Stress intensity factors for surface cracks in single‐edge notch bend specimen by a three‐dimensional weight function method

Stress intensity factors for half‐elliptical surface cracks at a semi‐circular notch in a recently developed single‐edge notch bend specimen are determined for a wide range of geometrical parameters using a three‐dimensional weight function method. Two load cases of pin loading and uniform remote tension are considered. The results are in good agreement with abaqus/franc3d finite element analysis. It is found that the Ziegler–Newman engineering similitude approach (programmed into the Fatigue Crack Growth Structural Analysis life‐prediction code) produces good results for a wide range in a/c ratios. Expressions by multi‐variable curve fitting to the weight function results are presented for easy engineering applications.     

Solutions of the second elastic-plastic fracture mechanics parameter in test specimens

Extensive finite element analyses have been conducted to obtain solutions of the A-term, which is the second parameter in three-term elastic-plastic asymptotic expansion, for test specimens. Three mode I crack plane-strain test specimens, i.e. single edge cracked plate (SECP), center cracked plate (CCP) and double edge cracked plate (DECP) were studied. The crack geometries analyzed included shallow to deep cracks. Solutions of A-term were obtained for material following the Ramberg-Osgood power law with hardening exponent of n = 3, 4, 5, 7 and 10. Remote tension loading was applied which covers from small-scale to large-scale yielding. Based on the finite element results, empirical equations to predict the A-terms under small-scale yielding (SSY) to large-scale yielding conditions were developed. In addition, by using the relationships between A and other commonly used second fracture parameters such as Q factor and A₂-term, the present solutions can be used to calculate parameters A₂ and Q as well. The results presented in the paper are suitable to calculate the second elastic-plastic fracture parameters for test specimens for a wide range of crack geometries, material strain hardening behaviors and loading conditions.     

A scanning electron microscopy specimen holder for viewing different angles of a single specimen

The specimen holder for scanning electron microscopy described herein allows a single specimen to be examined in any possible view and significantly improves object illumination. The specimen is glued to a fine pin and flexibly mounted on a double‐sided adhesive conductive pad on a rotatable pivot. A milled pot placed beneath the specimen acts as an electron trap. This provides a homogeneous black image background by minimizing noisy signals from the specimen's surroundings. Microsc. Res. Tech. 73:1073–1076, 2010. © 2010 Wiley‐Liss, Inc.     

Limitations on the use of the mixed-mode delaminating beam test specimen: Effects of the size of the region of K-dominance

The mixed-mode delaminating beam (MMDB) is a widely used test geometry designed to measure the fracture resistance of bimaterial interfaces under mixed-mode loading conditions. In the present work, linear-elastic finite element analyses are employed to determine the complex stress intensity factor, K, for an interfacial crack in this sample; results are found to confirm those of previous studies of the bilayer specimen. However, the numerical results further reveal that the region of K-dominance near the crack tip is very limited, extending merely 1/100 to 1/1000 of the sample height, about an order of magnitude smaller than for other common fracture-mechanics test samples. Analyses performed for this specimen geometry modified to include a thin sandwiched interlayer also indicate a very limited region of K-dominance, for example, extending 1/10 of the height of the sandwiched layer from the crack tip for very thin sandwiched layers. For the sandwiched geometry, two situations leading to a useful small scale yielding condition are described. Examples of the use of this specimen in the evaluation of the fracture toughness of ceramic joints are cited from the literature and comparisons are made between the size of the K-dominant region and the extent of crack tip plasticity. Based on these comparisons, the geometry-independent predictive power of linear-elastic fracture mechanics for common bimaterial couples and specimen dimensions using this geometry is challenged.     

Preparation of lithium specimens for transmission electron microscopy

A method of preparing undeformed thin lithium specimens for TEM is described. A solution of dehydrated methanol and toluene is used both for initial dishing of the foil by chemical polishing and also for final thinning. Under electron beam irradiation in the TEM, new pure Li crystals can grow out of the existing Li specimen. These in situ crystals can be used for the study of the microstructure and electronic structure of Li using TEM and electron energy loss spectrometry.     

LGH-01型空气质量自动监测系统准确度检查方法探讨

LGH一01型空气自动监测系统因其独特的技术优势,在国内占有较大的市场份额,已广泛应用于城市环境空气质量监测。如何做好仪器的使用维护工作,保证监测结果的真实有效,是一线环境监测工作者每天必须面对的问题。本文针对DOAS系统准确度检查方法进行实验探讨,期望能提供给同行参考。     

无侧限试件制作设备的改进

对现有无侧限试件制作过程和试验设备进行了研究,并对试验设备进行了改良,以达到降低操作劳动强度,节约设备成本的目的,通过平行试验,使改良后的设备对试验数据没有影响,从而促进无侧限试件制作设备的改进.     

钢框架加腋节点的应力分布与计算方法

用ANSYS软件对NIST/AISC研究项目中的UCSD模型进行受力分析,与试验结果进行对比,绘制关键部位的应力图,分析加腋区域的应力分布规律,给出钢框架加腋节点加腋区域应力的新的简化计算方法。     

Transient and steady state crack growth kinetics for stress corrosion cracking of a cold worked 316L stainless steel in oxygenated pure water at different temperatures

The stress corrosion cracking (SCC) growth kinetics for a cold worked 316L stainless steel was continuously monitored in high purity water at different temperatures and dissolved oxygen (DO) levels under a K (or K_max) of 30 MPa m^0.5. The total SCC test time was more than 8000 h to make sure the steady state crack growth rate under each test condition could be reached. Crack growth rate (CGR) increases with increasing temperature in the range 110-288 °C. A typical intergranular-cracking mode is identified. Depending on the previous test condition, especially the temperature, three kinds of crack growth kinetics, i.e., increasing with testing time then becoming steady, being constant during the whole period, or decreasing with test time then becoming steady, are identified and discussed. Time-dependent and testing history-dependent crack growth modes were confirmed in two series of tests in 2 ppm DO and 7.5 ppm DO pure water. The apparent activation energies are calculated and compared with other data in different environments under different applied loading levels for understanding the cracking mechanism.     

Advanced Space Facilities for Higher Plant Culture and Animal Embryo Culture in Microgravity

The Higher Plant Culture Device (HPCD) and the Animal Embryo Culture Device (AECD) were developed for life science experiments on board of the SJ-8 satellite and are discussed in the present paper. System composition modes and key technologies are described in detail, i.e. the photomicroscope with self-focus algorithm, the optical imaging path and the flexible positioning method of flowers, the special-purpose embryo vessel for culture and observation with lighting, in total four representative and innovative items of the key technology. Results and shortages of this space experiment are discussed briefly demonstrating that facilities work well in the microgravity environment. Finally, future improving principles are proposed.