基于单磨粒动态冲击效应的光学玻璃磨削亚表面裂纹研究

发布时间：2018-02-13 19:18

本文关键词： 光学玻璃磨削亚表面裂纹单颗磨粒动态冲击效应　出处：《哈尔滨工业大学》2017年博士论文　论文类型：学位论文

【摘要】：光学玻璃等硬脆材料磨削过程中形成的亚表面裂纹,对光学元件尤其在空、天使役环境中的光学元件的性能及应用影响十分显著,因此硬脆光学材料磨削亚表面裂纹生成机理是光学制造领域的重要基础性科学问题之一。现有关于光学玻璃磨削机理及亚表面裂纹形成的研究多是基于压痕断裂力学和静态加载条件,没有考虑磨削过程中砂轮磨粒高速动态冲击效应的影响,与生成裂纹/亚表面裂纹的实际情况不符。所以磨粒冲击速度对光学玻璃磨削裂纹/亚表面裂纹深度的影响规律的研究成为当前面临的重要课题。处理磨粒冲击作用下的冲击动力学问题时,必须计及材料的惯性效应和应变率效应,因此本文基于应力波理论、动态断裂力学理论及应变率效应研究了磨粒冲击作用下的光学玻璃亚表面裂纹深度。本文根据光学玻璃单颗磨粒切削的特点,由点冲击载荷及弹性柱面应力波理论,建立了基于单磨粒动态冲击效应的冲击动力学应力波数学模型。根据动态断裂力学脆断理论和裂纹动态扩展规律,建立了基于动态应力强度因子的动态裂纹起始扩展、传播和止裂的数学模型。利用数值仿真技术分析了在砂轮磨粒动态冲击作用下,光学玻璃单颗磨粒切削亚表面裂纹生成机理。根据应力波和最大拉应力理论,研究了磨粒速度对光学玻璃材料内部应力波的影响规律、磨粒速度对应力波作用区域的影响规律以及磨粒不同作用时间下应力波强度的变化规律。研究发现应力波最大拉应力的大小与磨粒速度正相关,且磨粒速度增大,最大拉应力达到材料抗拉极限的时间缩短,最大拉应力达到材料抗拉极限的位置与磨粒接触区域的距离缩短;随磨粒速度的提高,应力波强度增大。利用应力波和动态应力强度因子理论计算仿真了径向裂纹的扩展过程,得到了裂纹扩展的深度,仿真结果表明磨粒冲击速度增大,亚表面径向裂纹的扩展深度减小。根据应力张量理论,分析了柱面应力波的应力张量的主方向,确定了裂纹系统的方向即最大拉应力方向,裂纹系统的方向包括径向裂纹和环向裂纹。为了研究光学玻璃单颗磨粒切削亚表面裂纹生成机理,研制了单颗磨粒切削的实验装置,采用截面抛光的方法进行了亚表面裂纹系统的检测。通过光学玻璃单颗磨粒切削实验,发现了亚表面微裂纹形式包括径向裂纹和环向裂纹,环向裂纹的存在是动态冲击所致裂纹的典型特征。根据微裂纹系统及断裂表面微观形貌分析,发现了在一定切深条件下磨粒动态冲击光学玻璃材料为脆性颗粒状崩碎断裂。为了研究磨削过程中磨粒冲击速度对光学玻璃亚表面裂纹深度的影响规律,分析了光学玻璃单颗磨粒切削过程中运动接触弧的变化规律,提出了砂轮转速与工件进给速度协同实验方案,实现了磨粒速度不同而切深相同时,单颗磨粒切削的运动接触弧长完全一致,达到了以磨粒冲击速度作为单一因素的实验目的。利用砂轮转速与工件进给速度的协同实验,进行了不同磨粒速度下的光学玻璃单颗磨粒切削亚表面裂纹深度的检测,统计在不同速度、不同切深条件下的亚表面裂纹深度值。通过磨削参数协同实验发现,在单颗磨粒运动接触弧长度不变、切深相同的条件下随磨粒速度的提高,亚表面裂纹深度呈现出下降趋势。光学玻璃平面磨削实验表明,在其它条件不变的情况下,磨削速度增大,亚表面裂纹层深度减小,与单颗粒磨削实验结果一致。对比分析了光学玻璃直线低速刻划与直线动态冲击实验,光学玻璃试件直线低速刻划划痕缺口轮廓不清晰,划痕缺口周围存在向内部开裂的长裂纹,而直线动态冲击缺口轮廓清晰可见,且存在环向裂纹,长裂纹及向内部扩展裂纹不明显。利用霍普金森压杆(SHPB)实验研究了K9光学玻璃的应变率效应,分析了磨削条件下应变率的变化规律,建立了基于磨粒动态冲击应变率效应的亚表面裂纹深度公式,揭示了光学玻璃单颗粒切削亚表面裂纹深度的影响规律。理论研究和实验结果表明随着磨粒速度的提高,磨粒作用区域材料的应力波强度增大,裂纹尖端的应力强度因子增大,同时磨粒作用区域材料的应变率增大,进而材料的动态弹性模量增大,最大拉应力达到材料抗拉强度极限的位置与磨粒接触区域的距离缩短,因此产生裂纹的区域缩小,磨削过程中的亚表面裂纹的深度减小。
[Abstract]:Sub surface crack formation of the grinding process of optical glass and other hard brittle materials, especially in the air of the optical components, properties and application effects of optical elements in the environment of the battle angel is very significant, so the formation mechanism of grinding hard brittle optical materials sub surface crack is one of the most important parts of basic science to the field of optical manufacturing. The existing research about optical glass grinding mechanism and sub surface crack formation is the indentation fracture mechanics and based on static loading conditions, without considering the impact effects of high-speed dynamic grain grinding wheel in the grinding process, and the formation of cracks / inconsistent with the actual situation of sub surface crack. So the particle impact velocity of law of crack / sub grinding of optical glass the surface crack depth has become an important issue currently facing. Treatment grinding dynamics of grain under impact, and the effect of inertia materials The effect of strain rate, so this paper based on the theory of stress wave, the dynamic fracture mechanics theory and the effect of strain rate on the grinding of optical glass sub surface crack depth of grain under impact. Based on the optical glass single grain cutting characteristics, from the point of impact load and elastic cylinder stress wave theory, stress wave mathematical model the impact dynamics of single particle dynamic impact effect based on established. According to the dynamic fracture mechanics theory of brittle fracture and crack propagation rule, establishes the dynamic dynamic stress intensity factors of crack initiation and crack propagation based on the extended mathematical model is analyzed. Using the numerical simulation technology of abrasive wheel in dynamic impact. Optical glass single grain cutting sub surface crack formation mechanism. According to the stress wave and the maximum tensile stress theory, studied the particle velocity effect of stress wave on the internal optical glass material, grinding The strength variation of the stress wave effect of the particle velocity of stress wave and abrasive action area at different time. The study found that stress wave maximum tensile stress and particle velocity are related, and the particle velocity increases, the maximum tensile stress reaches the tensile strength of the material was shortened, the maximum tensile the tensile stress reaches the limit of material position and abrasive contact area to shorten the distance; with the abrasive particle velocity increases, the stress wave intensity increases. The stress wave and the dynamic simulation of the propagation process of radial crack stress intensity factor theory, the crack propagation depth, the simulation results show that the abrasive impact increase the speed of expansion, the depth of subsurface radial cracks decreased. According to the stress tensor theory, analysis of the cylinder stress wave the principal directions of the stress tensor, the crack system is the direction of maximum tensile stress, crack system. To include the radial and circumferential cracks. In order to study the optical glass single grit cutting sub surface crack formation mechanism, developed a single grain cutting experiment device, using the method of cross section polishing tested sub surface crack system. Through the optical glass single grit cutting experiment, found the form of micro the sub surface cracks and crack including radial circumferential crack, circumferential cracks are typical characteristics of dynamic impact caused by crack. According to the analysis of micro crack system and fracture surface morphology, found in certain depth of cut under dynamic impact abrasive optical glass material is brittle fracture. In order to study the granular disintegration in the process of grinding mill the particle impact velocity of optical glass sub surface crack depth, analyzed the change law of motion of optical glass single grain cutting process in the contact arc, the rotating speed of the grinding wheel and work A feed speed collaborative experiment scheme, realizes the particle velocity and different depth of cut at the same time, single grain cutting contact arc length is completely consistent, achieved by abrasive impact velocity as the purpose of the experiment of single factor. Using wheel speed and feed speed of the collaborative experiment, the different particle velocity the optical glass single grain cutting sub surface crack depth detection and statistics at different speeds, sub surface crack depth under different cutting depth value. Through collaborative experiment of grinding parameters, contact arc length does not change in a single grain movement, cutting depth under the same conditions with the abrasive particle velocity increases sub surface crack depth, showing a downward trend. It shows that optical glass grinding experiment, under the same condition, the grinding speed increased, sub surface crack depth decreases, and the single grain grinding on the experimental results are consistent. Analysis of optical glass straight line speed and linear dynamic impact experimental characterization, optical glass specimen characterization of linear low scoring gap outline is not clear, long crack to internal cracking exists around the gap and scratches, linear dynamic impact profile is clear, and the existence of circumferential crack, long crack and to internal crack use is not obvious. Hopkinson pressure bar (SHPB) strain rate effect experiment of K9 optical glass, analyzed the variation of grinding conditions of the strain rate, the establishment of sub surface crack depth formula of abrasive dynamic strain rate effect based on the influences of single particle optical glass cutting sub surface crack depth. Theoretical research and experiment the results show that with the increasing speed of abrasive, abrasive materials should increase the intensity of regional stress wave, crack tip increase of stress intensity factor, and the abrasive action zone The strain rate of the material increases, and the dynamic elastic modulus of the material increases. The maximum tensile stress reaches the location of the tensile strength limit of the material and the distance from the contact area of the abrasive zone shortens, so the area of the crack decreases, and the depth of the sub surface crack decreases during grinding.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ171.734

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