A fundamental step in the production of an industrial catalyst is its crushing strength assessment. Limited literature exists in which the strength reliability of supported catalysts is investigated from production to...A fundamental step in the production of an industrial catalyst is its crushing strength assessment. Limited literature exists in which the strength reliability of supported catalysts is investigated from production to their application in a reactor. In this work, cylindrical supports were prepared by pelletizing high poros- ity γ-alumina powder, and Cu-Znf/γ-Al2O3 catalysts were prepared by impregnation of the pelletized γ-alumina supports with an aqueous solution of copper and zinc nitrates. The support-forming variables, such as binder concentration, compaction pressure, calcination temperature, and drying procedure were investigated. The Weibull method was used to analyze the crushing strength data of the supports, and the fresh and used catalysts before and after the low-temperature water gas shift reaction. Support formation at a 50 wt% binder concentration, 1148 MPa compaction pressure, 500 ℃ calcination temperature, and rapid drying （100 ℃, 8 h） led to the maximum support mechanical reliability. The most reliable catalyst with respect to simultaneous appropriate catalytic performance and mechanical strength was prepared from a support with the lowest mean crushing strength （26.25 MPa）. This work illustrates the impor- tance of the Weibull modulus as a useful mechanical reliability index in manufacturing a supported solid catalyst.展开更多
In this paper, we proposed a dynamic stress–strength model for coherent system. It is supposedthat the system consists of n components with initial random strength and each component issubjected to random stresses. T...In this paper, we proposed a dynamic stress–strength model for coherent system. It is supposedthat the system consists of n components with initial random strength and each component issubjected to random stresses. The stresses, applied repeatedly at random cycle times, will causethe degradation of strength. In addition, the number of cycles in an interval is assumed to followa Poisson distribution. In the case of the strength and stress random variables following exponential distributions, the expression for the reliability of the proposed dynamic stress–strengthmodel is derived based on survival signature. The reliability is estimated by using the best linearunbiased estimation (BLUE). Considering the Type-II censored failure times, the best linear unbiased predictors (BLUP) for the unobserved coherent system failure times are developed basedon the observed failure times. Monte Carlo simulations are performed to compare the BLUE ofparameters with different values and compute the BLUP. A real data set is also analysed for anillustration of the findings.展开更多
The fuzzy sets theory is introduced into the fatigue reliability analysis. The concepts of maximizing set and minimizing set are developed to decide the ordering value of each fuzzy number, and these values can be use...The fuzzy sets theory is introduced into the fatigue reliability analysis. The concepts of maximizing set and minimizing set are developed to decide the ordering value of each fuzzy number, and these values can be used to determine the order of the fuzzy numbers. On the basis of the works mentioned above, the membership function defining the fuzzy safety event can be calculated, and then the fuzzy reliability in the case of stress and fuzzy fatigue strength is deduced. An example is given to illustrate the method.展开更多
The aim of this paper is to evaluate the fatigue reliability with hybrid uncertain parameters based on a residual strength model. By solving the non-probabilistic setbased reliability problem and analyzing the reliabi...The aim of this paper is to evaluate the fatigue reliability with hybrid uncertain parameters based on a residual strength model. By solving the non-probabilistic setbased reliability problem and analyzing the reliability with randomness, the fatigue reliability with hybrid parameters can be obtained. The presented hybrid model can adequately consider all uncertainties affecting the fatigue reliability with hybrid uncertain parameters. A comparison among the presented hybrid model, non-probabilistic set-theoretic model and the conventional random model is made through two typical numerical examples. The results show that the presented hybrid model, which can ensure structural security, is effective and practical.展开更多
Ceria-stabilized tetragonal zirconia(Ce-TZP)has become an interesting alternative for the widely used yttria-stabilized zirconia(Y-TZP),whereas efforts are needed to control its microstructure in order to im-prove the...Ceria-stabilized tetragonal zirconia(Ce-TZP)has become an interesting alternative for the widely used yttria-stabilized zirconia(Y-TZP),whereas efforts are needed to control its microstructure in order to im-prove the strength of Ce-TZP ceramics.In this work,CaO was used to co-dope Ce-TZP ceramics.More specifically,0.2-2.0 mol%Ca(NO_(3))_(3)·4H_(2)O precursor-based CaO was used to dope 10 mol%ceria-stabilized zirconia.Sintering was performed at 1300,1350,or 1400℃,which is lower than the temperatures commonly applied for zirconia ceramics.The microstructure and mechanical properties were investigated and correlated,revealing that 0.2 mol%CaO-doped CeO_(2)-stabilised zirconia sintered at 1350℃ exhibited a fully dense fine-grained tetragonal ZrO_(2) microstructure with high toughness(10.4 MPa m1/2)and biax-ial bending strength(1210±43 MPa),and a narrow strength distribution(weibull modulus of 32.5).1.5 and 2.0 mol% CaO-doping resulted in excellent biaxial bending strength but wider strength distribution and lower fracture resistance.The homogeneously distributed Ca(NO_(3))_(3)·4H_(2)O precursor prevented cubic zirconia-phase formation for CaO-doping up to 2.0 mol%.CaO-doped(≥0.2 mol%)10Ce-TZP sintered at 1350℃ also highly resisted hydrothermal degradation.Furthermore,CaO-doping enabled to make Ce-TZP ceramics as translucent as different commercially available 3Y-TZP ceramics,opening possibilities to use Ce-TZP for dental restorations.展开更多
Based on the Mg58.5Cu30.5Y11 alloy, 10% Ti, 10% Be and 10% Ti70Be30 （mole fraction） were respectively added to the alloy and samples with a diameter of 3 mm were fabricated by conventional Cu-mold casting method. Th...Based on the Mg58.5Cu30.5Y11 alloy, 10% Ti, 10% Be and 10% Ti70Be30 （mole fraction） were respectively added to the alloy and samples with a diameter of 3 mm were fabricated by conventional Cu-mold casting method. The phase constituent, thermal stability and microstructure of the alloys were investigated by using X-ray diffraction, differential scanning calorimetry and scanning electron microscopy, respectively. The effects of alloying elements Ti and Be on the microstructure and mechanical properties of Mg58.sCu3o.sYll alloy were discussed. The results show that CuTi phase is distributed in （Mg0.585Cu0.305Y0.11）90Ti10 and （Mg58.5Cu30.5Y11）90（Ti0.7Be0.3）10 alloys, while CuYBe glassy phase containing CuY crystals is embedded in the matrix of （Mg58.5Cu30.5Y11）90Be10 alloy. Under uniaxial compressive loading, the largest compressive fracture strengths for （Mg58.5Cu30.5Y11）90Ti10, （Mg58.5Cu30.5Y11）90Be10 and （Mg58.5Cu30.5Y11）90（Ti0.7Be0.3）10 alloys are 797.6, 952.6 and 1007.8 MPa, respectively, and the strengths are increased by about 17%, 40% and 48% compared with Mg58.5Cu30.5Y11 alloy. The strength reliability for the three alloys is much improved according to the strength distribution region of 10 samples of each alloy.展开更多
文摘A fundamental step in the production of an industrial catalyst is its crushing strength assessment. Limited literature exists in which the strength reliability of supported catalysts is investigated from production to their application in a reactor. In this work, cylindrical supports were prepared by pelletizing high poros- ity γ-alumina powder, and Cu-Znf/γ-Al2O3 catalysts were prepared by impregnation of the pelletized γ-alumina supports with an aqueous solution of copper and zinc nitrates. The support-forming variables, such as binder concentration, compaction pressure, calcination temperature, and drying procedure were investigated. The Weibull method was used to analyze the crushing strength data of the supports, and the fresh and used catalysts before and after the low-temperature water gas shift reaction. Support formation at a 50 wt% binder concentration, 1148 MPa compaction pressure, 500 ℃ calcination temperature, and rapid drying （100 ℃, 8 h） led to the maximum support mechanical reliability. The most reliable catalyst with respect to simultaneous appropriate catalytic performance and mechanical strength was prepared from a support with the lowest mean crushing strength （26.25 MPa）. This work illustrates the impor- tance of the Weibull modulus as a useful mechanical reliability index in manufacturing a supported solid catalyst.
基金This work is supported by the National Natural Science Foundation of China[71571144,71401134,71171164,11701406]The Natural Science Basic Research Program of Shaanxi Province[2015JM1003]The Program of international Cooperation and Exchanges in Science and Technology Funded by Shaanxi Province[2016KW-033].
文摘In this paper, we proposed a dynamic stress–strength model for coherent system. It is supposedthat the system consists of n components with initial random strength and each component issubjected to random stresses. The stresses, applied repeatedly at random cycle times, will causethe degradation of strength. In addition, the number of cycles in an interval is assumed to followa Poisson distribution. In the case of the strength and stress random variables following exponential distributions, the expression for the reliability of the proposed dynamic stress–strengthmodel is derived based on survival signature. The reliability is estimated by using the best linearunbiased estimation (BLUE). Considering the Type-II censored failure times, the best linear unbiased predictors (BLUP) for the unobserved coherent system failure times are developed basedon the observed failure times. Monte Carlo simulations are performed to compare the BLUE ofparameters with different values and compute the BLUP. A real data set is also analysed for anillustration of the findings.
基金This project is supported by National Naied Science Foundation of China(59475043). Manuscript received on July 8,1999 revised m
文摘The fuzzy sets theory is introduced into the fatigue reliability analysis. The concepts of maximizing set and minimizing set are developed to decide the ordering value of each fuzzy number, and these values can be used to determine the order of the fuzzy numbers. On the basis of the works mentioned above, the membership function defining the fuzzy safety event can be calculated, and then the fuzzy reliability in the case of stress and fuzzy fatigue strength is deduced. An example is given to illustrate the method.
基金supported by the National Natural Science Foundation of China (90816024, 10872017 and 10876100)the 111 Project (B07009)the Innovation Foundation of Beihang University for PhD Graduates
文摘The aim of this paper is to evaluate the fatigue reliability with hybrid uncertain parameters based on a residual strength model. By solving the non-probabilistic setbased reliability problem and analyzing the reliability with randomness, the fatigue reliability with hybrid parameters can be obtained. The presented hybrid model can adequately consider all uncertainties affecting the fatigue reliability with hybrid uncertain parameters. A comparison among the presented hybrid model, non-probabilistic set-theoretic model and the conventional random model is made through two typical numerical examples. The results show that the presented hybrid model, which can ensure structural security, is effective and practical.
基金the China Scholarship Council(CSC No.201806460096)for financial supportthe Scientific Research-Flanders(FWO-Vlaanderen)for her post-doctoral fellowships(grant Nos.12S8418N and 12S8421N)supported by the Research Fund of KU Leuven project No.C2-17-00402 and the Fund for Scientific Research-Flanders(FWO-Vlaanderen)(grant Nos.G.0431.10N and G.0959.20N).
文摘Ceria-stabilized tetragonal zirconia(Ce-TZP)has become an interesting alternative for the widely used yttria-stabilized zirconia(Y-TZP),whereas efforts are needed to control its microstructure in order to im-prove the strength of Ce-TZP ceramics.In this work,CaO was used to co-dope Ce-TZP ceramics.More specifically,0.2-2.0 mol%Ca(NO_(3))_(3)·4H_(2)O precursor-based CaO was used to dope 10 mol%ceria-stabilized zirconia.Sintering was performed at 1300,1350,or 1400℃,which is lower than the temperatures commonly applied for zirconia ceramics.The microstructure and mechanical properties were investigated and correlated,revealing that 0.2 mol%CaO-doped CeO_(2)-stabilised zirconia sintered at 1350℃ exhibited a fully dense fine-grained tetragonal ZrO_(2) microstructure with high toughness(10.4 MPa m1/2)and biax-ial bending strength(1210±43 MPa),and a narrow strength distribution(weibull modulus of 32.5).1.5 and 2.0 mol% CaO-doping resulted in excellent biaxial bending strength but wider strength distribution and lower fracture resistance.The homogeneously distributed Ca(NO_(3))_(3)·4H_(2)O precursor prevented cubic zirconia-phase formation for CaO-doping up to 2.0 mol%.CaO-doped(≥0.2 mol%)10Ce-TZP sintered at 1350℃ also highly resisted hydrothermal degradation.Furthermore,CaO-doping enabled to make Ce-TZP ceramics as translucent as different commercially available 3Y-TZP ceramics,opening possibilities to use Ce-TZP for dental restorations.
基金Project(2011CB606301)supported by the National Basic Research Program of China
文摘Based on the Mg58.5Cu30.5Y11 alloy, 10% Ti, 10% Be and 10% Ti70Be30 （mole fraction） were respectively added to the alloy and samples with a diameter of 3 mm were fabricated by conventional Cu-mold casting method. The phase constituent, thermal stability and microstructure of the alloys were investigated by using X-ray diffraction, differential scanning calorimetry and scanning electron microscopy, respectively. The effects of alloying elements Ti and Be on the microstructure and mechanical properties of Mg58.sCu3o.sYll alloy were discussed. The results show that CuTi phase is distributed in （Mg0.585Cu0.305Y0.11）90Ti10 and （Mg58.5Cu30.5Y11）90（Ti0.7Be0.3）10 alloys, while CuYBe glassy phase containing CuY crystals is embedded in the matrix of （Mg58.5Cu30.5Y11）90Be10 alloy. Under uniaxial compressive loading, the largest compressive fracture strengths for （Mg58.5Cu30.5Y11）90Ti10, （Mg58.5Cu30.5Y11）90Be10 and （Mg58.5Cu30.5Y11）90（Ti0.7Be0.3）10 alloys are 797.6, 952.6 and 1007.8 MPa, respectively, and the strengths are increased by about 17%, 40% and 48% compared with Mg58.5Cu30.5Y11 alloy. The strength reliability for the three alloys is much improved according to the strength distribution region of 10 samples of each alloy.
