【作者】 童景琳；

【导师】 赵波； 李济顺；

【作者基本信息】 河南理工大学 ， 机械制造及其自动化， 2015， 博士

【摘要】 难加工材料(如陶瓷、钛合金等)的可加工性差,加工效率低,限制了它们在工业中的应用。大量的研究已经证明,超声振动磨削加工具有较高的材料去除率、较小的磨削力,较低的表面损伤和较高的加工精度,迄今为止,而对这种加工方法所产生这些优点的本质机理研究的还不够深入。本文基于非局部理论,着重探索了超声波与ZTA纳米复相陶瓷材料的微观作用机理,从材料本构特性、宏观力学特性和微观形貌等方面研究了超声激励对纳米陶瓷加工特性的影响,揭示超声加工时所产生的延性高效现象的理论本质,为进一步完善超声加工的理论奠定基础。本文主要研究内容如下:考虑ZTA陶瓷的内禀长度和外部超声波波长之间的相互作用关系,通过引入非局部理论,建立超声振动下的非局部本构模型。通过分析超声纵波和横波在陶瓷材料的波频散特性,得出波速和频率的关系,解释了波速的衰减现象,根据波速的计算公式,分别获得纵向波和横向波标准化非局部模量(非局部模量与经典模量的比值)随频率以及影响域的变化规律。为了研究纳米复相陶瓷超声作用下的非局部磨削应力特性,以ZTA纳米复相陶瓷为加工对象,提出一种新型的二维超声振动磨削技术,基于超声振动理论和压痕断裂力学,给出了新型二维磨削下材料去除率模型和磨削力模型。基于该磨削力模型,通过核函数建立宏-微观联系,建立陶瓷材料超声激励裂纹尖端的非局部弹性解析应力场,发现发生在裂纹尖端的最大应力是有限的,该结论从理论上消除了物理上不现实的裂纹尖端应力奇异性,显示了裂纹尖端应力场的本来面目。为超声振动加工延性去除机理的研究提供理论保证和指导。为研究超声主要参数(频率、振幅等)与陶瓷磨削时的非局部应力之间的关系,建立了超声振动拉伸和超声振动三点弯曲试验装置,基于波动理论,完成了具有复杂曲线的复合多段式变幅杆设计,对研究超声参数(频率和振幅)对陶瓷的作用机理提供理论很大的帮助,同时,基于波动理论和非局部理论完成了三点弯曲试样和拉伸试样的设计。通过超声激励三点弯曲和轴向拉伸试验,研究了超声振动下材料的断裂行为,分析了ZTA纳米复相陶瓷材料在超声振动条件下裂纹形成及扩展方式,得出不同超声参数下非局部弹性核函数与长程作用域的关系是断裂应力随着振幅和频率的增加而减小。通过对三点弯曲和拉伸断口的电镜观察表明,超声拉伸下的断口有明显的晶粒断面,在大量的晶粒上有裂纹出现,说明ZTA陶瓷发生了穿晶/沿晶混合断裂。随着超声激励振幅和频率的增大,断口的空隙逐渐增多,平整度也得到很大的改善,对试件拉伸断口物相分析,发现超声激励作用在很大程度上改善了陶瓷材料的力学性能,ZrO2在应力诱导下发生t→m相变从而吸收应变能,有较好的塑性力学性能,不仅从理论上而且在试验上均验证了非局部衰减率的理论变化规律。通过二维超声辅助磨削方式进行了磨削试验,基于非局部弹性理论和冲击断裂力学,从二维超声辅助磨削技术的加工特性进行解释,分析了二维超声振动参数及磨削加工参数对磨削力的影响规律。借助于扫描电镜,研究了ZTA纳米复相陶瓷二维超声辅助磨削表面/亚表面损伤特征,并用非局部理论做了对比验证,指出二维超声辅助磨削对获得具有较好微观特性的ZTA陶瓷磨削表面十分有益。研究表明非局部本构模型对于超声振动加工陶瓷硬脆材料力学特征的适用性,符合其显著增加延性域切削深度的现象。更多还原

【Abstract】 Poor machinability of hard-to-machine materials(such as advanced ceramics,titanium)limits their applications in industries.Ultrasonic vibration grinding(UVG)is a cost-effective these materials.It is generally known that UVG causes the micro-fracture of the workpiece,which are capable of achieving high material removal rate while maintaining the lower surface/subsurface damage,reduced lower grinding force and improved accuracy.However,the mechanism of UVAG so far has not been further researched.In this paper,the interaction mechanism between the ultrasonic wave and microstrcture was researched based on nonlocal theory,and the effect of ultrasonic vibration on grinding characteristics of nano-composite ceramics were studied from material constitutive properties,macroscopic mechanical properties and material surface microtopography,etc..The essential theory of the high efficiency and ductility phenomenon under ultrasonic machining is revealded,and It has laid a foundation for the further perfection of ultrasonic machining theory.The main work and the achievements of this dissertation are list as follows:The mechanics behavior of the ceramics under the action of ultrasonic vibration is analyzed according to the relationship between the internal character length and the external character length(i.e.ultrasonic wave length)for ZTA nano-composite ceramics.To interpret this phenomenon,the nonlocal theory is introduced to establish the constitutive model under the ultrasonic condition.The wave speed attenuation and the relationship between wave speed and frequency are obtained through analyzing the frequency dispersion characteristic of longitudinal wave and transverse wave propagation in ceramics.According to expressions of phase velocity,the variation of normalized nonlocal moduli(longitudinal and transverse propagation)with different frequencies are calculated(the ratio of nonlocal moduli and classical moduli).The nonlocal stress attenuation rule can be obtained when the normalized nonlocal moduli are integrated.In order to study thenonlocal stress characteristicof nano-composite ceramics under ultrasonic vibration grinding,a new kind method of two-dimensional ultrasonic vibration grinding(TUVG)was put forward.Based on the theory of ultrasonic vibrationand indentation fracture mechanics,the material removal rate and grinding force model under TUVG were established.Based this grinding force model,Nonlocal elastic stress field which is near the crack tip of ceramics materials under ultrasonic excitation is established.It is found that the maximum stress that occurs near the crack tip is limited.The stress singularity of crack tip which is unrealistic in physics is eliminated theoretically and the nature of stress field near the crack tip are revealed.It provides a theoretical guarantee and guidance for ultrasonic vibration machining ductile removal mechanism of ceramics.For the study of the relationship between ultrasonic main parameters(frequency,amplitude,etc.)and ceramic grinding nonlocal stress,the ultrasonic vibration tensile and three-point bending experiment device were built.The composite sections horns having complex curve were designed based on the wave dynatics theory,which provided great help for studing action mechanism of the ultrasonic parameters(frequency and amplitude)on the ceramic,at the same time,three-point bend specimens and the tensile samples were designed based on the nonlocal theory and Ultrasonic wave theory.Through ultrasonic irradiation three-point bending and axial tensile test,the fracture behaviors of materials under the ultrasonic vibration were studied,cracks formation and propagation of the ZTA material nanocomposite ceramics under the condition of ultrasonic vibration were analyzed.The relationships between nonlocal elasticity nuclear function and long-range scope under different ultrasonic parameters were obtained from these tests,which are fracture stress decreases with the increase of amplitude and frequency.The SEM photographs of three point bending and tensile fracture of ZTA ceramics show that there are obvious grain sections and large amounts of micro-crack on the fracture morphology under ultrasonic irradiation,which happened to transgranular/the intergranular mixed fracture for the ZTA ceramic under ultrasonic action.the gap roughness have been greatly improved with the increase of ultrasonic excitation amplitude and frequency of fracture increase gradually.Through phase analysis of tensile fracture specimen,it finds that mechanical properties of ceramic materials are improved significantly under ultrasonic excitation,the ceramics materials present phase transition t→m which is induced by stress to absorb strain energy and itshows better plasticity mechanics performance,which the theory of nonlocal attenuation change rule is verified not only in the experiment but also in the theoretically.Through two-dimensional ultrasonic assisted grinding way grinding experiment was carried out,based on the nonlocal elastic theory and impact fracture mechanics,the influence of the ultrasonic vibration parameters and grinding parameters on grinding force are analyzes studied.Was studied by means of scanning electron microscopy(sem),ZTA two-dimensional ultrasonic assisted grinding nanocomposite ceramics surface/subsurface damage characteristic,and contrasted the nonlocal theory is verified,points out that the two-dimensional ultrasonic assisted grinding to obtain good microscopic characteristics of ZTA ceramic grinding surface is very good.Based on the nonlocal elastic theory and impact fracture mechanics,two-dimensional ultrasonic assisted grinding experiment was carried out,the influence rule of ultrasonic parameter(such as frequency and amplitude)and grinding parameters on the grinding force was analyzed from characteristics of processing.Was studied,ZTA the surface/subsurface damage characteristicof nanocomposite ceramics under two-dimensional ultrasonic assisted grinding was studied by means of scanning electron microscopy(SEM),and the nonlocal theory is verified.It is found that the ultrasonic parameter have the effect on the microcosmic characteristic and material removing style,which is the reason to illustrates the improvement of surface quality essentially with ultrasonic grinding.The applicability of the nonlocal constitutive model which has been established to mechanics characteristic of ceramics materials under ultrasonic vibration machining correspond with the phenomenon that the cutting depths are increased significantly in ductile domain.更多还原