航空钛合金高速切削有限元建模

为了正确模拟钛合金Ti6Al4V高速切削过程中锯齿状切屑形成的过程,深入研究有限元建模过程中有限元模型的建立、材料本构关系、切屑分离准则、材料失效准则、切削热动态耗散与热传导等关键技术.结合实例,分别采用热力耦合分析和绝热分析对钛合金Ti6Al4V的加工过程进行正交切削有限元模拟.通过对2种模型获得的应力分布、温度分布、切削力曲线进行分析,以及将2种模型获得的锯齿状切屑与实际切屑形状进行对比,证明了绝热剪切是导致高速切削钛合金生成锯齿状切屑的原因.     

钛合金切削绝热剪切带形成过程的有限元分析

采用有限元模拟方法对钛合金切削加工中的绝热剪切带形成过程进行了研究.通过对材料本构模型、刀-屑接触摩擦、切屑分离和绝热剪切等关键物理环节建模,建立了切削加工有限元模型.利用该有限元模型模拟和分析了钛合金TC4切削绝热剪切带形成的全过程,得到了与试验相似的锯齿状切屑,切屑中绝热剪切带分布规律与试验结果较为一致,切削力模拟结果与试验数据相吻合.研究结果表明,刀尖处首先形成小的变形区并逐渐扩展至切屑表面,变形区发生集中滑移,锯齿节块滑出,最终形成变形高度集中的剪切带;绝热剪切带内的温度相当高,而其两侧材料温度较低;绝热剪切带的形成与弹性能释放密切相关,弹性模量越小,切屑锯齿化程度和剪切带间隔时间越大.     

切削工艺参数对Ti6Al4V合金切屑形貌的影响规律

为解决当前传统钛合金的切割加工过程只考虑单一性能,导致加工功能较差的问题,以Ti6Al4V合金为研究对象,研究切削进给速度、刀具前角角度等对切屑尺寸及形貌的影响.设定不同的切削速度、进给速度和刀具前角度,对锯齿金相的齿距、自由表面、带倾角以及带宽进行测量,根据测量结果分析切削工艺参数对Ti6Al4V合金切屑形貌的影响规律.结果表明:随着进给速度的增加,锯齿间距和自由表面尺寸增加显著,剪切带倾角随着切削厚度的增大而减小;当刀具前角为0°时,剪切带倾角从63. 21°降至50. 80°,刀具前角为8°时,剪切带倾角从68. 93°降至最低时为49. 8°,刀具前角的变化对剪切带倾角的影响不大.     

基于有限元模拟的钛合金锯齿状切屑形成机理

为了研究钛合金切削加工中的锯齿状切屑形成机理,通过对材料本构模型、刀屑接触摩擦、切屑分离和绝热剪切等关键物理环节建模,建立了切削加工有限元模型,并经试验验证了该模型的正确性.利用该有限元模型模拟了钛合金Ti6Al4V锯齿状切屑形成的全过程,通过分析一个锯齿节块的形成过程,以及该过程中的切削力同步发展变化规律和第一变形区中不同部位的三点应力、温度曲线,揭示了钛合金锯齿状切屑的形成机理是靠近切削尖处的材料发生热塑性失稳,继而在整个第一变形区诱发集中滑移,造成绝热剪切,从而形成节块状的锯齿状切屑.     

正交车铣高强度钢切屑形成机理的研究

对正交车铣高强度钢的不同切屑形态进行了研究,结果表明,正交车铣切屑属于短的锯齿形切屑,不会损伤已加工表面,易于排屑,可以满足自动化生产要求.分析了正交车铣切屑的扫描电子显微镜的照片,发现有绝热剪切发生,证明正交车铣锯齿形切屑产生的原因是切屑内部的局部产生突变性剪切所造成的.     

高速铣削P20淬硬钢的试验研究

使用TiAIN涂层整体圆柱立铣刀,对P20淬硬钢(41HRC,32HRC)进行了高速铣削试验,考察了各种切削速度下的切屑变形,微观硬度、切削温度和切削力.切削参数包括:切削速度151～942 m/min,每齿进给量0.1 mm/齿,轴向切削深度1.0 mm.切削宽度1.0 mm.结果表明:两种硬度的P20钢都产生了锯齿形切屑,切削温度随切削速度的增加而增大,工件硬度、切削速度对切屑变形和切削力有重要的影响.     

H70黄铜局域化剪切变形行为研究

借助分离式霍普金森压杆和金相显微镜研究了高应变速率下H70黄铜中的绝热剪切现象。实验结果表明,当应变速率为5.0×10~4s~(-1)、6.0×10~4s~(-1)时,加载后H70黄铜中均出现绝热剪切带,且带内原始粗大晶粒发生动态再结晶而细化。另外,随着应变速率从5.0×10~4 s~(-1)增加到6.0×10~4s~(-1),对应的临界应变和绝热剪切形成能分别从1.346、723.71 kJ/m~3增加到1.578、805.94 kJ/m~3,即随着应变速率的增加,应力坍塌点对应的临界应变和绝热剪切形成能均增加,表明H70黄铜的绝热剪切敏感性随着应变速率增加而降低。     

907A钢绝热剪切行为研究

利用压剪试样 ,采用Hopkinson压杆试验技术 ,研究了船用 90 7A钢在应变率 γ 2 .0 × 1 0 5s-1的条件下的绝热剪切行为 ,结果表明压剪试样韧带的变形是一个两端向中间传播的剪切变形过程 ;在该应变率条件下 ,该钢的绝热剪切带属于相变剪切带 .     

大直径菲涅尔透镜模具加工机理

针对大直径菲涅尔透镜模具的加工难题,基于有限元仿真软件ABAQUS和模态实验方法对大直径菲涅尔透镜模具切削过程加工机理进行分析.介绍了菲涅尔透镜设计及模具加工原理,结合材料本构关系、材料失效准则等,建立正交切削二维模型,得到仿真切屑,与模态实验得到的切屑进行对比,验证了仿真切削模型的可行性.研究了切削速度、进给速度对切屑形成过程的影响.研究结果表明:在H62黄铜模具加工过程中,材料强度和塑脆性对切屑形态产生重要影响,随着变形速度的提高,材料强度提高,材料塑性降低,切屑的演化过程依次分为带状切屑、锯齿切屑、单元切屑.     

切屑变形的微观研究

经观察分析，建立了计算直角自由切削切屑卷曲半径的新模型，新模型比Ｒａｍａｌｉｎｇａｍ模型计算的切屑卷曲半径更接近实测值，对圆弧刃切削的层片厚度与变形系数的关系进行了试验研究，试验结果为“变形愈小，层片愈厚”的结论提供了新的证据。     

Characterization of plastic flow in two Zr-based bulk metallic glasses

1 Introduction Bulk metallic glasses (BMGs) have attracted a great attention due to their excellent properties, such as high strength, good wear resistance, excellent elasticity and easily forming in viscous state. However, structural applications are currently limited by the lack of macroscopic plasticity at room temperature, characterized by strain-softening which results in the formation of intense localized shear bands. Fracture typically occurs after very small plastic strain in compress…     

Adiabatic shear localization evolution for steel based on the Johnson-Cook model and gradient-dependent plasticity

Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural effect （interactions and interplay among microstructures） due to heterogeneity of texture plays an important role in the process of development or evolution of an adiabatic shear band with a certain thickness depending on the grain diameter. The distributed plastic shear strain and deformation in the shear band are derived and depend on the critical plastic shear strain corresponding to the peak flow shear stress, the coordinate or position, the internal length parameter, and the average plastic shear strain or the flow shear stress. The critical plastic shear strain, the distributed plastic shear strain, and deformation in the shear band are numerically predicted for a kind of steel deformed at a constant shear strain rate. Beyond the peak shear stress, the local plastic shear strain in the shear band is highly nonuniform and the local plastic shear deformation in the band is highly nonlinear. Shear localization is more apparent with the increase of the average plastic shear strain. The calculated distributions of the local plastic shear strain and deformation agree with the previous numerical and experimental results.     

不同温度下AZ31镁合金绝热剪切变形局域化

为了了解镁合金在不同温度高应变率载荷作用下发生变形局域化的特点,进而揭示镁合金在高速冲击载荷作用下发生绝热剪切的特殊规律,采用分离式Hopkinson压杆对挤压态AZ31镁合金进行了常温及高温的高速冲击压缩试验,而后对不同温度冲击后的试样通过光学显微镜、扫描电镜和透射电镜进行变形机制的分析.结果表明:常温下试样在受到剪切力后,在剪切区的裂纹周围产生了大量的孪晶;高温下试样的剪切区内产生了明显的绝热剪切带,并且在剪切带周围发现了大量平行的孪晶.在TEM下观察到剪切带内为等轴晶晶粒,在剪切区内发生了动态再结晶过程.     

Analysis of adiabatic shearing failure mechanism for aluminum matrix composites based on experimental and numerical simulation

Adiabatic shear behavior and the corresponding mechanism of TiB2/Al composites were researched by split Hopkinson pressure bar (SHPB).Results show that the flow stresses of the TiB2/Al composites exhibit softening tendency with the increasing of strain rates. All the composites fail in splitting and cutting with a 45 degree, and the phase transformed bands of molten aluminum are found on the adiabatic shear layers. The deformation behavior and shear localization of the TiB2/Al composites specimens were simulated by finite element code MSC.Marc. The Johnson-Cook model was used to describe the thermo-viscoplastic response of the specimen material. There was unanimous between the numerical result and the experimental result on the location of the adiabatic shear band. From the numerical simulation and experiment, it was concluded that the instantaneous failure of the composite was ascribed due to the local low strength area where the formation of adiabatic shear band was, and the stress condition had significant effect on the initiation and propagation of adiabatic shear band (ASB).     

奥氏体高锰钢的切削过程与形变强化规律

金属切削过程是切削层金属的塑性变形和断裂过程 .切削过程中 ,金属的形变强化、裂纹形成与长大的知识对理解切屑分离和流出是必要的 .本文应用快速落刀及金相分析方法研究了奥氏体温锰钢 5 0Mn18Cr4切削变形过程中的形变强化和微裂纹形成与扩展规律 .研究表明 ,切削过程中的形变强化规律符合幂函数规律 ;切削刃处切削材料的分离是该局部材料形变强化达到断裂应力的结果 ;奥氏体高锰钢切屑属挤裂型切屑 ;切屑断裂源于剪切带 ;在切屑沿前刀面流出过程中 ,因流速不等而产生的弯矩是导致切屑局部剪切失稳的重要原因     

Chip formation in high speed milling of Ti-6Al-4V alloy under nitrogen-oil-mist

High speed milling experiments using nitrogen-oil-mist as the cutting medium were carried out to investigate the characteristics of chip formation for Ti-6Al-4V alloy.Within the range of conditions employed（cutting speed,vc=190-300 m/min;cutting depth of axial,ap=5,7 mm）,saw-tooth chips were produced in these experiments.During the macro and micro analysis of the Ti-6Al-4V chips,an optical microscope and a scanning electron microscope（SEM）were used to study the microstructure and the morphology of the chips,and the X-ray photoelectron spectroscopy（XPS）was employed for chemical analysis.Comparisons were made to study the influence of different cutting media（nitrogen-oil-mist,air-oil-mist and dry cutting condition）on chip formation.Results indicate that cutting media have significant effects on chip formation.Nitrogen-oil-mist is more suitable for improving the contact condition at chip-tool interface and increasing the tool life in high speed milling of Ti-6Al-4V alloy than air-oil-mist and dry cutting.     

高温合金锯齿形切屑绝热剪切带内材料组织演变及形成机理

为了研究不同铣削条件下切屑的宏观形态,设计了高速铣削单因素试验。通过单因素试验考察了各个铣削参数对铣削力的影响,并对改变铣削速度后得到的切屑的宏观形态进行了分析。对铣削加工中得到的切屑进行镶嵌、抛光、腐蚀,得到其金相显微组织照片,使用Digimizer测量软件对切屑形态各参数进行测量,研究了铣削速度对锯齿化程度和锯齿齿距的影响。通过得到的金相组织照片,对不同铣削参数下的切屑基体和绝热剪切带内材料的组织变化进行分析,得出了锯齿形切屑的形成机理。