LY12CZ铝合金中Ⅱ型裂纹疲劳扩展

对ＬＹ１２ＣＺ铝合金材料中Ⅱ型裂纹的疲劳扩展规律进行了研究。结果表明，Ⅱ型裂纹在ＬＹ１２ＣＺ材料中发生了稳定扩展。文中分析了Ⅱ型裂纹疲劳扩展速率ｄａ／ｄＮ与应力强度因子幅△КⅡ之间的相关性。得到了它们之间的关系式，二者可以用类似Ⅰ型裂纹的Ｐａｒｉｓ公式来描述。比较子该种材料中Ⅱ型裂纹的扩展速率与Ⅰ型裂纹扩展速率的关系式，在相同的应力强度因子幅值下（ｄａ／ｄＮ）Ⅱ远大于（ｄａ／ｄＮ）Ⅰ。对断口进行了     

使用疲劳裂纹扩展数据的疲劳裂纹扩展的可靠性分析方法

利用现有的疲劳裂纹扩展数据或疲劳裂纹扩展试验的不完全数据 ,对疲劳裂纹随机扩展的可靠性进行了研究。基于疲劳裂纹扩展的确定性模型 ,导出了疲劳裂纹扩展的随机公式。利用现有的疲劳裂纹扩展数据或疲劳裂纹扩展试验的不完全数据 ,对疲劳裂纹扩展随机公式中的随机变量的分布进行了估计 ,得到了其分布的数字特征 ,用Monte Carlo方法得到了疲劳裂纹扩展寿命的失效概率的点估计。实例分析表明了本文方法的实用性和可行性     

考虑裂尖疲劳损伤的材料疲劳裂纹扩展行为研究

基于低周疲劳Manson-Coffin关系,定义I型裂纹疲劳扩展区内关于应变幅的平均疲劳损伤参量,并结合Miner线性累积损伤理论,通过弹塑性有限元法实现材料疲劳裂纹扩展速率的预测模拟,同时也建立以显式理论公式来描述疲劳裂纹扩展速率规律的新型预测模型。在进行有限元模拟分析中借助裂尖单调塑性区平均疲劳损伤达到临界损伤即完成一次步进扩展的假定。在显式理论公式推导中采用裂尖循环塑性区平均疲劳损伤达到临界损伤即完成一次步进扩展的假定。以大型汽轮机转子材料Cr2Ni2MoV钢、航空材料TA12合金和304不锈钢材料为例,应用所提出的两种疲劳裂纹扩展速率预测方法对其进行预测,并同试验结果进行对比。对比分析表明,两种方法对材料的疲劳裂纹扩展速率行为预测均具有较高的模拟精度,而理论预测模型相比有限元模拟方法预测范围拓宽,预测精度更好,方便于根据包括材料手册的资料中低周疲劳Manson-Coffin试验关系来直接获取I型裂纹疲劳裂纹扩展速率表达式。     

焊接残余应力对疲劳裂纹萌生和扩展的影响

通过疲劳试验,研究焊接残余应力对疲劳裂纹萌生和扩展性能的影响,以及残余应力的再分配。试验结果表明,垂直于裂纹方向的纵向残余应力促进孔边疲劳裂纹的萌生和扩展;残余应力随焊缝金属的应变松弛而降低,它对疲劳裂纹扩展速率的影响相应减小;残余应力场中疲劳裂纹扩展速率仍可以用Ｐａｒｉｓ ／公式计算。     

表面裂纹贯穿板厚后的疲劳扩展行为

本文研究了双轴载荷状态下平直表面裂纹和斜表面裂纹贯穿板厚后的疲劳扩展行为。文中给出了所设计的双轴试板当裂纹贯穿板厚后的应力强度因子标定式,据此所得的裂纹贯穿后的疲劳扩展速率与贯穿前有良好的线性性,可以用统一的公式描述,与单轴载荷下的疲劳裂纹扩展速率相比较,表明单轴和双轴载荷下的扩展速率无明显差别。     

环境湿度对铸铝合金超声疲劳裂纹扩展速率的影响研究

针对铸铝合金A356-T6开展了不同环境湿度下的超声疲劳裂纹扩展试验和实验室环境湿度下的常规疲劳裂纹扩展试验。由试验结果可知,超声疲劳在干空气环境中的疲劳裂纹扩展速率最低,而在蒸馏水环境中的疲劳裂纹扩展速率最高。常规疲劳在实验室环境中的疲劳裂纹扩展速率和超声疲劳在蒸馏水环境中的疲劳裂纹扩展速率几乎一致。针对Wei建立的环境湿度对铝合金材料疲劳裂纹扩展速率预测模型进行了修正,得到了铸铝合金A356-T6在任意环境湿度和试验频率下的疲劳裂纹扩展速率预测模型。     

不同碳含量的CrNiMo钢疲劳裂纹扩展特性

三种不同碳含量的ＣｒＮｉＭｏ 钢的疲劳扩展试验结果表明,随着钢中碳含量升高,裂纹扩展速率升高。回归分析表明,ＣｒＮｉＭｏ 钢的疲劳裂纹扩展速率符合以下公式：ｄａ／ｄｎ＝ Ｂ（ｄｋ－ ｄｋｔｈ ）２ ,其中疲劳裂纹扩展系数Ｂ值可以由材料拉伸性能估算。该式的有效性还以不同应力比下的疲劳裂纹扩展数据进行了验证。     

SCT试样高应变区疲劳裂纹扩展规律研究

本文研究了SCT试样高应变区的疲劳裂纹闭合效应和疲劳裂纹扩展速率。结果表明:高应变塑性区的存在对疲劳裂纹扩展有较大延缓作用,疲劳裂纹扩展速率可用经U修整后的δ和Paris公式表示,结果与标准试样的结果较为吻合。     

三种输送管疲劳裂纹扩展特性研究

通过试验对ＳＳＡＷ、ＥＲＷ、ＵＯＥ三种焊管的疲劳裂纹扩展特性进行了研究。结果表明,三种焊管各区的疲劳裂纹扩展速率的Ｐａｒｉｓ方程表达式ΔＫ的指数均在３．１～４．３之间,且ＳＳＡＭ焊管表现出较低的疲劳裂纹扩展速率。随着加载应力比的提高,疲劳裂纹扩展速率将随之增大。     

PD3和U71Mn钢轨钢疲劳裂纹扩展速率研究

利用MTS试验机, 在常温下对两种钢轨PD3和U71Mn进行疲劳裂纹扩展速率试验研究,根据Paris公式确定两种钢轨的疲劳裂纹扩展速率,利用极大似然估计法计算带有一个随机变量描述的疲劳裂纹扩展速率的概率方程.结果表明,裂纹扩展速率曲线符合一般疲劳裂纹扩展规律;PD3的强度性能优于U71Mn,但U71Mn表现出更好的抗疲劳裂纹扩展性能,扩展速率低于PD3钢轨;疲劳裂纹扩展速率的不确定性方程与试验结果相符.     

五轴数控机床万能主轴头空间误差建模研究

五轴机床万能主轴头空间误差建模的传统方法采用齐次变换矩阵(HTM)进行运算,计算过程复杂,物理意义很难理解。提出了一种主轴头空间误差的简化建模方法。综合考虑了主轴头两个旋转轴的运动误差和刀具热误差对主轴头空间精度造成的影响。优化了机床运动坐标系设置,从而降低了空间误差模型的复杂性。基于刚体运动学原理,描述了主轴头的运动误差传递关系。结合实例,推导出了主轴头空间误差的数学表达式,其建模过程简单,物理意义明确。     

各向同性损伤与损伤扩展力

讨论用双标量表征各向同性损伤的具体形式，扼要阐明损伤扩展力的物理含义和各向同性损伤扩展力的计算表达式，导出各向同性损伤、损伤扩展力与细观的裂纹密度参数之间的定量关系。最后给出计算实例。     

Computation of the configuration degree of freedom of a spatial parallel mechanism by using reciprocal screw theory

In this paper, we propose a programmable algorithm to investigate the configuration degree of freedom (CDOF) of a spatial parallel mechanism in one Cartesian coordinate system with reciprocal screw theory. According to the physical meaning of reciprocal screws, we first obtain the terminal constraints of every kinematic chain which connects the end-effector with the fixed base, and then gain the free motion(s) of the end-effector and its degree of freedom (DOF). Through analyzing the controllability of the end-effector, we investigate the instantaneous screw expressions for the free motions of the end-effector of a spatial parallel mechanism and the CDOF of the mechanism. The whole mathematical analysis process can be directly embedded in a kind of CAD software, in which the imperfect Kutzbach Grübler formulas or its amendments are mostly utilized to analyze the DOF.     

Digital Focusing of Aperture when Probing Test Object by All Elements of Antenna Array in One Emission–Reception Cycle

Russian Journal of Nondestructive Testing - We describe the physical meaning of the method of visualization by several sendings of probing ultrasonic waves with a plane front into the...     

自适应神经元实现的直线永磁同步电机伺服系统的预见前馈补偿

介绍了高精度微进给直线永磁同步电机伺服系统的IP位置控制，提出了对该系统的最优预见前馈补偿，以提高系统的跟踪性能。为了能适应系统参数的变化，采用自适应神经元来实现预见前馈补偿，自适应神经元的输入向量为预见步数，权值为预见前馈系数，权值具有明确的物理意义，而且权的初始值不是随机数，而是系统在额定情况下算出的预见前馈系数，从而加快了神经元的调整速度，提高了系统的跟踪能力，仿真实验结果证明了所提出方案的有效性。     

Re-analysis of the degree-of-freedom configuration of the platforms in spatial parallel mechanisms with constraints spaces

The degree-of-freedom (DoF) configuration of a mechanism, which is an important concept in the field of mechanisms and is the key problem to be solved before mechanisms are designed, has been discussed in our previous article [1]. In this paper, we will further analyze the DoF configuration of the platforms of spatial parallel mechanisms with constraints spaces. According to the physical meaning of reciprocal screws, we can solve the constraints spaces spanned by reciprocal screws, and then solve the free mobility spaces of the platform and its DoF configuration. With this methodology, not only can we differentiate the system from its members, but we also extend the concept of DoF configuration, which should have the attributes of number, type, and direction.     

Theoretical analysis of atomic-scale friction in frictional-force microscopy

We perform a theoretical analysis of frictional-force microscopy(FFM) images of a cleaved graphite surface. The Tomlinson model with a single-atom tip is powerful for reproducing experimental FFM images. A mapping relation between the tip atom position and the cantilever basal position obtained by a stable equilibrium condition, gives a clear explanation of the physical meaning of FFM image patterns. This revised version was published online in June 2006 with corrections to the Cover Date.     

用杨氏干涉模型解释Lau效应

用杨氏干涉模型解释了Lau效应,以简洁的运算,清晰的物理图象给出了Lau效应中α、β参数的物理意义。     

A novel methodology to study the singularity of spatial parallel mechanisms

In this paper, a novel methodology to study the singularity of spatial parallel mechanisms is presented. With the theory of reciprocal screws, we make a thorough analysis of the kinematic screws of each branch mechanism. According to the physical meaning of the inverse screws of kinematic screws, we introduce the static equilibrium equations to gain a novel methodology to study the singularities of the dynamic mechanisms. Through the novel methodology, we obtain universal criteria that the mechanism will be singular.     

On a mode of application of the perturbation method in solid mechanics

This paper is primarily concerned with the uses of constants describing physical properties of the material as perturbation parameters in asymptotic methods of analysis of surface-like structural elements. By means of a concrete example, a former misconception is clarified. In addition, several simple nonlinear expressions for displacements and stresses in a slack circular membrane under a point load have been obtained as a by-product.