Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application f...Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application for structural components in the aerospace field,but their oxidation behavior remains largely unknown.In this study,Yb_(2)Si_(2)O_(7)modified SiC/SiC(SiC/SiC-Yb_(2)Si_(2)O_(7))mini-composites were prepared by introducing Yb_(2)Si_(2)O_(7)as anti-oxidation phase into SiC fiber bundles via Sol-Gel and depositing SiC matrix by chemical vapor deposition(CVD).Influence of Yb_(2)Si_(2)O_(7)on microstructure,mechanical property and oxidation behavior of SiC/SiC mini-composites was investigated.The results showed that after oxidation in air at 1200 and 1400℃for 50 h,the tensile strength retentions of SiC/SiC mini-composites were 77%and 69%,respectively,and the fracture morphology exhibited flat.The Yb_(2)Si_(2)O_(7)introduced by Sol-Gel partially distributed in layers,contributing to the toughening of the material.On the fracture surface,there was interlayer debonding,which extended energy dissipation mechanism of SiC/SiC mini-composites.Tensile strength of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites at room temperature was 484 MPa.After oxidation in air at 1200 and 1400℃for 50 h,the tensile strengths decreased to 425 and 374 MPa,resulting in retention rates of 88%and 77%,respectively.It displayed typical non-brittle fracture characteristics.The interface oxygen content of SiC/SiC mini-composites at the fracture surface was higher than that of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites,indicating that introduction of Yb_(2)Si_(2)O_(7)could alleviate oxygen diffusion towards the interface,and therefore improve the oxidation resistance of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites.展开更多
A novel FEM called interface finite element method(I-FEM)is proposed for the step size-varying electro-quasistatic field(EQS)in this paper.First,the corresponding equation and interface conditions for I-FEM are given....A novel FEM called interface finite element method(I-FEM)is proposed for the step size-varying electro-quasistatic field(EQS)in this paper.First,the corresponding equation and interface conditions for I-FEM are given.Then,the numerical principle of I-FEM is conducted.In the proposed method,by the inverse matrix modification lemma,the calculation amount of I-FEM is decreased greatly.Furthermore,the corresponding example is given to verify the effectiveness and correctness of IFEM.At last,the error analysis and universal promotion of the proposed I-FEM are given.Compared with the normal FEM,I-FEM can greatly decrease the calculation amount while the numerical accuracy of I-FEM is even better than the normal FEM in some case.展开更多
In this paper,a novel numerical method called interface finite volume method(I-FVM)for calculation of step-varying Electro-quasistatic(EQS)field is proposed.First,the principle of I-FVM is derived.Then,with numerical ...In this paper,a novel numerical method called interface finite volume method(I-FVM)for calculation of step-varying Electro-quasistatic(EQS)field is proposed.First,the principle of I-FVM is derived.Then,with numerical example of double layers parallel plate structure under step voltage which has an analytical solution,effectiveness and correctness of the I-FVM are verified.It can be found the calculating time of I-FVM is only 30%of normal FVM without decreasing accuracy during the whole calculating process.Furthermore,an engineering example about the electric field of DBC(Direct Bonding Copper)structure in a high voltage IGBT device is given.It can be found that accuracy of the I-FVM is the same as normal FVM,while time cost of I-FVM is only 20.8%of normal FVM.At last,the I-FVM is extended to one dimension based on the two-direction tri-diagonal matrix algorithm(TDMA)method given in this paper which can save processing of LU decomposition compared to one-dimensional traditional TDMA.In conclusion,the novel method called I-FVM proposed in this paper can decrease calculating amount for a step size varying electro-quasistatic field calculation problem.It may be a good method for large-scale EQS field calculation.展开更多
The formation of heterogeneous particle structure in skim milk powder has been investigated in a post- crystallization facility using experimental and a mathematical model. Various processing conditions were used to p...The formation of heterogeneous particle structure in skim milk powder has been investigated in a post- crystallization facility using experimental and a mathematical model. Various processing conditions were used to produce these heterogeneous structures. The experimental process parameters were used as initial and boundary conditions for the model. The modelled data agreed well with the experimental data. The experimental and modelling results show that the powder processed at high water activity （aw = 0.7） with low initial moisture content （X0 = 0.01 kg/kg） developed a crystalline surface layer while the core of the particle remained amorphous. This structure is referred to as an egg-shell structure. The powder that was processed at low water activity （αw = 0.1） with high initial moisture content （X0 = 0.2 kg/kg） developed a crystalline core while the surface of the particle remained amorphous. This structure is referred to as an egg-yolk structure. Understanding the dependency of particle microstructures on the processing conditions could be useful when developing procedures to control the drying equipment because the particle microstructure affects the physicochemical properties of the powder and potential applications and behaviour of the powder.展开更多
基金National Natural Science Foundation of China(52222202)National Key R&D Program of China(2022YFB3707700)+2 种基金Project of Shanghai Science and Technology Innovation Action Plan(21511104800)Shanghai Pilot Program for Basic Research-Chinese Academy of Science,Shanghai Branch(JCYJ-SHFY-2021-001)Science Center for Gas Turbine Project(P2022-B-Ⅳ-001-001)。
文摘Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application for structural components in the aerospace field,but their oxidation behavior remains largely unknown.In this study,Yb_(2)Si_(2)O_(7)modified SiC/SiC(SiC/SiC-Yb_(2)Si_(2)O_(7))mini-composites were prepared by introducing Yb_(2)Si_(2)O_(7)as anti-oxidation phase into SiC fiber bundles via Sol-Gel and depositing SiC matrix by chemical vapor deposition(CVD).Influence of Yb_(2)Si_(2)O_(7)on microstructure,mechanical property and oxidation behavior of SiC/SiC mini-composites was investigated.The results showed that after oxidation in air at 1200 and 1400℃for 50 h,the tensile strength retentions of SiC/SiC mini-composites were 77%and 69%,respectively,and the fracture morphology exhibited flat.The Yb_(2)Si_(2)O_(7)introduced by Sol-Gel partially distributed in layers,contributing to the toughening of the material.On the fracture surface,there was interlayer debonding,which extended energy dissipation mechanism of SiC/SiC mini-composites.Tensile strength of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites at room temperature was 484 MPa.After oxidation in air at 1200 and 1400℃for 50 h,the tensile strengths decreased to 425 and 374 MPa,resulting in retention rates of 88%and 77%,respectively.It displayed typical non-brittle fracture characteristics.The interface oxygen content of SiC/SiC mini-composites at the fracture surface was higher than that of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites,indicating that introduction of Yb_(2)Si_(2)O_(7)could alleviate oxygen diffusion towards the interface,and therefore improve the oxidation resistance of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites.
基金supported by National Natural Science Foundation of China under Grant No.52077073.
文摘A novel FEM called interface finite element method(I-FEM)is proposed for the step size-varying electro-quasistatic field(EQS)in this paper.First,the corresponding equation and interface conditions for I-FEM are given.Then,the numerical principle of I-FEM is conducted.In the proposed method,by the inverse matrix modification lemma,the calculation amount of I-FEM is decreased greatly.Furthermore,the corresponding example is given to verify the effectiveness and correctness of IFEM.At last,the error analysis and universal promotion of the proposed I-FEM are given.Compared with the normal FEM,I-FEM can greatly decrease the calculation amount while the numerical accuracy of I-FEM is even better than the normal FEM in some case.
基金the National Natural Science Foundation of China under Grant 52077073by the Fundamental Research Funds for the Central Universities under Grant2021MS001.
文摘In this paper,a novel numerical method called interface finite volume method(I-FVM)for calculation of step-varying Electro-quasistatic(EQS)field is proposed.First,the principle of I-FVM is derived.Then,with numerical example of double layers parallel plate structure under step voltage which has an analytical solution,effectiveness and correctness of the I-FVM are verified.It can be found the calculating time of I-FVM is only 30%of normal FVM without decreasing accuracy during the whole calculating process.Furthermore,an engineering example about the electric field of DBC(Direct Bonding Copper)structure in a high voltage IGBT device is given.It can be found that accuracy of the I-FVM is the same as normal FVM,while time cost of I-FVM is only 20.8%of normal FVM.At last,the I-FVM is extended to one dimension based on the two-direction tri-diagonal matrix algorithm(TDMA)method given in this paper which can save processing of LU decomposition compared to one-dimensional traditional TDMA.In conclusion,the novel method called I-FVM proposed in this paper can decrease calculating amount for a step size varying electro-quasistatic field calculation problem.It may be a good method for large-scale EQS field calculation.
文摘The formation of heterogeneous particle structure in skim milk powder has been investigated in a post- crystallization facility using experimental and a mathematical model. Various processing conditions were used to produce these heterogeneous structures. The experimental process parameters were used as initial and boundary conditions for the model. The modelled data agreed well with the experimental data. The experimental and modelling results show that the powder processed at high water activity （aw = 0.7） with low initial moisture content （X0 = 0.01 kg/kg） developed a crystalline surface layer while the core of the particle remained amorphous. This structure is referred to as an egg-shell structure. The powder that was processed at low water activity （αw = 0.1） with high initial moisture content （X0 = 0.2 kg/kg） developed a crystalline core while the surface of the particle remained amorphous. This structure is referred to as an egg-yolk structure. Understanding the dependency of particle microstructures on the processing conditions could be useful when developing procedures to control the drying equipment because the particle microstructure affects the physicochemical properties of the powder and potential applications and behaviour of the powder.
