Delayed failure of ceramic matrix composites in tension at elevated temperatures

Ultimate tensile strength of five different continuous fiber-reinforced ceramic matrix composites (CMCs), including SiC_f/BSAS (two dimensional (2D), 2 types), SiC_f/MAS (2D), SiC_f/SiC (2D), and C_f/SiC (2D, 2 types), was determined as a function of test rate at 1100–1200 °C in air. All five CMCs exhibited a significant dependency of ultimate tensile strength on test rate such that the ultimate tensile strength decreased with decreasing test rate. The dependency of ultimate tensile strength on test rate, the applicability of preload technique, and the predictability of life from one loading configuration (constant stress-rate loading) to another (constant stress loading) all suggested that the overall, phenomenological delayed failure of the CMCs would be governed by a power-law type of slow crack growth.     

Efficient random walks in the presence of complex two-dimensional geometries

This paper details an efficient algorithm for particles undergoing random walks in the presence of complex, two-dimensional, solid boundaries. The scheme is developed for the simulation of vortex diffusion using the random vortex method. Both vortex blobs and sheets are handled. The relevant modifications for using the algorithm with the vorticity redistribution technique are also discussed. The algorithm is designed to be used in the framework of an existing fast multipole implementation. A measure for the geometric complexity of a body is introduced and the algorithm’s efficiency is studied as various parameters are changed for bodies of varying complexity.     

Non-destructive testing of rock bolts using guided ultrasonic waves

The research outlined in this paper is aimed at the development of a portable non-destructive testing instrument for evaluating the condition of rock bolts. In applications such as coal mine roof reinforcement, the opportunities for rock bolt inspection are currently limited to destructive techniques such as the pull-out test. It is proposed that guided ultrasonic waves can be used to solve this inspection problem, using a pulse-echo test carried out from the free end of the bolt. Suitable test frequencies have been identified through the use of modelling software, and successful laboratory and site trials have been undertaken. The research has shown that the proposed approach is capable of determining the bolt length, and of identifying major defects such as necking, deformation, and loss of resin encapsulation.     

Friction-transfer test for the assessment of in situ strength and adhesion of cementitious materials

Since in concrete industry, the quality control is generally accomplished by the testing of separately prepared samples, the accurate estimate of the in situ strength of concrete has become a necessity. The main discrepancies between the measured cube strength and the actual in situ strength of concrete, relates to their different conditions associated with the development of strength. In addition, due to chemical deterioration or damage, accurate estimate of in situ concrete strength provides valuable information about the present situation of the structure, when making decisions about the required repair and/or strengthening systems. The Friction-Transfer method, which is described in this paper, can be used to estimate the in situ strength of concrete and other materials. In this method a specially devised apparatus fits on to the top of the partial core and is clamped to it. To measure the concrete compressive strength, a torque is applied using an ordinary torque-meter and the maximum shear stress at failure is used to estimate the cube compressive strength by means of a calibration graph. In order to measure the adhesion between different layers of cementitious and/or resinous materials, their torsional shear strengths are calculated along the failed inter-facial surfaces of the layers. Laboratory and in situ tests, to evaluate the performance of the method are described. Also in view of the accurate and reliable results attainable, some specific applications are proposed.     

An updated correlation for crack-arrest fracture toughness for nuclear reactor pressure vessel steels

An updated and statistically-rigorous correlation is provided for crack-arrest toughness values versus normalized temperature for light-water nuclear reactor pressure vessel (RPV) steels. The database used in this effort is larger than applied heretofore and includes results from tests of laboratory-size specimens and from tests of large-scale specimens, which contain features prototypical of operating RPVs. The mathematical methodology used is based on a lognormal distribution, with its parameters calculated by orthogonal distance regression. This correlation was developed as one of several items updated for use in the US Nuclear Regulatory Commission's extensive program to evaluate and potentially revise its rule for ensuring structural integrity of operating RPVs when subjected to pressurized thermal-shock transients.     

基于Solidworks的零件建模的若干方法

介绍零件的Solidworks三维建模的几种方法。利用Solidworks的Toolbox插件构造常见的零件模型;利用Solidworks曲线插入功能构造草图,或利用二维图形设计软件进行草图绘制,然后输出到Solidworks中特征构造。