基于独立分量分析理论的大块非晶合金切削信号检测（英文）

研究了在大块非晶合金切削力信号检测时利用独立分量分析法对检测信号进行去噪处理技术。在试验中,采用独立分量分析法对切削测量系统测量的大块非晶合金切削力信号进行迭代分离,从而提取出主切削力信号。并针对大块非晶合金在不同切削深度下的变形特征,运用扫瞄式电子显微镜观察了大块非晶合金的切削带特征。主切削力信号频谱的快速傅里叶变换分析表明,随着切削深度的增加,切削力信号高频部分的振幅越来越大,而大块非晶合金切削力信号高频部分是由切削带形成过程的特征引起的,并随着切削深度的增加而增加,且主切削力Fz的频率为115 Hz。研究结果表明:采用独立分量分析法进行噪声分离后更能精确识别切削力信号中的主要信息,减少噪声造成的误判。     

Zr_(41.2)Ti_(13.8)Cu_(12.5)Ni_(10.0)Be_(22.5)大块非晶合金的切屑和切削力试验(英文)

为了解非晶合金的切削机理,对大块非晶合金Zr41.2Ti13.8Cu12.5Ni10.0Be22.5进行了不同切削深度的切削实验,然后用扫描电镜、X光衍射仪和测力系统对切屑形态和切削力进行观察和测量。实验结果表明:Zr基非晶合金在受拉的时候,比全脆性材料有更好的塑性表现,其切屑形态独特且具有塑性剪切带特征;主切削力Fz随切削深度的增加而增长,但Fx和Fy则几乎没有变化。     

ZR41.2TI13.8CU12.5NI10.0BE22.5大块非晶合金的切屑和切削力试验研究

为了解非晶合金的切削机理,对大块非晶合金Zr41.2Ti13.8Cu12.5Ni10.0Be22.5进行了不同切削深度的切削实验,然后用扫描电镜、X光衍射仪和测力系统对切屑形态和切削力进行观察和测量。实验结果表明：Zr基非晶合金在受拉的时候,比全脆性材料有更好的塑性表现,其切屑形态独特且具有塑性剪切带特征;主切削力Fz随切削深度的增加而增长,但Fx和Fy则几乎没有变化。     

大块非晶合金车削力特性试验

非晶合金具有独特的非晶体结构,其力学特性与传统金属不同。为了了解大块非晶合金的切削力特性,对Zr41.2Ti13.8Cu12.5Ni10.0Be22.5进行车削实验并采集切削力信号;然后通过小波分析对切削信号进行处理,从而得到非晶合金的车削力特性。结果表明:切削力信号能量随切削参数增加趋向于低频分布,大块非晶合金车削变形机理呈现为微观脆性断裂。     

Fe基非晶态合金切削性实验研究

通过与45钢对比,分析了Fe基非晶合金在不同切削速度和切削深度的交互作用对主切削力和切削合力的影响,结果表明:在相同切削参数下,Fe基非晶合金主切削力小于45钢,而切削合力却大于45钢,切削力都表现出随着切削速度的增加逐渐减少,以及随着切削深度的增加均匀增大的趋势。研究发现切削速度在80 m/min下产生的切屑晶化程度多达52.5%,认为Fe基非晶合金锯齿状切屑的形屑机制为局部突变性剪切,在切削速度为60 m/min时切屑的片状结构中会出现大量微孔洞,而切削速度达到80 m/min以上时,黏滞流变会增加,微孔洞数量减少。     

Zr基大块非晶合金铣削力实验研究

为了了解非晶合金的切削力学特性,以Zr基大块非晶合金和45钢为对比试样,通过正交实验探明非晶合金的铣削力特点以及铣削参数对切削力的影响,并利用线性回归方法建立了实验条件下的铣削力经验公式。实验结果表明:非晶合金Y轴铣削力最大,X轴最小,而且Y轴铣削力受铣削参数变化影响最大,其次为X轴,Z轴则几乎不受影响;轴向切削深度和径向切削深度对铣削力的影响明显,进给量和切削速度的影响较小。     

单晶γ-TiAl合金纳米切削过程声发射响应的原子模拟

本工作采用分子动力学方法研究了单晶γ-TiAl合金纳米切削过程的声发射响应。从原子尺度阐述了单晶γ-TiAl合金切削过程中裂纹形成机理。研究发现：切削初期随着切削力持续增大,剪切区域产生周期性的剪切带;与此同时,在高压应力和弹性应力波共同作用下,类晶粒晶界的非晶原子带的产生阻碍了剪切带的持续发射,使主剪切区的应力无法及时通过剪切带释放,产生局部应力集中现象,导致裂纹萌生并扩展;通过对采集的声发射信号分析,压应力会导致切削过程中声发射功率下降。在时域上,通过对微观缺陷演化和声发射功率-频率对比分析,阐述了纳米切削过程中晶格振动、剪切带以及裂纹萌生与扩展的声发射响应特征,并通过聚类分析得到了损伤的功率和频率特性。     

PCBN刀具切削中锯齿形切屑形态的动态切削力识别

精密硬态切削过程锯齿形切屑对动态切削力、切削温度波动、PCBN刀具寿命和已加工表面质量有重要作用。本文依据锯齿形切屑锯齿的形成和终了过程可以在动态切削力高频信号中体现出来的特征，采用小波分析硬态切削力的高频信号，分析结果表明不同形态的锯齿形切屑形态对应不同的切削力高频信号。从切削力高频信号的切削速度、进给量、采样频率和时间可以定性描述锯齿形切屑形态和剪切失稳的特征参数。依据Shaw建立的锯齿形生成频率模型。在精密硬态切削条件下，锯齿形切屑的生成频率要远小于切削力高频信号的频率，高速切削条件下两者频率逐渐趋于相等。实验及分析结果表明可以采用动态切削力的小波分析来判别锯齿形切屑的基本特征。     

PVD涂层刀具高速铣削砂岩切削力研究

单因素实验研究金刚石涂层刀具高速铣削石墨,改变切削用量等因素对切削力的影响。研究切削力参数,找出其显著性因素,为提高砂岩表面加工精度,改善机床的动力学特性提供理论依据。通过设计正交试验方案,在不同的切削参数(切削速度、进给量、切削深度)下进行PVD涂层刀具高速铣削砂岩切削力试验。利用测力仪测出各组试验的切削力信号图,并记录各组切削力的试验结果。分析单一切削参数的变化对切削力的影响情况,采用最小二乘法原理对切削力经验公式回归系数进行参数估计,并对经验公式进行相关性检验,检验结果表明显著性很高。最终得出结论:对切削力影响最大的因素是切削深度,且随着切削深度的增加切削力增加;切削力影响最小的因素是切削速度,且随着切削速度的增加切削力减小。     

基于声发射技术金刚石组合圆锯片干切混凝土的切削状态研究

通过自行设计的多孔与非等弧长节块组合金刚石锯片与普通锯片的对比分析,揭示组合结构金刚石锯片的切削特征.通过分析金刚石圆锯片在锯切过程中混凝土声发射信号和锯切力信号特征,得出切削速度、进给速度、切削深度对AErms峰值平均值和Z轴锯切力的影响.结论表明声发射信号的变化规律与锯切力信号的变化规律有较好的一致性.其它切削条件不变,随着切削速度的增加,声发射均方根值和切削力平均值都减小;随着进给速度、切削深度的增加,声发射均方根值和切削力平均值都增大.且自行设计的组合锯片整体性能优于普通锯片.     

Chip formation, cutting forces, and tool wear in turning of Zr-based bulk metallic glass

The chip light emission and morphology, cutting forces, surface roughness, and tool wear in turning of Zr-based bulk metallic glass (BMG) material are investigated. Machining results are compared with those of aluminum 6061-T6 and AISI 304 stainless steel under the same cutting conditions. This study demonstrates that the high cutting speeds and tools with low thermal conductivity and rake angle activate the light emission and chip oxidation in BMG machining. For the BMG chip without light emission, serrated chip formation with adiabatic shear band and void formation is observed. The cutting force analysis further correlates the chip oxidation and specific cutting energy and shows the significant reduction of cutting forces for machining BMG at high cutting speeds. The machined surface of BMG has better surface roughness than that of the other two work materials. Some tool wear features, including the welding of chip to the tool tip and chipping of the polycrystalline cubic boron nitride (PCBN) tool edge, are reported for turning of BMG. This study concludes that BMG can be machined with good surface roughness using conventional cutting tools.     

In-situ synthesis and mechanical properties of Zr-based bulk metallic glass matrix composites manipulated by nitrogen additions

Our study investigates in-situ synthesis and mechanical properties of Zr-based bulk metallic glass (BMG) matrix composites via arc plasma-induced accelerated displacement reaction (APADR) process. The aluminum nitride precursor under arc plasma-induced ultra-high temperature results in higher contents of dissolved nitrogen as well as precipitation of zirconium nitride (ZrN) particles in a Zr-based amorphous matrix. The nitrogen in the matrix results in a decrease of crystallization resistance (lower T_x and reduced glass-forming ability), but an increase of mechanical stability (a decrease of strain burst sizes). In particular, in-situ formed ZrN, which exhibits a homogeneous distribution and strong interfacial bonding with the matrix, causes an increase in compressive fracture strength and significant plastic deformation in the composite compared with the monolithic BMG. The formation of multiple shear bands and the enhancement of shear band interactions by the dissolved nitrogen as well as the in-situ formed ZrN particles were carefully confirmed by a statistical analysis on serrated flows. These results give us a guideline on how to manipulate nitrogen contents and fabricate in-situ BMG matrix composites with improved mechanical properties via APADR process.     

Stable flowing of localized shear bands in soft bulk metallic glasses

This paper reports a novel class of Zr–Cu–Fe–Al bulk metallic glasses (BMGs) with high Zr content and unusual deformation behavior. Higher content of Zr results in lower hardness, but favors the generation of highly localized shear bands, even if nanocrystalline phases precipitate in the glassy matrix. Moreover, flow of the dominant shear band proceeds slowly under compressive stress without rapid shear rupture and facture. The unusual deformation behavior suggests that designing BMG with a high content of solvent element and low hardness might be a promising new way of developing ductile BMG.     

Analysis of plastic strain and deformation mode of a Zr-based two-phase bulk metallic glass in compression

A ductile phase-separated Zr-based bulk metallic glass (BMG) deformed to different strains at room temperature and low strain rate was characterized. The BMG samples were compressed to nominal strains of 3%, 7%, and 10%, after which the samples were unloaded for morphological observation using scanning electron microscopy. The morphological observation was subsequently used for the interpretation of the measured load–displacement curves. It was found that the BMG exhibited apparent uniform deformation initially (at plastic strain <1%) and, then, visible local shear bands began to developed. Afterwards, a principal shear band was soon developed and dominated the deformation process until fracture. In this study, we also found that the local shear strain varies along the principal shear plane and decreases monotonically from the shear band initiation site.     

直角切削剪切角与剪切带有限元仿真分析北大核心

有限元方法是研究切削加工中切削机制的一个重要途径。在OXLEY解析模型中,切削过程中的剪切角、第一变形区剪切带宽度以及第二变形区剪切带宽度,是研究切削力、切削温度等的重要基础。建立Deform2D切削模型,通过后处理界面测量剪切角。在考虑第二变形区剪切应变的情况下,建立新的剪切角求解模型。将新的剪切角模型与测量得到的剪切角对比,具有较好的一致性。最后通过应变率、应变分布云图,分别确定了第一、第二剪切带厚度,并探究其与切削速度、切深的关系。     

原位晶态相增强Mg-Cu-Dy非晶基块状复合材料

采用铜模喷铸法制备出直径为3 mm的原位Mg晶态相增强块状Mg70Cu17Dy13非晶基复合材料,对Mg-Cu-Dy类合金的力学性能和变形行为进行研究。结果表明,Mg70Cu17Dy13非晶基复合材料受压时产生加工硬化并获得最大抗压强度为702.38 MPa和塑性变形率为0.81%。这缘于其中Mg相有效的承载能力、塑性变形能力及Mg相对剪切带及裂纹扩展的有效抑制作用,可从其剪切变形、断裂方式和断裂面上密集的熔滴及凸凹不平得到证实     

刀具磨损声谱特征的分析

刀具在切削过程中，会产生大量的声信号。文中运用统计方法对切削声信号进行了深入分析，并对可听阈内的声信号按低频带、中频带和高频带分别进行了功率谱分析。研究结果表明，切削声信号中100—8kHz频带内的特征频率分量反映了刀具磨损状态及其变化规律，这为利用声信号进行刀具实时在线监测奠定了基础。     

PCBN刀具高速铣削TC4钛合金切削性能与工艺参数优化研究

针对钛合金TC4(Ti-6Al-4V)的加工特性,采用PCBN刀具,基于单因素试验,研究高速铣削条件下工艺参数对切削力、切削振动等的影响规律,提出综合考虑切削力、切削振动、表面粗糙度的工艺参数优选方法。研究表明:切削力和切削振动随切削速度v和每齿进给量f_z的增大呈现一定的波动,随径向切深a_e和轴向切深a_p的增大而增大,切削振动受切削力影响较为显著。考虑切削性能,以材料切除率为优化目标,以切削力、切削振动和表面粗糙度等为约束条件,建立工艺参数优选模型,可得到不同约束条件下工艺参数的优选组合。     

不锈钢网增强锆基非晶复合材料的压铸制备及力学性能研究

全程真空压铸技术的快速发展为大块非晶合金的工业化应用提供了可能,受到了广泛关注。但是,非晶合金的室温脆性限制了压铸结构件在一些关键领域的应用。本论文利用压铸工艺高速充型及高压凝固的特性,通过在Vit1锆基非晶合金中引入304不锈钢网叠层焊接制造的骨架,成功制备出了不同体积分数晶态相增强的非晶复合材料,并系统研究了不锈钢网体积分数对力学性能的影响。研究结果表明,不锈钢网在非晶基体中均匀分布,与非晶合金存在冶金界面结合。力学性能测试显示,随着不锈钢编织网的引入,室温脆性的压铸Vit1块体金属玻璃的塑性得到了显著提升。随着不锈钢网目数增大(对应晶态相体积分数增大),非晶复合材料的塑性呈增大的趋势,但是,当目数超过200时,过细的孔洞会导致骨架局部区域无法填充,恶化性能。当晶态相的体积分数为53.7％时,断裂应变达到最大值,约为10％左右,其值高于传统不锈钢纤维增韧的Zr基非晶复合材料。韧化机制分析表明,压铸非晶合金出现脆-延性转变的根本原因是不锈钢网对剪切带扩展进行高效抑制,促进剪切带的增殖和萌生,减少宏观塑性变形的局域化。本研究为非晶复合材料的结构设计提供了新的思路,对于促进非晶合金的更广泛应用具有重要的工程价值。     

Cyclic compression behavior of a Cu–Zr–Al–Ag bulk metallic glass

The cyclic compression behavior of a Cu₄₅Zr₄₅Al₅Ag₅BMG was investigated in order to elucidate the damage initiation and growth mechanisms. The present Cu₄₅Zr₄₅Al₅Ag₅ BMG was found to have a fatigue-endurance limit of 1418 MPa and fatigue ratio of 0.77. Fracture under cyclic compression occurred in a pure shear mode. The fracture surface forms an angle of 41° with respect to the loading axis. This angle was similar to the monotonic compressive fracture angle for the present BMG. The cyclic compression fracture surface displays a morphology nearly identical to the monotonic compression fracture surface. In addition to many shear bands and cracks, areas of “chipping” were commonly found on the outside surfaces of the fatigue specimens. An attempt was made to measure crack growth rates, and two types of crack growth behavior were found. With the first type, the growth rate decreased with cycles due to the decrease in the driving force for crack propagation. With the second type, the crack growth rate increased with cycles after chipped areas developed. The fatigue deformation process for BMGs under cyclic compression was carefully studied and rationalized.