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
Bead sttape in underwater rotating arc welding was affected by several welding parameters. RVM ( relevance vector machine) was used to build a model to predict weld bead shape. The training data set of RVM eortsists...Bead sttape in underwater rotating arc welding was affected by several welding parameters. RVM ( relevance vector machine) was used to build a model to predict weld bead shape. The training data set of RVM eortsists of the welding parameters which are rotational frequency, rotational radius, height of torch and welding current and the features of the bead shape. The maximum error and mean error for prediction of width are 0. 10 mm and 0. 09 mm, respectively, and the maximum error and mean error for prediction of penetration are 0. 31 mm and 0. 12mm, respectively, which are showed that the prediction model can achieve higher prediction precision at reasonably small size of training data set.展开更多
Digital control system for pulsed MIG welding power based on STM32 is set up with 32-bit STM32FlO3ZET6 directing against the pulse waveform modulation of pulsed MIG welding. High-frequency inverter and medium-low freq...Digital control system for pulsed MIG welding power based on STM32 is set up with 32-bit STM32FlO3ZET6 directing against the pulse waveform modulation of pulsed MIG welding. High-frequency inverter and medium-low frequency pulse waveform modulation of pulsed MIG welding are realized by using the integrated PWM module within STM32 to generate PWM signals of phase-shifted full-bridge soft-switching and constant-current control of output current is achieved by means of anti-windup PI control algorithm to improve the stability and reliability of control system. Experimental results demonstrate that the designed digital control system based on STM32 can achieve pegrect pulsed MIG welding technique with stable welding process and good weld appearance, fully demonstrating the advantages of digital control based on STM32.展开更多
To improve energy transfer efficiency and quality controllability of plasma cutting process of thick plate, a 50 kW digital inverter type plasma cutting power supply is developed. The power supply main circuit is comp...To improve energy transfer efficiency and quality controllability of plasma cutting process of thick plate, a 50 kW digital inverter type plasma cutting power supply is developed. The power supply main circuit is composed of two similar power electronic building blocks, using full-bridge high frequency inverter topology to achieve efficient energy transformation. To realize accurate digital control of the plasma cutting power supply and cooperative work of the two power electronic building blocks, the Cortex-M4 type ARM microprocessor-TM4C123GH6PGE is used as the cybernetic core of the control system. To improve the response performance and reliability of the power system, close-loop control and peak current feedback control modes are adopted. In the end, the experimental study of the performance testing and cutting of the developed prototype is carried out. The results indicate that the design is rational and feasible, and the developed high power plnsma cutting power supply works reliably with excellent performance.展开更多
A design idea was proposed that it was about intelligent digital welding machine with self-learning and self- regulation functions. The overall design scheme of software and hardware was provided. It was introduced th...A design idea was proposed that it was about intelligent digital welding machine with self-learning and self- regulation functions. The overall design scheme of software and hardware was provided. It was introduced that a parameter self-learning algorithm was based on large-step calibration and partial Newton interpolation. Furthermore, experimental verification was carried out with different welding technologies. The results show that weld bead is pegrect. Therefore, good welding quality and stability are obtained, and intelligent regulation is realized by parameters self-learning.展开更多
Packaged piezoelectric ceramic actuators (PPCAs) and compliant mechanisms are attractive for nanopositioning and nanomanipulation due to their ultra- high precision. The way to create and keep a proper and steady co...Packaged piezoelectric ceramic actuators (PPCAs) and compliant mechanisms are attractive for nanopositioning and nanomanipulation due to their ultra- high precision. The way to create and keep a proper and steady connection between both ends of the PPCA and the compliant mechanism is an essential step to achieve such a high accuracy. The connection status affects the initial position of the terminal moving plate, the positioning accuracy and the dynamic performance of the nanoposi- tioning platform, especially during a long-time or high- frequency positioning procedure. This paper presents a novel external preload mechanism and tests it in a 1-degree of freedom (I-DOF) compliant nanopositioning platform. The 1-DOF platform utilizes a parallelogram guiding mechanism and a parallelogram load mechanism to provide a more accurate actual input displacement and output displacement. The proposed stiffness model simulation results verify the and dynamic model of the platform. The values of the preload displacement, actual input displacement and output displacement can be measured by three capacitive sensors during the whole positioning procedure. The test results show the preload characteristics vary with different types or control modes of the PPCA. Some fitting formulas are derived to describe the preload displacement, actual input displacement and output displacement using the nominal elongation signal of the PPCA. With the identification of the preload characteristics, the actual and comprehensive output characteristics of the PPCA can be obtained by the strain gauge sensor (SGS) embedded in the PPCA.展开更多
In the present investigation a wrought magnesium alloy AZ31 was successfully processed by the accumulative roll-bonding (ARB) at gradient temperature up to six cycles with the lowest temperature of 250 °C. This...In the present investigation a wrought magnesium alloy AZ31 was successfully processed by the accumulative roll-bonding (ARB) at gradient temperature up to six cycles with the lowest temperature of 250 °C. This is performed through different thermomechanical processing routes (different ARB cycles at different temperatures of 350-200 °C). The microstructures and mechanical properties were investigated. The results indicate that significant grain refinement is observed after the first two cycles at the highest ARB temperature as a result of dynamic recrystallization, which is necessary for the subsequently ARB cycles at relatively lower temperature with the aim to restrict grain growth. No significant finer grain size was observed through the fifth and sixth cycles while the microstructure homogeneity is further improved. The grain structure can be effectively refined at lower ARB processing temperature and higher cycles. The resulting material exhibited high strength and relatively high ductility at ambient temperature when ARB deformed above 250 °C. The mechanical properties of the ARB deformed materials are strongly dependent on several main factors: the amount and the homogeneity of strain achieved, grain size and microstructure homogeneity, textures developed during ARB and interface bonding quality.展开更多
Direct methanol fuel cell(DMFC)has great potential to replace the traditional battery in the field of portable power sources.This study investigates the operational and structural aspects of a vapor-feed semi-passive ...Direct methanol fuel cell(DMFC)has great potential to replace the traditional battery in the field of portable power sources.This study investigates the operational and structural aspects of a vapor-feed semi-passive DMFC supplied with concentrated methanol.The effectiveness of using vaporous methanol to improve the cell performance is experimentally validated.Results indicate that there exits an optimal value of methanol concentration that favors both methanol supply and control of methanol crossover(MCO).With the increase in vaporization temperature,the cell performance can be enhanced.Based on the traditional structural design,a sintered porous metal plate is further used to depress the impact of MCO so that the cell performance can be significantly improved at a relatively higher methanol concentration.This is of great importance to enhance the energy density and operating duration for portable applications.The mechanisms related to the performance behaviors are discussed in detail.展开更多
In order to develop an efficient identification method for Fallopia plants and drugs,molecular analysis of the partial matK gene sequences was performed on 6 Fallopia species.Based on the matK sequences,a phylogenetic...In order to develop an efficient identification method for Fallopia plants and drugs,molecular analysis of the partial matK gene sequences was performed on 6 Fallopia species.Based on the matK sequences,a phylogenetic tree was constructed,which showed that different populations of inter-and intra-species could be specified and distinguished.The matK gene sequences of the 6 Fallopia species were all found to be of 1 271 bp in length,with some nucleotide variations throughout the entire sequences.The nucleotide difference at position 1 041 could distinguish F.denticulata from others,while specific nucleotide at position 1 154 became identification markers for F.aubertii.Moreover,four specific marker sites for F.multiflora var.ciliinerve at positions 216,224,1 060 and 1 179,seven for F.convolvulus at 318,765,772,874,936,952 and 1 036,and seven for F.dentate alata at 111,192,366,450,457,1 032 and 1 074 were also observed.By detecting the marker nucleotides and analyzing the phylogenetic relationship,the botanical origins of five inspected drugs were determined,suggesting that matK sequences can be used for authenticating Fallopia plants and drugs.展开更多
Protecting the skin from UV light irradiation in wet and underwater environments is challenging due to the weak adhesion of existing sunscreen materials but highly desired.Herein we report a polyethyleneimine/thioctic...Protecting the skin from UV light irradiation in wet and underwater environments is challenging due to the weak adhesion of existing sunscreen materials but highly desired.Herein we report a polyethyleneimine/thioctic acid/titanium dioxide(PEI/TA/TiO_(2))coacervate-derived hydrogel with robust,asymmetric,and reversible wet bioadhesion and effective UV-light-shielding ability.The PEI/TA/TiO_(2)complex coacervate can be easily obtained by mixing a PEI solution and TA/TiO_(2)powder.The fluid PEI/TA/TiO_(2)coacervate deposited on wet skin can spread into surface irregularities and subsequently transform into a hydrogel with increased cohesion,thereby establishing interdigitated contact and adhesion between the bottom surface and skin.Meanwhile,the functional groups between the skin and hydrogel can form physical interactions to further enhance bioadhesion,whereas the limited movement of amine and carboxyl groups on the top hydrogel surface leads to low adhesion.Therefore,the coacervate-derived hydrogel exhibits asymmetric adhesiveness on the bottom and top surfaces.Moreover,the PEI/TA/TiO_(2)hydrogel formed on the skin could be easily removed using a NaHCO3 aqueous solution without inflicting damage.More importantly,the PEI/TA/TiO_(2)hydrogel can function as an effective sunscreen to block UV light and prevent UV-induced MMP-9 overexpression,inflammation,and DNA damage in animal skin.The advantages of PEI/TA/TiO_(2)coacervate-derived hydrogels include robust,asymmetric,and reversible wet bioadhesion,effective UV light-shielding ability,excellent biocompatibility,and easy preparation and usage,making them a promising bioadhesive to protect the skin from UV light-associated damage in wet and underwater environments.展开更多
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The authors wish to thank the financial support for this research from National Natural Science Foundation of China ( No. 50705030) , Natural Science Foundaiion of Guangdong Province of China (No. 9151008019000008 ) and the Fundamental Research Funds for the Central Universities (No. 2009ZM0318).
文摘Bead sttape in underwater rotating arc welding was affected by several welding parameters. RVM ( relevance vector machine) was used to build a model to predict weld bead shape. The training data set of RVM eortsists of the welding parameters which are rotational frequency, rotational radius, height of torch and welding current and the features of the bead shape. The maximum error and mean error for prediction of width are 0. 10 mm and 0. 09 mm, respectively, and the maximum error and mean error for prediction of penetration are 0. 31 mm and 0. 12mm, respectively, which are showed that the prediction model can achieve higher prediction precision at reasonably small size of training data set.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 51205136) , the Specialized Research Fund for the Doctoral Program of Higher Education of China ( Grant No. 20100172120003 ) and the Fundamental Research Funds for the Central Universities (Key Program) ( Grant No. 2013ZZ034).
文摘Digital control system for pulsed MIG welding power based on STM32 is set up with 32-bit STM32FlO3ZET6 directing against the pulse waveform modulation of pulsed MIG welding. High-frequency inverter and medium-low frequency pulse waveform modulation of pulsed MIG welding are realized by using the integrated PWM module within STM32 to generate PWM signals of phase-shifted full-bridge soft-switching and constant-current control of output current is achieved by means of anti-windup PI control algorithm to improve the stability and reliability of control system. Experimental results demonstrate that the designed digital control system based on STM32 can achieve pegrect pulsed MIG welding technique with stable welding process and good weld appearance, fully demonstrating the advantages of digital control based on STM32.
基金This investigation is supported by National Natural Science Foundation of China (51375173) and Guangdong Provincial Science and Technology Project (2012B091000009, 2012A032300007).
文摘To improve energy transfer efficiency and quality controllability of plasma cutting process of thick plate, a 50 kW digital inverter type plasma cutting power supply is developed. The power supply main circuit is composed of two similar power electronic building blocks, using full-bridge high frequency inverter topology to achieve efficient energy transformation. To realize accurate digital control of the plasma cutting power supply and cooperative work of the two power electronic building blocks, the Cortex-M4 type ARM microprocessor-TM4C123GH6PGE is used as the cybernetic core of the control system. To improve the response performance and reliability of the power system, close-loop control and peak current feedback control modes are adopted. In the end, the experimental study of the performance testing and cutting of the developed prototype is carried out. The results indicate that the design is rational and feasible, and the developed high power plnsma cutting power supply works reliably with excellent performance.
文摘A design idea was proposed that it was about intelligent digital welding machine with self-learning and self- regulation functions. The overall design scheme of software and hardware was provided. It was introduced that a parameter self-learning algorithm was based on large-step calibration and partial Newton interpolation. Furthermore, experimental verification was carried out with different welding technologies. The results show that weld bead is pegrect. Therefore, good welding quality and stability are obtained, and intelligent regulation is realized by parameters self-learning.
基金This research was supported by the National Natural Science Foundation of China (Grant No. 91223201), the Natural Science Foundation of Guangdong Province (Grant No. S2013030013355), Project GDUPS (2010) and the Fundamental Research Funds for the Central Universities (Grant No. 2012ZP0004). These supports are greatly acknowl- edged.
文摘Packaged piezoelectric ceramic actuators (PPCAs) and compliant mechanisms are attractive for nanopositioning and nanomanipulation due to their ultra- high precision. The way to create and keep a proper and steady connection between both ends of the PPCA and the compliant mechanism is an essential step to achieve such a high accuracy. The connection status affects the initial position of the terminal moving plate, the positioning accuracy and the dynamic performance of the nanoposi- tioning platform, especially during a long-time or high- frequency positioning procedure. This paper presents a novel external preload mechanism and tests it in a 1-degree of freedom (I-DOF) compliant nanopositioning platform. The 1-DOF platform utilizes a parallelogram guiding mechanism and a parallelogram load mechanism to provide a more accurate actual input displacement and output displacement. The proposed stiffness model simulation results verify the and dynamic model of the platform. The values of the preload displacement, actual input displacement and output displacement can be measured by three capacitive sensors during the whole positioning procedure. The test results show the preload characteristics vary with different types or control modes of the PPCA. Some fitting formulas are derived to describe the preload displacement, actual input displacement and output displacement using the nominal elongation signal of the PPCA. With the identification of the preload characteristics, the actual and comprehensive output characteristics of the PPCA can be obtained by the strain gauge sensor (SGS) embedded in the PPCA.
基金supported by the National Natural Science Foundation of China(No.50801027)Public Foundation of Guangdong Key Laboratory for Advanced Metallic Materials Processing, South China University of Technology, China(No.2007001)
文摘In the present investigation a wrought magnesium alloy AZ31 was successfully processed by the accumulative roll-bonding (ARB) at gradient temperature up to six cycles with the lowest temperature of 250 °C. This is performed through different thermomechanical processing routes (different ARB cycles at different temperatures of 350-200 °C). The microstructures and mechanical properties were investigated. The results indicate that significant grain refinement is observed after the first two cycles at the highest ARB temperature as a result of dynamic recrystallization, which is necessary for the subsequently ARB cycles at relatively lower temperature with the aim to restrict grain growth. No significant finer grain size was observed through the fifth and sixth cycles while the microstructure homogeneity is further improved. The grain structure can be effectively refined at lower ARB processing temperature and higher cycles. The resulting material exhibited high strength and relatively high ductility at ambient temperature when ARB deformed above 250 °C. The mechanical properties of the ARB deformed materials are strongly dependent on several main factors: the amount and the homogeneity of strain achieved, grain size and microstructure homogeneity, textures developed during ARB and interface bonding quality.
基金supported by the Natural Science Foundation of Guangdong Province (S2013040016899)the Fundamental Research Funds for the Central Universities (2013ZM0003)+1 种基金the National Natural Science Foundation of China (51275180)the Open Fund of Shanghai Key Laboratory of Digital Manufacture for Thin-walled Structures (2013001)
文摘Direct methanol fuel cell(DMFC)has great potential to replace the traditional battery in the field of portable power sources.This study investigates the operational and structural aspects of a vapor-feed semi-passive DMFC supplied with concentrated methanol.The effectiveness of using vaporous methanol to improve the cell performance is experimentally validated.Results indicate that there exits an optimal value of methanol concentration that favors both methanol supply and control of methanol crossover(MCO).With the increase in vaporization temperature,the cell performance can be enhanced.Based on the traditional structural design,a sintered porous metal plate is further used to depress the impact of MCO so that the cell performance can be significantly improved at a relatively higher methanol concentration.This is of great importance to enhance the energy density and operating duration for portable applications.The mechanisms related to the performance behaviors are discussed in detail.
基金Supported by the Natural Science Foundation of Guangdong Province(06019716)
文摘In order to develop an efficient identification method for Fallopia plants and drugs,molecular analysis of the partial matK gene sequences was performed on 6 Fallopia species.Based on the matK sequences,a phylogenetic tree was constructed,which showed that different populations of inter-and intra-species could be specified and distinguished.The matK gene sequences of the 6 Fallopia species were all found to be of 1 271 bp in length,with some nucleotide variations throughout the entire sequences.The nucleotide difference at position 1 041 could distinguish F.denticulata from others,while specific nucleotide at position 1 154 became identification markers for F.aubertii.Moreover,four specific marker sites for F.multiflora var.ciliinerve at positions 216,224,1 060 and 1 179,seven for F.convolvulus at 318,765,772,874,936,952 and 1 036,and seven for F.dentate alata at 111,192,366,450,457,1 032 and 1 074 were also observed.By detecting the marker nucleotides and analyzing the phylogenetic relationship,the botanical origins of five inspected drugs were determined,suggesting that matK sequences can be used for authenticating Fallopia plants and drugs.
基金the National Key Research and Development Program(2022YFB3804403)the Collaborative Research Fund from the Research Grants Council of Hong Kong(Project No.C5044-21G)+1 种基金the Research Grants Council of the Hong Kong Special Administration Region(project no.GRF/14202920,GRF/14204618,GRF/14108720,T13-402/17-N and AoE/M-402/20)National Natural Science Foundation of China(22205264).
文摘Protecting the skin from UV light irradiation in wet and underwater environments is challenging due to the weak adhesion of existing sunscreen materials but highly desired.Herein we report a polyethyleneimine/thioctic acid/titanium dioxide(PEI/TA/TiO_(2))coacervate-derived hydrogel with robust,asymmetric,and reversible wet bioadhesion and effective UV-light-shielding ability.The PEI/TA/TiO_(2)complex coacervate can be easily obtained by mixing a PEI solution and TA/TiO_(2)powder.The fluid PEI/TA/TiO_(2)coacervate deposited on wet skin can spread into surface irregularities and subsequently transform into a hydrogel with increased cohesion,thereby establishing interdigitated contact and adhesion between the bottom surface and skin.Meanwhile,the functional groups between the skin and hydrogel can form physical interactions to further enhance bioadhesion,whereas the limited movement of amine and carboxyl groups on the top hydrogel surface leads to low adhesion.Therefore,the coacervate-derived hydrogel exhibits asymmetric adhesiveness on the bottom and top surfaces.Moreover,the PEI/TA/TiO_(2)hydrogel formed on the skin could be easily removed using a NaHCO3 aqueous solution without inflicting damage.More importantly,the PEI/TA/TiO_(2)hydrogel can function as an effective sunscreen to block UV light and prevent UV-induced MMP-9 overexpression,inflammation,and DNA damage in animal skin.The advantages of PEI/TA/TiO_(2)coacervate-derived hydrogels include robust,asymmetric,and reversible wet bioadhesion,effective UV light-shielding ability,excellent biocompatibility,and easy preparation and usage,making them a promising bioadhesive to protect the skin from UV light-associated damage in wet and underwater environments.