疲劳门槛值统一理论模型的比较及验证

针对应力比对疲劳裂纹扩展及门槛值的影响，依据裂纹闭合与裂纹扩展驱动力机制的统一思想，阐述了Zhu-Xuan模型与Kwofie-Zhu模型的建立过程，并基于25Cr2Ni2MoV转子钢焊接接头的疲劳裂纹扩展试验数据对模型进行验证。结果表明，两种模型在近门槛值区和Paris区均有良好的预测效果，其中Zhu-Xuan模型形式简单，对CrMoV钢具有普适性，预测门槛值的误差在10%以内，而Kwofie-Zhu模型预测结果更准确，但应用过程涉及参数求解，过程较复杂。研究认为，裂纹闭合与扩展驱动力机制的统一模型描述疲劳裂纹扩展行为的应力比相关性是合理可行的，且具有较好精度。     

高温蠕变条件下表面裂纹扩展行为分析

裂纹的存在及其扩展严重限制着高温承压部件的使用寿命，而目前对结构三维蠕变裂纹扩展行为的认识及其预测仍比较有限。以典型耐热钢P91为例，在650℃下对其开展了不同应力和不同初始裂纹尺寸的表面裂纹蠕变扩展试验，通过断面观察获得了蠕变裂纹扩展形貌演化，并采用基于多轴蠕变损伤模型的有限元法、基于蠕变裂纹尖端参量C^*的有限元法以及英国标准BS7910推荐的简化计算方法进行表面裂纹蠕变扩展分析。结果表明，基于多轴蠕变损伤模型的有限元法能够合理地描述裂纹最终轮廓并准确地预测裂纹扩展时间。相比之下，基于C^*的有限元法和BS7910简化计算方法计算的裂纹形貌预测有明显偏差，并且较依赖于紧凑拉伸试样的蠕变裂纹扩展试验数据及其拟合的参数C和q，易导致过于保守的裂纹扩展时间预测。评估了不同计算方法对于表面裂纹蠕变扩展行为的预测能力。     

分形裂纹扩展对材料疲劳行为的影响

研究了分形裂纹扩展对材料疲劳行为的影响。在实验观测的基础上建立了分形裂纹扩展模型。研究表明，分形裂纹扩展分维Ｄ是裂纹弯折角θ的函数，分形裂纹扩展在裂纹尖端由于弯折而形成“局部混合模式”和裂纹的分形长度效应均很强地影响疲劳裂纹的有效应务强度与有效裂纹扩展速率。本文的理论民一些材料的实验结果取得了很好的一致。     

金属材料疲劳短裂纹萌生与扩展研究综述

系统梳理了金属材料疲劳短裂纹的定义、分类、试验方法、萌生机理及典型扩展率模型，对当前短裂纹行为研究面临的问题进行了总结与展望。研究结果表明，在萌生机理方面，材料自身的微观结构对短裂纹萌生及扩展有重要影响，短裂纹扩展至晶界处，受晶粒取向及晶界阻力影响，扩展率会下降，裂尖突破晶界束缚后，短裂纹扩展路径出现局部偏折。在扩展行为描述方面，短裂纹的扩展驱动力与承受的载荷水平、残余应力、表面处理方式、局部磨损状况等有关。扩展过程中，裂纹尖端材料在小范围内屈服而产生局部塑性区。同时，塑性尾迹区也逐渐形成，进而产生塑性诱导闭合，导致裂纹扩展门槛值降低。此外，晶体位错之间的相互作用和位错塞积会阻碍位错发展。机器学习算法作为一种先进技术手段，已在短裂纹扩展行为表征中得到应用，对提升预测精度有促进作用。随着金属材料短裂纹行为研究的进一步深入，未来可重点关注短裂纹萌生与扩展实时监测、试验影响因素控制、数据离散性分析、扩展率模型的工程应用等问题，探索建立适用于工程结构与零部件的在役长、短裂纹扩展率统一表征模型和实时监测与安全评估技术，结合先进的机器学习算法，实现对工程关键金属结构更有效、更准确的安全性评定和剩余...     

复杂载荷作用下裂纹扩展的最弱环模型

工程中已提出许多模型描述裂纹扩展，其中考虑了解超载等因素的影响。这类模型的提出，一般应坚持这样的原则；（1）必须从大量实验观察中得出，要反映裂纹扩展的机     

填充天然橡胶材料裂纹扩展模型的建模方法

填充天然橡胶材料疲劳裂纹扩模型是指裂纹扩展速率与撕裂能峰值之间的关系,它是用于橡胶减振元件疲劳寿命预测的重要模型。在裂纹扩展试验得到的填充天然橡胶材料裂纹扩展长度与循环次数的数据中,由于橡胶的应力软化现象,试验后期的部分数据不可用。为此,建立了数据处理方法,获得有效的裂纹扩展长度与循环次数数据。基于单轴拉伸载荷下填充天然橡胶材料最大应变能密度与最大应变满足幂函数关系的假设,建立了变幅加载工况下裂纹扩展长度与循环次数的数学模型和识别其模型参数的优化方法。在建立的裂纹扩展长度与循环次数模型的基础上,建立了裂纹扩展速率与撕裂能峰值关系的模型和确定模型中参数的数值方法。利用一组哑铃型试片的疲劳寿命实测数据,对建立的裂纹扩展速率模型进行了验证,证明了所建立模型的正确性。     

循环压载下缺口旁疲劳裂纹扩展

对承受循环压载的缺口试件的疲劳问题进行了试验和理论研究。结果表明，疲劳裂纹是在残余拉应力和循环压应力作用下萌生和扩展的，压塑性变形是裂纹萌生和扩展和扩展的必要条件。循环压载下仍存在着裂纹张开和裂纹闭合，其机理与拉伸循环下不同。以试验中采用的ＬＹ１２ＣＡ材料边缺口试件为例，提出了考虑裂纹闭合效应的扩展率计算模型，结果与试验吻合得较好。     

变幅载荷下的钢板弹簧疲劳裂纹扩展研究

钢板弹簧疲劳裂纹在变幅载荷作用下的扩展预测模型主要是Schütz疲劳裂纹扩展模型,但此模型未考虑裂纹闭合效应对疲劳裂纹扩展的影响,忽略了参数C和n随应力比的联系,疲劳裂纹门槛值△Kth也只考虑应力比为0的特殊工况.因此对Schütz疲劳裂纹扩展唯象模型进行修正,使修正后的模型各参数物理意义更加明确,适用于不同的工况.并将实车试验所测的应力幅值运用于修正后的模型,表征变幅载荷作用下钢板弹簧疲劳裂纹扩展进程.表明加载幅值增大,疲劳裂纹扩展速率加快,试验结果与模型预测结果良好吻合,为变幅载荷作用下疲劳裂纹扩展速率的计算提供了理论依据.     

TC21钛合金的疲劳裂纹扩展研究

建立了新型损伤容限性钛合金TC21的疲劳裂纹扩展模型;研究了疲劳裂纹扩展速率da／dN与疲劳裂纹扩展门槛值之间的关系。该模型预测了TC21钛合金的疲劳裂纹扩展速率,其预测结果与实验结果非常吻合。     

十字横向承载焊接接头疲劳裂纹扩展寿命估算

利用一种新的计算模型，用有限元法计算了十字焊接接头疲劳裂纹尖端的应力强度因子值，并拟合了裂纹在焊根和焊趾处扩展的应力强度因子表达式。据此利用Ｆｏｒｍａｎ疲劳模型，考虑显微金相组织的影响，估算了裂纹扩展寿命，与实验值比较，结果合理。     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

交通荷载作用下桥梁结构参数识别方法

应用动力节点加载法,将作用在桥梁上的交通荷载转化为等效节点荷载,再用两步构造法识别结构物理参数.第1步,用Newmark-β方法变换结构运动方程,并用结构的加速度响应求得变换空间内的位移、速度和加速度响应;第2步,基于最小二乘原理,构造出变换空间内求解结构参数的递推式,进行结构物理参数识别.数值模拟结果表明,在交通荷载作用下,该方法能够快速、准确地进行桥梁结构参数识别.     

RLS and LMS blind adaptive multi-user detection method and comparison in acoustic communication

RLS and LMS blind adaptive multi-user detection algorithm and multi-user detector was proposed to solve the problem of multi-user signal detection problem encountered in underwater acoustic communication networks.In simulation analysis,RLS and the LMS blind adaptive multi-user detector were designed and tested for synchronous and asynchronous multi-user communication process.The results of SIR comparison and MMSE comparison show that,both of the two methods can realize blind adaptive detection when any user change in multi-user communication,during this process,the training communication sequences are not needed.The RLS algorithm has about 5 dB higher in SIR compared with LMS algorithm,and the convergence velocity of RLS algorithm is also higher than LMS algorithm when the communication users change.RLS algorithm has better ability in multi-user detection than that of LMS algorithm,and it has great attraction and guiding significance for solving the problem of multiple access interference(MAI) in multi-user communication.     

Robust Impedance Control of Robots Using an Adaptive Interaction Force Observer

For robot interaction control,the interaction force between the robot and the manipulated object or environment should be monitored.Impedance control is a type ...     

Research on key techniques of expendable conductivity temperature depth measuring system

This paper analysis the developing of expendable conductivity temperature depth measuring system(XCTD)and introduce its principle of measuring about temperature,salinity and depth of ocean.Some key techniques are put forward.According to the real needs of XCTD,conductivity sensor with high sensitivity is designed by principle of electromagnetic induce,the ocean conductivity from induced electromotive force has been calculated.Adding temperature correction circuit would help to reduce error of conductivity measurement because of sharply changing temperature.Advanced temperature measuring circuit of high precision and the constant current source is used to weaken effect of self-heating of resistance and fluctuation of the source.On respect of remote data transmission,LVDS is a good choice for the purpose of guarantee the quality of data transmitted and the transmission distance is reaching to thousand meters in the seawater.Modular programming method is also brought into this research aimed at improve the stability,reliability and maintainability of the whole measuring system.In February,2015,the trials in South China Sea demonstrate that the developed XCTD realize effective measurement at a speed of 6 knots and detection depth at 800 m.The consistency coefficient of the acquired data is greater than 0.99 and the success rate of probe launching is above 90%.     

CHARACTERISTCS OF FLUID FILM IN OPTIMIZED SPIRAL GROOVE MECHANICAL SEAL

In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relationship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.     

Quantum Cooperative Robotics and Autonomy

The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisci...     

OPTIMIZATION METHOD ON IMPELLER MERIDIONAL CONTOUR AND 3D BLADE

An optimization method for 3D blade and meridional contour of centrifugal or mixed-flow impeller based on the 3D viscous computational fluid dynamics (CFD) analysis is proposed. The blade is indirectly parameterized using the angular momentum and calculated by inverse design method. The design variables are separated into two categories: the meridional contour design variables and the blade design variables. Firstly, only the blade is optimized using genetic algorithm with the meridional contour remained constant. The artificial neural network (ANN) techniques with the training sample data schemed according to design of experiment theory are adopted to construct the response relation between the blade design variables and the impeller performance. Then, based on the ANN approximated relation between the meridional contour design variables and impeller performance, the meridional contour is optimized. Fewer design variables and less calculation effort is required in this method that may be widely used in the optimization of three-dimension impellers. An optimized impeller in a mixed-flow pump, where the head and the efficiency are enhanced by 12.9% and 4.5% respectively, confirms the validity of this newly proposed method.