钛合金（Ti—17）的动态力学性能和损伤特性

利用分离式Ｈｏｐｋｉｎｓｏｎ压杆冲击加载装置,采用圆柱和锥台两种试样,在高应变速率加载条件下研究Ｔｉ－１７合金的应力应变响应和动态损伤特征实验结果表明,动态屈服应力和断裂应力比静态相应值高宏观损伤对应变速率敏感,而对应力不敏感,出现宏观损伤的临界应变速率．试样微观解剖显示绝热剪切带是材料宏观损伤的先兆,试样主要沿剪切带发生破坏、在垂直加载轴的横截面上,绝热剪切带呈圆弧形,平行加载轴剖面上绝热剪切带沿最大剪切应力方向．锥台试样中绝热剪切带的应变从始点到终点逐渐减小     

微波烧结钨合金挤压棒材的微观结构及动态力学性能研究

采用分离式Hopkinson动态压缩装置对微波烧结93W-4.9Ni-2.1Fe合金棒材切割试样进行了动态力学性能研究,采用扫描电镜、光学电镜和纳米压痕硬度仪分别对合金试样微观组织和显微硬度进行了表征和测试。结果表明:微波烧结试样在受到冲击压缩时,钨晶粒与粘结相都发生均匀变形;应变率为2200s-1时,合金的最大应力为2587MPa,钨晶粒和粘结相显微硬度分别为8.716和6.267GPa;当应变速率为2200s-1时合金粘结相变形产生明显热软化效应,在与冲击力呈45°的方向形成了绝热剪切带,位于剪切带中心区域的钨晶粒沿其扩展方向发生变形被拉成纤维状。     

工业纯钛动态压缩特性及破坏的实验研究

用分离式霍普金森压杆对TA2工业纯钛进行了动态压缩及绝热剪切破坏实验研究,得到了不同应变率和不同温度下的宏观应力-应变曲线。通过对压缩本构特性及微观金相破坏的比较分析,讨论了应变率、表观压缩本构特性对绝热剪切形成的影响。结果显示:TA2试样动态压缩呈现绝热剪切破坏特征,绝热剪切带在空间呈对称的双锥形状;应变率越高,形成绝热剪切带的临界应变越小;分析表明,动态压缩实验无法得到关于绝热剪切起始、发展过程的本构软化信息。     

纯锆的动态力学行为及绝热剪切带

使用分离式霍普金森压杆装置(SHPB)对纯锆在室温下进行动态压缩实验,应变速率为800～4000 s-1。采用金相显微镜和Quanta200型扫描电子显微镜对绝热剪切带及压缩断口进行观察。结果表明,纯锆具有较低的应变速率敏感性,由于高应变条件下产生了高密度的孪晶,材料硬化显著增强,真应力-真应变曲线随应变增加呈上升趋势,最大抗压强度为843 MPa。纯锆试样中观察到明显的绝热剪切带,且沿剪切带出现裂纹,压缩断口呈韧性断裂。绝热剪切带的出现和发展是材料失效的主要原因。对剪切带内部的温度进行了估算,结果表明,纯锆剪切带内部最高温度为1564℃。     

ZnAl10Cu2合金在热压缩条件下绝热剪切带的形成及其特征

采用Gleeble-1500D热模拟试验机研究了ZnAl10Cu2合金热变形行为,使用光学显微镜(OM)、扫描电镜(SEM)分析了压缩后合金试样的显微组织。结果表明,绝热剪切带的宽带随应变速率的增加而减小,位于剪切带中心区域的初生枝晶沿其扩展方向被剧烈拉长成纤维状,且表现出塑性流动局域失稳的特征。基体β相发生动态再结晶,形成细小的等轴晶粒。     

Ti40Zr25Ni8Cu9Be18块体非晶合金低温动态压缩性能研究

采用铜模喷铸法制备Ti40Zr25Ni8Cu9Be18块体非晶合金,通过分离式霍普金森压杆装置(SHPB)对Ti40Zr25Ni8Cu9Be18块体非晶合金进行室温(25℃)和液氮温度(–196℃)条件下的高应变率加载动态压缩测试,结合S-4800型扫描电镜(SEM)对压缩试样断口进行观察,对比在室温和液氮温度下Ti40Zr25Ni8Cu9Be18块体非晶合金动态压缩性能及其断口形貌特征的差异。结果表明:Ti40Zr25Ni8Cu9Be18块体非晶合金室温动态压缩时,随应变率提高抗压强度无明显变化,没有应变率硬化效应。在液氮温度动态压缩时,抗压强度随着应变率提高有较大幅度增加,存在应变率硬化效应。液氮温度时的动态抗压强度明显高于室温动态抗压强度。Ti40Zr25Ni8Cu9Be18块体非晶合金室温动态压缩为剪切断裂,微观形貌上出现脉状花样和剪切带,剪切带诱发了裂纹的形成,裂纹沿着剪切带扩展。液氮温度下断口微观形貌有解理台阶和河流花样。室温动态断裂过程中,局域应变集中产生塑性变形;液氮温度下压缩动能转化的热量大部分被抵消,削弱了绝热剪切作用。     

热挤压处理后Mg-12Gd-3Y-0.5Zr镁合金的高速冲击行为研究

为了研究Mg-12Gd-3Y-0.5Zr镁合金在高速冲击下的绝热剪切行为,采用该合金的方形试样和帽形试样,在不同初始应变速率下利用Hopkinson压杆进行冲击。采用SEM对试样进行了观察。采用热粘塑性形式的Johnson-cook模型对冲击时试样内应力的分布以及断裂模式进行模拟。结果表明:方形试样中未发现绝热剪切带,而在帽形试样中则出现了明显的绝热剪切带。     

U-5.7Nb合金动载下绝热剪切带的形成及其演化机制

研究了U-5.7Nb合金在应变速率为8000s~(-1)下绝热剪切带的形成及其演化机制。通过控制应变速率,采用应变限位环的方法实现了U-5.7Nb合金在不同应变下的动态变形。结果表明:随着应变的增加,U-5.7Nb合金动载下会形成两种类型的绝热剪切带:形变带和转变带。形变带形成所需的临界应变值接近于0.33,而转变带形成所需的临界应变值接近于0.39。显微组织观察表明形变带内部由严重拉长的畸变组织组成,而转变带内部主要由细小等轴的晶粒组成。基于不同应变下绝热剪切带的表征,预测了U-5.7Nb合金动载下塑性变形及其断裂过程。     

Ti2AlNb合金高应变率下流动应力特征与本构关系

利用电子万能试验机和分离式Hopkinson压杆得到Ti_2AlNb合金准静态拉伸曲线及高应变率下动态压缩应力-应变曲线,观察分析变形后试样的微观组织,研究其高应变率下的流动应力特征。结果表明:在应变率2500～7500 s-1范围内,Ti_2AlNb合金的流动应力对应变率有较强的敏感性,且具有应变强化、应变率增强及增塑效应;应变率为5500、6500、7500s-1的3组试样中观察到了与加载方向约成45°的绝热剪切带。改进Johnson-Cook本构模型,拟合实验数据得到Ti_2AlNb合金室温下的动态塑性本构关系,与实验对比,改进后的模型能够较好地描述Ti_2AlNb合金在高应变率下的流动应力。     

高应变率下细晶W-Ni-Fe合金的力学行为与局部绝热剪切带的形成

研究晶粒细化和添加微量稀土元素Y对93W-4.9Ni-2.1Fe合金在动态压缩状态下力学行为的影响,观察分析显微组织的变化.结果表明,93W-4.9Ni-2.1Fe合金在高应变率加载下会出现应变硬化和热软化现象,合金强度和延性随着应变率的增大而增加;与传统W-Ni-Fe合金相比,细晶W-Ni-Fe合金在高应变率下具有更高的合金强度和延性,同时能在较低应变率下形成明显的局部绝热剪切带.表明细化晶粒能提高W-Ni-Fe合金的强度以及绝热剪切敏感性;另外,添加微量稀土元素Y能提高W-Ni-Fe合金在高应变率下的强度和延性,并且在低应变率下发生绝热剪切,稀土元素Y的添加有利于绝热剪切带的形成.     

高应变率下热挤压态细晶钨合金的动态力学性能及失效行为

采用快速热挤压技术对细晶93W-4.9Ni-2.1Fe-0.03Y%进行变形强化,研究了高应变率下挤压态细晶钨合金动态力学性能及失效行为。结果表明:在较低应变速率下的挤压态细晶钨合金的屈服强度相近,约2000 MPa;断面上的钨颗粒被严重拉长直至破碎,破碎的细小钨颗粒粘附在软化的粘结相中,随着应变率的增加钨颗粒变形更加明显;剖面观察发现:沿着断裂面的钨颗粒发生了高度的剪切变形,而内部区域则基本没有变形,表现出了剪切局域化迹象。实验结果证明了挤压态细晶钨合金在动态加载条件下的失效方式是绝热剪切失效。     

粉末烧结钨合金材料的绝热剪切变形局域化实验研究

在分离式Ｈｏｐｋｉｎｓｏｎ压杆装置上对斜圆柱粉末烧结钨合金试件进行了冲击实验,实验中观察到试件的宏观破断现象;用光学和扫描电子显微镜观察到钨合金中出现绝热剪切带这一变形局域化现象。实验结果表明,钨颗粒的形状和空间取向对钨合金剪切变形形式有明显的影响。     

Microstructural Evolutions of AA7055 Aluminum Alloy Under Dynamic and Quasi-static Compressions

The microstructural evolution of AA7055 aluminum alloy under dynamic impact loading with the strain rate of 1.3 × 10^4 s^-1 controlled by a split Hopkinson pressure bar was investigated, and compared with that under quasi-static mechanical loading in compression with strain rate of 1.0 × 10^-3 s^-1. The quasi-static-compressed sample exhibited equiaxed dislocation cells, which were different from the elongated and incomplete dislocation cells for the alloy undergoing dynamic compression. The high strain-rate compression also induced the formation of localized shear bands in which the recrystallizations characterized as fine equiaxed grains were observed. The microstructural evolutions under both quasi-static and dynamic compressions are rationalized in terms of the dislocation cell model combined with the dislocation kinetics, in addition to the adiabatic temperature rise in shear bands at high strain rate.     

挤压态钨合金绝热剪切局域化及微裂纹萌生现象研究

研究变形量对挤压态钨合金动态力学行为的影响及钨合金绝热剪切带内的微观开裂行为。结果表明,加载方向垂直于纤维取向时,随变形量由0增加至40.8%,挤压态钨合金绝热剪切敏感性显著增大;由对钨合金绝热剪切带内微观组织的SEM观察可知,靠近绝热剪切带中心处出现在微裂纹且微裂纹萌生于W-M界面及W颗粒内部;进一步的TEM观察可知,剪切带内W-M界面处存在大量的位错塞积,W颗粒中则出现亚晶内部及沿亚晶界扩展的微裂纹     

冲击载荷作用下钨合金材料绝热剪切带形成机理

对钨合金材料在受冲击载荷作用下绝热剪切带形成机理进行了研究,重点考察了受力条件的影响,用分离式Ｈｏｐｋｉｎｓｏｎ压杆装置对阶梯圆柱形、哑铃形和直圆柱形钨合金试件进行了冲击加载,利用光学显微镜对冲击后的试件进行了显微组织观察。用ＡＢＡＱＵＳ大型数值分析软件对试件进行有限元分析,材料模型采用热粘塑性形式的Ｊｏｈｓｎｏｎ－Ｃｏｏｋ模型,实验和数值计算结果表明：受力条件对钨合金材料的变形、损伤（微型纹和绝     

Microstructure and dynamic mechanical properties of tungsten-based alloys in the form of extruded rods via microwave heating

The dynamic mechanical properties of 93W–4.9Ni–2.1Fe alloys in the form of extruded rods sintered by microwave heating were investigated under dynamic compression using a split Hopkinson Pressure Bar. The microstructure and microhardness values of the sintered specimens after dynamic compression were analyzed and tested. The results show that the deformation amount and microhardness of specimens increase with increasing strain rate. When the strain rate is 3000 S^− 1, the deformation amount is increased to the maximum value of 59.8%, and the microhardness values of the tungsten grains and the matrix phase are also promoted to the maximum values of 7.66 and 6.92 Gpa, respectively. The formation of cracks during compressive deformation initiates before the appearance of the adiabatic shear bands. As the strain rate increases, cracks initiating at the edge of specimens gradually propagate to the bulk alloy, and the adiabatic shear band is observed at about 45° to the loading direction under the strain rate of 3000 S^− 1. These findings suggest that tungsten-based alloys extruded rods sintered by microwave heating would be an ideal material with excellent self-sharpening and penetration performance for penetrators.     

Adiabatic shear banding of hot-extruded tungsten heavy alloy under cryogenic temperature

The effect of cryogenic temperature on adiabatic shear banding (ASBing) of tungsten heavy alloy (WHA) processed by hot-hydrostatic extrusion was investigated.Results show that,when the initial temperature is decreased,the dynamic flow stress,the critical failure time,and the dynamic failure energy of specimens show an increasing tendency,while the susceptibility to ASB of WHA shows a decreasing tendency,which is characterized by decreased shear strain and increased width of shear bands.Microstructure analysis shows that the number of microcracks within ASB exhibits an increasing tendency with decreased initial temperature,and the dynamic recrystallization (DRX) process within ASB is evidently suppressed at the lower temperature.As a result of the lower temperature,the motion and rearrangement of dislocation are effectively suppressed,which is mainly responsible for the incomplete DRX process within ASB and decreases susceptibility to ASB.     

The Effects of Specimen Geometry on the Plastic Deformation of AA 2219-T8 Aluminum Alloy Under Dynamic Impact Loading

The effects of specimen geometry on shear strain localization in AA 2219-T8 aluminum alloy under dynamic impact loading were investigated. The alloy was machined into cylindrical, cuboidal and conical (frustum) test specimens. Both deformed and transformed adiabatic shear bands developed in the alloy during the impact loading. The critical strain rate for formation of the deformed band was determined to be 2500 s^?1 irrespective of the specimen geometry. The critical strain rate required for formation of transformed band is higher than 3000 s^?1 depending on the specimen geometry. The critical strain rate for formation of transformed bands is lowest (3000 s^?1) in the Ø5 mm × 5 mm cylindrical specimens and highest (> 6000 s^?1) in the conical specimens. The cylindrical specimens showed the greatest tendency to form transformed bands, whereas the conical specimen showed the least tendency. The shape of the shear bands on the impacted plane was also observed to be dependent on the specimen geometry. Whereas the shear bands on the compression plane of the conical specimens formed elongated cycles, two elliptical shaped shear bands facing each other were observed on the cylindrical specimens. Two parallel shear bands were observed on the compression planes of the cuboidal specimens. The dynamic stress–strain curves vary slightly with the specimen geometry. The cuboidal specimens exhibit higher tendency for strain hardening and higher maximum flow stress than the other specimens. The microstructure evolution leading to the formation of transformed bands is also discussed in this paper.     

钨丝增强铜基复合材料的动态力学性能及断裂特性

通过渗流铸造的方法制备出Wf/Cu82Al10Fe4Ni4复合材料,采用分离式霍普金森压杆(SHPB)和扫描电镜(SEM)研究其动态压缩行为及断裂特性。结果表明:复合材料界面结合紧密,受冲击时体现出良好的界面结合强度;在应变率为2000s-1下动态压缩材料发生部分塑性变形,局部表面出现裂纹;在应变率为3000s-1下动态压缩材料的动态压缩强度达到2500MPa,材料内部出现钨丝劈裂、钨丝弯曲断裂以及基体合金断裂3种破坏模式。同时,在材料的断裂面上出现大量熔化带,分析认为熔化是随着应变率的提高而出现的,它改变了复合材料的断裂方式,加速了Wf/Cu82Al10Fe4Ni4复合材料的整体失效。