钢筋混凝土裂缝机理与控制措施

钢筋混凝土裂缝分析与控制,全文共4部分:1、裂缝是不可避免而又可以尽量减轻的自然灾害;2、收缩裂缝分析及控制;3、温度收缩裂缝分析及控制;4、裂缝控制的综合技术措施。较全面地论述了钢筋混凝土裂缝机理及控制措施,文末附有100多篇参考文献。     

Recent developments in the understanding of fretting fatigue

Considerable progress has been made in the understanding of fretting fatigue over the last decade. Experiments have become more standardised and carefully controlled and this has provided the data necessary for development of methods for predicting fretting fatigue performance. This paper reviews a number of recent developments, starting with attempts to apply multiaxial initiation criteria to the fretting problem. The importance of the size effect is highlighted and an analogy is made between fretting and notch fatigue. Methods for characterising crack initiation using asymptotic analysis are discussed, together with short crack arrest concepts which provide a means of predicting fretting fatigue limits from plain fatigue data.     

A weight function methodology for the assessment of embedded and surface irregular plane cracks

A low cost numerical tool for the calculation of mode I stress intensity factors K in embedded and surface irregular cracks is presented in this paper. The proposed tool is an extension of the O-integral algorithm due to Oore and Burns for the assessment of embedded plane cracks using the weight function methodology. The performance of the O-integral is assessed first by comparing its K results to exact solutions for embedded elliptical and rectangular cracks. From the analysis of this data it is found that the error in the K results systematically depends on the crack aspect ratio and the local crack front curvature. Based on this evidence a corrective function is derived in order to remediate the limitations of the O-integral. Solutions due to Newman and Raju are used to account for the effects of free surfaces and finite thickness. The accuracy of the proposed procedure is assessed by solving a number of examples and by comparing the obtained results to those available in the literature.     

The intrinsic XFEM: a method for arbitrary discontinuities without additional unknowns

A new method for treating arbitrary discontinuities in a finite element (FE) context is presented. Unlike the standard extended FE method (XFEM), no additional unknowns are introduced at the nodes whose supports are crossed by discontinuities. The method constructs an approximation space consisting of mesh‐based, enriched moving least‐squares (MLS) functions near discontinuities and standard FE shape functions elsewhere. There is only one shape function per node, and these functions are able to represent known characteristics of the solution such as discontinuities, singularities, etc. The MLS method constructs shape functions based on an intrinsic basis by minimizing a weighted error functional. Thereby, weight functions are involved, and special mesh‐based weight functions are proposed in this work. The enrichment is achieved through the intrinsic basis. The method is illustrated for linear elastic examples involving strong and weak discontinuities, and matches optimal rates of convergence even for crack‐tip applications. Copyright © 2006 John Wiley & Sons, Ltd.     

大方坯凝固过程鼓肚应变及内裂纹形成的研究

通过建立大方坯凝固过程的传热模型,获得大方坯冷却传热过程的主要凝固参数,在此基础上建立了凝固前沿坯壳所承受的应变模型,讨论了大方坯凝固过程的主要应变及其主要影响因素,并针对实际铸机的设备和工艺状况,计算大方坯凝固过程的鼓肚应变,讨论了具体钢种产生裂纹的可能性.     

Nondestructive testing for crack of tunnel lining using GPR

Lining craze, as a common engineering damage, affects the bearing capacity and the safety of tunnels.To improve the capabilities of the surface crack detection in the tunnel lining, ground penetrating radar(GPR) was employed. The principle and method of GPR for cracks investigation of tunnel lining were expounded. As an application example, some field measurements in order to detect the depth of cracks for the tunnel lining were achieved in a new tunnel. All GPR investigations were made with the antennae of 1 GHz. The cracks of concrete structure were located, and the distributing and depth of cracks are inspected and estimated by GPR. The results of investigation show GPR is accurate and efficient to detect cracks of tunnel lining.     

KNR860C车轮崩裂原因分析

KNR860C车轮在运行过程中发生大块裂损事故。为确定车轮失效原因，对其进行解剖检验分析。踏面酸洗后出现多条横向裂纹，断裂起源于踏面表面，源区微观形貌为沿晶断。通过对缺陷的金相分析，认为，踏面存在的马氏体、球状珠光体组织及热裂纹是长期受到强烈的热影响造成的，断裂源区位于热影响区较深的区域；车轮的崩裂是由热裂引起的。     

高速钢方坯修磨后再酸洗裂纹原因的探讨

针对高速钢方坯料经过酸洗、修磨后再酸洗检查时出现表面裂纹的现象，对有缺陷方坯料与正常方坯料的修磨部位在相同条件下酸洗、修磨、再酸洗以后的表面宏观状态进行了观察和比较、对其硬度值做了对比，金相分析认为高速钢锻造方坯料经修磨后再酸洗时产生裂纹的原因是坯料未经退火或退火不充分，提出为防止裂纹产生高速钢坯料必须及时进行充分退火。     

An assessment of stress intensity factors for surface flaws in a tubular member

In the safety assessment of pressure vessels and pipes with circumferential surface cracks, it is often necessary to consider fatigue crack propagation and fracture among the possible modes of failure. The stress intensity factors at crack tips are important parameters for estimating residual life and criticality. The purpose of this paper is to present a method to calculate the mode I stress intensities for semi-elliptical cracks in pipes. This method uses the finite element technique to analyse a crack but does not require the crack to be modelled explicitly. This method is ideal for use with either fatigue life calculations or use with structural optimisation processes. Accurate results are obtained using only a relatively small number of degrees of freedom without the need to explicitly mesh cracks. In this paper a range of examples are presented to demonstrate the accuracy of this method.     

The fracture mechanics of finite crack extension

This paper describes a modification to the traditional Griffith energy balance as used in linear elastic fracture mechanics (LEFM). The modification involves using a finite amount of crack extension (Δa) instead of an infinitesimal extension (da) when calculating the energy release rate. We propose to call this method finite fracture mechanics (FFM). This leads to a change in the Griffith equation for brittle fracture, introducing a new term Δa/2: we denote this length as L and assume that it is a material constant. This modification is extremely useful because it allows LEFM to be used to make predictions in two situations in which it is normally invalid: short cracks and notches. It is shown that accurate predictions can be made of both brittle fracture and fatigue behaviour for short cracks and notches in a range of different materials. The value of L can be expressed as a function of two other material constants: the fracture toughness K_c (or threshold ΔK_th in the case of fatigue) and an inherent strength parameter σ₀. For the particular cases of fatigue-limit prediction in metals and brittle fracture in ceramics, it is shown that σ₀ coincides directly with the ultimate tensile strength (or, in fatigue, the fatigue limit), as measured on plain, unnotched specimens. For brittle fracture in polymers and metals, in which larger amounts of plasticity precede fracture, the approach can still be used but σ₀ takes on a different value, higher than the plain-specimen strength, which can be found from experimental data. Predictions can be made very easily for any problem in which the stress intensity factor, K is known as a function of crack length. Furthermore, it is shown that the predictions of this method, FFM, are similar to those of a method known as the line method (LM) in which failure is predicted based on the average stress along a line drawn ahead of the crack or notch.