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  • Table of Content
      Nov. 2000, Volume 0 Issue 11 Previous Issue    Next Issue
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    Creep Damage Evolution and Remaining Life under Two Level Stresses
    WEI Nan, JIN Yao, SUN Xun-fang
    2000, 0 (11): 3-5.  
    Abstract ( 201 HTML( PDF (788KB)( 157 Citation
    The sum of time-ratios is connected with creep loading order. It means creep damage evolution is affected by loading history. In present paper, creep law taking account of damage and hardening state was used to deduce the creep damage evolution equation, which includes loading history effect. Damage evolution and remaining life under conditions of two-level creep loading were discussed. The result shows that proposed method of predicting remaining life coincides with experiment and can reflect loading order effect.
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    Approach of Life Prediction for Creep/Fatigue Interaction
    JIN Yao, SUN Ya-fang, SUN Xun-fang, DENG Yong, LIU Hong-jie, TU Yong
    2000, 0 (11): 6-8.  
    Abstract ( 264 HTML( PDF (140KB)( 542 Citation
    Making use of loading patterns transformation, the cyclic loading with hold time is substituted by another cyclic loading without hold time. Approach of life prediction is proposed. Creep/fatigue tests is performed for both 12Cr1MoV steel and its weld metal. Result shows this approach is convenient and practical. A new parameter, creep/fatigue life ratio, is introduced to express creep/fatigue interaction behavior. Analysis shows that creep/fatigue interaction behavior of materials depends on this ratio. Positive or negative interaction behavior is not intrinsic material property, also is influenced by loading condition.
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    Research of Welding Effect on Creep Damage of High Temperature Furnace Tubes
    GONG Jian-ming, TU Shan-dong, LING Xiang, YU Hong-mei
    2000, 0 (11): 9-12.  
    Abstract ( 313 HTML( PDF (318KB)( 520 Citation
    Among the failure cases of high temperature components, premature failures of weldments have taken a large percentage that indicates the detrimental effect of welding on structural integrity. In the present paper, a local damage mechanics approach is introduced to study the damage development and creep rupture of waisted cross-weld specimens and HK-40 furnace tubes due to the presence of a weld. It is illustrated that although the weldment belongs to a creep-hard weld, damage is prone to the weld in the later period of service life, creep dmage localization occurs, and the final failure takes place in the weld. Metallographical research also indicates that the weld may have a higher damage rank. It is thus concluded that the weldments may become the weak link in HK-40 furnace tubes.
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    Thermal-mechanical Fatigue Crack Growth Behavior in Ni3Al Superalloy
    HE Yu-huai, LIU Shao-lun
    2000, 0 (11): 13-14.  
    Abstract ( 264 HTML( PDF (97KB)( 400 Citation
    The experimental study about the behavior of thermal-mechanical fatigue (TMF) crack growth were conducted in Ni3Al intermetallic compound, which is candidate material for the heat components of high thrust-weight aeronautical engine with thermal cycle of 450 to 990℃. It was investigated that the effects of phase angle, load-hold, temperature and frequency on thermal-mechanical fatigue crack growth rate in Ni3Al superalloy, respectively. The key results drawn from this study are as follows:Increasing temperature and decreasing frequency accelerate crack growth rate; The crack growth rate of in-phase thermal-mechanical fatigue is much larger than that of out-phase thermal-mechanical fatigue and both of them are between the crack growth rates of 450℃ isothermal and 990℃ isothermal tests; Load-hold also accelerates crack growth.
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    The Creep Behavior under Long Term Deformation of Ni-base Superalloy Udimet500
    DONG Jian-xin, XIE Xi-shan, Fujio Abe
    2000, 0 (11): 15-17.  
    Abstract ( 251 HTML( PDF (295KB)( 301 Citation
    Incorporating with microstructure analysis, the creep deformation behaviors of Udimet 500 alloy at the temperature of both 800℃ and 900℃ under different long term deformation conditions were systematically analyzed. The results show that the creep deformation of this alloy is mainly controlled by the creep accelerating stage, or the creep deformation get to its stable stage quickly and then get to the third stage instantaneously. Perhaps the coarsening of gamma prime phase, the precipitation and growth of phases at the grain boundary and the precipitation of sigma phase are the primary reasons for creep acceleration of this alloy.
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    Effect of Temperature on Dynamic Properties for SiCp Reinforced Aluminum Matrix Composites with Low Ductility
    ZHANG Xing-an, LIU Shao-lun, TANG Zhen-ting
    2000, 0 (11): 18-20.  
    Abstract ( 242 HTML( PDF (132KB)( 201 Citation
    In this paper, these parameter, impact energy, yield stress, maximum stress, and strain have been obtained using impacting energy testing for SiCp reinforced aluminum matrix composites with low ductility. Effect of temperature on these parameters has been analyzed, and it has been suggested that the first peak value in relationship curve about total energy and temperature are acted as the optimum used temperature.
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    The Evaluation of Fracture Toughness for SiC Ceramic at Elevated Temperatures
    BAI Shi-hong, QIAO Sheng-ru, SHU Wu-bing, LI Mei
    2000, 0 (11): 21-22,25.  
    Abstract ( 362 HTML( PDF (195KB)( 663 Citation
    The influence of different testing methods (CN, SENB and SEPB) on fracture toughness KIC of recrystallized SiC ceramic at elevated temperatures has been investigated by four point bending method. The result indicate that KIC is various corresponding to different testing methods, at lower temperatures, the KIC for CN is bigger, while that is smaller for SEPB. When T<800℃, the fracture toughness of SiC changes unapparently with increasing temperatures for different testing methods; when T>800℃, the fracture toughness shows different trend with increasing temperatures:the KIC for CN increases and it decreases for SENB, but it exhibits no change for SEPB with increasing temperatures.
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    The Development of GH4145 Superalloy
    YU Mao-jun, WANG Wei-li
    2000, 0 (11): 23-25.  
    Abstract ( 340 HTML( PDF (173KB)( 486 Citation
    On the base of inconel X-750 alloy, GH4145 alloy was developed by adding Mg,Zr and B.Using proper heat treatment, GH4145 alloy possesses higher plasticity at the temperature range of 500~700℃,and eliminates notch sensitivities compared with Inconel X-750. The new alloy can meet the requirement of steam turbine fastening bolts.
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    Multiphase Strengthening of Al3Ti based Intermetallic Alloy
    ZHANG Jin-xu, FU Yun-yi, SUN Jian, HU Geng-xiang
    2000, 0 (11): 26-28,31.  
    Abstract ( 377 HTML( PDF (233KB)( 386 Citation
    A Nb-modified multiphase Al3Ti-based alloy,which has a L12 matrix with dispersed Al3(Ti,Nb) precipitates,has been developed. The room temperature and high temperature strength of this alloy are higher than the ternary Al3Ti alloys and its toughness is also improved. The microstructures and mechanical properties of the alloy prepared by different techniques have been investigated. It is determined that the Al67Ti24Mn8Nb1 alloy consolidated from high energy ball milled powders has a much higher strength and better fracture toughness than others. The temperature dependence of yield strength also shows very good results. SEM and TEM investigations were conducted to explore the mechanisms of strengthening and toughening.
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    The Probabilistic Calculation of Creep Damage and the Parameter Sensitivity Analysis
    ZHOU Chang-yu, TU Shan-dong
    2000, 0 (11): 29-31.  
    Abstract ( 297 HTML( PDF (772KB)( 292 Citation
    Due to the scatter and uncertainty of material property data and damage development model, the result of creep was uncertainty. The influence of uncertainty can be quantitatively analyzed by probabilistic method. A new probabilistic creep damage model was proposed in this paper based on the deterministic model. And the sensitivity of the parameters was analyzed in detail. The probabilistic creep damage model would provide the effective means to assess the reliability of the high temperature components.
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    Thermal-mechanical Fatigue behavior of Nickel based Superalloy K417
    LIU Feng, WANG Yue-chen, ZHANG Hui, AI Su-hua, WANG Zhong-guang
    2000, 0 (11): 32-34,37.  
    Abstract ( 296 HTML( PDF (264KB)( 428 Citation
    The thermal-mechanical fatigue behavior of a nickel-based superalloy K417 was investigated. Both In-phase and Out-phase thermal-mechanical experiments were conducted using computer controlled servohydroulic uniaxial fatigue machine equipped with ceramic extensometer. The experiment result shows that to compare with low cycle fatigue, both In-phase and Out-phase thermal mechanical fatigue leads much less fatigue lives, though there is difference between In-phase and Out-phase case. Further more, to reveal the thermal-mechanical fatigue mechanism more clearly, the time-dependent component (creep) and time-independent component (pure plastic deformation) of the inelastic components should be separated. At last, SEM observation reveals the fractography,and the micro-mechanism of cracking is discussed.
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    Prediction of Creep Crack Incubation Time and Its Propagation by Local Damage Approach
    ZHOU Bing-sheng, WANG Zheng-dong, TANG Xiao-ying
    2000, 0 (11): 35-37.  
    Abstract ( 258 HTML( PDF (152KB)( 196 Citation
    Based on the local damage hypot hesis and utilizing similarity solutions,this paper presents a procedure for estimating the incubation time prior to the onset of creep crack growth.Also, a theoretical equation for the calculation of creep crack growth rate has been derived. Tests under constant load have been carried out in a 2.25Cr-1Mo steel. It has been shown that the experimental time is close to the lower limit because of high constraint.Damage evolution analy zed by FEM indicates that creep crack growth rate(CCGR)fits experimental result swell,while ignoring of uncrack ligament deterioration make prediction of CCGR slightly under experimental data.
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    Fracture and Microstructure Analysis of Nickel-based Single Crystal Superalloy DD100
    ZHOU Can-dong, YU Jin-xing, ZHANG Yuan-hu, YANG Zheng-rui, JIANG Guo-chang
    2000, 0 (11): 38-40,44.  
    Abstract ( 311 HTML( PDF (206KB)( 215 Citation
    the microstructure of DD100 single crystal superalloy has been analyzed. The results show that there are many γ/γ′ eutectic with γ'-depleted white band and many island-like microstructures distributing dispersingly on the γ/γ′ microstructure. There also exists much microporosity in the microstructure. The margin of the γ/γ′ eutectics and island-like microstructures and microporosity in DD100 are the sites which are favorable for the initiating of the cracks and are also the easy ways for the crack propagation.
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    Nonlinear Creep Behaviour of Viscoelastic Medium with Structure Changes by Means of Irreversible Thermodynamics
    DAI Guang-ze
    2000, 0 (11): 41-44.  
    Abstract ( 267 HTML( PDF (1604KB)( 369 Citation
    A metal subjected to a constant tensile load at an elevated temperature will creep and undergo a time-dependent increase in length. In the present study, the so-called structure parameters are firstly introduced to indicate their influence on Helmholtz free energy. The corresponding nonlinear evolution equation is then derived based on the linear one proposed by Biot by means of irreversible thermodynamics. As a worked example, the above nonlinear evolution equation is applied to an ideal viscoelastic solid rod to predict its uniaxial creep behaviour. Under the strain-induced anisotropic effect due to the configurational structure changes, the rod gradually becomes transversely isotropic during the deformation process. The final results show that when the applied longitudinal stress is below a certain value, the creep strain will get towards an asymptotic value at a decreasing strain rate, and that when it is over this, the creep strain will initially increase at a decreasing strain rate and then it will increase at an accelerative rate.
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    Study on t he Low Cycle Fatigue Property of a Nickel Based Superalloy IN738LC at Elevated Temperature
    CHEN Hong-jun, H. Wever
    2000, 0 (11): 45-48.  
    Abstract ( 304 HTML( PDF (207KB)( 374 Citation
    The low cycle fatigue(LCF) property of two kinds of specimens that one is of cubic γ′phase with 450nm edge length and another is of ball one with 80nm diameter, which was done by special heat treatment, was investigated at 1223K. It is found that the mechanism of cyclic deformation is different under different strain rate whether the specimens contain either larger γ′phase or smaller one. At the high strain rate, the deformation mechanism is a shearing of γ′phase and at the low strain rate,the mechanism is a creep mode. In the test for specimens with small γ′phase a cyclic soft ening is observed.
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