共查询到20条相似文献,搜索用时 31 毫秒
1.
Hyeong-Yeon Lee Gyeong-Hoi Koo Jae-Han Lee 《Journal of Mechanical Science and Technology》2010,24(2):481-487
An assessment of creep-fatigue crack initiation and growth for a 316L stainless steel structure has been carried out according
to the current (2007 edition) and previous (2002 edition) versions of the French RCC-MR A16 procedure. Some significant changes
have been made in terms of the formulae and material properties, which may cause big differences in the assessment. In this
study, the changes in the A16 guide have been quantified for a 316L austenitic stainless steel structure, and the assessment
results were compared with those of the observed images from a structural test for a welded component. 相似文献
2.
Dianyin HU Xiyuan WANG Jianxing MAO Rongqiao WANG 《Frontiers of Mechanical Engineering》2019,14(3):369
This study aims to examine the crack growth behavior of turbine disc GH4169 superalloy under creep-fatigue loading. Crack growth experiments were performed on compact tension specimens using trapezoidal waveform with dwell time at the maximum load at 650 °C. The crack growth rate of GH4169 superalloy significantly increased with dwell time. The grain boundaries oxidize during the dwell process, thereby inducing an intergranular creep-fatigue fracture mode. In addition, testing data under the same dwell time showed scattering at the crack growth rate. Consequently, a modified model based on the Saxena equation was proposed by introducing a distribution factor for the crack growth rate. Microstructural observation confirmed that the small grain size and high volume fraction of the d phase led to a fast creep-fatigue crack growth rate at 650 °C, thus indicating that two factors, namely, fine grain and presence of the d phase at the grain boundary, increased the amount of weakened interface at high temperature, in which intergranular cracks may form and propagate. 相似文献
3.
Chang-Min Suh Yong-Goo Kang Duck-Young Suh Byung-Won Hwang 《Journal of Mechanical Science and Technology》1987,1(2):115-120
This paper deals with the basic characteristics of surface micro-cracks on unnotched smooth specimens of Type 304 stainless steel under creep and creep-fatigue condition with holding time of 1 and 10 minutes respectively at 538°C in air. The behaviors of the microcracks have been analysed via surface replica method and photomicrographs techniques. Quantitative information, such as initiation period, growth and coalescence behavior, statistical distributions of crack length, density of cracks, distribution patterns and crack growth properties, was obtained. Knowledge of these parameters is critical for the application of fracture mechanics to the life assessment and the damage evaluation of structures at elevated temperature. 相似文献
4.
Hyeong-Yeon Lee Jae-Hyuk Eoh Yong-Bum Lee 《Journal of Mechanical Science and Technology》2013,27(9):2729-2735
A high temperature design and creep-fatigue damage evaluation for a helical type sodium-to-air heat exchanger (AHX) in a 600MWe sodium-cooled fast reactor (SFR) has been conducted. The AHX is a safety-grade component in a passive decay heat removal (DHR) system. Safe and reliable decay heat removal is one of the most important tasks in the successful design of a sodium-cooled fast reactor. Therefore, independent, diverse and redundant DHR systems incorporating both passive and active mechanisms have been employed in the demonstration SFR developed by Korea Atomic Energy Research Institute (KAERI). One of the key DHR components is sodium-to-air heat exchanger, which has a helically coiled tube arrangements. A creep-fatigue damage evaluation has been performed according to the elevated temperature design codes of ASME Subsection NH and RCC-MRx based on a full 3D finite element analysis. The integrity of the heat exchangers under creep-fatigue loading was confirmed and code comparisons were made as well. 相似文献
5.
In this study, a fretting fatigue test has been equipped with an acoustic emission (AE) device in order to identify the successive crack propagation mechanisms. The fretting fatigue crack nucleation and propagation is a complicated process. Cracks initiate and propagate firstly due to shearing (mode II) and then by tension (mode I). The crack propagation generates mechanical energy emission. Elastic waves appear and can be detected through AE. A complete analysis of the AE signals (multi-parameter analysis, location of the AE in the loading cycle and a statistical analysis) led to an identification of three different steps in the crack propagation process. The evolution of the shearing and the tension influences in the crack propagation process is recognizable separately. Therefore, the three crack propagation steps have been identified as (a) crack propagation in mode II, (b) mixed mode crack propagation and (c) pure mode I crack propagation. 相似文献
6.
Initiation and propagation of interfacial crack along bimaterial interface are considered in this study. A biaxial loading device for a single specimen is used for obtaining a wide range of mode-mixities. The specimen is an edge-cracked bimaterial strip of glass and epoxy; the biaxial loading device, being capable of controlling displacements in two perpendicular directions, is developed. A series of interfacial crack initiation and propagation experiments are conducted using the biaxial loading device for various mixed modes. Normal crack opening displacement (NCOD) is measured near crack front by a crack opening interferometry and used for extracting fracture parameters. From mixed mode interfacial crack initiation experiments, large increase in toughness with shear components is observed. The behavior of interfacial crack propagation analyzed as a function of mode-mix shows that initial crack propagation is delayed with increase of mode-mixity, and its velocity is increased with positive mode-mixity but decreased with negative case. However, it is found that crack propagation is less accelerated with positive mode-mixity than the negative mode-mixity, which may be caused by contact and/or effects of friction between far field and near-tip field along the interfacial crack. 相似文献
7.
8.
Heung-Shik Lee Sung-Ho Bang Tae-Won Kim 《Journal of Mechanical Science and Technology》2014,28(10):4037-4047
A corrosion fatigue crack propagation test for 430 stainless steel and its heat affected zone was conducted in pH buffer solutions, and the results were compared with model predictions. The bare corrosion effect on fatigue crack propagation, particularly in corrosive environments was evaluated by means of a modified Forman equation. As shown in the results, the average corrosion rate determined from the ratio of corrosion induced crack length to the entire crack length under a cycle load was 0.11 and 0.37 for the base metal and heat affected zone, respectively, with a load ratio of 0.5, frequency of 0.5, and a pH 10.0 environment. The modeling and experimental processes demonstrate a step towards a methodology enabling the corrosion effects on fatigue crack propagation behavior to be determined. 相似文献
9.
三维裂纹仿真分析和防断裂设计问题一直是断裂理论和工程应用研究的主要课题。管道系统是核动力工程中的关键部件。运用三维有限元分析软件 ANSYS 和裂纹分析专用程序 Franc3D,针对中国实验快堆(CEFR)一段余热排放系统中的含裂纹管道进行了三维裂纹仿真模拟分析和LBB(Leak -Before -Break)评定。快堆管道工作时处于高温状态,因此,采用适用于高温环境下的材料和法国结构安全设计规范 RCC -MR.A16标准文件。研究的管道材料为9Cr1Mo 钢的改良型———T91/P91管材,分析模型为含裂纹的三维结构,且包括管道高温工况和蠕变效应。仿真计算结果表明,针对所研究的工况,蠕变较疲劳对三维裂纹扩展的影响更大。采用 T91钢的管路系统能够满足相关规范中的 LBB 设计准则。该研究为快堆管道选材、含缺陷管道安全评估和高温完整性评定提供设计参考。 相似文献
10.
A new methodology for predicting crack initiation life for rolling contact fatigue based on dislocation and crack propagation 总被引:1,自引:0,他引:1
C. Richard Liu 《International Journal of Mechanical Sciences》2008,50(2):117-123
A new methodology for predicting crack initiation life is presented and validated experimentally. The methodology considers that the total fatigue life is the summation of crack initiation life and crack propagation life, since fatigue failures are due to crack initiation and crack propagation. It has been established that the crack propagation life can be estimated based on a modified Paris’ law when the size of crack is larger than a certain value. However, there has been no verified method for estimating the crack initiation life with good accuracy. The proposed methodology for predicting the crack initiation life is based on a dislocation model, and the constants for the model are determined by the crack initiation lives obtained by a new approach. This new approach determines the crack initiation life by subtracting the predicted crack propagation life from the experimentally obtained total fatigue life. The developed crack initiation life model is combined with a crack propagation life model for the prediction of fatigue life. It is noted that the standard deviation in the ratios of experimental life to predicted life by the developed fatigue life model is only 14% of that by the International Standard. 相似文献
11.
Choon Yeol Lee Han-Kyu Jeung Jae-Do Kwon 《Journal of Mechanical Science and Technology》2016,30(11):4937-4940
Several studies have been conducted on the fretting fatigue limit characteristics of Inconel alloy tube material used in steam generators of nuclear power plants. Nevertheless, additional research on fretting fatigue crack initiation and propagation behavior is necessary in order to evaluate its fretting fatigue life more accurately. In this study, crack growth tests of fretting fatigue are conducted, and the characteristics of fatigue crack initiation and propagation are analyzed on Inconel 690 alloy. Also, plain fatigue crack growth tests are performed on the same material, and the results are compared with those of fretting fatigue crack growth tests. From both of the plain and fretting fatigue crack growth test results, the ΔK-da/dN diagrams are obtained and the crack growth rates are compared. It is found that the crack growth rate for fretting fatigue tests is faster than that for plain fatigue tests under a certain value of DK. However, over this value of DK, the crack growth rate for fretting fatigue tests becomes slower than that for plain fatigue tests due to debris which is produced by fretting and trapped in the propagated cracks. Finally, the fracture surfaces examined by an optical microscope, and the initiation angles of the oblique cracks are determined under various applied stresses. Also, the microstructure of the fracture surfaces is observed by a Scanning electron microscopy (SEM). 相似文献
12.
The conventional fracture mechanics parameters KIC and/or JIC are used as fracture toughness criteria necessary for the start of crack propagation under plane strain conditions. These criteria are defined only for small-scale yielding or infinitesimal deformation, though actual fractures involve large plastic deformation. Hence, measurement of fracture resistance during crack propagation is difficult with the conventional parameters.Estimating the mechanical conditions around the propagating crack tip is very useful for reducing damage during accidental fracture. Therefore, establishing a criterion for crack propagation with large-scale yielding is very important for not only science fields but also some industrial fields. For fractures with large-scale yielding, micro- or mesoscale damage processes in the crack tip vicinity have to be considered.In this study, Gurson's constitutive model for void occurrence and growth was introduced into the finite element method to discuss failure behavior in the crack tip vicinity. Fast crack propagation behavior under high-speed deformation was simulated using the moving finite element method based on the Delaunay automatic triangulation. The excellent far-field integral path independence of the T* integral was verified for pure mode I fast crack propagation and non-straight crack propagation under mixed mode conditions. The void growth conditions near the crack propagation path were evaluated. 相似文献
13.
The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service
failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under
mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack
propagation direction. In modified range 0.3≤a/W≤0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact
tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue
cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using KI and KII(SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict
the crack propagation direction and the propagation behavior of fatigue cracks. 相似文献
14.
The metallographic characteristics of fatigue cracks in the titanium alloy IMI829 at 400°C and 600°C
High temperature fatigue tests under fluctuating axial tension were carried out on the alloy in the fully heat treated condition, the microstructure consisting of a β matrix containing colonies of aligned α-platelets. Fatigue cracks were initiated by fretting at temperatures of 400°C and 600°C. A detailed metallographic examination has been made of the fretted region and the resulting fatigue crack and these characteristics have been related to the microstructure of the alloy. At test temperatures of 400°C the fatigue cracks initially propagated at right angles to the α-platelets but where their orientation was unfavourable, propagation also occurred parallel to the α-platelets. At test temperatures of 600°C the initial direction of crack propagation was independent of the microstructure. 相似文献
15.
An important class of short-fiber reinforced composites is the sheet molding compound, which is recently developed and currently
used in many engineering applications. Fatigue failure of the composites is a subject of major concern in design and cyclic
crack propagation is of particular significance in the fatigue life prediction of short fiber composites. However, research
on the fatigue behavior of polymer injection weld, especially short glass fiber-filled polymer injection weld, has not been
carried out. In this study the analyses of the fatigue crack growth behaviors at weld line and in the bulk are performed based
on low cycle fatigue test. 相似文献
16.
A clamped laminated cylindrical shell is presented to investigate nonlinear structural behavior involving geometrically nonlinear deformation. In the investigation, transverse matrix cracks are considered in the stiffness of the laminated cylindrical shell. Stiffness degradation is examined for several laminated angles and transverse crack density. Micro-mechanics theory on the composite material was used to derive the degraded stiffness of the laminated cylindrical shell due to the crack density. Iterative numerical scheme was developed to calculate the degraded composite stiffness which is a complicated relation with the crack density. A nonlinear finite element program was developed using 3-D degenerated shell element and the fist order shear deformation theory to consider the large deformation of the clamped laminated cylindrical shell. The updated Lagrangian method is used for nonlinear finite element analysis. Nonlinear structural responses of the laminated cylindrical shell were examined for various stacking sequences and crack density under transversely loaded pressure. Also, the effect of crack opening/closed was considered in the examination. Through this study, it is realized that the transverse matrix crack causes moderate stiffness reduction and affects the responses of the composite shell. 相似文献
17.
本文通过试验获得了焊趾疲劳裂纹扩展特性,应用概率统计方法建立了焊趾疲劳裂纹扩展的统计模型,分析了焊趾疲劳裂纹扩展的统计分布规律。 相似文献
18.
19.
In order to improve the current grinding procedure of the back-up roll of CVC hot rolling mills, the ratcheting short crack propagation behavior of medium carbon bainitic back-up roll steel was experimentally investigated under its actual work conditions, and the mechanism was theoretically analyzed based on contact mechanics and shakedown theory. After nucleation, the ratcheting short cracks propagate by the shear growth mechanism driven by the plastic strain accumulation resulting from the process of ratcheting induced by repetitive asperity contacts. They arrest on reaching the maximum depth ranging from 1.6 to 4.5 μm due to the presence of a large “quiescent zone” for crack propagation under the depth at which the maximum orthogonal shear stress is equal to the shear yield strength. At about 70–80% of the surface distress life, the cracks resume propagating by turning parallel to contact surfaces because of the greatly enhanced effect of the lubricant fluid trapped due to the crack geometry change and the residual tensile stress in vertical direction occurring upon unloading due to plastic deformation in the thin surface layer induced by the high cyclic asperity contact stresses. According to the ratcheting short crack propagation behavior and its mechanism, the probable grinding interval and grinding depth were proposed based on the preventive grinding strategy. 相似文献
20.
In this paper, creep-fatigue damage under elevated temperatures is investigated for a tube sheet-to-shell structure, which
is one of the main structures under Gen-IV class 1 components. To do this, detailed step-by-step procedures, including the
elastic structural analysis and the ASME-NH code application, are described for a defined representative load cycle. From
the sensitivity studies for various design parameters, such as hold time duration, shell thickness, and operating temperature,
it is found that a reduction of thickness can decrease the thermal bending stresses, but the negative effect is that it may
increase the primary stress and enhance the creep damage. The normal operating temperature is the most significant parameter
in the creep-fatigue design. 相似文献