谢晓龙
,
赵震
,
虞松
,
陈军
,
李明辉
金属学报
精冲时材料在狭窄的凸模、凹模间隙附近形成局部塑性剪切带，极易产生断裂、塌角过大等成形缺陷。本文在MSC/MARC中建立了轴对称精冲有限元模型，利用混合位移－压力的更新拉各朗日有限元方法对精冲局部剧烈塑性变形进行模拟，克服了剪切自锁和体积自锁，结合基于应变梯度、表面曲率的网格自适应技术，精确捕捉了应变集中现象。并通过MARC用户子程序实现了Schiffmann损伤功密度的半耦合计算，预测了精冲过程中材料损伤的发展，并预测了不同工艺参数下的零件塌角高度、光亮带高度和精冲力，最后利用模拟得出的最佳工艺参数获得了合格的零件。
关键词:
精冲
,
damage
,
ductile fracture
,
mixed displacement-pressure FEM
材料科学技术（英文）
A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process, Si is used as an in-situ liquid forming phase and it is favorable for both the solid-liquid synthesis and the densification of Ti3SiC2 ceramics. The present work demonstrated that the temperature fluctuation synthesis/simultaneous densification process is one of the most effective and simple methods for the preparation of Ti3SiC2 bulk materials providing relatively low synthesis temperature, short reaction time, and simultaneous synthesis and densification. This work also showed the capability to control the microstructure, e.g., the preferred orientation, of the bulk Ti3SiC2 materials simply by applying the hot pressing pressure at different stages of the temperature fluctuation process. And textured Ti3SiC2 bulk materials with {002} faces of laminated Ti3SiC2 grains normal to the hot pressing axis were prepared.
关键词:
damage
A.Cherouat
,
H.Borouchaki
材料科学技术（英文）
Ductile damage often occurs during metal forming processes due to the large thermo-elasto (visco) plastic flow localisation. This paper presents a numerical methodology, which aims to virtually improve any metal forming processes. The methodology is based on elastoplastic constitutive equations accounting for nonlinear mixed isotropic and kinematic hardening strongly coupled with isotropic ductile damage. An adaptive remeshing scheme based on geometrical and physical error estimates including a kill element procedure is used. Some numerical results are presented to show the capability of the model to predict the damage initiation and growth during the metal forming processes.
关键词:
Finite elastoplasticity
,
elastoplasticity
,
Ductile
,
damage
,
E
Y.P.Jiang
,
Z.F.Yue
金属学报(英文版)
A unit cell model is applied to study the creep damage behavior after fiber fractures in the fiber-reinforced composites at high temperature. The user subroutine CREEP has been programmed for ABA QUS. The fiber breakage results in a new crack. The results show that the stress concentration factor resulted from the fiber breakage increases with the creep time. The creep damage takes place near the crack, and then grows in the matrix along a certain angle, up to the total failure. The influences of the ratio of modulus of the fiber to the matrix (Ef/Em) on the creep deformation, damage and stress distributions have been studied. With the increasing Ef/Em, the damage in the matrix increases. Analysis on the different ductility of matrix shows that the creep damage of low ductile matrix composites is higher than high ductile matrix composites.
关键词:
composites
,
null
,
null
Q.M.Yu
,
Z.F.Yue
金属学报(英文版)
Numerical calculations of creep damage development and life behavior of circular notched specimens of nickel-base single crystal had been performed. The creep stress distributions depend on the specimen geometry. For a small notch radius, von Mises stress has an especial distribution. The damage distribution is greatly influenced by the notch depth, notch radius as well as notch type. The creep crack initiation place is different for each notched specimen. The characteristics of notch strengthening and notch weakening depend on the notch radius and notch type. For the same notch type, the creep rupture lives decrease with the decreasing of notch radius. A creep life model has been presented for the multiaxial stress states based on the crystallographic slip system theory.
关键词:
creep
,
null
,
null
李娜
,
李玉龙
,
郭伟国
兵器材料科学与工程
doi:10.3969/j.issn.1004-244X.2009.04.028
首先测试83W旋锻(8Fe-9Ni-83W)和89W径锻(5Fe-6Ni-89W)两种钨合金棒材的各向异性情况,然后对两种钨合金材料分别进行了温度从-196℃到800℃的动、静态压缩试验(应变率10~(-3)～7 000 s~(-1))和拉伸试验(应变率10~(-3)～1 000 s~(-1)),得到了其应力应变关系曲线和失效应变.结果表明:两种棒材都存在各向异性特性,钨合金棒材沿径向硬度不均匀,越靠近棒心,硬度越低.随着应变率的升高和温度的降低,两种钨合金材料的流动应力升高;在所研究的温度范围内,一定应变率下两种钨合金材料都出现了动态应变时效现象;两种钨合金材料的失效应变随着应变率的增大而降低.最后观察钨合金试验后的金相照片,给出应变率和温度以及钨颗粒含量对其损伤模式的影响.
关键词:
钨合金
,
损伤
,
应变率
,
动态应变时效
,
各向异性
,
温度
,
损伤模式
王玲玲
,
方国东
,
梁军
复合材料学报
doi:10.13801/j.cnki.fhclxb.201501.002
开展了SiC(20vol％)-石墨(15vol％)/ZrB2复合材料室温及高温拉伸性能实验,发现高温时复合材料的拉伸强度和弹性模量有所降低,并且具有明显的非线性特征.引入热损伤来表征弹性模量随温度的衰减规律,利用强度统计分析方法确定单向应力状态下材料的机械损伤演化方程,建立了材料在热力耦合条件下的高温拉伸损伤非线性本构模型.分析表明:随着温度的升高,SiC-石墨/ZrB2复合材料的热损伤和机械损伤不断增加,延性增强,且脆性-延性破坏转变温度范围为1 250～1 350℃.
关键词:
ZrB2
,
陶瓷
,
复合材料
,
超高温
,
微裂纹
,
损伤
,
本构模型
冯喜奎
,
贾华坡
,
任毛丁
硬质合金
doi:10.3969/j.issn.1003-7292.2016.06.007
钢的异型小截面冷精轧在纺织器材、金属制品、线材加工等行业被广泛应用.为了有效解决此类冷精轧硬质合金轧辊高发损伤这一棘手的难题,归纳了此类冷精轧的特点,展示了其高速轧机的轧头结构,指出此类轧辊的高发损伤形式为爆点、毛边棱、边角垮塌、崩落扩展沟和断裂,突出特点是损伤的快速扩展.从材质的变形抗力、轧制强度、轧辊材质特性三个主要方面分析了所用复合式硬质合金轧辊损伤及扩展的诱因、形式及特点.指出抑制硬质相晶粒异常长大,提高强韧性,消除微观缺陷是前提.提高轧制系统精度,优化轧制工艺,完善轧机生产辅助条件,强化操作规范与技巧则是生产实践中控制轧辊损伤、降低轧辊耗用量的有效对策.
关键词:
硬质合金
,
轧辊
,
损伤
,
爆点
,
磨损
,
冷轧
,
变形抗力
颜莹
,
齐跃
,
陈立佳
,
李小武
中国有色金属学报(英文版)
doi:10.1016/S1003-6326(16)64193-6
为了探索应变速率对超细晶材料高温变形特点的影响，通过压缩实验以及显微观察，系统研究在不同温度和应变速率下等通道转角挤压 Al 的变形和损伤特点以及显微微组织。结果表明：应变速率的提高消除了等通道转角挤压 Al 在变形温度 T≤473 K 时表现出的应变软化现象，并且大大提高了变形温度在473~573 K 范围的屈服强度和流变应力。等通道转角挤压 Al 的塑性变形主要由剪切变形控制。当应变速率为1×10?3 s?1时，变形温度T ≥473 K 时可观察到沿剪切带形成了大量裂纹，并且二次剪切带基本消失。而当应变速率为1×10?2 s?1时，只有在变形温度低于473 K 时才能观察到沿剪切带形成的裂纹，并且当压缩温度 T≥473 K 时，二次剪切带变得更加清晰。等通道转角挤压 Al 的显微组织主要由亚晶组成，应变速率的提高抑制了亚晶的长大，从而导致高温屈服强度和流变应力的提高。
关键词:
等通道转角挤压
,
纯铝
,
应变速率
,
高温压缩
,
变形
,
损伤
,
显微组织
