微裂纹

Failure mechanics method is applied to analyze the effect of micro-cracks of matrix parallel to the fibres on delamination.

采用破坏力学的方法，深入地研究了分层尖端区内平行纤维的基体微裂纹损伤的演化及其对分层的影响。

The size of microalloyed carbides is very small and some is only 2~3nm. So microcrack extending can be restrained.

并且，由于微合金碳化物尺寸很小，可达2～3nm，对于微裂纹扩展有一定的约束作用。

In addition, there are bond areas between the new and the primary coverage because of the growing up of the plating coat, which may lead to the emergence of micro crack on the coating owing to such causes as too big or uneven impact during plating process, little distortion of global granular zinc dust inside the plating coat, less tight coalescence of the zinc dust flecks.

由于形成镀层的过程处在酸性环境，在镀层增厚过程中不可避免把酸性溶液包裹在镀层里面，酸性溶液会与金属基体和镀层反应，产生氢气，必然会寻找通道选出，形成微气孔；镀层是逐渐形成的，新生镀层与原有镀层之间存在结合面；镀覆过程由于撞击力过大或者不均匀，镀层内部球形颗粒状锌粉变形较小，球形颗粒与球形颗粒的结合不严密等，这些原因会导致镀层产生微裂纹。

Fatigue cracking is one of the major modes of premature distresses in asphalt pavements. Cracks of asphalt pavements start as microcracks and later propagate, densify, and coalesce due to repeated traffic loading or low temperature thermal stresses or combinations of both to form macrocracks, and result in structural distresses of asphalt pavements.

疲劳开裂是沥青路面主要的早期破损形式之一，由于交通荷载和低温应力的反复作用，沥青路面中的微裂纹不断扩展、增密并贯穿连通形成宏观裂纹，导致。。。

The big size anvil used wax as plasticizer at dewaxing. The main dewax stage from 270℃ to 400℃. Have gas release summit between 400℃ and 750℃. Setting up rational process date at dewax stage can prevent cemented carbide crack. But the crack will appear and impair the quality of products when the microcrack flaw inner compact.

石蜡工艺大制品顶锤在脱蜡阶段，270℃-400℃为成型剂石蜡的主要脱除阶段，400℃-750℃时有气体释放高峰状态，在脱蜡预烧阶段设置合理工艺参数可以防止合金裂纹，但压坯本身若存在微裂纹缺陷，必然会显露出来影响产品质量。

The characteristic of machined surface of high speed machining aluminum alloy 7050-T7451 is researched by micrographic experiments and analysis. The formation mechanics of machined metamorphism layer has been analyzed and studied. The dislocation-energy model in machined metamorphism layer was established and applied to explain the micrographic mechanics work-hardening using the thermo-mechanical coupling deformation theory and dislocation theory. The experimental results show that the interaction of high dislocation density effect on hardening is more remarkable than that of thermal stress in high speed machining.

利用显微观察方法对铝合金7050-T7451高速铣削加工的工件表面断面和不同深度的表层的微观形貌特征进行系统的研究，确定了高速切削加工铝合金7050-T7451的表面变质层深度为30～35μm；应用位错能量研究了高速铣削加工过程的热力耦合对变质层的影响机理，并通过微观形貌观察证明：与普通切削相比，高速铣削表层塑性变形的能量和位错密度更高；建立了位错密度的加工硬化的动力学模型，研究了加工硬化的热-力耦合形成机理；对微观裂纹的形成机理进行了理论分析，证明位错密度高的高速切削过程中较低速加工更容易产生明显的微裂纹，从分子级乃至原子级的水平进一步揭示高速切削加工表面变质层的形成特征。

The fracture reasons of high strength PC steel wire are analyzed, it's considered that center segregation, central cavitation, poriness and inclusion are the metallurgical reasons which lead to the facture of PC steel wire and in the rolling process, differential coping quality, microcrack caused by surface defect, abnormal microstructure caused by burnt and improper cooling velocity, the ears on the head of the wire, overlapping of the wire rod itself are the main reasons which lead to the facture of PC steel wire. At the same time, inappropriate pickling, differential phosphorization quality, the bad heat treatment quality, the generation of crack in the improper drawing and transverse crack caused by abnormal laying of the drawing die are also the reasons of the cracking of PC wire.

对高强度PC钢丝断裂原因进行了分析，认为连铸坯的中心偏析、中心缩孔、疏松和夹杂是导致PC钢丝断裂的冶金原因；轧制过程中，较差的修磨质量、表面缺陷导致的微裂纹，过烧以及不适当的冷却速度导致的非正常显微组织，盘条头部的耳子、盘条本身折叠是导致PC钢丝断裂的主要原因；同时，不恰当的酸洗、较差的磷化及热处理质量、不适当拉丝裂纹的产生、拉拔模具安放不正导致的横裂也是PC钢丝断裂的原因。

The processes of propagation, kinking of micro cracks in concrete and the interaction among cracks as well as the induced failure are analyzed by using the model describing the wing type crack from the view point of micromechanics.

本文从混凝土细观机理出发，采用翼型裂纹模型分析了围压荷载下混凝土内微裂纹扩展、弯折和相互作用直至材料破坏的过程。

The results show that the steel in different solution has better performance of anti-hydrogen induced cracking,there is no cracking inside the steel; micro-cracking on the specimen surface mainly nucleates at pitting corrosion pits and expands along the polygonal ferrite; the expansion mode is mostly transgranular type, and the expansion terminates in acicular ferrite.

研究结果表明：该管线钢在两种溶液中均具有较好的抗氢致开裂性能，试样内部没有发现裂纹；试样表面的微裂纹主要在点蚀坑处形核并沿多边形铁素体扩展，扩展模式多为穿晶型，并终止于针状铁素体。

The works studied in the thesis are follows: Firstly, by means of controlling the macroscopic stress triaxiality and Lodes parameters of the cubic cell model, the void expanding analysis of penny-shaped crack and sphere-shaped void have been carried out by using finite element method.

本文研究主要集中在以下三个方面：（1）采用体胞模型并运用控制体胞宏观应力三维度和Lode参数的方法，对含有币形微裂纹的材料的损伤演化进行了有限元计算模拟与分析，并与微孔洞的情形作了比较。

According to the clear water experiment, aeration performance of the new equipment is good with high total oxygen transfer coefficient and oxygen utilization ratio.

曝气设备的动力效率在叶轮转速为120rpm～150rpm时取得最大值，此时氧利用率和充氧能力也具有较高值。

The environmental stability of that world - including its crushing pressures and icy darkness - means that some of its most famous inhabitants have survived for eons as evolutionary throwbacks, their bodies undergoing little change.

稳定的海底环境─包括能把人压扁的压力和冰冷的黑暗─意谓海底某些最知名的栖居生物已以演化返祖的样态活了万世，形体几无变化。