Analytical Approaches to Stress Intensity Factor Evaluation for Indentation Cracks

In the present paper, an analytical solution for the stress intensity factor in the case of cracks produced by Vickers indenters has been extended to the cases of triangular indenters, i.e., Berkovich and cube-corner. According to the adopted approach, median/radial cracks produced by indentations are modeled as loaded by either a point-force or a symmetric disk-shaped wedge. The wedge diameter is assumed to be equal to the plastic zone size whereas the wedge thickness is evaluated by comparing the wedge volume with the hardness-impression volume. The point-force and the disk-shaped wedge analyses produce an upper and a lower bound, respectively, of the geometry-dependent parameter appearing in the expression for the fracture toughness. The predictions of the present analysis are in good agreement with similar experimental and numerical results.     

聚乙烯管道热熔接头环向裂纹应力强度因子的数值分析

应力强度因子K是缺陷结构安全评定的重要参数。基于粘弹性理论,将聚乙烯管材料的粘弹性参数用Prony级数表示,运用非线性有限元法,在ANSYS中建立聚乙烯管热熔接头环向裂纹模型,并对K进行计算和分析。通过有限元的模拟,总结得到聚乙烯管最可能发生断裂的时间为产生裂纹时刻,从而得出分析聚乙烯管环向表面裂纹应力强度因子时不必考虑聚乙烯管的黏弹性,环向表面裂纹缺陷的主要影响因素是裂纹深度与聚乙烯管的厚度之比。     

立式钢制储罐大角焊缝处裂纹的应力强度因子分析

为了研究大角焊缝处裂纹的断裂性能,建立了大角焊缝处含Ⅰ型裂纹的100 000m³立式钢制储罐有限元简化模型,并基于断裂力学理论分析了裂纹最深处的应力强度因子K_I值及其与主要影响参数的关系。基于分析结果,根据裂纹的位置将大角焊缝附近的裂纹分为底板裂纹、焊缝裂纹和焊趾裂纹,并分别拟合了3类裂纹的K_I值计算公式,据此可以根据现场实际检测的裂纹尺寸和裂纹位置简单有效地对此类裂纹的断裂性能进行工程评估。     

内压作用下含内表面环向裂纹弯管的应力强度因子和极限载荷

应用大型有限元软件ANSYS对在内压作用下合内拱内表面环向裂纹弯管的应力强度因子和极限栽荷进行研究.计算出不同尺寸弯管的应力强度因子和极限载荷并加以分析,其结果可供工程安全评定使用.     

接触问题中应力强度因子的有限元分析

为分析刚性压头与弹性半平面接触时的触压场边缘应力场以及应力强度因子,以碳钢的弹性半平面为例,运用ANSYS软件进行了具体模拟分析。结果表明,触压场应力是对称分布的,且在边缘处急剧增大至最大,存在明显的应力集中现象;不同的载荷、材料特性、几何形状对应力强度因子均有不同的影响。据此可对不同工况的触压场中应力强度因子在没有理论值的情况下通过有限元方法得到。     

Hertzian Stress Cracks in Beryllia and Glass

The effect of Hertzian stresses resulting from loads acting at the points of contact of beryllia spheres was determined. As-drawn glass and glass ground with various grades of silicon carbide were indented with beryllia spheres, 1 in. in diameter. Also, pairs of these beryllia spheres were pressed together. Circular cracks due to Hertzian stresses were produced; an optical technique was developed for detecting them in a beryllia surface. The outer crack radius was proportional to the cube root of the maximum applied load. Average values obtained for the respective inner crack radii were used to determine average values of the minimum load to fracture these materials. The average minimum load to fracture 1 in. diameter beryllia spheres in air at room temperature under dynamic loading was 235 1b. The crack radius in glass and beryllia was about 20% greater than the radius of the contact surface. This was not significantly affected (in glass) by flaw density. It is considered that the Hertz analysis does not give the correct location and value of the maximum tensile stress when finite displacements of material occur.     

Interfacial Cracks in Ceramic-to-Metal Bonds under Transient Thermal Loads

The effect of a transient thermal load on an interfacial edge crack and center crack between a ceramic-to-metal bond was analyzed with the use of fracture mechanics. The deformations of the crack and the strain energy release rate were calculated for the case of a ceramic layer of equal thickness to the metal, one with one-tenth the thickness of the metal, and one with 10 times the thickness of the metal. It was determined that for an edge crack, under slow cooling conditions, the steady-state value of G is the largest, and G is largest for equal thicknesses of ceramic and metal. For a center crack, a maximum transient G occurs which is larger than the steady-state value and the strain energy release rate is smallest for equal thicknesses of ceramic and metal.     

内压作用下斜接弯管纵向半穿透裂纹应力强度因子研究

采用三维有限元技术,应用ANSYS对内压作用下含纵向半穿透裂纹斜接弯管的应力强度因子进行了系统的分析。建立了三维有限元裂纹模型,对裂纹前沿应力强度因子的影响因素进行了研究,分析了不同内压下无量纲参数裂纹相对深度a/t、裂纹相对形状b/a、管壁相对厚度Do/t对应力强度因子的影响。     

电泳漆边角覆盖缺陷研究

介绍了检验电泳漆边角覆盖性的试验方法、电泳及烘干过程中尖端部位涂层的变化,对引起电泳漆边角部腐蚀的原因进行分析,列举了提高电泳漆边角覆盖性的途径。     

Measurements of Stress Intensity Factors of an Interface Crack Under Mixed Mode Loading

The optical method of caustics has been utilised to measure both the stress intensity factor for a crack lying along the interface of an aluminium/epoxy bimaterial specimen, and the mode mixity arising from the difference in the elastic properties across the interface. Measurements were carried out by using a novel modification to the method whereby caustics are produced and measured from both sides of the specimen, so compensating automatically for the distortion induced in the specimen due to misaligned loading fixtures. A flat reflective surface across the interface was obtained by adhering a reflective coating to the specimen. Verification that this coating does not affect measurement accuracy was obtained by comparing stress intensity factors measured from coated and uncoated monolithic aluminium specimens where good agreement was found to exist between both measurements.     

位移应力及其强度条件

管道设计规范中所述的位移应力包括温差、端点位移等荷载产生的应力．而在容器设计规范中将温差引起的应力归为二次应力。本文通过一简单例子对温差荷载和端点位移荷载所产生应力的计算过程、应力性质进行了分析,指出由于位移应力具有自限性特点,因此位移应力就是二次应力。然后,对管道设计规范和容器设计规范中针对位移应力和二次应力的强度条件进行了讨论。     

现浇楼板板角裂缝成因分析及预防措施

1　概述近年来 ,建筑物阳角部位现浇楼板板角裂缝时有出现 ,其特点是 :①裂缝在建筑物的阳角部位 ,与纵、横墙成 4 5°角 ;②多为上下贯通的裂缝 ;③多出现在除屋面、首层地面 (大地下室 )以外的各个楼层 ;④多出现在竣工验收后半年左右的空置房间。板角裂缝的形成原因众说不一     

不锈钢设计应力的研讨

欧洲关于压力溶器的指令已于１９９９年１２月开始生效,这个新的,统一的指令将逐步地取代现有的国家标准（欧洲国）,奥氏体不锈钢的许用应力将取决于屈服强度Ｒp1.0和抗拉强度Ｒmo,而双相不锈钢将遵照铁素体钢的原则,按屈服强度Ｐp0.2和室温时的抗拉强度Rm0ASMⅧ－１规范也于１９９９年７月作了改动,将抗拉强度的安全系数由４降至３．５,本文在比较各规范的同时,也对国标ＧＢ进行了讨论。     

Threshold Stress Intensity for Crack Growth in Silicon Carbide Ceramics

Measurements of threshold stress intensities for crack growth, K _h, of three polycrystalline SiC materials were attempted using interrupted static fatigue tests at 1200°–1400°C. Weibull statistics were used to calculate conservative K_th values from test results. The K _th of a chemically vapor deposited β-SiC could not be determined, as a result of its wide variations in strength. The K_th ≥ 3.3,2.2, and 1.7 MPa·m^1/2 for an Al-doped sintered α-SiC; and K_th ≥ 3.1, 2.7, and 2.2 MPa·m^1/2 for a hot isostatically pressed α-SiC, both at 1200°, 1300°, and 1400°C, respectively. A damage process concurrent with subcritical crack growth was apparent for the sintered SiC at 1400°C. The larger K_th 's for the HIPed SiC (compared to the sintered SiC) may be a result of enhanced viscous stress relaxation caused by the higher silica content and smaller grain size of this material. Values measured at 1300° and 1400°C were in good agreement with the K_th's predicted by a diffusive crack growth model, while the measured K_th 's were greater than the predicted ones at 1200°C.     

基于有限元的三通管应力分析与强度评定

通过三通的有限元分析,获得了内压作用下三通的应力分布特性;依据ASME Ⅷ-Ⅱ《美国压力容器规范分析》进行应力强度评定,工程应用表明,采用有限元分析软件能很好地解决设备开孔产生的应力问题,特别是当管口承受复杂外载荷情况下的应力计算.     

Stress Intensity Factor for a Peripherally Cracked Spherical Cap

Stress intensity factors are estimated for a spherical cap surrounded by a peripheral crack in a semi-infinite body. Using finite element analysis, the stress concentration of a spherical cap was determined as a function of the radius and depth of the cap. This stress concentration was then taken into account in developing the appropriate stress intensity factor for the peripheral crack around the spherical cap.     

圆筒与椭圆形封头联接处的边缘应力分析

根据液化石油气储罐设计事例的具体要求，分析了容器边缘应力，同时对应力进行了校对计算。以此为强度计算的一部分，设计和开发了液化石油气储罐。     

含纵向内裂纹管道的应力分析及应力强度因子研究

裂纹是压力管道中常见的缺陷形式,其失稳扩展将引起灾难性事故。以断裂力学基本理论为依据,采用1/4节点法和二维奇异单元建立了含纵向内裂纹管道的有限元分析模型,对含裂纹管道进行了应力分析,并对裂纹尖端的应力强度因子进行了分析计算。研究结果对于压力容器及管道的安全分析具有重要的参考价值。     

汽车钢化玻璃边部应力分析与控制

通过对汽车用钢化玻璃边部应力产生原理、影响因素进行分析,提出了控制边部应力的有效方法,从而降低钢化玻璃的自爆率。