尖端导体电晕放电辐射场的计算与实验

为研究输电线电磁辐射问题,以尖端导体电晕放电为研究对象,利用偶极子模型和传输线模型尖端导体电晕放电辐射场进行理论计算,得出了电磁辐射信号特征;在实验室进行直流高压下尖端电晕放电模拟和实验研究,验证了理论分析的正确性。研究结果表明,电流注入导体产生的辐射场要比空气电晕区产生的辐射场强的多,在对尖端导体电晕放电辐射场的远距离探测时,空气电晕区产生的辐射场可以忽略不计;尖端导体电晕放电辐射场主要是垂直极化场,由电晕电流在导体两端来回反射引起的;信号的时域波形呈衰减振荡形式,信号的峰值随外加电压的升高而增大,正电压下信号的强度明显比负电压下信号的强度大;信号首脉冲的方向随外加电压的极性不同而相反;信号的持续时间在几百ns数量级,而且随着导体长度的增加,信号的持续时间有增大的趋势。该研究结果对于输电线电晕抑制及周围电磁环境评价具有重要意义。     

Comparison of CTOD standards: BS 7448-Part 1 and revised ASTM E1290

Crack tip opening displacement (CTOD) has been calculated using the plastic hinge model with an assumed rotational center since the British Standards Institution (BS) standardized BS5762 in 1979. The American Society for Testing and Materials (ASTM) accepted the plastic hinge model and standardized E1290 in 1989. However, ASTM revised E1290 in 2002, and has proposed a conversion from J to CTOD. CTOD-based fracture toughness evaluation has been widely used for the defect assessment of many welded structural components, and two different CTOD calculations could lead to confusion for Fitness-for-Service. In this study, the effects of CTOD testing methodologies on CTOD values were investigated according to round robin tests conducted by the Japan Welding Engineering Society (WES), and the concept of CTOD as a fracture parameter is discussed.     

Fracture surface topography analysis (FRASTA)—Development, accomplishments, and future applications

In the late 1970s, Dr. George Irwin suggested to his colleagues at the University of Maryland that valuable information about a fracture event was recorded in fracture surface topography. Under his urging, Takao Kobayashi, an associate professor at the time, began quantifying and interpreting topographical features. Over the subsequent 30 years the procedures for quantifying and interpreting fracture surface topography grew continuously into an established technology that allows a fracture event to be reconstructed in microscopic detail. FRASTA (fracture surface topography analysis) has now been applied to achieve solutions to a wide variety of failure problems. This paper chronicles the historical development of FRASTA, recounts several notable achievements, and presents the plan for further development and future applications.     

三点弯曲梁法研究砼双K断裂参数及其尺寸效应

本文采用三点弯曲梁试件利用在试验中测得的最大荷载Ｐｍａｘ及对应的裂缝口张开位移ＣＭＯＤｃ等参数,根据虚拟裂缝模型求得了砼裂缝亚临界扩展量Δａｃ、起裂断裂韧度Ｋ＾ｉｎｉＩＣ、失稳断裂韧度Ｋ＾ｕｎＩＣ（即双Ｋ断裂参数）及临界裂缝尖端张开位移ＣＴＯＤｃ。结果表明,砼双Ｋ断裂参数及ＣＴＯＤｃ均与试件尺寸无关,可以作为描述砼结构裂缝的起裂、稳定扩展及失稳断裂全过程的材料常数,而且试验方法简单,无需加卸载过程     

抗弹陶瓷的犁削机理和自锐作用研究

研制了铬刚玉抗弹陶瓷，其抗弹能力比标准均质钢有很大的提高，通过分析讨论，其主要抗弹机制为犁削机理和自锐作用。     

Investigation of atomic structure ahead of crack tip by STM and AFM

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采用叶尖速比法和爬山搜索法相结合的风力发电系统最大功率点跟踪研究

在风力发电机控制中采用叶尖速比法,可以实现快速功率跟踪,但常由于风速测量值与实际风速值不一致,导致无法达到最大功率点。由于爬山搜索法不需要测量风速,所以采用爬山搜索法和叶尖速比控制法相结合来实现快速最大功率跟踪。当风速变化超过±1 m/s时,采用叶尖速比控制法,按测量风速计算出参考转速,迅速跟随,达到指定转速后,切换到爬山搜索法,实现精确的最大功率跟踪。在Matlab环境下,建立了永磁直驱式风力发电机模型,仿真分析了风速变化时,采用叶尖速比法和爬山搜索法相结合的方法能够实现最大功率快速而精确的跟踪,且具有很好的动态特性和稳态特性。     

双凹槽叶顶轴流风机噪声预估及叶片静力结构分析

叶顶结构型式对轴流风机性能、噪声及叶片静力特性等均有一定影响。以OB-84型带后置导叶的轴流式通风机为对象,采用Fluent数值模拟软件及Ansys有限元分析模块,通过比较开槽前后风机轴功率的变化探讨双凹槽叶顶结构的节能效果,分析了原叶顶及双凹槽叶顶下风机噪声及叶片的静力结构特性。研究表明:双凹槽叶顶下风机轴功率有所下降,设计工况下轴功率较原叶顶时下降了3.96%,可在一定程度下降低风机的能耗;双凹槽叶顶下风机噪声有较大幅度提高,设计工况下噪声较原叶顶时增长约14.88%,给风机正常运行带来不利影响;不同叶顶下叶片的静强度校核结果均满足要求,即采用双凹槽叶顶结构不会引起叶片的变形及断裂失效。     

Crack–Tip Toughness of a Soft Lead Zirconate Titanate

Crack–opening displacement (COD) measurements were performed on a commercial lead zirconate titanate (PZT). The intrinsic fracture toughness (or crack–tip toughness) of this material was determined using a new evaluation procedure, which takes into account the near–tip CODs and complete crack profile CODs. The crack–tip toughness K _I0 was determined from an extrapolation of COD data obtained at various loading stages, thus avoiding the complications caused by subcritical crack growth in PZT. Results for plane strain and plane stress condition are presented.     

Consideration of the mechanical behaviour of small fatigue cracks

The mechanical behaviour of small fatigue cracks is investigated for a low, medium and high strength material. At first an elastic consideration is performed which give a good impression how the stress fields change with crack size. In part 2 a full elastic-plastic analysis of short cracks is performed using a new numerical scheme to simulate the growth of shear bands emanating from the crack tip. The influence of material and loading paramters as well as of the crack size on the plastic crack tip opening displacement is discussed. It is also investigated how it is possible to get a conservative estimate of the crack tip deformation at small cracks.