A β SiC whisker reinforced pure aluminum composites expected to exhibit high strain rate superplasticity has been successfully fabricated by a new processing route consisting of pressure infiltration, extrusion with ...A β SiC whisker reinforced pure aluminum composites expected to exhibit high strain rate superplasticity has been successfully fabricated by a new processing route consisting of pressure infiltration, extrusion with a low extrusion ratio and rolling. The composites exhibite a total elongation of 220%～380% in the initial strain rates within 1.0×10 -2 ～1.0×10 -1 s -1 and at 893～903 K. According to differential thermal analysis(DTA) and microstructure observation, it is concluded that an appropriately small amount of liquid phase is necessary to cause a good high strain rate superplasticity in aluminum matrix composites in addition to fine and uniform microstructure.展开更多
In this paper,the superplastic characteristics of the beta-SiC whisker reinforced 2024aluminum composite, fabricated by squeeze casting and hot-rolling after extrusion were investigated. The compsite had a fine grain ...In this paper,the superplastic characteristics of the beta-SiC whisker reinforced 2024aluminum composite, fabricated by squeeze casting and hot-rolling after extrusion were investigated. The compsite had a fine grain size of about 2μm, and exhibited a strain rate sensitivity of about 0.35 and a maximum elongation of 350% at an initial strain rate of 1.1×10-1s-1 at 803K. In addition, the superplastic deformation mechanisme of the composite were also examined.展开更多
60% white corundum used for aggregate, 5% aluminium powder for fixed additions and 35% various additives for matrix were prepared for specimens 1#,2#,3#. They were mixed uniformly with the suitable resin as a binder a...60% white corundum used for aggregate, 5% aluminium powder for fixed additions and 35% various additives for matrix were prepared for specimens 1#,2#,3#. They were mixed uniformly with the suitable resin as a binder and pressed under pressure of 315 ton forging press, then dried at 200℃ for 24 h. Effects of various additives on 1500 ℃×2 h creep properties of Al3CON reinforced corundum composite were researched. The experimenal results show that creep coefficients of specimens 1#,2#,3# at 1500 ℃×2 h are 1.4×10^- 4, -9.4×10^-4, -22.6×10^-4, respectively. Crushing strength of the slide plate added with suitable additive A after fired at 1500 ℃ ×3 h reaches to 225 MPa, the creep rate is positive all the time from 0% to 0.014% at 1500 ℃ for 2 h. The microstructure result analysis shows that reinforced phases of Al3CON fiber composite have been formed after fired with Al powder in coke at high temperatures for specimen 1#, and the strength of the composite is increased. The hot modulus of rupture is up to 59 MPa at 1400 ℃ and the RUL is obviously higher than that at 1700 ℃. Its service life is two times as that of Al2O3-C slide plate when used in the process of pouring steel. The mechanism of creep rate resistance of the composites can be discovered by means of SEM and EDAX analysis. It is concluded that the active Al3CON and Al2O3 multiphases that were formed by N2 in gas, C, Al and Al2O3 inside the matrix of the composites during in-situ reaction,which gives the composites outstanding creep rate resistance for the dense zone resuiting from Al3CON oxidation that inhibits contraction at the high temperature. Besides, the matrix will turn into the multiphase with high refractoriness, N content and its Al3CON reinforced fiber will further increase accordingly. In addition, Al3CON formed by Al2O3 and C, Al in the matrix with N2 in gas will inhibit the creep rate and also greatly improve the creep rate resistance of the composites.展开更多
TiN_p/1N90Al composite was fabricated by powder metallurgy method with a reinforcement volume fraction of 15%. The tensile experiment, DSC and SEM were used to study the high strain rate superplasticity of the TiN_p/1...TiN_p/1N90Al composite was fabricated by powder metallurgy method with a reinforcement volume fraction of 15%. The tensile experiment, DSC and SEM were used to study the high strain rate superplasticity of the TiN_p/1N90Al composite. The DSC result shows that the incipient melting temperature of the TiN_p/1N90Al composite is 906K. The tensile tests were carried out over a range of deformation temperature from 918 to 928K and strain rate from 1.7 to 1.7×10 -3 s -1. The maximum elongation of 201% is realized at 923K with a strain rate of 1.7×10 -1 s -1. Otherwise all the elongations are higher than 100% in the strain rate range of 3.3×10 -2-6.7×10 -1 s -1 at the three deformation temperatures. The curves of m value of the TiN_p/1N90Al composite can be divided into two stages with the variation of strain rate at different deformation temperatures and the critical strain rate of 10 -1 s -1. When the strain rate is higher than 10 -1 s -1, the m values of the three curves are smaller than 0.3, but the m values of the three curves are about 0.37 when the strain rate is higher than 10 -1 s -1.展开更多
To solve the flight safety problem caused by nonlinear instabilities（category II pilot induced oscillations, PIOs） of the closed-loop pilot-vehicle system with rate-limiting actuator, the antiwindup（AW） compensati...To solve the flight safety problem caused by nonlinear instabilities（category II pilot induced oscillations, PIOs） of the closed-loop pilot-vehicle system with rate-limiting actuator, the antiwindup（AW） compensation method to avoid category II PIOs is investigated. Firstly, the AW compensation method originally used for controlling input magnitude limited system is introduced, then this method is extended for controlling input rate-limiting system through a circle criterion theorem. Secondly, the establishment of the AW compensator is transformed into the solving of linear matrix inequalities. Finally, an AW compensator establishment algorithm for the closed-loop pilot-vehicle system with the rate-limiting actuator is obtained. The effectiveness of the AW compensation method to avoid category II PIOs is validated by time-domain simulations,and compared with rate-limited feedback（RLF） command rate compensation method. The results show that the AW compensation method can effectively suppress category II PIOs and maintain the nominal performance when the closed-loop pilot-vehicle system is normal. Unlike the command rate compensator which works upon system uninterruptedly, the AW compensation method affects the closed-loop pilot-vehicle system only when the rate-limiting of actuator is activated, so it is a novel PIO avoidance method.展开更多
The effects of modified inorganic water-based matrix content on the properties of friction material was studied in the present paper, the regular pattern of the influence of friction material’s friction coefficient a...The effects of modified inorganic water-based matrix content on the properties of friction material was studied in the present paper, the regular pattern of the influence of friction material’s friction coefficient and wear rate on matrix content have been got. It provides technical support for the study of cold forming friction material, and provides the basis for the development and production of the green pollution-free friction material.展开更多
Adiabatic shear behavior and the corresponding mechanism of TiB2/Al composites were researched by split Hopkinson pressure bar （SHPB）.Results show that the flow stresses of the TiB2/Al composites exhibit softening t...Adiabatic shear behavior and the corresponding mechanism of TiB2/Al composites were researched by split Hopkinson pressure bar （SHPB）.Results show that the flow stresses of the TiB2/Al composites exhibit softening tendency with the increasing of strain rates. All the composites fail in splitting and cutting with a 45 degree, and the phase transformed bands of molten aluminum are found on the adiabatic shear layers. The deformation behavior and shear localization of the TiB2/Al composites specimens were simulated by finite element code MSC.Marc. The Johnson-Cook model was used to describe the thermo-viscoplastic response of the specimen material. There was unanimous between the numerical result and the experimental result on the location of the adiabatic shear band. From the numerical simulation and experiment, it was concluded that the instantaneous failure of the composite was ascribed due to the local low strength area where the formation of adiabatic shear band was, and the stress condition had significant effect on the initiation and propagation of adiabatic shear band （ASB）.展开更多
We propose a Rate-Distortion (RD) optimized strategy for frame-dropping and scheduling of multi-user conversa- tional and streaming videos. We consider a scenario where conversational and streaming videos share the fo...We propose a Rate-Distortion (RD) optimized strategy for frame-dropping and scheduling of multi-user conversa- tional and streaming videos. We consider a scenario where conversational and streaming videos share the forwarding resources at a network node. Two buffers are setup on the node to temporarily store the packets for these two types of video applications. For streaming video, a big buffer is used as the associated delay constraint of the application is moderate and a very small buffer is used for conversational video to ensure that the forwarding delay of every packet is limited. A scheduler is located behind these two buffers that dynamically assigns transmission slots on the outgoing link to the two buffers. Rate-distortion side information is used to perform RD-optimized frame dropping in case of node overload. Sharing the data rate on the outgoing link between the con- versational and the streaming videos is done either based on the fullness of the two associated buffers or on the mean incoming rates of the respective videos. Simulation results showed that our proposed RD-optimized frame dropping and scheduling ap- proach provides significant improvements in performance over the popular priority-based random dropping (PRD) technique.展开更多
Aluminium metal matrix composites are finding increased applications in many areas. Adding of the third element to the metal matrix make the composite hybrid. This paper presents the study on the surface roughness cha...Aluminium metal matrix composites are finding increased applications in many areas. Adding of the third element to the metal matrix make the composite hybrid. This paper presents the study on the surface roughness characteristics of a hybrid aluminium metal matrix (Al6061-SiC-Al2O3) composites. The experimental studies were carried out on a lathe. The composites were prepared using the liquid metallurgy technique, in which 3, 6 and 9 wt % of particulates SiC and Al2O3 were dispersed in the base matrix. The obtained cast composites were carefully machined. The characteristics that influence the surface roughness such as feed rate, depth of cut and cutting speed were studied, which made the analysis come to a conclusion that the surface roughness is increases with the increase of feed rate and it reduces the surface roughness with the increase of cutting speed.展开更多
现有的基于评论与评分的方法通常使用相同的模型分别对用户和项目进行建模,但其局限在浅层特征层面,如果能够充分挖掘用户个性化偏好与项目深层特征,则会促进模型学习两种表示之间更深层次的关系从而提升预测结果.因此,本文提出一种融...现有的基于评论与评分的方法通常使用相同的模型分别对用户和项目进行建模,但其局限在浅层特征层面,如果能够充分挖掘用户个性化偏好与项目深层特征,则会促进模型学习两种表示之间更深层次的关系从而提升预测结果.因此,本文提出一种融合评论与评分的个性化推荐方法,用于深度挖掘用户偏好与项目特征.在对评论文本进行处理的过程中,首先通过ALBERT获得评论文本中单词的向量表示.其次,提出的个性化注意模块将用户的个性化偏好信息与评论文本向量结合,得到深层的基于评论的用户表示.在Amazon Digital Music、Grocery and Gourmet Food、Video Games数据集上进行实验,本文方法较基准方法在NDCG指标上分别提升了5%、11%、8%.代码已在https://github.com/ZehuaChenLab/paperCode/tree/main/DuWenNa/PRM-RR公开.展开更多
文摘A β SiC whisker reinforced pure aluminum composites expected to exhibit high strain rate superplasticity has been successfully fabricated by a new processing route consisting of pressure infiltration, extrusion with a low extrusion ratio and rolling. The composites exhibite a total elongation of 220%～380% in the initial strain rates within 1.0×10 -2 ～1.0×10 -1 s -1 and at 893～903 K. According to differential thermal analysis(DTA) and microstructure observation, it is concluded that an appropriately small amount of liquid phase is necessary to cause a good high strain rate superplasticity in aluminum matrix composites in addition to fine and uniform microstructure.
文摘In this paper,the superplastic characteristics of the beta-SiC whisker reinforced 2024aluminum composite, fabricated by squeeze casting and hot-rolling after extrusion were investigated. The compsite had a fine grain size of about 2μm, and exhibited a strain rate sensitivity of about 0.35 and a maximum elongation of 350% at an initial strain rate of 1.1×10-1s-1 at 803K. In addition, the superplastic deformation mechanisme of the composite were also examined.
基金Funded by the National Torch Plan of China (No. 2005EB031110)the Key Scientific and Technical Innovation Project of Xi’an University of Ar-chitecture and Technology ( No. ZX 0402)
文摘60% white corundum used for aggregate, 5% aluminium powder for fixed additions and 35% various additives for matrix were prepared for specimens 1#,2#,3#. They were mixed uniformly with the suitable resin as a binder and pressed under pressure of 315 ton forging press, then dried at 200℃ for 24 h. Effects of various additives on 1500 ℃×2 h creep properties of Al3CON reinforced corundum composite were researched. The experimenal results show that creep coefficients of specimens 1#,2#,3# at 1500 ℃×2 h are 1.4×10^- 4, -9.4×10^-4, -22.6×10^-4, respectively. Crushing strength of the slide plate added with suitable additive A after fired at 1500 ℃ ×3 h reaches to 225 MPa, the creep rate is positive all the time from 0% to 0.014% at 1500 ℃ for 2 h. The microstructure result analysis shows that reinforced phases of Al3CON fiber composite have been formed after fired with Al powder in coke at high temperatures for specimen 1#, and the strength of the composite is increased. The hot modulus of rupture is up to 59 MPa at 1400 ℃ and the RUL is obviously higher than that at 1700 ℃. Its service life is two times as that of Al2O3-C slide plate when used in the process of pouring steel. The mechanism of creep rate resistance of the composites can be discovered by means of SEM and EDAX analysis. It is concluded that the active Al3CON and Al2O3 multiphases that were formed by N2 in gas, C, Al and Al2O3 inside the matrix of the composites during in-situ reaction,which gives the composites outstanding creep rate resistance for the dense zone resuiting from Al3CON oxidation that inhibits contraction at the high temperature. Besides, the matrix will turn into the multiphase with high refractoriness, N content and its Al3CON reinforced fiber will further increase accordingly. In addition, Al3CON formed by Al2O3 and C, Al in the matrix with N2 in gas will inhibit the creep rate and also greatly improve the creep rate resistance of the composites.
文摘TiN_p/1N90Al composite was fabricated by powder metallurgy method with a reinforcement volume fraction of 15%. The tensile experiment, DSC and SEM were used to study the high strain rate superplasticity of the TiN_p/1N90Al composite. The DSC result shows that the incipient melting temperature of the TiN_p/1N90Al composite is 906K. The tensile tests were carried out over a range of deformation temperature from 918 to 928K and strain rate from 1.7 to 1.7×10 -3 s -1. The maximum elongation of 201% is realized at 923K with a strain rate of 1.7×10 -1 s -1. Otherwise all the elongations are higher than 100% in the strain rate range of 3.3×10 -2-6.7×10 -1 s -1 at the three deformation temperatures. The curves of m value of the TiN_p/1N90Al composite can be divided into two stages with the variation of strain rate at different deformation temperatures and the critical strain rate of 10 -1 s -1. When the strain rate is higher than 10 -1 s -1, the m values of the three curves are smaller than 0.3, but the m values of the three curves are about 0.37 when the strain rate is higher than 10 -1 s -1.
基金supported by the National Basic Research Program(973Program)(2015CB755805)the National Natural Science Foundation of China(61374145)
文摘To solve the flight safety problem caused by nonlinear instabilities（category II pilot induced oscillations, PIOs） of the closed-loop pilot-vehicle system with rate-limiting actuator, the antiwindup（AW） compensation method to avoid category II PIOs is investigated. Firstly, the AW compensation method originally used for controlling input magnitude limited system is introduced, then this method is extended for controlling input rate-limiting system through a circle criterion theorem. Secondly, the establishment of the AW compensator is transformed into the solving of linear matrix inequalities. Finally, an AW compensator establishment algorithm for the closed-loop pilot-vehicle system with the rate-limiting actuator is obtained. The effectiveness of the AW compensation method to avoid category II PIOs is validated by time-domain simulations,and compared with rate-limited feedback（RLF） command rate compensation method. The results show that the AW compensation method can effectively suppress category II PIOs and maintain the nominal performance when the closed-loop pilot-vehicle system is normal. Unlike the command rate compensator which works upon system uninterruptedly, the AW compensation method affects the closed-loop pilot-vehicle system only when the rate-limiting of actuator is activated, so it is a novel PIO avoidance method.
文摘The effects of modified inorganic water-based matrix content on the properties of friction material was studied in the present paper, the regular pattern of the influence of friction material’s friction coefficient and wear rate on matrix content have been got. It provides technical support for the study of cold forming friction material, and provides the basis for the development and production of the green pollution-free friction material.
基金the National Engineering Research Center Open Fund(No.2011007B)Natural Science Foundation of GuangDong Province(No.10451064101004631)
文摘Adiabatic shear behavior and the corresponding mechanism of TiB2/Al composites were researched by split Hopkinson pressure bar （SHPB）.Results show that the flow stresses of the TiB2/Al composites exhibit softening tendency with the increasing of strain rates. All the composites fail in splitting and cutting with a 45 degree, and the phase transformed bands of molten aluminum are found on the adiabatic shear layers. The deformation behavior and shear localization of the TiB2/Al composites specimens were simulated by finite element code MSC.Marc. The Johnson-Cook model was used to describe the thermo-viscoplastic response of the specimen material. There was unanimous between the numerical result and the experimental result on the location of the adiabatic shear band. From the numerical simulation and experiment, it was concluded that the instantaneous failure of the composite was ascribed due to the local low strength area where the formation of adiabatic shear band was, and the stress condition had significant effect on the initiation and propagation of adiabatic shear band （ASB）.
基金Project (No. STE1093/1-1) supported by the German ResearchFoundation, Germany
文摘We propose a Rate-Distortion (RD) optimized strategy for frame-dropping and scheduling of multi-user conversa- tional and streaming videos. We consider a scenario where conversational and streaming videos share the forwarding resources at a network node. Two buffers are setup on the node to temporarily store the packets for these two types of video applications. For streaming video, a big buffer is used as the associated delay constraint of the application is moderate and a very small buffer is used for conversational video to ensure that the forwarding delay of every packet is limited. A scheduler is located behind these two buffers that dynamically assigns transmission slots on the outgoing link to the two buffers. Rate-distortion side information is used to perform RD-optimized frame dropping in case of node overload. Sharing the data rate on the outgoing link between the con- versational and the streaming videos is done either based on the fullness of the two associated buffers or on the mean incoming rates of the respective videos. Simulation results showed that our proposed RD-optimized frame dropping and scheduling ap- proach provides significant improvements in performance over the popular priority-based random dropping (PRD) technique.
文摘为应对新能源机组随机波动导致的外送断面过载约束复杂多变的问题,提出一种计及新能源特性的自动发电控制(automatic generation control,AGC)断面越限预防和校正控制方法。首先,提出计及新能源特性、涵盖主站-厂站-机组三级架构的AGC断面功率越限控制模型;其次,基于潮流转移比矩阵快速计算N-1故障后线路负载率矩阵,快速评估AGC断面功率越限风险;最后,推导线路N-1故障后负载率相对发电机组出力的灵敏度,明确不同机组功率调节对断面功率的差异化影响,以新能源机组消纳最大、AGC机组调节量最小为控制原则,提出基于线路负载率灵敏度的AGC断面越限校正控制方法。在PSD Power Tools中搭建实际电网仿真算例验证了所提方法的正确性和有效性。
文摘Aluminium metal matrix composites are finding increased applications in many areas. Adding of the third element to the metal matrix make the composite hybrid. This paper presents the study on the surface roughness characteristics of a hybrid aluminium metal matrix (Al6061-SiC-Al2O3) composites. The experimental studies were carried out on a lathe. The composites were prepared using the liquid metallurgy technique, in which 3, 6 and 9 wt % of particulates SiC and Al2O3 were dispersed in the base matrix. The obtained cast composites were carefully machined. The characteristics that influence the surface roughness such as feed rate, depth of cut and cutting speed were studied, which made the analysis come to a conclusion that the surface roughness is increases with the increase of feed rate and it reduces the surface roughness with the increase of cutting speed.
文摘现有的基于评论与评分的方法通常使用相同的模型分别对用户和项目进行建模,但其局限在浅层特征层面,如果能够充分挖掘用户个性化偏好与项目深层特征,则会促进模型学习两种表示之间更深层次的关系从而提升预测结果.因此,本文提出一种融合评论与评分的个性化推荐方法,用于深度挖掘用户偏好与项目特征.在对评论文本进行处理的过程中,首先通过ALBERT获得评论文本中单词的向量表示.其次,提出的个性化注意模块将用户的个性化偏好信息与评论文本向量结合,得到深层的基于评论的用户表示.在Amazon Digital Music、Grocery and Gourmet Food、Video Games数据集上进行实验,本文方法较基准方法在NDCG指标上分别提升了5%、11%、8%.代码已在https://github.com/ZehuaChenLab/paperCode/tree/main/DuWenNa/PRM-RR公开.
