拱坝非线弹性损伤分析

本文以损伤力学为基础，将Ｖａｌｌｉａｐａｎ三维各向异性损伤本构模型应用到有限元法计算中，建立了以应变损伤判据为基础的三维各向异性损伤演化方程。用改进的抹平式裂缝模式模拟混凝土单元的损伤破坏，对拱坝进行了三维各向异性非线弹性有限元分析。     

Application of a strip-yield model to predict crack growth under variable-amplitude and spectrum loading – Part 1: Compact specimens

Fatigue-crack-growth tests were conducted on compact, C(T), specimens made of D16Cz (clad) aluminum alloy under constant-amplitude loading, a single spike overload, and simulated aircraft spectrum loading. Constant-amplitude tests were conducted to generate crack-growth-rate data from threshold to near fracture over a wide range of stress ratios (R = P_min/P_max = 0.1–0.75) using the new compression pre-cracking test methods. Comparisons were made between test data generated on the C(T) specimens with test data from the literature on middle-crack-tension, M(T), specimens machined from the same sheet. A crack-closure analysis was used to collapse the rate data from both specimen types into a narrow band over many orders of magnitude in rates using proper constraint factors. The constraint factors were established from constant-amplitude (CA) and single-spike overload tests. The life-prediction code, FASTRAN, which is based on the strip-yield model concept, was used to calculate crack-length-against-cycles under CA loading and a single-spike overload (OL) test, and to predict crack growth under simulated aircraft spectrum loading tests on C(T) specimens. The calculated crack-growth lives under CA loading were generally within about ±25% of the test results, but slower crack growth under the double-shear fatigue mode, unlike the single-shear mode (45^o slant crack growth), may be the reason for some of the larger differences. The predicted results under the single-spike overload and the Mini-Falstaff+ spectrum were within 10% of the test data.     

超声波检测混凝土裂缝深度的方法与比较

本文讨论了在选取不同测距检测不同深度的混凝土裂缝时,现有常用的两种方法(CECS21:2000规程规定的TC～T0法和BS-1881法)之间优劣性。实验发现,对于不同深度的裂缝无论哪种方法,测距的选择是很重要的。对于本实验范围内的深度在150mm以内的裂缝,TC～T0法具有一定的优越性;BS-1881法对于深度在100mm以上的裂缝有一定的应用价值。在对BS-1881标准中固定的测距作出相应修正后,BS-1881法可适用于常见的深度在100mm以下的裂缝的检测。     

Creep/fatigue crack growth testing standardisation assessment and validation for specimens containing weld mismatch

Abstract

Testing and modelling of creep and creep/fatigue in welded components are essential tools for improving safe lifing methodologies. Key factors which determine a successful methodology for modelling failure in engineering components are good testing data and the development of appropriate and accurate correlating parameters to treat the results in a the unified and verifiable manner. This work considers the first two aspects and identifies important issues and improvements in the development and standardisation in creep and creep/fatigue crack growth testing or welds. Under the auspices of the Versailles Agreement on Materials and Standards (VAMAS) committee a Code of Practice on creep crack growth of components has been developed. The procedure identifies methods of testing for non-standard, welded feature test components in VAMAS TWA31 Technical Working Area on Creep and Creep/Fatigue Crack Growth of weldments containing residual stress. The overview highlights the important elements in these pre-standardisation collaborative efforts by presenting the methods of analyses and example of their application to standard fracture mechanics weld and feature type plate and pipe specimens.     

控制棒环焊缝的脉冲钨极氩弧焊

介绍了巴基斯垣恰希玛核电站（ＰＣ）控制棒环焊所采用的脉冲钨极氩弧焊（以下简称脉冲ＴＩＧ焊）的工艺特点以及对０Ｃｒ１８Ｎｉ１１Ｔｉ冷作奥氏体不锈钢材料的适用性,分析总结了焊接缺陷产生的原因和采取的措施。     

转子裂纹检测与寿命预测技术研究

现代的抗疲劳设计法——损伤容限设计使零件在出现疲劳裂纹后通过严格的检修、剩余寿命计算和断裂控制仍能安全使用 ,使充分利用零件的剩余强度成为可能。对损伤容限设计的关键技术——初始缺陷或服役中出现的疲劳裂纹检测和疲劳剩余寿命预测技术进行了研究。成功地研制了一套性能优良的交流电位表面裂纹监测系统 ,分辨率为 0 .1 mm,测量精度达到± 2 % ,测量范围为 0～ 1 0 0 mm;开发出一套微机平台上的基于断裂力学的 (含表面裂纹 )转子剩余寿命计算程序 ,为分析裂纹扩展形态和概率断裂力学方法估算剩余寿命提供了快速计算途径。有较强的工程实用性和良好的市场开发前景。     

Fail-safe design of integral metallic aircraft structures reinforced by bonded crack retarders

This paper presents an investigation on the effectiveness of crack growth retarders bonded to integral metallic structures. The study was performed by both numerical modelling and experimental tests. It focuses on aluminium alloy panels reinforced by bonded straps made of carbon-epoxy, glass-epoxy composite materials or a titanium alloy. The goal was to develop a fail-safe design for integrally stiffened skin-stringer panels applicable to aircraft wing structures. The modelling strategy and finite element models are presented and discussed. The requirements that the models should meet are also discussed. The study has focused on establishing the extent of crack retarder benefits, in terms of fatigue crack growth life improvement, by numerical simulation and experimental tests of various crack retarders. The results of predicted fatigue crack growth retardation have been validated by tests of laboratory samples. This study concludes that by bonding discrete straps to an integral structure, the fatigue crack growth life can be significantly improved.     

Fracture mechanics testing on specimens with low constraint--standardisation activities within ISO and ASTM

Fracture mechanics tests are traditionally designed to measure material resistance to stable or unstable crack extension using specimens that are highly constrained to plastic deformation. For a variety of reasons, structural members may be made of thin gage-materials with inherently low constraint to plastic deformation. There is currently little guidance for measuring crack extension resistance under such conditions. The international standards organisations ISO and ASTM are responding to that need, and this paper describes one aspect of their current activity.Two procedures are being developed; one based on the δ₅ crack opening displacement parameter, the other on the constant value of the crack tip opening angle, ψ_c. The measurement of δ₅ is well established and relatively simple, whereas ψ_c is more difficult to determine experimentally. Evaluations of ψ_c from finite-element analyses are currently the most accurate approach, since measurements can only be made on the exterior surfaces similar to δ₅. Questions naturally arise regarding the correspondence of surface indication with full-thickness response in the laboratory experience. Both measures of crack extension resistance are suitable for structural assessment. The δ₅ concept is applied by means of crack driving force formulae from existing assessment procedures and hence relatively easy to use. On the other hand, the CTOA concept is potentially more accurate and can be applied to cases of multiple cracks and complex structures. But its structural application requires numerical methods, which have been successful in predicting the failure of large-scale cracked structural components.     

A multi-scale numerical modelling of crack propagation in a 2D metallic plate

A new multi-scale model of brittle fracture growth in an Ag plate with macroscopic dimensions is proposed in which the crack propagation is identified with the stochastic drift-diffusion motion of the crack-tip atom through the material. The model couples molecular dynamics simulations, based on many-body interatomic potentials, with the continuum-based theories of fracture mechanics. The Ito stochastic differential equation is used to advance the tip position on a macroscopic scale before each nano-scale simulation is performed. Well-known crack characteristics, such as the roughening transitions of the crack surfaces, as well as the macroscopic crack trajectories are obtained.     

Quantitative validation of Eddy current stimulated thermal features on surface crack

Thermography is an established technique in Non-Destructive Testing and Evaluation (NDT&E) for detecting and visualizing defects. The acquired thermal image sequences contain valuable information in the spatial, time and frequency domains. Many thermal feature extraction methods have been previously proposed to detect and quantify defects. However, the quantitative assessment and error analysis remain as challenges. In the present work, a quantitative analysis strategy is proposed for validating detection performance of various thermal feature extraction techniques based on Eddy Current Stimulated Thermography. F-score is adopted as a global quantitative evaluation indicator to assess the crack detectability. The quantitative validation is carried out based on a large number of simulations and experiments for cracks on the nonferromagnetic material. The detectability in relation to the variations in crack size and the different thermal feature extraction methods have been critically analyzed. The insights obtained from the present findings can serve as guidelines to other types of thermal-based NDT&E to improve the defect visibility and detectability.