复印压作用下光学玻璃的微裂纹交互作用
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摘要
对超声振动辅助磨削加工中BK7光学玻璃材料表面及亚表面的微裂纹扩展过程中的交互作用进行研究,使用维氏金刚石压头进行了BK7光学玻璃二次印压实验来模拟超声振动作用影响下单颗磨粒对光学玻璃的反复印压作用,同时采用界面黏结法获得了不同印压载荷及印压距离下产生的压痕及微裂纹的形态特征及分布情况。实验结果表明:在相同载荷加载情况下,第二次印压产生的亚表面中位裂纹扩展最大深度受到侧向裂纹影响减小了30μm,同时侧向裂纹闭合后在光学玻璃材料表面及内部产生破碎。基于压痕断裂力学理论,分析了准静态载荷作用下光学玻璃内部应力场的分布及应力场驱动下微裂纹的扩展机制,对超声振动效应影响下微裂纹扩展的交互作用进行研究。结果表明:磨削过程中使用轴向超声振动辅助,能够有效地降低光学玻璃材料亚表面裂纹的深度,改善亚表面及表面加工质量,同时促进了工件材料的去除。
To investigate the interactive effects of micro-cracks on the surfaces and subsurfaces of BK7 optical glass materials during ultrasonic vibration assisted grinding,agroup of twice-indentation experiments using Vickers diamond indenters were conducted on BK7 optical glass to simulate the multiindention effect of single abrasive grit on optical glass under ultrasonic vibration.In addition,the bonded interface technique was performed on the specimens to determine the morphologies of the indentations and micro-cracks on the surface and subsurface of the optical glass.The experimental results show that the maximum depth of subsurface cracks produced by the second indentation is affected by the previous lateral cracks and is reduced by 30μm under the same loading conditions.Furthermore,the optical glass materials will be broken after lateral crack are closed on the surface or inside of the optical glass.Based on indentation fracture mechanics,a model of elastic/plastic stress fields in the BK7 optical glass under indention loading was established to analyze the mechanism of microcracks propagation and the shield effect.The analysis of the interaction of micro-cracks as influenced by ultrasonic vibration reveals that the depth of subsurface cracks decreases and the material removal efficiency is improved with ultrasonic vibration assistance.
To investigate the interactive effects of micro-cracks on the surfaces and subsurfaces of BK7 optical glass materials during ultrasonic vibration assisted grinding,agroup of twice-indentation experiments using Vickers diamond indenters were conducted on BK7 optical glass to simulate the multiindention effect of single abrasive grit on optical glass under ultrasonic vibration.In addition,the bonded interface technique was performed on the specimens to determine the morphologies of the indentations and micro-cracks on the surface and subsurface of the optical glass.The experimental results show that the maximum depth of subsurface cracks produced by the second indentation is affected by the previous lateral cracks and is reduced by 30μm under the same loading conditions.Furthermore,the optical glass materials will be broken after lateral crack are closed on the surface or inside of the optical glass.Based on indentation fracture mechanics,a model of elastic/plastic stress fields in the BK7 optical glass under indention loading was established to analyze the mechanism of microcracks propagation and the shield effect.The analysis of the interaction of micro-cracks as influenced by ultrasonic vibration reveals that the depth of subsurface cracks decreases and the material removal efficiency is improved with ultrasonic vibration assistance.
引文
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[2]SINGH R P,SINGHAL S.Rotary ultrasonic machining:a review[J].Materials and Manufacturing Processes,2016,31(14):1795-1824.
[3]ZHANG CH L,FENG P F,ZHANG J F.Ultrasonic vibration-assisted scratch-induced characteristics of C-plane sapphire with a spherical indenter[J].International Journal of Machine Tools&Manufacture,2013,64(4):38-48.
[4]CAO J G,WU Y B,LU D,et al..Material removal behavior in ultrasonic-assisted scratching of SiC ceramics with a single diamond tool[J].International Journal of Machine Tools&Manufacture,2014,79:49-61.
[5]WANG J J,FENG P F,ZHANG J F,et al..Investigations on the critical feed rate guaranteeing the effectiveness of rotary ultrasonic machining[J].Ultrasonics,2017,74:81-88.
[6]GU W B,YAO ZH Q,LIANG X G.Material removal of optical glass BK7during single and double scratch tests[J].Wear,2011,270(3-4):241-246.
[7]ZHAO P Y,ZHOU M,HUANG SH N.Sub-surface crack formation in ultrasonic vibration-assisted grinding of BK7optical glass[J].The International Journal of Advanced Manufacturing Technology,2017,93(5-8):1685-1697.
[8]BANDYOPADHYAY P,DEY A,MANDAL A K,et al..New observations on scratch deformations of soda lime silica glass[J].Journal of Non-Crystalline Solids,2012,358(16):1897-1907.
[9]赵培轶.BK7光学玻璃超声振动磨削脆塑性转变及加工质量研究[D].哈尔滨:哈尔滨工业大学,2017.ZHAO P Y.Research on Brittle Ductile Transition and Machining Quality in Ultrasonic Vibration Assisted Grinding of BK7 Optical Glass[D].Harbin:Harbin Institute of Technology,2017.(in Chinese)
[10]LAWN B R,SWAIN M V.Microfracture beneath point indentations in brittle solids[J].Journal of Materials Science,1975,10(1):113-122.