MOLECULAR DYNAMICS SIMULATIONS OF DFZ

Dislocation emission from the crack tip in copper under mode II loading is simulated with molecular dynamics method. After 26 partial dislocations are emitted and then relaxed to reach the equilibrium under the constant displacement, the double pile-ups (including an inverse pile-up and a pile-up) are formed. i.e., the first dislocation is piled up before the obstruction, and the last dislocation is piled up ahead of the crack tip. These results conform to the TEM observations.

DFZ—B型高频电治疗仪治疗腋臭1640例临床观察

1988年,我们与成都电子研究所联合研制成功DFZ—B型高频电治疗仪,先后在警内外200多家医院、门诊部、卫生队推广。1989年1月～1990年8月,我们总队26个卫生队应用该治仪疗治疗腋臭1640例,疗效显著,现综合报道如下。

Ni基高温合金单晶裂尖位错行为的动态研究——Ⅰ.DFZ 的形成及微裂纹的扩展

用透射电镜原位观察方法对 Ni 基高温合金单晶裂纹尖端位错行为进行了研究。发现在裂纹扩展的同时伴随着位错的发射,并在裂纹尖端形成无位错区(DFZ)。γ/γ′界面的存在阻碍位错的运动,并使DFZ 变短。

氢对裂尖释放位错临界应力强度因子K_e和无位错区DFZ的影响

理论计算得出:氢降低位错运动点阵阻力,使得裂尖释放位错临界应力强度因子降低;氢的存在使裂尖所释放的位错受到附加吸引力,缩短了 DFZ。TEM 原位拉伸实验表明(i)在氢气氛中,纯铁裂尖位错释放的临界应力强度因子降低。(ii)对 Fe-3%Si 单晶体,电解充氢后裂尖DFZ 消失。(iii)Fe-3%Si 多晶体预形变后充氢,裂尖存在 DFZ。实验结果证实了作者提出的理论模型。

东非被动大陆边缘盆地演化及大气田形成主控因素:以鲁武马盆地为例

东非被动大陆边缘盆地近年来发现了一系列大气田,主要分布于鲁武马盆地,其可采储量达3.8×1012 m3。盆地经历了卡鲁裂谷期、马达加斯加裂谷期和马达加斯加漂移期等3期构造演化。其中,马达加斯加裂谷期形成下侏罗统—中侏罗统湖相-滨浅海相烃源岩,于早白垩世进入生油门限,晚白垩世达到生油高峰,渐新世进入生气窗。受马达加斯加漂移期东非陆上断裂系统活动影响,大量富砂沉积物以块体搬运和深海滑塌方式向深水区堆积,形成了盆地内面积广、厚度大、岩性相对均一且物性良好的超大型深水重力流沉积砂体;漂移期海相泥页岩则为良好的区域性盖层。东非陆上早期隆升和三角洲进积作用使鲁武马盆地形成重力滑动和盐底辟构造,渐新统—上新统内形成东非被动陆缘正断层带(EANFZ)和逆冲断层带(EATFZ),下伏中—下侏罗统烃源岩生成油气沿正断层和深水区逆冲断层向上运移,聚集于构造-岩性-地层、构造圈闭中,形成大气田。

升温速率对1933铝合金铸锭均匀化组织的影响

采用光学显微镜、扫描电镜、能谱分析、透射电镜和X线衍射分析等试验手段,研究升温速率对1933铝合金铸锭均匀化显微组织的影响。研究结果表明:合金铸态中主要存在α(Al)+η(MgZn2)非平衡共晶组织、AlZnCu相和AlCuFe相;均匀化处理后共晶组织被消除,η相溶解,合金中残留有AlZnCu相和AlCuFe相;合金经465℃/24 h、升温速率为200℃/h均匀化处理后,晶界附近存在一个明显的无Al3Zr粒子析出带(DFZ)。

Ⅰ型裂纹的连续位错模型

用连续位错分布模拟裂纹和裂尖塑性区，建立了中心对称有限长Ⅰ型裂纹的无位错区（ＤＦＺ）模型．对一个主裂纹和四个对称滑移带情形推导出基本方程．计算表明，随着外加应力的增大，位错密度增大，位错活动明显加剧，在滑移带，位错密度在紧接ＤＦＺ的塑性区中某点达最大。

ODS铁素体钢中微裂纹形核过程的TEM原位观察

采用透射电子显微镜原位拉伸薄膜试样法研究了ODS铁素体钢中位错发射及微裂纹形核、钝化和扩展的过程．结果表明，ODS铁素体钢在原位拉伸时，裂尖首先发出大量位错并形成无位错区，保持恒位移，纳米级微裂纹在裂纹顶端连续形核或在DFZ中不连续形核，这个微裂纹并不钝化成孔洞．

氢对Ⅲ型裂纹尖端应力场中螺位错受力的影响

根据理论分析和实验观察表明．Ⅲ型裂纹尖端应力场中存在的偏聚氢原子将对该应力场中的发射位错产生附加作用力．此作用力使裂尖发射出的螺位错离开裂尖区域的阻力增大．导致裂尖无位错区变短．同时、裂尖区域偏聚氢原子促进螺位错以交滑移的方式运动．

Effect of fine precipitates on initiation and propagation of micro-cracks in low alloy Cr-Mo-V steel

The effect of fine precipitates on the initiation and propagation of micro cracks and the length of dislocation free zone (DFZ) in a low alloy Cr Mo V steel was studied by in situ TEM observation for the specimens both in embrittled and toughened conditions. The results show that in the embrittled specimen, dislocations emitted from the crack tip can easily slip by cutting through the precipitates and move away from the crack tip region, so that a long DFZ forms and the brittle fracture occurs via cleavage cracks initiating and propagating. The size of DFZ mainly depends upon the diameter and the interparticle distance of the precipitates in the matrix. In the toughened specimens, the size of DFZ extremely changes with the interparticle distance. Mobile dislocations are emitted from the crack tip and bypassing the particles. The interaction between the dislocations and the particles results in the dislocation pile up and tangle, leading to diminishing of the DFZ. The crack tip is easy to blunt or chang the propagating direction and the crack propagation shows a jagged path.

Dislocation Behaviour near the Crack Tip in Bulk Fe-3% Si Single Crystal

An investigation has been made of the disloca- tion distribution and dislocation free zone near the crack tip in bulk Fe-3% Si single crystal during deformation in SEM.It has been found that a number of dislocations were emitted from the crack tip during deformation.After that,the dislocations moved rapidly away from the crack tip,which indi- cated that they were strongly repelled by the stress field at the crack tip.Between the crack tip and the plastic zone there is a region of dislocation-free, which is referred to as dislocation-free zone (DFZ). The length of DFZs is roughly estimated 100 μm which is much longer than that found in thin foil specimen.The variation of dislocation density as a function of the distance from the crack tip was measured,which showed that the dislocations are inversely piled up in the plastic zone.The length of DFZs increased with both the length of pre-crack and the amplitude of applied stress.

一汽解放系列车型数据表(四)

近年来,商用车产品的更新换代步伐不断加快,为方便企事业单位和个人购车,现刊出“一汽解放商用车系列车型数据表”,以后还将陆续推出我国各大企业主要商用车车型及配置情况,并不断更新。

In situ Observations of Microcrack Nucleation and Bluntness in Ductile Fracture

Nucleating of a microcrack within nanometres and blunting into a void are studied through in situ tensile test for thin foil specimens of type 310 steel by transmission electron microscopy (TEM). The mechanism of microcrack nucleation is analyzed by means of microfracture mechanics. The results show that a main crack tip may be still sharp after dislocations are emitted from the crack tip and dislocation free zone (DFZ) forms so that the local stress near the crack tip in the DFZ is high enough to equal the cohesive strength and then a microcrack initiates in the DFZ. The microcracks initiating in the DFZ will blunt into voids through the movement o. the existing dislocations and/or those emanated from the crack tip and nearby dislocation sources. The discontinuous voids resulting from the blunt of the microcracks in the DFZ will link with each other and with the main crack, resulting in a zig-zag crack propagation. A microcrack will nucleate at the main crack tip and the new crack will blunt rather

Fe—3%Si单晶体裂纹尖端位错行为及氢效应的TEM动态观察

在透射电镜中对 Fe-3%Si 单晶体薄膜进行拉伸试验,观察了在受力状态下裂纹尖端的位错行为及固溶氢的影响。结果表明,在受力时裂尖会自动发射位错。位错一旦从裂尖发射,便很快离开裂纹尖端以反塞积群形式存在于塑性区中。在裂纹尖端与塑性区之间存在一无位错区(DFZ)。裂纹扩展包括裂尖发射位错的塑性过程以及 DFZ 解理的脆性过程。固溶的氢改变了裂纹尖端的位错分布,促进了位错从裂尖发射,致使 DFZ 的长度减小甚至消失。

Failure modes after exhaustion of dislocation glide ability in thin crystals

The changes of microstructures after the exhaustion of dislocation glide ability but before cracking, as well as microcrack initiation by them, were studied in detail by in-situ transmission electron microscopy (TEM) for pure copper, aluminum and iron. Thinning occurred in the thicker regions through dislocation gliding in the three metals. After that, {111} 【112】 twinning or tensile cracking took place in thinned zones in fcc metals. In the case of twinning, new microcracks were initiated along another {111} plane by the high stress concentration near the growing tip of the twin, while in iron (bcc), many nanocracks were initiated in the thinned areas just ahead of the crack front, resulting in misorientation microstructure from which microcracks or microvoids were developed.

大块Fe-3%Si单晶体裂纹尖端无位错区的观察

利用蚀坑技术和扫描电镜动态观察方法研究了大块 Fe-3%Si 单晶体裂纹尖端的形变行为。证实了裂纹尖端与塑性区之间存在无位错区(DFZ),且无位错区尺寸随变形量的增加而增加。