Open-channel turbulent flow over non-uniform gravel beds

the measurements of flow over non-uniform gravel open channel have been conducted with Laser Doppler Velocimetry (LDV). The experimental results indicate that the distribution of mean velocity agrees well with the Nikuradse's law. From the distributions of resistance coefficient, reference level and turbulence intensity, the classification of small scale roughness case is obtained.Project supported by the National Science Foundation of China     

Stress concentration around a spheroidal crack caused by a harmonic wave incident at an arbitrary angle

A method is proposed to study the stress concentration around a shallow spheroidal crack in an infinite elastic body. The stress concentration is due to the diffraction of a low-frequency plane longitudinal wave by the crack. The direction of wave propagation is established in which the combined concentration of mode I and mode II stresses is maximum __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 1, pp. 70–77, January 2006.     

Determining stress intensity factors in orthotropic composites from far-field measured temperatures

We demonstrate the ability to determine stress intensity factors in orthotropic materials directly from measured temperatures away from the crack and using far-field expressions for the stresses. This is advantageous, recognizing that recorded thermoelastic data can be very unreliable near the tip of a crack. In addition to singular terms that govern in the immediate vicinity of the crack tip, the present series expressions for the stresses contain higher-order finite terms. Little measured input information is needed and data acquisition positions can be selected largely at the user's discretion.     

Modification of the fracture criterion for V-shaped notches (plane problem). Relationship between toughness and strength and structural parameters

A fracture criterion of the type of the Neuber-Novozhilov criterion is proposed to describe the fracture in the vicinity of the tip of a V-shaped notch under tensile and shear loading. In the proposed criterion, the limits of averaging of the stresses along the notch axis depend on the presence, location, and size of the initial defects in the material. The crystal lattice parameter of the initial material is chosen for the characteristic linear size. For a V-shaped notch subjected to tension and shear, simple equations are obtained that relate the stress intensity factors for the modified singularity coefficients, the singularity coefficients themselves, and the theoretical tensile and shear strengths of a single crystal of the material taking into account the damage to the material in the vicinity of the notch tip. The equations obtained allow a passage to the limit from a notch to a crack. It is shown that the classical critical stress intensity factor used in the strength analysis of cracked solids is not a material constant.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 106–115, January–February, 2005.     

压荷载下类岩石材料中的锯齿形裂纹分析

针对类岩石材料的复杂性和非均质性，特别是材料中一些强度相对较弱的晶界的存在等，对形状较为复杂的两种锯齿形裂纹：内张型滑动裂纹和单翼滑动裂纹的应力强度因子进行了分析．结合经典的滑动裂纹模型，讨论了裂纹起裂角、侧压以及翼裂长度等对应力强度因子的影响．分析的结果为进一步研究类岩石材料的断裂损伤机理提供了理论基础．     

低温环境下光纤位移传感器测试系统的实验研究

作者进行了光纤位移传感器在低温环境下的实验研究，分析了传感器的原理，测试了其室温、液氮温度下的静态传输特性，并进行了标定。实验时采取的参考光强度补偿的措施，消除了光源、光纤衰减等波动对测试结果的影响。利用本传感器系统测试了19芯纯Ag包套的高温超导带材Bi222在液氮温度下的应力－应变关系，以及应力－临界电流之间的关系，结果与理论分析相一致。实验结果表明，该传感器可以在液氮温度下正常工作，且具有测量范围大、测试精度高等优点，同时还克服了低温应变片仅能测试出复合材料基体或者包套应变的缺点。     

压-剪复合应力波作用下材料动态断裂韧性研究

提出亚微秒单脉冲应力波载荷作用下Ⅱ型裂纹的平板冲击实验技术 .加载率为dK dt～ 10 8MPa·m1 2 ·s-1.实验中由锰铜应力片和弹性波理论分别测定和计算了压应力 ;通过微观分析确定了动态裂纹的平均扩展长度 ;引进等效应力强度因子 ,用动态断裂理论确定了 6 0 #钢的动态断裂韧性KⅠd和KⅡd ;建立了亚微秒冲击载荷作用下确定材料动态断裂韧性的方法     

焦散线法对双折射材料断裂性能的研究

提出了双折射材料Ⅰ-Ⅱ混合型裂纹问题焦散线的形成原理,讨论了μ(=K_I/K_I)及光学各向异性系数ξ对焦散线形状及其几个特征量的影响,得到了双折射材料应力强度因子K_Ⅰ、K_Ⅱ的求法.以聚碳酸脂、环氧树脂为例,确定了它们在不同裂纹及不同载荷条件下的应力强度因子K_Ⅰ、K_Ⅱ.     

功能梯度压电材料反平面裂纹问题

基于三维弹性理论和压电理论，导出了材料系数在横观各向同性平面内梯度分布的压电体的状态方程，进而对材料系数指数函数规律分布的半无限大压电体中的反平面裂纹问题进行了求解，利用Fourier变换给出了半无限大压电体中位移，应力，电势及电位移的解析表达式，并求得了裂纹尖端的应力强度因子和电位移强度因子，分析了不同的非均匀材料系数及几何尺寸对它们的影响。     

动态J积分及Rice J积分一致性比较与分析

首先回顾了动态J积分的发展进程,然后给出了两种常用动态J积分和Rice J积分的数学计算式,并对它们的一致性加以讨论,由此提出一种广义J积分的定义。然后通过算例,基于ANSYS软件,建立平面应变情形下纯I型中心裂纹模型,并利用编写的APDL程序计算了各个J积分,通过结果比较,进一步验证了在动态加载条件下,动态J积分比Rice J积分具有更好的路径守恒性,但仍可以看出它们的取值具有一定的一致性。最后,通过J积分间接法和裂尖位移外推法分别计算裂纹动态应力强度因子,所得结果吻合很好,验证了编写程序的正确性。