A near-equiatomic NiTi shape memory alloy was fabricated by rapid solidification process through vacuum arc melting followed by vacuum suction casting in water-cooled thick copper mold. The rapidly solidified （or suc...A near-equiatomic NiTi shape memory alloy was fabricated by rapid solidification process through vacuum arc melting followed by vacuum suction casting in water-cooled thick copper mold. The rapidly solidified （or suction cast） NiTi alloy shows much finer grains and homogenous microstructure, in particular a uniform distribution of various fine precipitates, compared to the conventional cast one. The resultant alloy also exhibits the homogenous Ni distribution in the matrix of the alloy, allowing the martensitic transformation to take place throughout the NiTi alloy matrix simultaneously and resulting in sharper transformation peaks compared to the conventional cast alloy. Moreover, the suction cast NiTJ alloy shows a significant improvement over the conventional cast one, in terms of possessing higher deformation recovery rates and displaying the increased compressive strength and damping capacity by 4% and 20%, respectively.展开更多
The damping performance evaluation for electromechanical oscillations in power systems is crucial for the stable operation of modern power systems.In this paper,the connection between two commonly-used damping perform...The damping performance evaluation for electromechanical oscillations in power systems is crucial for the stable operation of modern power systems.In this paper,the connection between two commonly-used damping performance evaluation methods,i.e.,the damping torque analysis(DTA)and energy flow analysis(EFA),are systematically examined and revealed for the better understanding of the oscillatory damping mechanism.First,a concept of the aggregated damping torque coefficient is proposed and derived based on DTA of multi-machine power systems,which can characterize the integration effect of the damping contribution from the whole power system.Then,the pre-processing of measurements at the terminal of a local generator is conducted for EFA,and a concept of the frequency-decomposed energy attenuation coefficient is defined to screen the damping contribution with respect to the interested frequency.On this basis,the frequency spectrum analysis of the energy attenuation coefficient is employed to rigorously prove that the results of DTA and EFA are essentially equivalent,which is valid for arbitrary types of synchronous generator models in multi-machine power systems.Additionally,the consistency between the aggregated damping torque coefficient and frequency-decomposed energy attenuation coefficient is further verified by the numerical calculation in case studies.The relationship between the proposed coefficients and the eigenvalue(or damping ratio)is finally revealed,which consolidates the application of the proposed concepts in the damping performance evaluation.展开更多
The rapid solidification of Fe-17%Mn alloy was performed to investigate the influence of cooling rate on its damping performance and martensitic transformation mechanism. A proper heat treatment was also carried out t...The rapid solidification of Fe-17%Mn alloy was performed to investigate the influence of cooling rate on its damping performance and martensitic transformation mechanism. A proper heat treatment was also carried out to clarify its coupled effects with rapid solidification. The stacking fault probability and martensitic transformation temperature were determined to demonstrate their relationship with the cooling rate and the heat treatment process. With the increase of cooling rate, the volume fraction of ε-martensite increased and the stacking fault probability of ε-martensite was enhanced. The formation ofε-martensite phase was remarkable for the increase of damping capacity and microhardness. It was found that rapid solidification was beneficial for the formation of ε-martensite and the improvement of damping capacity. This effect can be facilitated by the incorporation of the heat treatment process.展开更多
Wood composites glued with thermosetting synthetic resins tend to show inadequate damping performance caused by the cured resinous matrix.Waste rubber maintains prominent elasticity and is feasible to be an optional m...Wood composites glued with thermosetting synthetic resins tend to show inadequate damping performance caused by the cured resinous matrix.Waste rubber maintains prominent elasticity and is feasible to be an optional modifier.To that end,composite panels of granulated tire rub-ber(GTR)powders and thermal-mechanically pulped wood fibers were fabricated in this study.Urea formaldehyde(UF)resin was applied as the bonding agent(10%based on wood/rubber total weight).Dynamical mechanical analysis(DMA)was conducted to disclose the thermo-mechanical behaviors of the rubber-filled wood fiber composites.Influence of two technical pa-rameters,i.e.,GTR powder size(0.55-1.09 mm)and addition content(10%,20%and 30%based on wood/rubber total weight),was specifically discussed.The results showed that storage modu-lus(E’)of the rubber-filled composite decreased while loss factor(tan𝛿)increased monotonously along with elevated temperature.A steady“plateau”region among 110-170°C was found where both E’and tan𝛿keep constant.Accordingly,tan𝛿showed two peak values at 103-108 and 231-233°C due to glass transition of lignin and thermal degradation of hemicellulose,respectively.Addition of rubber fillers resulted in lower bending and internal bonding strengths as well as stor-age modulus values.When the temperature was above 183°C,all the rubber-filled composites showed higher tan𝛿values than the control.The findings above fully demonstrate the improved damping performance of the UF-bonded wood fiber composites on account of rubber component.Further work is still needed to optimize the rubber/fiber interfacial bonding strength.展开更多
基金supported by the National Natural Science Foundation of China under grant Nos. 50871039 and 51205135Guangdong Provincial Natural Science Foundation under grant Nos. 10151064101000017 and S2011040001436the Fundamental Research Funds for Central Universities (SCUT2011ZM0001)
文摘A near-equiatomic NiTi shape memory alloy was fabricated by rapid solidification process through vacuum arc melting followed by vacuum suction casting in water-cooled thick copper mold. The rapidly solidified （or suction cast） NiTi alloy shows much finer grains and homogenous microstructure, in particular a uniform distribution of various fine precipitates, compared to the conventional cast one. The resultant alloy also exhibits the homogenous Ni distribution in the matrix of the alloy, allowing the martensitic transformation to take place throughout the NiTi alloy matrix simultaneously and resulting in sharper transformation peaks compared to the conventional cast alloy. Moreover, the suction cast NiTJ alloy shows a significant improvement over the conventional cast one, in terms of possessing higher deformation recovery rates and displaying the increased compressive strength and damping capacity by 4% and 20%, respectively.
基金This work was supported in part by the National Natural Science Foundation of China(No.51807171)the Guangdong Science and Technology Department(No.2019A1515011226)+1 种基金the Hong Kong Research Grant Council(No.15200418)the Department of Electrical Engineering,The Hong Kong Polytechnic University for the Start-up Fund(No.1-ZE68).
文摘The damping performance evaluation for electromechanical oscillations in power systems is crucial for the stable operation of modern power systems.In this paper,the connection between two commonly-used damping performance evaluation methods,i.e.,the damping torque analysis(DTA)and energy flow analysis(EFA),are systematically examined and revealed for the better understanding of the oscillatory damping mechanism.First,a concept of the aggregated damping torque coefficient is proposed and derived based on DTA of multi-machine power systems,which can characterize the integration effect of the damping contribution from the whole power system.Then,the pre-processing of measurements at the terminal of a local generator is conducted for EFA,and a concept of the frequency-decomposed energy attenuation coefficient is defined to screen the damping contribution with respect to the interested frequency.On this basis,the frequency spectrum analysis of the energy attenuation coefficient is employed to rigorously prove that the results of DTA and EFA are essentially equivalent,which is valid for arbitrary types of synchronous generator models in multi-machine power systems.Additionally,the consistency between the aggregated damping torque coefficient and frequency-decomposed energy attenuation coefficient is further verified by the numerical calculation in case studies.The relationship between the proposed coefficients and the eigenvalue(or damping ratio)is finally revealed,which consolidates the application of the proposed concepts in the damping performance evaluation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 52074230, 52088101 and 51871186)the Fundamental Research Funds for the Central Universities
文摘The rapid solidification of Fe-17%Mn alloy was performed to investigate the influence of cooling rate on its damping performance and martensitic transformation mechanism. A proper heat treatment was also carried out to clarify its coupled effects with rapid solidification. The stacking fault probability and martensitic transformation temperature were determined to demonstrate their relationship with the cooling rate and the heat treatment process. With the increase of cooling rate, the volume fraction of ε-martensite increased and the stacking fault probability of ε-martensite was enhanced. The formation ofε-martensite phase was remarkable for the increase of damping capacity and microhardness. It was found that rapid solidification was beneficial for the formation of ε-martensite and the improvement of damping capacity. This effect can be facilitated by the incorporation of the heat treatment process.
基金supported by Innovation Center of Forestry Resources Utilization,Jiangsu Province(No.KY202200174).
文摘Wood composites glued with thermosetting synthetic resins tend to show inadequate damping performance caused by the cured resinous matrix.Waste rubber maintains prominent elasticity and is feasible to be an optional modifier.To that end,composite panels of granulated tire rub-ber(GTR)powders and thermal-mechanically pulped wood fibers were fabricated in this study.Urea formaldehyde(UF)resin was applied as the bonding agent(10%based on wood/rubber total weight).Dynamical mechanical analysis(DMA)was conducted to disclose the thermo-mechanical behaviors of the rubber-filled wood fiber composites.Influence of two technical pa-rameters,i.e.,GTR powder size(0.55-1.09 mm)and addition content(10%,20%and 30%based on wood/rubber total weight),was specifically discussed.The results showed that storage modu-lus(E’)of the rubber-filled composite decreased while loss factor(tan𝛿)increased monotonously along with elevated temperature.A steady“plateau”region among 110-170°C was found where both E’and tan𝛿keep constant.Accordingly,tan𝛿showed two peak values at 103-108 and 231-233°C due to glass transition of lignin and thermal degradation of hemicellulose,respectively.Addition of rubber fillers resulted in lower bending and internal bonding strengths as well as stor-age modulus values.When the temperature was above 183°C,all the rubber-filled composites showed higher tan𝛿values than the control.The findings above fully demonstrate the improved damping performance of the UF-bonded wood fiber composites on account of rubber component.Further work is still needed to optimize the rubber/fiber interfacial bonding strength.
