纯铁在大应变速率范围内的变形和断裂行为  

Deformation and Fracture Behaviors of Pure Iron Over a Large Range of Strain Rates

作　　者：冯利民 苏国胜[1] 刘义 张红霞[1] FENG Li-min;SU Guo-sheng;LIU Yi;ZHANG Hong-xia(School of Mechanical&Automotive Engineering,Qilu University of Technology(Shandong Academy of Sciences),Jinan 250353,China)

机构地区：[1]齐鲁工业大学(山东省科学院)机械与汽车工程学院,济南250353

出　　处：《齐鲁工业大学学报》2021年第2期41-49,共9页Journal of Qilu University of Technology

基　　金：国家自然科学基金(51675289,51775285);山东省重点研发计划(2018GGX103023);济南市高校创新团队项目(2018GXRC005)。

摘　　要：通过MTS万能试验机和改进的分离式霍普金森压杆(SHPB)装置对纯铁DT8试样进行剪切试验。其应变率范围为3.30×10^(-3)~2.50×10^(5)s^(-1)。利用金相显微镜和扫描电镜(SEM)分析了变形区的金相组织和断口形貌。结果表明,应变率对纯铁的塑性变形和断裂行为有较大影响。在等温变形/断裂(ε·<1.55×10^(3)s^(-1))阶段,剪切带的变形速率很低以至于处于等温状态。剪切带出现颈缩,然后发生拉伸断裂。在绝热变形/断裂(8.00×103 s-1<ε·<1.74×10^(5)s^(-1))阶段,局部剪切带(LSB)形成。热量在LSB内集中导致了断裂应变的增加,并形成了伸长的断裂韧窝。在声速变形/断裂(ε·>1.74×10^(5)s^(-1))阶段,断裂应变开始减小,发生较小的塑性应变便不久后在剪切面出现裂纹。断裂面出现了多层椭圆形韧窝的准解理断裂。Shear tests of pure iron DT8 specimens were carried out on the MTS testing machine and the improved split Hopkinson pressure bar(SHPB)device with strain rate was from 3.30×10^(-3)to 2.50×10^(5)s^(-1).Metallographic structure and fracture morphology of deformed zones were analyzed by metallographic and scanning electron microscopes(SEM).Results show that strain rate has great influences on the plastic deformation and fracture behaviors of pure iron.In the isothermal deformation/fracture(ε·<1.55×10^(3)s^(-1)),the deformation rate in the shear zone is so low that the deformation therein is in isothermal state.Necking of the shear band and then tensile fracture takes place.In the adiabatic deformation/fracture(8.00×10^(3)s^(-1)<ε·<1.74×10^(5)s^(-1)),localized shear band(LSB)is formed.The heat concentrated in the LSB leads to the increase of fracture strain and resultant long-stretched fracture dimples.In the sound velocity deformation/fracture(ε·>1.74×10^(5)s^(-1)),the fracture strain begins to decrease.Cracks appear in shear planes shortly after little plastic straining.Quasi-cleavage fractures of multi-layer oval dimples appear.

关 键 词：纯铁 高应变率 局部剪切 变形 断裂 

分 类 号：TH142.1[一般工业技术—材料科学与工程]