共查询到17条相似文献，搜索用时 265 毫秒
1.
Fatigue and fracture behavior of nickel-based superalloy Inconel 718 up to the very high cycle regime 总被引：2，自引：0，他引：2
Xian-feng Ma Zheng Duan Hui-ji Shi Ryosuke Murai Eiichi Yanagisawa 《浙江大学学报(A卷英文版)》2010,11(10):727-737
The fatigue and fracture behavior of nickel-based superalloy Inconel 718 was investigated up to the very high cycle regime under rotary bending tests at room temperature. It was found that this superalloy can still fracture after exceeding 107 cycles. Fractographic analysis revealed that there was a transition from fatigue crack initiation at multi-sites to single initiation with decreasing stress levels. The fracture surface can be divided into four areas according to the appearance, associated with fracture mechanics analysis of the corresponding stress intensity factors. The fracture mechanism dominant in each area was disclosed by scanning electron microscope examination and analyzed in comparison with those obtained from the crack growth tests. Subsequently, life prediction modeling was proposed by estimating the crack initiation and propagation stage respectively. It was found that Chan （2003）＇s model for initiation life and the Paris law for growth life can provide comparable predictions against the experimental life. 相似文献
2.
The fracture processes of concrete were described by a cohesive crack model based on initial toughness criterion. The corresponding analytical method to predict the instability state was proposed. In this model, the initial toughness was adopted as the crack propagation criterion and the weight function method was used to calculate the stress intensity factor and the crack opening displacement caused by the cohesive stress. The unstable toughness can be easily obtained using the proposed method without measuring parameters at the critical state that was necessary in traditional methods. The proposed method was verified by existing experimental data of wedge splitting specimens with different grades of concrete and the sensitivity of the results on the tensile softening curve was discussed. The results demonstrate that the proposed method can well predict the peak load, the critical effective crack length, and the unstable toughness of concrete specimens. Moreover, the calculated unstable toughness is not sensitive to the tensile softening curve. 相似文献
3.
Calculation Model of Equivalent Strength for Induced Crack Based on Double-K Fracture Theory and Its Optimizing Setting in RCC Arch Dam 总被引：2，自引：0，他引：2
By means of fracture testing on roller-compacted concrete (RCC) three-point bending beams with two different specimen sizes, the P-CMOD complete curve for RCC was gained. Furthermore, by applying double-K fracture theory, KIC^ini,KIC^un, as well as the critical effective crack length and the critical crack tip opening displacement, were evaluated. Based on the double-K fracture parameters above, the calculation model of equivalent strength for induced crack was established, thus the calculation method on its initiation, stable propagation and unstable fracture was ascertained. Moreover, the finite element simulation analysis of stress field in ShaPai arch dam and the on-site observational splaying points of induced crack at different altitudes validated the reliability of the model. Finally, crack inducer‘s optimal setting in RCC arch dam was studied. It improves the design level of induced crack in RCC arch dam and satisfies the necessity of engineering practice. 相似文献
4.
Fatigue tests were conducted on tapered plain concrete prism specimens under triaxial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2fc and the upper stress ranged from 0.20ft to 0.65ft. Three constant lateral pressures were 0.1fc, 0.2fc and 0.3fc respectively. Based on the results, the three-stage evolution nile of the fatigue stiffness, maximttm(minimum) longitudinal strain and damage were analyzed, and a unified S-N curve to calculate fatigue strength factors was worked out. The results show that the fatigue strength and fatigue life under triaxial constant-amplitude tension-compression cyclic loading are smaller than those under uniaxial fatigue condition. Moreover, the secondary strain creep rate is related to the fatigue life, a formula for describing their relation was derived. The investigation of this paper can provide information for the fatigue design of concrete structures. 相似文献
5.
Software has been developed for digital control of WDW series testing machine and the measurement of fracture toughness by modularized design. Development of the software makes use of multi-thread and serial communication techniques, which can accurately control the testing machine and measure the fracture toughness in real-time. Three-point bending specimens were used in the measurement. The software operates stably and reliably, expanding the function of WDW series testing machine. 相似文献
6.
Junaidi Syarif Agung Iswadi Mariyam Jameelah Ghazali Zainuddin Sajuri Mohd Zaidi Omar 《浙江大学学报(A卷英文版)》2013,14(12):906-914
The effect of solute Cu and Cu precipitates on the wear behavior of ferritic iron under an unlubricated condition was investigated. The specific wear rate of Cu-containing steel abruptly decreased up to 50 N of load, and then gradually decreased with further increased load. The specific wear rate of the as-quenched specimen, in which Cu was in a solid solution, was the lowest among all the specimens at low loads, and all specimens had almost the same specific wear rate at high loads. Subsurface observation showed that the hardness increments of all specimens decreased with increased depth below the worn surface. The as-quenched specimen had a relatively large depth of deformed region than the other specimens even though the increments in hardness were almost the same for all specimens at low loads. With the same hardness at an unworn state, the as-quenched and over-aged specimens exhibited a substantial increase in hardness and large deformed regions below the worn surfaces. This finding indicated that the enhancement in plastic deformation and work hardening led to the decrease in the specific wear rate of the as-quenched specimen at low loads and the improvement in the wear resistance of all specimens at high loads. 相似文献
7.
Aiming at the large deformation and support problems of high-stress and broken-expansion surrounding rock, and taking 1 000 m level roadway of Mine II in Jinchuan as the research object, an investigation on the deformation and damage of roadway surrounding rock and an analysis of its mechanism were carried out. The gray correlation theory was used in support scheme optimization design. First, causes and mechanism of deformation of the 1 000 m horizontal transport channel were analyzed through field investigation, laboratory test and data processing methods. We arguued that poor engineering geological conditions and deep pressure increases were the main factors, and the deformation mechanism was mainly the ground deformation pressure. Second, the gray correlation theory was used to construct supporting optimization decision method in the deep roadway. This method more comprehensively considers various factors, including construction, costs, and supporting material functions. The combined support with pre-stressed anchor cables, shotcrete layer, bolt and metal net was put forward according to the actual roadway engineering characteristics. Finally, 4 support schemes were put forward for new roadways. The gray relational theory was applied to optimizing the supporting method, undertaking technical and economic comparison to obtain the correlation degree, and accordingly the schemes were evaluated. It was concluded as follows： the best was the flexible retaining scheme using the steel strand anchor; the second best was the one using plate anchors on the top and rigid common screw steel bolt on the two sides; the ttiird was; the rigid common screw steel bolt in full section of roadway; and the worst is the planished steel rigid support. The optimized scheme was applied to the 1000 m level of new excavation roadway. The results show that the roadway surrounding rock can reach a stable state after 5 to 6 months monitoring, with a convergence rate less than 1 mm/d. 相似文献
8.
The failure mode and adhesion of thermal barrier coating (TBC) 8YSZ (ZrO2+8% (w/w) Y2O3) deposited on NiCoCrAlTaY bond coat by atmospheric plasma spraying were investigated. A grooved modified three-point bending specimen that can generate a single interface crack to facilitate the control of crack growth was adopted for testing, which was conducted at the ambient temperature of 100 °C. The morphology and composition of fractured surfaces were examined by means of a scanning electron microscopy (SEM) and an energy disperse spectroscopy (EDS). Images and spectrum show that cracks are initiated and propagated exclusively within YSZ layer adjacent to top/bond coat interface. The load-displacement curves obtained exhibit similar shapes that indicate two distinct stages in crack initiation and stable crack growth. Finite element analyses were performed to extract the adhesion strength of the TBCs. The delamination toughness of the plasma-sprayed 8YSZ coatings at 100 °C, in terms of critical strain energy release rate Gc, can be reliably obtained from an analytical solution. 相似文献
9.
Broadband ultrasound signals will produce distortion in viscoacoustic medium, which may influence the accuracy of time-of-flight (TOF) measurement. Under the condition of single-frequency acoustic source, the wave propagation process in viscoacoustic medium was analyzed and an approximate solution of the wave propagation was given. Instances of broadband ultrasound were analyzed and simulated based on the single-frequency results. A single-frequency matching pursuits (SFMP) algorithm was then introduced to solve the waveform distortion problem. Time-frequency decomposition was applied to extracting the single-frequency compositions from broadband ultrasound signals, and then these compositions were sent to the matching pursuits (MP) algorithm for calculating the TOF parameters. Compared with the broadband signals, the shapes of extracted single-frequency signals change more slightly as distance and attenuation coefficient increase. The residuals of SFMP were far less than those of MP algorithm. Experimental results show that the SFMP algorithm is able to eliminate waveform distortion of broadband ultrasound in viscoacoustic medium, which helps improve the accuracy of TOF measurement. 相似文献
10.
The European Structural Integrity Assessment Procedure(SINTAP) was applied to the assessment of welded joints of the API 5L X65 pipeline steel with an assumed embedded flaw and surface flaw at the weld toe. At default level (level 0), the assessment point was established by estimating fracture toughness value KIC conservatively from Charpy energy test data. At the same time, the analysis level 1 (basic level)was applied based on the fracture toughness CTOD. Then the two assessment levels were compared. The assessment results show that all assessment points are located within the failure lines of analysis levels 0 and 1. So the welded joint of the pipeline is safe. It can be concluded that the assessment based on Charpy absorbed energy is practicable when other fracture toughness data are not available, or cannot be easily obtained. The results are conservative. 相似文献
11.
提出了一种利用非对称三点弯曲加载下的单边垂直切槽深梁试件(SEVNDB)开展岩石Ⅰ-Ⅱ复合断裂韧度测试方法。通过有限元法对试件的无量纲应力强度因子进行了数值分析与标定,研究了无量纲应力强度因子YⅠ、YⅡ及无量纲T应力T*与裂纹长度a、支座间距S1、S2之间的关系,定量刻画了实现纯Ⅱ型加载对应的裂纹长度a、支座间距(S1和S2)数值。研究结果表明,该方法在不改变试样裂缝倾角的前提下,通过调整裂缝长度a和支座间距S1、S2,即可方便地实现从纯Ⅰ型到纯Ⅱ型任意复合度载荷作用下的岩石断裂韧度测试。 相似文献
12.
郑如杰毕贤顺 《福建工程学院学报》2017,(3):224-228
利用断裂力学方法对含有裂纹混凝土试件的断裂韧度进行了研究。通过预制不同裂纹深度的混凝土试件,采用三点弯曲试验方法对含裂纹混凝土梁的断裂韧度进行实验,同时利用ABAQUS软件,采用最大主应力牵引损伤开裂准则与线性软化损伤模型进行数值模拟。结果表明,实验结果和数值模拟比较一致,最大误差不超过15%,当初始缝纹长度为40~120 mm时,起裂断裂韧度KiniIC变化幅度较小,失稳断裂韧度KunIC有明显的减小趋势。 相似文献
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1 Ｉｎｔｒｏｄｕｃｔｉｏｎ Ｔｈｅｄｅｓｔｒｕｃｔｉｏｎｏｆｒｏｃｋｗａｓａｌｗａｙｓｒｅｌｅｖａｎｔｔｏｔｈｅｔｉｍｅｆａｃｔｏｒ,ｗｈｉｃｈｗａｓｔｙｐｉｃａｌｌｙｍａｎｉｆｅｓｔｅｄａｓｔｈｅｔｉｍｅｄｅｐｅｎｄｅｎｔｇｒａｄｕａｌｂｒｅａｋｉｎｇｐｒｏｃｅｓｓ.Ｔｈｅｄｏｍｉｎａｎｔｆａｃｔｏｒｄｕｒｉｎｇｔｈｅｄｅｓｔｒｕｃｔｉｖｅｐｒｏｃｅｓｓｗａｓｅｘｔｅｎｓｉｏｎｏｆｍａｃｒｏｃｒａｃｋｓ,ｗｈｉｃｈｈａｄｂｅｅｎｔｅｓｔｅｄｏｕｔｂｙｓｉｔｅｓｕｒｖｅｙｉｎＴｈｒｅｅＧｏｒｇｅｓ… 相似文献
15.
Based on the traditional theory of fracture, time-dependence of rock fracture is taken into account and the creep fracture
criteria are given. The effect of the microcrack zone on fracture toughness is analyzed. Finally, a model for time prediction
of rheological fracture is derived and its feasibility is proven.
Supported by the National Natural Science Foundation of China (59809005) and the Science Foundation of Shanghai Municipal
Commission of Science and Technology (96QF14009) 相似文献
16.
采用反射式焦散线方法对水泥石中添加玻璃纤维后的强度变化问题进行了实验研究.首先,制作了不添加与添加玻璃纤维的2种水泥石试件,并采用镜面移植方法在试件的表面进行反射镜面的制作与加工.然后,采用多火花式高速摄影系统对试件在冲击断裂过程中的裂纹扩展和裂纹尖端焦散线的情景进行记录.最后,对2种试件的裂纹起裂时间、动态应力强度因子和裂纹扩展速度等参数进行计算和对比分析.分析发现,玻璃纤维提高了水泥石的断裂韧度、延迟了裂纹的起裂时间,对水泥石具有明显的强化效应.实验结果对研究水泥石的断裂力学属性特征具有一定意义. 相似文献
17.
The definition ofJ-integral of interfacial crack was introduced.The three.point bending tests were carried out to obtain the criticaI lOading values when the interfacial crack initiation occurred between coatings and substrates.The finite element analysis(FEA)was adopted to analyze the stress distribution in the specimens and compute the J-integral of the interfaciaI crack between LX88A coating and Chinese 0345 steel.The results showed that the average value of critical J-integral iS 0.70 N/m.which can be taken as the fracture parameter to evaluate the interfaciaI fracture behavior for the three-point bending specimens of LX88A coating/Q345 steel system. 相似文献