Creep fracture mechanics parameters for internal axial surface cracks in pressurized cylinders and creep crack growth analysis

In the present study, a low alloy Cr–Mo steel cylinder subjected to internal pressure at high temperature with a semi-elliptical crack located at the inner surface is considered. The creep crack driving force parameter C1-integrals calculated by finite element (FE) method, are compared with results from previous studies, which indicates that empirical equations may be inaccurate under some conditions. A total of 96 cases for wide practical ranges of geometry and material parameters are performed to obtain systematic FE results of C1-integral, which are tabulated and formulated in this paper. It is observed that the maximum C1-integral may occur neither at the deepest point nor at the surface point when the aspect ratio is large enough and the value of C1-integral is significantly sensitive to the crack depth ratio. Furthermore, based on the proposed equations for estimating C1-integrals and a step-by-step analysis procedure, crack profile development, crack depth, crack length and remaining life prediction are obtained for surface cracks with various initial aspect ratios. It is found that when the crack depth ratio is increased, there is no obvious convergence of crack aspect ratio observed. The magnitude of half crack length increment is always minor compared with the crack depth increment. In addition, the remaining life is much more dependent on the surface crack depth than on the surface crack length.     

Study on cracking of welding overlay based on the theory of diffusion-induced stress

Hydrogen diffusion in the wall of hydrogenation reactor for three situations,i.e.operating,normal shutdown and abnormal shutdown,was numerically simulated based on the finite element program-ABAQUS.The formula of diffusion-induced stress was deduced for model of the thin walled cylinder.Distribution of diffusion-induced stress in the wall of hydrogenation reactor was studied.The results showed that the maximum stress was at the fusion surface between welding overlay and base metal,and which would increase w...     

304不锈钢钎焊板翅结构疲劳断裂机理分析

对304不锈钢板翅结构进行疲劳试验,分析疲劳断裂机理.疲劳裂纹从上钎角萌生,然后向翅片扩展,最终导致失效.在钎焊过程中,钎角处生成了较多的脆性化合物,且钎角处应力高度集中,使得裂纹从钎角萌生.疲劳裂纹的扩展经历了4个阶段:(1)裂纹在循环载荷作用下,在钎角脆性化合物启裂;(2)裂纹启裂后,在循环载荷作用下,沿钎角扩展;(3)裂纹跨越钎角和固溶体组织的界面,沿固溶体组织扩展;(4)裂纹跨越翅片和固溶体的界面,进入翅片区域扩展,直至完全断裂.     

纳晶金属材料氢脆的微观力学模型

针对纳晶金属材料的氢脆问题,该文提出一个新的理论模型。在该模型的理论框架内,认为堆积在距裂纹尖端最近晶界上的氢原子会阻止位错从裂纹尖端的发射,从而抑制裂纹的钝化,同时促进纳晶金属材料的脆性断裂。该文在有氢和无氢两种条件下,对纳晶镍的临界应力强度因子与晶粒尺寸之间的相互关系进行了对比。结果表明:由于氢原子的脆化作用,纳晶镍的临界应力强度因子下降30％之多,这种氢致纳晶金属材料脆化的现象随其晶粒尺寸的变小而愈加显著。     

加氢反应器裂纹扩展临界状态的研究

利用Hartman-Schijve公式计算加氢反应器材料2．25CrlMo钢裂纹疲劳扩展的应力强度因子理论门槛值,与实用门槛值比较结果表明后者偏于危险,二者相差约为42．55％。由此进一步引用推导公式,计算得到某加氢反应器材料断裂韧度的值。综合裂纹深度和长度方向两方面因素,对裂纹扩展状态进行分析,推导出裂纹扩展的临界尺寸,作为加氢反应器裂纹扩展评判依据。     

Numerical analysis of gas tightness of seals in pSOFCs based on Lattice Boltzmann Method simulation

To better understand the leakage mechanism of compressive seals in planar solid oxide fuel cells (pSOFCs), a theoretical method of leakage prediction is proposed that combines three numerical techniques. The Lattice-Boltzmann method was introduced to simulate the nonlinear flow in rough wall interfacial gaps due to its flexibility when dealing with flow problems related to complex boundaries. A numerical three-dimensional (3D) rough-surface generation technique was applied for the geometry configuration of interface gaps, and finite element analysis was adopted for micro-contact mechanics of single asperities to determine the gap height under stress. Based on this method, the 3D flow characteristics of the gas in interface gaps were numerically studied, and two important dimensionless flow factors (the flow factor Φ_σ of roughness and the flow factor Φ_h of height) were proposed. All numerical results were fitted as dimensionless criteria for calculating the interface leakage rate. These criteria can be directly used to predict the leakage rate of a given compressive seal under specific working conditions without relying on any experimental empirical formula. Furthermore, leakage rate predictions were compared to existing experimental data and good agreement was obtained, corroborating the accuracy of the method. In addition, the effects of influencing parameters on leakage according to the rate-temperature relationship were discussed. Several important conclusions were drawn to guide the design of compressive seals for pSOFC.     

Experimental study on spontaneous ignition and flame propagation of high-pressure hydrogen release through tubes

An experimental study was conducted to research the mechanism of spontaneous ignition induced by high-pressure hydrogen release through tubes with a diameter of 10 mm and varying lengths from 0.3 to 3 m. The pressure and light signals inside the tube were collected. The propagation of shock wave inside and outside the tube was also systematically investigated. The development process of the jet flame in the atmosphere was completely recorded, and the multiple Mach disks at the tube exit were observed by using a high-speed camera. The results show that the minimum release pressure, at which the jet flame is formed, is found to be 3.87 MPa with the tube length of 1.7 m. When the tube length was longer than 1.7 m, the critical pressure for forming jet flame increased rapidly. The velocity attenuation of the shock wave is mainly affected by the burst pressure but not sensitive to the tube length, and the flame propagates in the tube at a slower velocity than the shock wave. The compression of the hydrogen-air mixture by the Mach disk causes it to burn more violently after passing through the Mach disk. It is confirmed that the flame at the tube exit is lifted in the atmosphere, then a jet flame initiates behind the second Mach disk.     

三轴加速度计在水下结构振动测试中的应用

采用基于MEMS技术的ADXL330三轴加速度计芯片，设计了适合水下结构振动测试的加速度传感器，并应用于某输水管线闸门振动监测系统中。分析了ADXL330结构、原理和标定方法。根据水下结构振动测试特点和要求，设计了应用电路、防水结构以及振动测试系统。现场应用表明，采用该芯片设计的三轴加速度传感器能够满足水下结构振动监测的需要，具有低成本、高精度、易安装和安全可靠等特点。     

Prediction of temperature and velocity profiles in a single compartment fire by an improved neural network analysis

A novel hybrid Artificial Neural Network (ANN) model, denoted GRNNFA, has been developed for fire studies. The major feature of the model is its ability to work in a noisy environment, which is usually the case with fire experiment data. The GRNNFA model is applicable in the determination of the location of the thermal interface in a single compartment fire. The performance of the GRNNFA has been proven to be comparable to that of the Computational Fluid Dynamics (CFD) model. In addition, the computational speed of the GRNNFA model is much faster than that of the CFD model. However, the original GRNNFA model is only capable of handling the training samples with scalar output. This shortcoming restricts the application area of the model. Hence, this paper presents a modification of the original GRNNFA model for multi-dimensional prediction problems. It also demonstrates the first application of ANN techniques to predicting the velocity and temperature profiles at the center of the doorway in a single compartment fire. These profiles are commonly used to benchmark the performances of CFD models. They are employed in this study to evaluate the performance of the modified GRNNFA model. The predicted profiles are compared with the experimental results and the results simulated by the CFD model. These results show that the prediction errors of the GRNNFA model are less than those of the CFD model in actual application.