This research focused on the dynamic mechanical and thermal properties of woven mat jute/kenaf/jute(J/K/J)and kenaf/jute/kenaf(K/J/K)hybrid composites.Dynamic mechanical analysis(DMA)and Thermo-gravimetric Analysis(TG...This research focused on the dynamic mechanical and thermal properties of woven mat jute/kenaf/jute(J/K/J)and kenaf/jute/kenaf(K/J/K)hybrid composites.Dynamic mechanical analysis(DMA)and Thermo-gravimetric Analysis(TGA)were used to study the effect of layering sequence on the thermal properties of kenaf/jute hybrid composites.The DMA results;it was found that the differences in the stacking sequence between the kenaf/jute composites do not affect their storage modulus,loss modulus and damping factor.From the TGA and DMA results,it has been shown that stacking sequence has given positive effect to the kenaf/jute hybrid composite compared to pure epoxy composite.This is because kenaf and jute fibre has increased the Tg values of the composites,thus affect the thermal degradation.Results showed that the storage modulus for kenaf/jute hybrid composites increased compared with pure epoxy composites with increasing temperature and the values of remained almost the same at glass transition temperature(Tg),the hybrid composite perhaps due to the improved fibre/matrix interface bonding.The preliminary analysis could provide a new direction for the creation of a novel hybrid composite which offers unique properties which cannot be accomplished in a single material system.展开更多
Cross-linked polystyrene/glass fiber composites were fabricated using cross-linked polystyrene （CLPS） as matrix and E-glass fiber as the reinforcement. Surfaces of E-glass fibers were modified by vinyl triethoxysila...Cross-linked polystyrene/glass fiber composites were fabricated using cross-linked polystyrene （CLPS） as matrix and E-glass fiber as the reinforcement. Surfaces of E-glass fibers were modified by vinyl triethoxysilane （VTES）, vinyl trimethoxysilane （VTMS） and γ-methacryloylpropyl trimethoxysilane （MPS）. The treated glass fibers were analyzed by fourier transform infrared spectroscopy （FTIR）. Dynamic mechanical thermal analysis （DMTA） and thermo-gravimetric analysis （TGA） were employed to investigate the effect of glass fibers surface modification on viscoelastic behavior and thermal properties. The morphology of fracture surfaces of various composites was observed by scanning electron microscopy （SEM）. The results revealed that these coupling agents were connected to the surfaces of the fibers by chemical bonding. Dynamic mechanical properties as well as thermal stability of the composites were improved considerablely, but to varying degrees depending on the fiber modification. The diversities of improvement of properties were attributed to the different interfacial adhesion between CLPS matrix and the glass fibers.展开更多
We investigated the temperature dependency of the dynamic mechanical properties of cement asphalt paste by the dynamic mechanical thermal analysis（DMTA） method. The experimental results show that the dynamic mechani...We investigated the temperature dependency of the dynamic mechanical properties of cement asphalt paste by the dynamic mechanical thermal analysis（DMTA） method. The experimental results show that the dynamic mechanical properties of cement asphalt pastes are sensitive to temperature due to the inclusion of asphalt, and may go through different states within a temperature range of-40 ℃ to 60 ℃, which is different from that of pure cement and asphalt. As the temperature of the cement asphalt paste increases, a considerable change of dynamic mechanical properties, including storage modulus（E＇）, loss modulus（E＇＇） and loss factor（tand） is observed. Moreover, the influence of asphalt to cement（A/C） ratio on the temperature sensitivity of the dynamic mechanical properties of cement asphalt composites was investigated. The temperature dependency of cement asphalt composites is ascribed to the temperature dependency of the asphalt and its interaction with cement paste. A simple fractional model is proposed to describe the viscoelastic behavior of cement asphalt composites.展开更多
Vibrational behavior of thermally actuated cantilever micro-beams and their mechanical response at moderately high frequency under a non-harmonic periodic loading is studied in this paper. Two different configurations...Vibrational behavior of thermally actuated cantilever micro-beams and their mechanical response at moderately high frequency under a non-harmonic periodic loading is studied in this paper. Two different configurations are considered: 1) a straight beam with two actuation layers on top and bottom which utilizes the bimorph effect to induce bending;2) a uniform beam with base excitation, where the beam is mounted on an actuator which moves it periodically at its base perpendicular to its axis. Generally, vibrating micro-cantilevers are required to oscillate at a specified frequency. In order to increase the efficiency of the system, and achieve deflections with low power consumption, geometrical features of the beams can be quantified so that the required vibrating frequency matches the natural frequencies of the beam. A parametric modal analysis is conducted on two configurations of micro-cantilever and the first natural frequency of the cantilevers as a function of geometrical parameters is extracted. To evaluate vibrational behavior and thermo-mechanical efficiency of micro-cantilevers as a function of their geometrical parameters and input power, a case study with a specified vibrating frequency is considered. Due to significant complexities in the loading conditions and thermo-mechanical behavior, this task can only be tackled via numerical methods. Selecting the geometrical parameters in order to induce resonance at the nominal frequency, non-linear time-history (transient) thermo-mechanical finite element analysis (using ANSYS) is run on each configuration to study its response to the periodic heating input. Approaches to improve the effectiveness of actuators in each configuration based on their implementation are investigated.展开更多
In addition to being used for pattern transfer,the negative photoresist SU-8 iswidely used as a structural material in microelectromechanical systems(MEMS).Due to its good photopatternability,SU-8 has lower manufactur...In addition to being used for pattern transfer,the negative photoresist SU-8 iswidely used as a structural material in microelectromechanical systems(MEMS).Due to its good photopatternability,SU-8 has lower manufacturing costs than many other materials,but its mechanical properties are relatively weak to some extent,which limits its performance.The mechanical properties of epoxy-like SU-8 can be enhanced by addingmicro-or nano-fillers such as carbon nanotube,clay,and SiC nanowire,which have superior elastic modulus.In this study,SiC nanowires were used to improve the mechanical properties of SU-8 while the SU-8 retains its photopatternability.The SiC nanowires were uniformly dispersed in SU-8 by stirring and ultrasonication.SU-8 materials with different SiC nanowire contents were fabricated into dog bone samples by lithography.The elastic modulus,storage modulus,and damping factor of the samples were measured by the Dynamic mechanical analysis(DMA)Q800.The experiment result shows that the rigidity and toughness increased,and the damping reduced.The 2 wt%SiC nanowires-reinforced SU-8 had a 73.88%increase in elastic modulus and a 103.4%increase in elongation at break.Furthermore,a spring component made by SiC-doped SU-8 could withstand greater acceleration.The SiC nanowires-reinforced SU-8 has the potential tomeet higher requirements in the design andmanufacture of MEMS and greatly reduce the manufacturing costs of MEMS devices.展开更多
The thermodynamic parameters of FRW fire-retardant plywood at different temperatures were measured by dynamic mechanical analysis (DMA) equipment such as storage modulus, loss modulus and loss angle tangent. The influ...The thermodynamic parameters of FRW fire-retardant plywood at different temperatures were measured by dynamic mechanical analysis (DMA) equipment such as storage modulus, loss modulus and loss angle tangent. The influences on the thermodynamic properties of FRW fire-retardant plywood by the FRW fire retardant were analyzed between the FRW fire-retardant plywood and the untreated plywood. The results showed that the transition temperature of FRW fire-retardant plywood’s storage modulus was delayed than the untreated plywood. Its value was also higher than the untreated plywood. Meanwhile the glass transition temperature of plywood treated by FRW fire retardant was raised. FRW fire-retardant plywood could keep the better mechanical performances and ability of deformation-resistance at higher temperature and during longer period than the untreated plywood.展开更多
金沙江流域作为我国重要的生态屏障和清洁能源输出地,其下游干热河谷地段是高温频发地区,针对该区域开展高温天气环流特征和诊断对提高高温灾害预报水平和提高该区域能源调度效率具有重要意义。利用1981—2020年逐日最高气温资料和欧洲...金沙江流域作为我国重要的生态屏障和清洁能源输出地,其下游干热河谷地段是高温频发地区,针对该区域开展高温天气环流特征和诊断对提高高温灾害预报水平和提高该区域能源调度效率具有重要意义。利用1981—2020年逐日最高气温资料和欧洲中期天气预报中心(the European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析数据集ERA5(Reanalysis v5),通过K-means聚类分析法对金沙江下游高温天气环流形势进行分型,并对各类高温天气的动力和热力因子进行诊断,提炼出各型高温的物理量阈值。结果表明:金沙江下游高温天气的环流背景可分为暖脊型、副热带高压-青藏高压型和青藏高压型3种类型。高温期间中高层均有≥0.25 Pa·s^(-1)的下沉气流,天空晴朗无云,晴空辐射强,且近地面受到≤800 hPa强度的热低压直接加热作用。热力诊断发现金沙江下游高温主要由非绝热加热引起,温度平流对局地升温的贡献为负,垂直绝热变化贡献接近于0,但下沉气流有利于地面接收更多太阳辐射,使近地层非绝热加热增加,从而导致金沙江下游出现高温天气。展开更多
On the basis of Hamilton's principle and dynamic version of von Karman's equations, the nonlinear vibration and thermal-buckling of a uniformly heated isotropic annular plate with a completely clamped outer ed...On the basis of Hamilton's principle and dynamic version of von Karman's equations, the nonlinear vibration and thermal-buckling of a uniformly heated isotropic annular plate with a completely clamped outer edge and a fixed rigid mass along the inner edge are studied. By parametric perturbation and numerical differentiation, the nonlinear response of the plate-mass system and the critical temperature in the mid-plane at which the plate is in buckled state are obtained. Some meaningful characteristic curves and data tables are given.展开更多
基金This work is supported by UPM under GP-IPS Grant 9486400.
文摘This research focused on the dynamic mechanical and thermal properties of woven mat jute/kenaf/jute(J/K/J)and kenaf/jute/kenaf(K/J/K)hybrid composites.Dynamic mechanical analysis(DMA)and Thermo-gravimetric Analysis(TGA)were used to study the effect of layering sequence on the thermal properties of kenaf/jute hybrid composites.The DMA results;it was found that the differences in the stacking sequence between the kenaf/jute composites do not affect their storage modulus,loss modulus and damping factor.From the TGA and DMA results,it has been shown that stacking sequence has given positive effect to the kenaf/jute hybrid composite compared to pure epoxy composite.This is because kenaf and jute fibre has increased the Tg values of the composites,thus affect the thermal degradation.Results showed that the storage modulus for kenaf/jute hybrid composites increased compared with pure epoxy composites with increasing temperature and the values of remained almost the same at glass transition temperature(Tg),the hybrid composite perhaps due to the improved fibre/matrix interface bonding.The preliminary analysis could provide a new direction for the creation of a novel hybrid composite which offers unique properties which cannot be accomplished in a single material system.
基金Supported by National Natural Science Foundation of China (No.50872101,A3 Foresight Program-50821140308)National Basic Research Program of China (No.2009CB939704)a joint project of National Nature Science Foundation of China and Russian Foundation for Basic Research(No.NSFC-RFBR 51011120252)
文摘Cross-linked polystyrene/glass fiber composites were fabricated using cross-linked polystyrene （CLPS） as matrix and E-glass fiber as the reinforcement. Surfaces of E-glass fibers were modified by vinyl triethoxysilane （VTES）, vinyl trimethoxysilane （VTMS） and γ-methacryloylpropyl trimethoxysilane （MPS）. The treated glass fibers were analyzed by fourier transform infrared spectroscopy （FTIR）. Dynamic mechanical thermal analysis （DMTA） and thermo-gravimetric analysis （TGA） were employed to investigate the effect of glass fibers surface modification on viscoelastic behavior and thermal properties. The morphology of fracture surfaces of various composites was observed by scanning electron microscopy （SEM）. The results revealed that these coupling agents were connected to the surfaces of the fibers by chemical bonding. Dynamic mechanical properties as well as thermal stability of the composites were improved considerablely, but to varying degrees depending on the fiber modification. The diversities of improvement of properties were attributed to the different interfacial adhesion between CLPS matrix and the glass fibers.
基金Funded by the National Natural Science Foundation of China(50878209 and 51208515)the National Basic Research Program of China(“973”Program)(2013CB036201)
文摘We investigated the temperature dependency of the dynamic mechanical properties of cement asphalt paste by the dynamic mechanical thermal analysis（DMTA） method. The experimental results show that the dynamic mechanical properties of cement asphalt pastes are sensitive to temperature due to the inclusion of asphalt, and may go through different states within a temperature range of-40 ℃ to 60 ℃, which is different from that of pure cement and asphalt. As the temperature of the cement asphalt paste increases, a considerable change of dynamic mechanical properties, including storage modulus（E＇）, loss modulus（E＇＇） and loss factor（tand） is observed. Moreover, the influence of asphalt to cement（A/C） ratio on the temperature sensitivity of the dynamic mechanical properties of cement asphalt composites was investigated. The temperature dependency of cement asphalt composites is ascribed to the temperature dependency of the asphalt and its interaction with cement paste. A simple fractional model is proposed to describe the viscoelastic behavior of cement asphalt composites.
文摘Vibrational behavior of thermally actuated cantilever micro-beams and their mechanical response at moderately high frequency under a non-harmonic periodic loading is studied in this paper. Two different configurations are considered: 1) a straight beam with two actuation layers on top and bottom which utilizes the bimorph effect to induce bending;2) a uniform beam with base excitation, where the beam is mounted on an actuator which moves it periodically at its base perpendicular to its axis. Generally, vibrating micro-cantilevers are required to oscillate at a specified frequency. In order to increase the efficiency of the system, and achieve deflections with low power consumption, geometrical features of the beams can be quantified so that the required vibrating frequency matches the natural frequencies of the beam. A parametric modal analysis is conducted on two configurations of micro-cantilever and the first natural frequency of the cantilevers as a function of geometrical parameters is extracted. To evaluate vibrational behavior and thermo-mechanical efficiency of micro-cantilevers as a function of their geometrical parameters and input power, a case study with a specified vibrating frequency is considered. Due to significant complexities in the loading conditions and thermo-mechanical behavior, this task can only be tackled via numerical methods. Selecting the geometrical parameters in order to induce resonance at the nominal frequency, non-linear time-history (transient) thermo-mechanical finite element analysis (using ANSYS) is run on each configuration to study its response to the periodic heating input. Approaches to improve the effectiveness of actuators in each configuration based on their implementation are investigated.
基金supports from the Shanghai Professional Technical Service Platform for Non-Silicon Micro-Nano Integrated ManufacturingProject funded by China Postdoctoral Science Foundation (No. 2018M630440)
文摘In addition to being used for pattern transfer,the negative photoresist SU-8 iswidely used as a structural material in microelectromechanical systems(MEMS).Due to its good photopatternability,SU-8 has lower manufacturing costs than many other materials,but its mechanical properties are relatively weak to some extent,which limits its performance.The mechanical properties of epoxy-like SU-8 can be enhanced by addingmicro-or nano-fillers such as carbon nanotube,clay,and SiC nanowire,which have superior elastic modulus.In this study,SiC nanowires were used to improve the mechanical properties of SU-8 while the SU-8 retains its photopatternability.The SiC nanowires were uniformly dispersed in SU-8 by stirring and ultrasonication.SU-8 materials with different SiC nanowire contents were fabricated into dog bone samples by lithography.The elastic modulus,storage modulus,and damping factor of the samples were measured by the Dynamic mechanical analysis(DMA)Q800.The experiment result shows that the rigidity and toughness increased,and the damping reduced.The 2 wt%SiC nanowires-reinforced SU-8 had a 73.88%increase in elastic modulus and a 103.4%increase in elongation at break.Furthermore,a spring component made by SiC-doped SU-8 could withstand greater acceleration.The SiC nanowires-reinforced SU-8 has the potential tomeet higher requirements in the design andmanufacture of MEMS and greatly reduce the manufacturing costs of MEMS devices.
文摘The thermodynamic parameters of FRW fire-retardant plywood at different temperatures were measured by dynamic mechanical analysis (DMA) equipment such as storage modulus, loss modulus and loss angle tangent. The influences on the thermodynamic properties of FRW fire-retardant plywood by the FRW fire retardant were analyzed between the FRW fire-retardant plywood and the untreated plywood. The results showed that the transition temperature of FRW fire-retardant plywood’s storage modulus was delayed than the untreated plywood. Its value was also higher than the untreated plywood. Meanwhile the glass transition temperature of plywood treated by FRW fire retardant was raised. FRW fire-retardant plywood could keep the better mechanical performances and ability of deformation-resistance at higher temperature and during longer period than the untreated plywood.
文摘金沙江流域作为我国重要的生态屏障和清洁能源输出地,其下游干热河谷地段是高温频发地区,针对该区域开展高温天气环流特征和诊断对提高高温灾害预报水平和提高该区域能源调度效率具有重要意义。利用1981—2020年逐日最高气温资料和欧洲中期天气预报中心(the European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析数据集ERA5(Reanalysis v5),通过K-means聚类分析法对金沙江下游高温天气环流形势进行分型,并对各类高温天气的动力和热力因子进行诊断,提炼出各型高温的物理量阈值。结果表明:金沙江下游高温天气的环流背景可分为暖脊型、副热带高压-青藏高压型和青藏高压型3种类型。高温期间中高层均有≥0.25 Pa·s^(-1)的下沉气流,天空晴朗无云,晴空辐射强,且近地面受到≤800 hPa强度的热低压直接加热作用。热力诊断发现金沙江下游高温主要由非绝热加热引起,温度平流对局地升温的贡献为负,垂直绝热变化贡献接近于0,但下沉气流有利于地面接收更多太阳辐射,使近地层非绝热加热增加,从而导致金沙江下游出现高温天气。
文摘On the basis of Hamilton's principle and dynamic version of von Karman's equations, the nonlinear vibration and thermal-buckling of a uniformly heated isotropic annular plate with a completely clamped outer edge and a fixed rigid mass along the inner edge are studied. By parametric perturbation and numerical differentiation, the nonlinear response of the plate-mass system and the critical temperature in the mid-plane at which the plate is in buckled state are obtained. Some meaningful characteristic curves and data tables are given.
