Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology. Microstructures and effect o...Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology. Microstructures and effect of thermal-cooling cycle treatment (TCCT) on the thermal expansion behaviors of three composites were investigated. The results show that the composites are free of porosity and SiC/Al2O3 particles are distributed uniformly. Inflections at about 300℃ are observed in coefficient of thermal expansion (CTE) versus temperature curves of two SiCp/Al composites, and this characteristic is not affected by TCCT. The TCCT has significant effect on thermal expansion behavior of SiCp/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles. However, no inflection is observed in Al2O3p/Al composite, while TCCT has effect on CTE of Al2O3p/Al composite. These results should be due to different relaxation behavior of internal stress in three composites.展开更多
The reinforcement distribution of metal matrix composites (MMCs) plays an important role in low cycle fatigue. Thus, it is essential to study the effect of reinforcement clustering on the crack initiation mechanism of...The reinforcement distribution of metal matrix composites (MMCs) plays an important role in low cycle fatigue. Thus, it is essential to study the effect of reinforcement clustering on the crack initiation mechanism of MMCs. In this study, the effect of reinforcement clustering on the microcrack initiation mechanism in a cast hybrid MMC reinforced with SiC particles and Al2O3 whiskers was investigated experimentally and numerically. Experimental results showed that microcracks always initiated in the particle-matrix interface, located in the cluster of the reinforcements. The interface debonding occurred in the fracture which created additional secondary microcracks due to continued fatigue cycling. The microcrack coalesced with other nearby microcracks caused the final fracture. To validate the experimental results on the microcrack initiation, three dimensional unit cell models using finite element method (FEM) were developed. The stress distribution in both the reinforcement clustering and non-clustering regions was analyzed. The numerical analysis showed that high stresses were developed on the reinforcements located in the clustering region and stress concentration occurred on the particle-matrix interface. The high volume fraction reinforced hybrid clustering region experienced greater stresses than that of the SiC particulate reinforced clustering region and low volume fraction reinforced hybrid clustering region. Besides, the stresses developed on the non-clustering region with particle-whisker series orientation were reasonably higher than that of the non-clustering region with particle-whisker parallel orientation. The high volume fraction reinforced hybrid clustering region is found to be highly vulnerable to initiate crack in cast hybrid MMC during low cycle fatigue.展开更多
In this paper,we intreduce the concept and discuss the properties of minimum cycle of row vector in a generalized circulant Fuzzy matrix. We present a new expression for circulant Fuzzy matrix,and discuss some propert...In this paper,we intreduce the concept and discuss the properties of minimum cycle of row vector in a generalized circulant Fuzzy matrix. We present a new expression for circulant Fuzzy matrix,and discuss some properties of the idempotent elements of the semigroup of generalized circulant Fuzzy matrixes in connection with minimum cycle of row vector.展开更多
The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composit...The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.展开更多
We present a novel formulation, based on the latest advancement in polynomial system solving via linear algebra, for identifying limit cycles in general n-dimensional autonomous nonlinear polynomial systems. The condi...We present a novel formulation, based on the latest advancement in polynomial system solving via linear algebra, for identifying limit cycles in general n-dimensional autonomous nonlinear polynomial systems. The condition for the existence of an algebraic limit cycle is first set up and cast into a Macaulay matrix format whereby polynomials are regarded as coefficient vectors of monomials. This results in a system of polynomial equations whose roots are solved through the null space of another Macaulay matrix. This two-level Macaulay matrix approach relies solely on linear algebra and eigenvalue computation with robust numerical implementation. Furthermore, a state immersion technique further enlarges the scope to cover also non-polynomial (including exponential and logarithmic) limit cycles. Application examples are given to demonstrate the efficacy of the proposed framework.展开更多
In this paper, we obtain explicit formulae for the number of 7-cycles and the total number of cycles of lengths 6 and 7 which contain a specific vertex v<sub>i</sub> in a simple graph G, in terms of the ad...In this paper, we obtain explicit formulae for the number of 7-cycles and the total number of cycles of lengths 6 and 7 which contain a specific vertex v<sub>i</sub> in a simple graph G, in terms of the adjacency matrix and with the help of combinatorics.展开更多
The AIN particle reinforced aluminum matrix composites with 50% volume fraction were fabricated by squeeze-casting technology. The thermal expansion behavior and its response to thermal cycling were studied between 20...The AIN particle reinforced aluminum matrix composites with 50% volume fraction were fabricated by squeeze-casting technology. The thermal expansion behavior and its response to thermal cycling were studied between 20℃ and 400℃. Compared with four theoretical models, the measured CTEs of the composite lie within the elastic bounds derived by Schapery’s analysis. Schapery’s model and Kerner’s model agree well with the CTEs of the composites at lower temperature and elevated temperature, respectively. Strain hysteresis was observed between heating and cooling curves during cycling. This was attributed primarily to the anelastic behavior of the matrix induced by matrix residual stresses.展开更多
The paper proposes a matrix-based approach that a designer can use to evaluate the sustainability of one or more design solutions in the conceptual phase of a product development process. The methodology is structured...The paper proposes a matrix-based approach that a designer can use to evaluate the sustainability of one or more design solutions in the conceptual phase of a product development process. The methodology is structured in two main phases. In the first one, a data structure, called Augmented-DSM (Design Structure Matrix), has to be drawn in order to collect design information such as functional links among product components, indicators that provide information about the life cycle of each element, connections with the environment and toward other systems. The matrix is based on a DSM format, where new records were introduced to store and organize different types of data and an editing protocol was formalized. In the second stage, a set of procedures have to be applied in order to evaluate sustainability of a design solution and compare it with the others. The presented procedures, in fact, allow designers to assess a product in its proper characteristics, evaluate a device during its use stage and verify the coherence of links present in the functional model. This new approach is conceived to manage different performance indicators and, as a support tool, it is an attempt to aid designers in a quantitative evaluation.展开更多
交流–电网换相换流器型高压直流输电(AC-line commutated converter high voltage direct current,AC-(LCC)DC)混联系统的电磁暂态初始化在计算模型上可表述为一个扰动的可分无源动力系统。因此,将无源动力系统的显式保积算法应用于电...交流–电网换相换流器型高压直流输电(AC-line commutated converter high voltage direct current,AC-(LCC)DC)混联系统的电磁暂态初始化在计算模型上可表述为一个扰动的可分无源动力系统。因此,将无源动力系统的显式保积算法应用于电磁暂态初始化计算。采用相空间分析方法,对基于逐次积分法的电磁暂态初始化方法的收敛条件以及收敛速率进行了定量分析。在上述基础上,提出了一类新的、系统化的初始化计算方法,该方法计算格式简单、易于编程,在计算效率上具有明显的优势。算例结果验证了所提方法的有效性。展开更多
基金Project(20080430895) supported by China Postdoctoral Science FoundationProject(2008RFQXG045) supported by Special Fund of Technological Innovation of HarbinProject(HITQNJS.2009.021) supported by Development Program for Outstanding Young Teachers in Harbin Institute of Technology
文摘Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology. Microstructures and effect of thermal-cooling cycle treatment (TCCT) on the thermal expansion behaviors of three composites were investigated. The results show that the composites are free of porosity and SiC/Al2O3 particles are distributed uniformly. Inflections at about 300℃ are observed in coefficient of thermal expansion (CTE) versus temperature curves of two SiCp/Al composites, and this characteristic is not affected by TCCT. The TCCT has significant effect on thermal expansion behavior of SiCp/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles. However, no inflection is observed in Al2O3p/Al composite, while TCCT has effect on CTE of Al2O3p/Al composite. These results should be due to different relaxation behavior of internal stress in three composites.
文摘The reinforcement distribution of metal matrix composites (MMCs) plays an important role in low cycle fatigue. Thus, it is essential to study the effect of reinforcement clustering on the crack initiation mechanism of MMCs. In this study, the effect of reinforcement clustering on the microcrack initiation mechanism in a cast hybrid MMC reinforced with SiC particles and Al2O3 whiskers was investigated experimentally and numerically. Experimental results showed that microcracks always initiated in the particle-matrix interface, located in the cluster of the reinforcements. The interface debonding occurred in the fracture which created additional secondary microcracks due to continued fatigue cycling. The microcrack coalesced with other nearby microcracks caused the final fracture. To validate the experimental results on the microcrack initiation, three dimensional unit cell models using finite element method (FEM) were developed. The stress distribution in both the reinforcement clustering and non-clustering regions was analyzed. The numerical analysis showed that high stresses were developed on the reinforcements located in the clustering region and stress concentration occurred on the particle-matrix interface. The high volume fraction reinforced hybrid clustering region experienced greater stresses than that of the SiC particulate reinforced clustering region and low volume fraction reinforced hybrid clustering region. Besides, the stresses developed on the non-clustering region with particle-whisker series orientation were reasonably higher than that of the non-clustering region with particle-whisker parallel orientation. The high volume fraction reinforced hybrid clustering region is found to be highly vulnerable to initiate crack in cast hybrid MMC during low cycle fatigue.
文摘In this paper,we intreduce the concept and discuss the properties of minimum cycle of row vector in a generalized circulant Fuzzy matrix. We present a new expression for circulant Fuzzy matrix,and discuss some properties of the idempotent elements of the semigroup of generalized circulant Fuzzy matrixes in connection with minimum cycle of row vector.
文摘The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.
文摘We present a novel formulation, based on the latest advancement in polynomial system solving via linear algebra, for identifying limit cycles in general n-dimensional autonomous nonlinear polynomial systems. The condition for the existence of an algebraic limit cycle is first set up and cast into a Macaulay matrix format whereby polynomials are regarded as coefficient vectors of monomials. This results in a system of polynomial equations whose roots are solved through the null space of another Macaulay matrix. This two-level Macaulay matrix approach relies solely on linear algebra and eigenvalue computation with robust numerical implementation. Furthermore, a state immersion technique further enlarges the scope to cover also non-polynomial (including exponential and logarithmic) limit cycles. Application examples are given to demonstrate the efficacy of the proposed framework.
文摘In this paper, we obtain explicit formulae for the number of 7-cycles and the total number of cycles of lengths 6 and 7 which contain a specific vertex v<sub>i</sub> in a simple graph G, in terms of the adjacency matrix and with the help of combinatorics.
基金The autbors gratefully acknowledge the support of this workby the National Natural Science Foundation of China(Grant No.50071019).
文摘The AIN particle reinforced aluminum matrix composites with 50% volume fraction were fabricated by squeeze-casting technology. The thermal expansion behavior and its response to thermal cycling were studied between 20℃ and 400℃. Compared with four theoretical models, the measured CTEs of the composite lie within the elastic bounds derived by Schapery’s analysis. Schapery’s model and Kerner’s model agree well with the CTEs of the composites at lower temperature and elevated temperature, respectively. Strain hysteresis was observed between heating and cooling curves during cycling. This was attributed primarily to the anelastic behavior of the matrix induced by matrix residual stresses.
文摘The paper proposes a matrix-based approach that a designer can use to evaluate the sustainability of one or more design solutions in the conceptual phase of a product development process. The methodology is structured in two main phases. In the first one, a data structure, called Augmented-DSM (Design Structure Matrix), has to be drawn in order to collect design information such as functional links among product components, indicators that provide information about the life cycle of each element, connections with the environment and toward other systems. The matrix is based on a DSM format, where new records were introduced to store and organize different types of data and an editing protocol was formalized. In the second stage, a set of procedures have to be applied in order to evaluate sustainability of a design solution and compare it with the others. The presented procedures, in fact, allow designers to assess a product in its proper characteristics, evaluate a device during its use stage and verify the coherence of links present in the functional model. This new approach is conceived to manage different performance indicators and, as a support tool, it is an attempt to aid designers in a quantitative evaluation.
文摘交流–电网换相换流器型高压直流输电(AC-line commutated converter high voltage direct current,AC-(LCC)DC)混联系统的电磁暂态初始化在计算模型上可表述为一个扰动的可分无源动力系统。因此,将无源动力系统的显式保积算法应用于电磁暂态初始化计算。采用相空间分析方法,对基于逐次积分法的电磁暂态初始化方法的收敛条件以及收敛速率进行了定量分析。在上述基础上,提出了一类新的、系统化的初始化计算方法,该方法计算格式简单、易于编程,在计算效率上具有明显的优势。算例结果验证了所提方法的有效性。