A new model for the analysis of fatigue crack growth in the metal structures was proposed. This model shows a promising capability of explaining various fatigue phenomena. The new crack growth model is further complet...A new model for the analysis of fatigue crack growth in the metal structures was proposed. This model shows a promising capability of explaining various fatigue phenomena. The new crack growth model is further completed by a continuous empirical formula for estimating the value of variable fracture toughness during crack propagation and a modified continuous equation for the crack tip stress/strain constraint factor used to calculate the stress intensity factor at the opening level. The prediction results are proved to agree well with the observed phenomena in test.展开更多
The effects of surface state and applied stress on the stress corrosion cracking （SCC） behaviors of thermally treated （TT） Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using...The effects of surface state and applied stress on the stress corrosion cracking （SCC） behaviors of thermally treated （TT） Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit （ground）, shot-peened （SP） and electro-polished （EP） and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.展开更多
作为氢能输送的关键技术,掺氢天然气管道中减压波特性的研究直接关系到管道的安全运行。针对纯氢与掺氢天然气管道中的减压波行为进行了仿真研究,旨在探究不同因素对减压波特性的影响。通过对比多种状态方程,发现天然气发热量计算方法—...作为氢能输送的关键技术,掺氢天然气管道中减压波特性的研究直接关系到管道的安全运行。针对纯氢与掺氢天然气管道中的减压波行为进行了仿真研究,旨在探究不同因素对减压波特性的影响。通过对比多种状态方程,发现天然气发热量计算方法—2008(Gas Research Institute Equation for Gas—2008,GERG—2008)状态方程在高压条件下对掺氢天然气密度的计算更为精确。基于等熵假设,建立了减压波传播速度的一维模型,并通过实验数据验证了模型的可靠性。研究结果表明,随着掺氢比的增加,减压波速度显著提升,从而降低了管道裂纹扩展的风险;初始压力的降低和初始温度的升高均有助于减缓减压波速度,抑制管道韧性开裂。研究结果为掺氢天然气管道的安全设计和运行提供了理论依据。展开更多
Time-dependant reliability is analyzed for the flexural cracking of prestressed concrete bridges under service limit state. The limit state function and random variables are derived from Chinese highway bridge design ...Time-dependant reliability is analyzed for the flexural cracking of prestressed concrete bridges under service limit state. The limit state function and random variables are derived from Chinese highway bridge design specifications. For deterioration of structural performances, chloride-induced reinforcement corrosion is emphasized. Through integrating first order reliability method （FORM） and time discretized approach, the time-variant reliability is evaluated. For illustrative propose, the reliability of a typical simply supported prestressed concrete beam is exemplified.展开更多
A new generic reaction in the form of PC_i→PC_m+[i,m]→PC_m+λi,m coke+surplusage has been proposed for describing the catalytic cracking behavior of petroleum narrow cuts or pseudo-components(PCs),where the rate con...A new generic reaction in the form of PC_i→PC_m+[i,m]→PC_m+λi,m coke+surplusage has been proposed for describing the catalytic cracking behavior of petroleum narrow cuts or pseudo-components(PCs),where the rate constant formula is derived from the transition state theory and the coking amount is correlated to the properties of the intermediate substance [i,m].In composing the cracking reaction network for feedstock and product oils,only the product PC m of the proposed generic reaction is used,which together with a criterion for excluding exothermic reactions,distinctly reduces the number of reactions in the network.With the proposed cracking reaction scheme coupled with special pseudo-components,a predictive one-dimensional steady state model for fluid catalytic cracking risers is formulated in the sense that for a given riser and given catalyst,the model parameters are independent of stock oils,product schemes and other operational conditions.The great correlating and predicting capability of the resulted model is tested with production data in different scenarios of four commercial risers.展开更多
基金supported by the Innovative Scholars Support Program of Jiangsu Province, 2008-2010
文摘A new model for the analysis of fatigue crack growth in the metal structures was proposed. This model shows a promising capability of explaining various fatigue phenomena. The new crack growth model is further completed by a continuous empirical formula for estimating the value of variable fracture toughness during crack propagation and a modified continuous equation for the crack tip stress/strain constraint factor used to calculate the stress intensity factor at the opening level. The prediction results are proved to agree well with the observed phenomena in test.
基金supported by the National Science and Technology Major Project(No. 20112x06004–009)the National Natural Science Foundation of China (No. 51025104)
文摘The effects of surface state and applied stress on the stress corrosion cracking （SCC） behaviors of thermally treated （TT） Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit （ground）, shot-peened （SP） and electro-polished （EP） and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.
文摘作为氢能输送的关键技术,掺氢天然气管道中减压波特性的研究直接关系到管道的安全运行。针对纯氢与掺氢天然气管道中的减压波行为进行了仿真研究,旨在探究不同因素对减压波特性的影响。通过对比多种状态方程,发现天然气发热量计算方法—2008(Gas Research Institute Equation for Gas—2008,GERG—2008)状态方程在高压条件下对掺氢天然气密度的计算更为精确。基于等熵假设,建立了减压波传播速度的一维模型,并通过实验数据验证了模型的可靠性。研究结果表明,随着掺氢比的增加,减压波速度显著提升,从而降低了管道裂纹扩展的风险;初始压力的降低和初始温度的升高均有助于减缓减压波速度,抑制管道韧性开裂。研究结果为掺氢天然气管道的安全设计和运行提供了理论依据。
文摘Time-dependant reliability is analyzed for the flexural cracking of prestressed concrete bridges under service limit state. The limit state function and random variables are derived from Chinese highway bridge design specifications. For deterioration of structural performances, chloride-induced reinforcement corrosion is emphasized. Through integrating first order reliability method （FORM） and time discretized approach, the time-variant reliability is evaluated. For illustrative propose, the reliability of a typical simply supported prestressed concrete beam is exemplified.
基金Supported by the National Natural Science Foundation of China(21676012)the Fundamental Research Funds for the Central Universities(Project YS1404)the National High Technology Research and Development Program of China(2007AA04Z191)
文摘A new generic reaction in the form of PC_i→PC_m+[i,m]→PC_m+λi,m coke+surplusage has been proposed for describing the catalytic cracking behavior of petroleum narrow cuts or pseudo-components(PCs),where the rate constant formula is derived from the transition state theory and the coking amount is correlated to the properties of the intermediate substance [i,m].In composing the cracking reaction network for feedstock and product oils,only the product PC m of the proposed generic reaction is used,which together with a criterion for excluding exothermic reactions,distinctly reduces the number of reactions in the network.With the proposed cracking reaction scheme coupled with special pseudo-components,a predictive one-dimensional steady state model for fluid catalytic cracking risers is formulated in the sense that for a given riser and given catalyst,the model parameters are independent of stock oils,product schemes and other operational conditions.The great correlating and predicting capability of the resulted model is tested with production data in different scenarios of four commercial risers.
