The effects of heat treatment process on microstrucature, micro-yield strength and dynamic dimensional stability of ZL114A aluminum alloy were investigated by optical microscopy （OM）, transmission electron microsco...The effects of heat treatment process on microstrucature, micro-yield strength and dynamic dimensional stability of ZL114A aluminum alloy were investigated by optical microscopy （OM）, transmission electron microscopy （TEM）, tensile testing and thermal cycling on-line measuring method. Fine dispersed eutectic Si phases are observed, and long strip eutectic Si and massive primary Si phases decrease in ZL114A alloy after high-temperature and long-time solution treatment, which result in the increase of micro-plastic deformation resistance. With the increasing of aging temperature, aging precipitation behaviour of ZLll4A alloy transforms from precipitation of GP zone and fl＇ phases simultaneously at lower temperature to precipitation of stable Mg2Si phases at higher temperature. Because coherent strengthening is the main strengthen mechanism for micro-plastic deformation, precipitation of stable Mg2Si phases is unfavorable to the improvement of micro-plastic deformation resistance. Micro-yield strength cannot characterize dimensional stability comprehensively, and dynamic dimensional stability under alternative temperature should also be tested cooperatively for better evaluation of dimensional stability.展开更多
Wood has no inherent natural resistance against agents of biodegradation. We evaluated the effects of metal bath heat treatment(MBHT) on decay resistance and dimensional stability of Chinese parasol(Firmiana simplex) ...Wood has no inherent natural resistance against agents of biodegradation. We evaluated the effects of metal bath heat treatment(MBHT) on decay resistance and dimensional stability of Chinese parasol(Firmiana simplex) and Chinese fir(Cunninghamia lanceolata) wood. A low melting point alloy was used as heating medium in the treatment of the wood samples at 150, 180, and 210 °C for2, 4, and 8 h. Heat-treated and control samples were exposed to brown rot fungus(Poria placenta) and white rot fungus(Coriolus versicolor) for decay resistance testing and anti-swelling efficiency(ASE). The improved decay resistance with increase temperatures with low mass losses of 7.3 and 7.3% for F. simplex, and 3.9 and 3.6% for C.lanceolata at 210 °C for 8 h against Coriolus versicolor and Poria placenta, respectively. ASE indicated that MBHT contributed to improved dimensional stability of both wood species after treatment. Scanning electron micrograph results indicate that metal bath-treated samples showed strong decay resistance. Therefore, our approach to thermally modify wood should be explored to overcome the energy utilization by using low melting point alloy for the heat treatment of wood.展开更多
The aim of the study was to investigate the effect of pre-treatments by using sodium hydroxide (NaOH) and acetic acid on oil palm Empty Fruit Bunch (EFB) fibres for the production of Medium Density Fibreboard (MDF). T...The aim of the study was to investigate the effect of pre-treatments by using sodium hydroxide (NaOH) and acetic acid on oil palm Empty Fruit Bunch (EFB) fibres for the production of Medium Density Fibreboard (MDF). The EFB fibres were treated with chemicals in the concentration range of 0.2%, 0.4%, 0.6% and 0.8% prior to refining. Single-homogenous layer MDF with 12 mm thickness and density of 720 kg/m3 was produced. Urea-Formaldehyde (UF) was applied at 10% loading (based on dry weight of dry fibres) as a binder. The physical properties (Water Absorption (WA) and Thickness Swelling (TS)) of the produced panels were tested according to European Standard, EN 622-5:2006. The results show that types of chemical used had greater effects than concentration on the dimensional stability of the MDF. EFB fibres treated with acetic acid produced MDF with better dimensional stability compared to the MDF NaOH treated fibres. High concentration of NaOH produced poor dimensional stability in the panels.展开更多
A method of alkaline pretreatment of particles was designed to produce three types of chips. The pretreatmentet of particles in 1% water solution of NaOH for 30 minutes offered a possibility of producing PF bonded par...A method of alkaline pretreatment of particles was designed to produce three types of chips. The pretreatmentet of particles in 1% water solution of NaOH for 30 minutes offered a possibility of producing PF bonded particleboards with minimal irrecoverable swell and a reduction in thickness swelling. The method used in this work could be used to produce more stable PF particeboard.展开更多
The dimensional change,residual stress,grain orientation difference,dislocation density,and dislocation distribution of beryllium after different hot isostatic pressing treatments were analyzed by laser length meter,R...The dimensional change,residual stress,grain orientation difference,dislocation density,and dislocation distribution of beryllium after different hot isostatic pressing treatments were analyzed by laser length meter,Raman spectrometer,nanoindentation meter,electron backscattered diffractometer,and transmission electron microscope,and the influence of thermal-cold cycling treatment on the dimensional stability of beryllium was analyzed.Results show that the size of the hot isostatic pressed beryllium tends to be stable after 6 cycles of thermal-cold cycling treatment from-100℃to 150℃,and it has good dimensional stability.The dimensional stabilization mechanism of beryllium is mainly the homogenization of dislocations within the grain and the homogenization of orientation difference caused by micro-plastic deformation.展开更多
In this paper,we were devoted to quantitatively analyzing the dimensional change of 2024 Al alloy during the aging process.Types of precipitates have been defined and the corresponding volume fraction has been measure...In this paper,we were devoted to quantitatively analyzing the dimensional change of 2024 Al alloy during the aging process.Types of precipitates have been defined and the corresponding volume fraction has been measured with Transmission Electron Microscopy(TEM)and Three-Dimensional Atom Probe Tomography(3 D-APT).Guinier-Preston-Bagaryatsky(GPB)zone(0.86 vol.%)was found after aging for 8 h.GPB zone(0.17 vol.%)and S'phase(1.02 vol.%)was found after aging for 24 h.The reduced dimensional change was attributed to the reduction of matrix lattice parameter.Relative to the initial supersaturated solid solution state,the lattice strain of-2.79×10^(-5)and-5.16×10^(-5)was produced after 8 h and 24 h aging respectively.The difference of the lattice parameters between the precipitates and matrix was also considered.A model was established to quantitatively describe the relationship between the precipitation process and dimensional change of 2024 Al alloy.展开更多
A multilayer flow is a stratified fluid composed of a finite number of layers with densities homogeneous within one layer but different from each other. It is an intermediate system between the single-layer barotropic...A multilayer flow is a stratified fluid composed of a finite number of layers with densities homogeneous within one layer but different from each other. It is an intermediate system between the single-layer barotropic model and the continuously stratified baroclinic model. Since this system can simulate the baroclinic effect simply, it is widely used to study the large-scale dynamic process in atmosphere and ocean. The present paper is concerned with the linear stability of the multilayer quasi-geostrophic flow, and the associated linear stability criteria are established. Firstly, the nonlinear model is turned into the form of a Hamiltonian system, and a basic flow is defined. But it cannot be an extreme point of the Hamiltonian function since the system is an infinite-dimensional one. Therefore, it is necessary to reconstruct a new Hamiltonian function so that the basic flow becomes an extreme point of it. Secondly, the linearized equations of disturbances in the multilayer quasi-geostrophic flow are derived by introducing infinitesimal disturbances superposed on the basic flows. Finally, the properties of the linearized system are discussed, and the linear stability criteria in the sense of Liapunov are derived under two different conditions with respect to certain norms.展开更多
The physical and dimensional characteristics, i.e. course and wale spacing, stitch density, tightness factor, diameter, porosity, dimensional stability and bursting strength of single jersey knitted items containing l...The physical and dimensional characteristics, i.e. course and wale spacing, stitch density, tightness factor, diameter, porosity, dimensional stability and bursting strength of single jersey knitted items containing lycra yarn with the variations in stitch length and lycra content have been examined and a detail investigation on the lycra filament has been discussed in this study. Six different samples were knitted with identical cotton and lycra yarn but different in lycra contents and stitch length. After conditioning in a controlled environment, all the samples were tested as per the established methods. After analyzing the test results, noticeable effects of variations in stitch length and lycra content on physical and dimensional characteristics of single jersey knitted fabric has been found. As smaller the stitch length and as greater the lycra content, the dimensional stability and bursting strength are better;on the other hand, the air permeability is lower.展开更多
The useful life of wooden pallets is lower because of the defects in lumbers. The quality of lumber can be significantly enhanced by heat treatment. In this paper,the larch pallet decks samples were heat-treated under...The useful life of wooden pallets is lower because of the defects in lumbers. The quality of lumber can be significantly enhanced by heat treatment. In this paper,the larch pallet decks samples were heat-treated under the conditions of different time and temperatures. The quantity of water uptake has reduced 16. 8% under the condition of 250 ℃ for 150 min. The resistance of water absorption efficiency increases 165. 34% under the condition of 175 ℃ for 90 min. The anti-shrink efficiency increases 72. 08% under the condition of 250 ℃ for 90min. The results showed that the dimension stability of larch panels can be improved by heat treatment. The condition of 250 ℃ for 180 min is the best heat treating condition to improve the dimension stability.展开更多
The elTcct of different dimension stabilization treatments on the dimension stability of SiC_(p)/Al composites were investigated by the measurement of microyield strength,microcreep properties,dimension,residual stres...The elTcct of different dimension stabilization treatments on the dimension stability of SiC_(p)/Al composites were investigated by the measurement of microyield strength,microcreep properties,dimension,residual stress and analyses of transmission electron microscopy.Results show that the heat cycle dimension stabilization techniques could efficiently decrease the residual stress,stabilize the dimension change,and increase resistance to microplastic deformation.The main reason was that the heat cycle dimension stabilization techniques might form stable dislocation structure in the SiC_(p)/A1 composites.展开更多
Efficient use of timber is a vital concern problem, especially in these regions where the forestry coverage ratio is decreasing. Studies on physical modification of wood have been taken more attention due to the incre...Efficient use of timber is a vital concern problem, especially in these regions where the forestry coverage ratio is decreasing. Studies on physical modification of wood have been taken more attention due to the increasing attentions on environmental protection. Thermal modification is emphasized and developed quickly in developing countries, especially in European countries. A large number of researches have been conducted and some industrial production plants have been built. This paper reviewed the history of heat treatment, exemplifies the industrial developments in several European countries, summarized the basic principle of heat treatment and describes the environmental characteristics. The properties of heat-treated wood and its usage are also summed up.展开更多
Dimensional stability properties of hot extruded 2024 Al alloy bar in T4 and T6 aging states and dif- ferent extruded directions were investigated by testing micro-yield strength (MYS), stress relaxation resistance (S...Dimensional stability properties of hot extruded 2024 Al alloy bar in T4 and T6 aging states and dif- ferent extruded directions were investigated by testing micro-yield strength (MYS), stress relaxation resistance (SRR), and dimensional change in thermal cycling and unloading conditions.The results show that micro-plastic deformation resistance in longitudinal(parallel to the axis of the extruded bar) direction is higher than that in transverse(perpendicular to the axis of the extruded bar) direction. Testing in short-term loading condition MYS value corresponding to micro-plastic strain of 1 *10m^(-5)in longitudinal direction is 1.4 times than that in transverse.Compared with the results of MYS and dimensional change in thermal cycling and unloading conditions, the values in T6 state are higher than that in T4 state. Using TEM the microstructures before micro-plastic deformation were observed.The analyses confirm that stability of thermodynamics condition and dislocation results in dimensional stability of the alloy.展开更多
Falcataria moluccana or sengon is one of the fast-growing wood species widely grown in Indonesia.However,its wood is low quality with low density,and poor strength,durability,and dimensional stability.This study deter...Falcataria moluccana or sengon is one of the fast-growing wood species widely grown in Indonesia.However,its wood is low quality with low density,and poor strength,durability,and dimensional stability.This study determined the effects of impregnation with monoethylene glycol(MEG)and nano-SiO2 on the characteristics of sengon wood,including its dimensional stability and density.Impregnation with MEG and nano-SiO2 had a significant effects on dimensional stability in terms of the weight percent gain,anti-swelling efficiency,water uptake,bulking effect,and density.The impregnated wood was examined by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction.The results show that MEG and nano-SiO2 were distributed homogeneously into cell walls of wood treated with 0.5%MEGSiO2.展开更多
To enhance mechanical properties and improve flame retardancy and smoke suppression of fast-growing poplar wood in wood applications,the wood was impregnated and modified.An organic phenolic prepolymer and inorganic s...To enhance mechanical properties and improve flame retardancy and smoke suppression of fast-growing poplar wood in wood applications,the wood was impregnated and modified.An organic phenolic prepolymer and inorganic sodium silicate was used as contrasting impregnation modifiers and wood samples were impregnated by a bionic“respiration”method with alternating positive and negative pressure.The weight percentage gain,density increase ratio,mechanical properties(bending and compressive strength and hardness),and water absorption rate of inorganic and organic-impregnated modified poplar wood(IIMPW and OIMPW,respectively)were compared and these properties in IIMPW were found to be higher than those of OIMPW with the exception of the water absorption rate which was lower than the OIMPW.This was attributed to the superior absorption of sodium silicate that also improved the impregnation,reinforcement,and dimensional stability in the IIMPW.The chemical structure,crystalline structure,internal morphology,flame retardancy,smoke suppression,and thermal stability of IIMPW and OIMPW were characterized by FT-IR,XRD,SEM,CONE,and TGA.FT-IR and XRD results showed that,although IIMPW cellulose crystallinity reduced the most,more chemical bonds were come into being in IIMPW,which explained the better physical and mechanical properties of IIMPW.Compared with OIMPW,IIMPW had better flame retardant and smoke suppression performance.展开更多
Water blown rigid polyurethane foams with different functionality were prepared. The physical properties of rigid foams were measured with rotational viscometer （NDJ-1 ）, universal testing machine （Instron3365）, s...Water blown rigid polyurethane foams with different functionality were prepared. The physical properties of rigid foams were measured with rotational viscometer （NDJ-1 ）, universal testing machine （Instron3365）, scanning electron microscope （SEM） and differential scanning calorimeter （DSC）. The results show that the viscosity of polyether polyol increases exponentially from 62 mPa s to 6 000 mPa s with the increase of functionality from 2 to 5.6, respectively. The overall density of foam increases slightly from 31.7 kg/m^3 to 37.4 kg/m^3 with increasing functionality while core density exhibited little difference. Compressive strength of foam shows the similar behavior with density except for 2-functional sample. At the same time, dimensional stability becomes better with increasing functionality except for 5.6-functional foam that has worse stability than 4.8-functional foam. From the SEM results, the functionality is not an important factor in determining distribution of cell size of foam. According to the results of thermal analysis, the glass transition temperature （T） shifts to a higher temperature from 128.9 ℃ to 166.3 ℃ for the 2 to 5.6 functional foam, respectively.展开更多
Chinese fir was compressed by vacuum hot pressing and conventional hot pressing at different temperatures(180℃,200℃ and 220℃),respectively.The color parameters of the heat-compressed sample were measured,the relati...Chinese fir was compressed by vacuum hot pressing and conventional hot pressing at different temperatures(180℃,200℃ and 220℃),respectively.The color parameters of the heat-compressed sample were measured,the relative mechanical properties of the material were tested and changes in the chemistry of fir were investigated using Fourier transform infrared spectroscopy(FTIR)and Xray photoelectron spectroscopy(XPS).The results indicated that the color difference between compressed and untreated wood increased gradually with the increase of temperature.Compared with the conventional hot pressing treatment,the color difference(ΔE*)of the Chinese fir treated by vacuum hot pressing decreased by 43.73%,69.91%,and 77.17%,respectively.The mechanical properties(bending elastic modulus and bending strength)of Chinese fir treated by vacuum hot pressing were significantly improved.The 24-hour water absorption thickness expansion rate of fir treated by vacuum hot pressing is smaller than that of conventional hot pressing.It is implied that vacuum hot pressing treatment is an effective method to produce compressed wood,which can improve the mechanical properties and dimensional stability of wood,and reduce the influence of carbonization on wood color.展开更多
For overcoming disadvantages of wood, an esterification process was employed and tetrabromophthalic anhydride (TBPA) was used as a reactive chemical agent to prepare an esterified wood with the high dimensional stabil...For overcoming disadvantages of wood, an esterification process was employed and tetrabromophthalic anhydride (TBPA) was used as a reactive chemical agent to prepare an esterified wood with the high dimensional stability, flame resistance, and resistance to biodegradation from water-leaching. The experimental results indicated that esterification of wood plus maleic anhydride / tetrabromophthalic anhydride / glycerol could endow wood with dimensional stability, the antiswelling efficiency during water absorption (ASEw), reduction in water absorptivity (RWA), antiswelling efficiency during moisture absorption (ASEm), moisture excluding efficiency (MEE), and oxygen index (OI) of treated wood increased with an increase in the weight percent gain (WPG). And the treated wood showed great decay resistance and resistance to water leaching, too.展开更多
Three kinds of polymeric materials are taken as example for the verification of linear ex-trapolation method from unified master lines with reduced universal equations on creep and stress relaxation tests. The theoret...Three kinds of polymeric materials are taken as example for the verification of linear ex-trapolation method from unified master lines with reduced universal equations on creep and stress relaxation tests. The theoretical values of long-term mechanical behavior and lifetime for a cured epoxide, polypropylene, poly（methyl-methacrylate）, and SBR rubber are directly evaluated with the universal equations on reduced creep compliance and reduced stress relax-ation modulus and are compared with their predicted values by the linear extrapolation from the unified master lines of creep and stress relaxation. The results show that the theoretical values of dimensional stability, bearing ability and lifetime are in an excellent agreement with the predicted values, it shows that the linear extrapolation method is more simple and reliable. The dependences of long-term mechanical behaviors and lifetime on the different aging times are discussed.展开更多
The effect of time and environment on the dimension precision and mass of LOM prototypes was experimentally investigated.It is to identify the stability of the dimension of LOM prototypes after forming.The results sho...The effect of time and environment on the dimension precision and mass of LOM prototypes was experimentally investigated.It is to identify the stability of the dimension of LOM prototypes after forming.The results show that the dimension and the mass tendency to grow,which is mainly caused by elastic recovery and moisture absorption and is characterized principally by the growth of Z dimension.Self restraint can be a significant factor to influence Z growth of LOM prototypes.展开更多
Adequate information is sparse for many tropical timbers on their engineering applications, which make their international promotion difficult. The physical and mechanical properties of Klainedoxa gabonensis Pierre ex...Adequate information is sparse for many tropical timbers on their engineering applications, which make their international promotion difficult. The physical and mechanical properties of Klainedoxa gabonensis Pierre ex Engl. （a lesserutilized species） and Entandrophragma cylindricum were compared. K. gabonensis contained more moisture with greater density at 12 % moisture content than E. cylindricum and had a tangential-radial ratio for swelling and shrinkage of 1.31-1.38 and 1.58-1.63, respectively, within acceptable thresholds for engineering/structural timbers. For K. gabonensis, shear parallel to grain was 32.2 ± 0.4-33.5 ±1 N mm^-2; compressive parallel to grain, 80.7 ± 1.4-90.6± 1 N mm^-2; modulus of rupture, 204± 4.0-214 ± 4.0 N mm^-2 and modulus of elasticity, 28,932 ± 664-29,493 ±822 N mm^-2. These properties were superior to those of E. cylindricum [（15.5 ± 0.9）- （15.6 ± 0.6）, （56.4 ± 4.5）-（63.6 ± 1.2）, （99.4 ± 4.7）- （121.3 ± 10.6）, and （9987.4 ± 207）-（10,051 ± 258） N mm^-2, respectively] and compared well with those of several traditional timbers for conslruction and furniture production. Its use would contribute to minimize pressure on the primary timbers in the forests and widen the raw material base for wooden products.展开更多
文摘The effects of heat treatment process on microstrucature, micro-yield strength and dynamic dimensional stability of ZL114A aluminum alloy were investigated by optical microscopy （OM）, transmission electron microscopy （TEM）, tensile testing and thermal cycling on-line measuring method. Fine dispersed eutectic Si phases are observed, and long strip eutectic Si and massive primary Si phases decrease in ZL114A alloy after high-temperature and long-time solution treatment, which result in the increase of micro-plastic deformation resistance. With the increasing of aging temperature, aging precipitation behaviour of ZLll4A alloy transforms from precipitation of GP zone and fl＇ phases simultaneously at lower temperature to precipitation of stable Mg2Si phases at higher temperature. Because coherent strengthening is the main strengthen mechanism for micro-plastic deformation, precipitation of stable Mg2Si phases is unfavorable to the improvement of micro-plastic deformation resistance. Micro-yield strength cannot characterize dimensional stability comprehensively, and dynamic dimensional stability under alternative temperature should also be tested cooperatively for better evaluation of dimensional stability.
基金financially supported by the Special Scientific Research Fund for Public Service Sectors of Forestry(Grant No.201504603)Science and Technology Projects of Fujian Province(2014NZ003)the National Natural Science Foundation of China(Grant Nos.31370560,31170520)
文摘Wood has no inherent natural resistance against agents of biodegradation. We evaluated the effects of metal bath heat treatment(MBHT) on decay resistance and dimensional stability of Chinese parasol(Firmiana simplex) and Chinese fir(Cunninghamia lanceolata) wood. A low melting point alloy was used as heating medium in the treatment of the wood samples at 150, 180, and 210 °C for2, 4, and 8 h. Heat-treated and control samples were exposed to brown rot fungus(Poria placenta) and white rot fungus(Coriolus versicolor) for decay resistance testing and anti-swelling efficiency(ASE). The improved decay resistance with increase temperatures with low mass losses of 7.3 and 7.3% for F. simplex, and 3.9 and 3.6% for C.lanceolata at 210 °C for 8 h against Coriolus versicolor and Poria placenta, respectively. ASE indicated that MBHT contributed to improved dimensional stability of both wood species after treatment. Scanning electron micrograph results indicate that metal bath-treated samples showed strong decay resistance. Therefore, our approach to thermally modify wood should be explored to overcome the energy utilization by using low melting point alloy for the heat treatment of wood.
文摘The aim of the study was to investigate the effect of pre-treatments by using sodium hydroxide (NaOH) and acetic acid on oil palm Empty Fruit Bunch (EFB) fibres for the production of Medium Density Fibreboard (MDF). The EFB fibres were treated with chemicals in the concentration range of 0.2%, 0.4%, 0.6% and 0.8% prior to refining. Single-homogenous layer MDF with 12 mm thickness and density of 720 kg/m3 was produced. Urea-Formaldehyde (UF) was applied at 10% loading (based on dry weight of dry fibres) as a binder. The physical properties (Water Absorption (WA) and Thickness Swelling (TS)) of the produced panels were tested according to European Standard, EN 622-5:2006. The results show that types of chemical used had greater effects than concentration on the dimensional stability of the MDF. EFB fibres treated with acetic acid produced MDF with better dimensional stability compared to the MDF NaOH treated fibres. High concentration of NaOH produced poor dimensional stability in the panels.
文摘A method of alkaline pretreatment of particles was designed to produce three types of chips. The pretreatmentet of particles in 1% water solution of NaOH for 30 minutes offered a possibility of producing PF bonded particleboards with minimal irrecoverable swell and a reduction in thickness swelling. The method used in this work could be used to produce more stable PF particeboard.
基金National Defense Basic Scientific Research Program of China(JCKY2018203B067)Youth Natural Science Foundation of Hunan Province(2019JJ50817)。
文摘The dimensional change,residual stress,grain orientation difference,dislocation density,and dislocation distribution of beryllium after different hot isostatic pressing treatments were analyzed by laser length meter,Raman spectrometer,nanoindentation meter,electron backscattered diffractometer,and transmission electron microscope,and the influence of thermal-cold cycling treatment on the dimensional stability of beryllium was analyzed.Results show that the size of the hot isostatic pressed beryllium tends to be stable after 6 cycles of thermal-cold cycling treatment from-100℃to 150℃,and it has good dimensional stability.The dimensional stabilization mechanism of beryllium is mainly the homogenization of dislocations within the grain and the homogenization of orientation difference caused by micro-plastic deformation.
基金sponsored by the National Natural Science Foundation of China with grant No.U1637201。
文摘In this paper,we were devoted to quantitatively analyzing the dimensional change of 2024 Al alloy during the aging process.Types of precipitates have been defined and the corresponding volume fraction has been measured with Transmission Electron Microscopy(TEM)and Three-Dimensional Atom Probe Tomography(3 D-APT).Guinier-Preston-Bagaryatsky(GPB)zone(0.86 vol.%)was found after aging for 8 h.GPB zone(0.17 vol.%)and S'phase(1.02 vol.%)was found after aging for 24 h.The reduced dimensional change was attributed to the reduction of matrix lattice parameter.Relative to the initial supersaturated solid solution state,the lattice strain of-2.79×10^(-5)and-5.16×10^(-5)was produced after 8 h and 24 h aging respectively.The difference of the lattice parameters between the precipitates and matrix was also considered.A model was established to quantitatively describe the relationship between the precipitation process and dimensional change of 2024 Al alloy.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.41575026,41275113,and 41475021)
文摘A multilayer flow is a stratified fluid composed of a finite number of layers with densities homogeneous within one layer but different from each other. It is an intermediate system between the single-layer barotropic model and the continuously stratified baroclinic model. Since this system can simulate the baroclinic effect simply, it is widely used to study the large-scale dynamic process in atmosphere and ocean. The present paper is concerned with the linear stability of the multilayer quasi-geostrophic flow, and the associated linear stability criteria are established. Firstly, the nonlinear model is turned into the form of a Hamiltonian system, and a basic flow is defined. But it cannot be an extreme point of the Hamiltonian function since the system is an infinite-dimensional one. Therefore, it is necessary to reconstruct a new Hamiltonian function so that the basic flow becomes an extreme point of it. Secondly, the linearized equations of disturbances in the multilayer quasi-geostrophic flow are derived by introducing infinitesimal disturbances superposed on the basic flows. Finally, the properties of the linearized system are discussed, and the linear stability criteria in the sense of Liapunov are derived under two different conditions with respect to certain norms.
文摘The physical and dimensional characteristics, i.e. course and wale spacing, stitch density, tightness factor, diameter, porosity, dimensional stability and bursting strength of single jersey knitted items containing lycra yarn with the variations in stitch length and lycra content have been examined and a detail investigation on the lycra filament has been discussed in this study. Six different samples were knitted with identical cotton and lycra yarn but different in lycra contents and stitch length. After conditioning in a controlled environment, all the samples were tested as per the established methods. After analyzing the test results, noticeable effects of variations in stitch length and lycra content on physical and dimensional characteristics of single jersey knitted fabric has been found. As smaller the stitch length and as greater the lycra content, the dimensional stability and bursting strength are better;on the other hand, the air permeability is lower.
文摘The useful life of wooden pallets is lower because of the defects in lumbers. The quality of lumber can be significantly enhanced by heat treatment. In this paper,the larch pallet decks samples were heat-treated under the conditions of different time and temperatures. The quantity of water uptake has reduced 16. 8% under the condition of 250 ℃ for 150 min. The resistance of water absorption efficiency increases 165. 34% under the condition of 175 ℃ for 90 min. The anti-shrink efficiency increases 72. 08% under the condition of 250 ℃ for 90min. The results showed that the dimension stability of larch panels can be improved by heat treatment. The condition of 250 ℃ for 180 min is the best heat treating condition to improve the dimension stability.
文摘The elTcct of different dimension stabilization treatments on the dimension stability of SiC_(p)/Al composites were investigated by the measurement of microyield strength,microcreep properties,dimension,residual stress and analyses of transmission electron microscopy.Results show that the heat cycle dimension stabilization techniques could efficiently decrease the residual stress,stabilize the dimension change,and increase resistance to microplastic deformation.The main reason was that the heat cycle dimension stabilization techniques might form stable dislocation structure in the SiC_(p)/A1 composites.
文摘Efficient use of timber is a vital concern problem, especially in these regions where the forestry coverage ratio is decreasing. Studies on physical modification of wood have been taken more attention due to the increasing attentions on environmental protection. Thermal modification is emphasized and developed quickly in developing countries, especially in European countries. A large number of researches have been conducted and some industrial production plants have been built. This paper reviewed the history of heat treatment, exemplifies the industrial developments in several European countries, summarized the basic principle of heat treatment and describes the environmental characteristics. The properties of heat-treated wood and its usage are also summed up.
文摘Dimensional stability properties of hot extruded 2024 Al alloy bar in T4 and T6 aging states and dif- ferent extruded directions were investigated by testing micro-yield strength (MYS), stress relaxation resistance (SRR), and dimensional change in thermal cycling and unloading conditions.The results show that micro-plastic deformation resistance in longitudinal(parallel to the axis of the extruded bar) direction is higher than that in transverse(perpendicular to the axis of the extruded bar) direction. Testing in short-term loading condition MYS value corresponding to micro-plastic strain of 1 *10m^(-5)in longitudinal direction is 1.4 times than that in transverse.Compared with the results of MYS and dimensional change in thermal cycling and unloading conditions, the values in T6 state are higher than that in T4 state. Using TEM the microstructures before micro-plastic deformation were observed.The analyses confirm that stability of thermodynamics condition and dislocation results in dimensional stability of the alloy.
文摘Falcataria moluccana or sengon is one of the fast-growing wood species widely grown in Indonesia.However,its wood is low quality with low density,and poor strength,durability,and dimensional stability.This study determined the effects of impregnation with monoethylene glycol(MEG)and nano-SiO2 on the characteristics of sengon wood,including its dimensional stability and density.Impregnation with MEG and nano-SiO2 had a significant effects on dimensional stability in terms of the weight percent gain,anti-swelling efficiency,water uptake,bulking effect,and density.The impregnated wood was examined by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction.The results show that MEG and nano-SiO2 were distributed homogeneously into cell walls of wood treated with 0.5%MEGSiO2.
基金the Scientific Research Project of Hunan Provincial Education Department,China(21B0238)Hunan Provincial Technical Innovation Platform and Talent Program in Science and Technology,China(2019RS2040)+1 种基金National Natural Science Foundation of China(32171708)The Science and Technology Innovation Program of Hunan Province(2021RC4062).
文摘To enhance mechanical properties and improve flame retardancy and smoke suppression of fast-growing poplar wood in wood applications,the wood was impregnated and modified.An organic phenolic prepolymer and inorganic sodium silicate was used as contrasting impregnation modifiers and wood samples were impregnated by a bionic“respiration”method with alternating positive and negative pressure.The weight percentage gain,density increase ratio,mechanical properties(bending and compressive strength and hardness),and water absorption rate of inorganic and organic-impregnated modified poplar wood(IIMPW and OIMPW,respectively)were compared and these properties in IIMPW were found to be higher than those of OIMPW with the exception of the water absorption rate which was lower than the OIMPW.This was attributed to the superior absorption of sodium silicate that also improved the impregnation,reinforcement,and dimensional stability in the IIMPW.The chemical structure,crystalline structure,internal morphology,flame retardancy,smoke suppression,and thermal stability of IIMPW and OIMPW were characterized by FT-IR,XRD,SEM,CONE,and TGA.FT-IR and XRD results showed that,although IIMPW cellulose crystallinity reduced the most,more chemical bonds were come into being in IIMPW,which explained the better physical and mechanical properties of IIMPW.Compared with OIMPW,IIMPW had better flame retardant and smoke suppression performance.
基金the Joint Research Foundation of CAS and Hebei Province,China(No.2004-015)
文摘Water blown rigid polyurethane foams with different functionality were prepared. The physical properties of rigid foams were measured with rotational viscometer （NDJ-1 ）, universal testing machine （Instron3365）, scanning electron microscope （SEM） and differential scanning calorimeter （DSC）. The results show that the viscosity of polyether polyol increases exponentially from 62 mPa s to 6 000 mPa s with the increase of functionality from 2 to 5.6, respectively. The overall density of foam increases slightly from 31.7 kg/m^3 to 37.4 kg/m^3 with increasing functionality while core density exhibited little difference. Compressive strength of foam shows the similar behavior with density except for 2-functional sample. At the same time, dimensional stability becomes better with increasing functionality except for 5.6-functional foam that has worse stability than 4.8-functional foam. From the SEM results, the functionality is not an important factor in determining distribution of cell size of foam. According to the results of thermal analysis, the glass transition temperature （T） shifts to a higher temperature from 128.9 ℃ to 166.3 ℃ for the 2 to 5.6 functional foam, respectively.
基金The Authors acknowledge funding support by the National Key R&D Program of China(2017YFC0703501)the Doctorate Fellowship Foundation of the Nanjing Forestry University and the China Double First Class University Plan.
文摘Chinese fir was compressed by vacuum hot pressing and conventional hot pressing at different temperatures(180℃,200℃ and 220℃),respectively.The color parameters of the heat-compressed sample were measured,the relative mechanical properties of the material were tested and changes in the chemistry of fir were investigated using Fourier transform infrared spectroscopy(FTIR)and Xray photoelectron spectroscopy(XPS).The results indicated that the color difference between compressed and untreated wood increased gradually with the increase of temperature.Compared with the conventional hot pressing treatment,the color difference(ΔE*)of the Chinese fir treated by vacuum hot pressing decreased by 43.73%,69.91%,and 77.17%,respectively.The mechanical properties(bending elastic modulus and bending strength)of Chinese fir treated by vacuum hot pressing were significantly improved.The 24-hour water absorption thickness expansion rate of fir treated by vacuum hot pressing is smaller than that of conventional hot pressing.It is implied that vacuum hot pressing treatment is an effective method to produce compressed wood,which can improve the mechanical properties and dimensional stability of wood,and reduce the influence of carbonization on wood color.
文摘For overcoming disadvantages of wood, an esterification process was employed and tetrabromophthalic anhydride (TBPA) was used as a reactive chemical agent to prepare an esterified wood with the high dimensional stability, flame resistance, and resistance to biodegradation from water-leaching. The experimental results indicated that esterification of wood plus maleic anhydride / tetrabromophthalic anhydride / glycerol could endow wood with dimensional stability, the antiswelling efficiency during water absorption (ASEw), reduction in water absorptivity (RWA), antiswelling efficiency during moisture absorption (ASEm), moisture excluding efficiency (MEE), and oxygen index (OI) of treated wood increased with an increase in the weight percent gain (WPG). And the treated wood showed great decay resistance and resistance to water leaching, too.
基金This work was supported by the National Natural Science Foundation of China （No.50973007）.
文摘Three kinds of polymeric materials are taken as example for the verification of linear ex-trapolation method from unified master lines with reduced universal equations on creep and stress relaxation tests. The theoretical values of long-term mechanical behavior and lifetime for a cured epoxide, polypropylene, poly（methyl-methacrylate）, and SBR rubber are directly evaluated with the universal equations on reduced creep compliance and reduced stress relax-ation modulus and are compared with their predicted values by the linear extrapolation from the unified master lines of creep and stress relaxation. The results show that the theoretical values of dimensional stability, bearing ability and lifetime are in an excellent agreement with the predicted values, it shows that the linear extrapolation method is more simple and reliable. The dependences of long-term mechanical behaviors and lifetime on the different aging times are discussed.
文摘The effect of time and environment on the dimension precision and mass of LOM prototypes was experimentally investigated.It is to identify the stability of the dimension of LOM prototypes after forming.The results show that the dimension and the mass tendency to grow,which is mainly caused by elastic recovery and moisture absorption and is characterized principally by the growth of Z dimension.Self restraint can be a significant factor to influence Z growth of LOM prototypes.
文摘Adequate information is sparse for many tropical timbers on their engineering applications, which make their international promotion difficult. The physical and mechanical properties of Klainedoxa gabonensis Pierre ex Engl. （a lesserutilized species） and Entandrophragma cylindricum were compared. K. gabonensis contained more moisture with greater density at 12 % moisture content than E. cylindricum and had a tangential-radial ratio for swelling and shrinkage of 1.31-1.38 and 1.58-1.63, respectively, within acceptable thresholds for engineering/structural timbers. For K. gabonensis, shear parallel to grain was 32.2 ± 0.4-33.5 ±1 N mm^-2; compressive parallel to grain, 80.7 ± 1.4-90.6± 1 N mm^-2; modulus of rupture, 204± 4.0-214 ± 4.0 N mm^-2 and modulus of elasticity, 28,932 ± 664-29,493 ±822 N mm^-2. These properties were superior to those of E. cylindricum [（15.5 ± 0.9）- （15.6 ± 0.6）, （56.4 ± 4.5）-（63.6 ± 1.2）, （99.4 ± 4.7）- （121.3 ± 10.6）, and （9987.4 ± 207）-（10,051 ± 258） N mm^-2, respectively] and compared well with those of several traditional timbers for conslruction and furniture production. Its use would contribute to minimize pressure on the primary timbers in the forests and widen the raw material base for wooden products.
