共查询到20条相似文献，搜索用时 484 毫秒
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为了探讨界面滑移效应对钢-竹组合楼板变形的影响,进行6块组合楼板受弯性能试验.试件共分为2组,一组为冷弯薄壁型钢与竹胶板界面仅周结构胶复合,另一组则在胶粘基础上用自攻螺钉强化,对组合楼板破坏形态、承载能力、跨中变形、界面相对滑移等进行研究.分析表明：第一组试件考虑滑移效应的跨中变形计算值与实测值吻合较好,因考虑了跨中附加挠度的影响,理论计算结果与换算截面法相比,其精度大约提高5％,更符合实际情况;第二组由于自攻螺钉的强化作用,整体性能提高很多,材料进入塑形阶段,所建理论模型不符合试验情况,有待进一步研究. 相似文献
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采用差示扫描量热仪(DSC)研究了聚对苯二甲酸乙二醇酯(PET)/聚对苯二甲酸丙二醇酯(PTT)共混合金的冷结晶性能,并用Avrami方程研究了共混合金的等温冷结晶动力学.结果表明,在不同温度下,PET/PTT共混合金具有相似的结晶行为；但随着冷结晶温度的升高,共混合金的结晶速率增大,达到一定的相对结晶度所需要的时间缩短；PTT中加入少量PET组分,会使结晶速率减小,不利于形成结晶；Avrami指数都大于4且为非整数,说明在冷结晶条件下,共混合金具有复杂的成核方式和生长维度. 相似文献
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自熔性合金系列为在钴、镍、铁等为基的合金中添加一定量的硅、硼，形成含有低熔点共晶化合物组织的粉末材料。一般的组成为：钴-铬-钨-硼-硅、镍-铬-硼-硅、铁-镍-铬-硼-硅，也有少量的铜基自熔性合金。 相似文献
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铜纤维/脲醛树脂复合膜片的导电性能 总被引：2，自引：1，他引：1
属纤维填充聚合物复合材料作为电磁屏蔽材料和吸波材料具有广泛的应用前景(John,1990;Chen et al.,2004;谭松庭等,1999).金属纤维由于长径比较大,在复合材料中能够有效地形成导电网络,因此大大减少了导电粉末填充时的"闲置体积",同时由于形成网络时的搭接次数多,因而使接触电阻减少很多,所以用较少的金属纤维用量即可赋予复合材料优良的导电性能(范五一等,1996;于杰等,2005).导电纤维填充脲醛树脂胶黏剂制备电磁屏蔽胶合板(华毓坤等,1995;刘贤淼,2005)是木基电磁屏蔽复合材料的研究主流,但现阶段该研究方向存在一些不足.目前该类研究主要将导电纤维直接与胶黏剂混炼后热压制备电磁屏蔽胶合板,通过增加导电纤维填充量来提高材料屏蔽效能,然而单一增大导电纤维填充量使得胶合板胶合强度大大降低,材料胶合强度与屏蔽性能产生了互相制约,表现出屏蔽效能低和频带窄的缺点. 相似文献
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张建辉 《林业机械与木工设备》2012,(10):23-26
使用万用电表、X射线衍射仪等仪器对竹材液化物碳纤维的电阻率、XRD结构参数等进行测量,初步研究了竹材液化物碳纤维电阻率随炭化温度、炭化时间以及XRD结构参数的变化规律,为进一步探讨其导电机理、导电性能以及将其作为电磁屏蔽材料提供基础数据. 相似文献
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为了提高工业废弃生物质的附加值和进一步改善木质素高温热解炭的导电性能,笔者通过简单的液氮冷冻-真空解冻预处理结合高温碳化的方法将玉米秸秆中提取的酶解木质素制备成具有更高导电性能的木质素导电炭材料(PLC)。通过电阻率测试探究了不同碳化温度、碳化保温时间以及预处理时间对导电炭电阻率的影响,同时采用扫描电子显微镜、X射线衍射仪、X射线光电子能谱仪和拉曼光谱等测试手段对不同碳化保温时间下炭材料的石墨化程度以及导电性能进行了评价。结果表明：经过预处理后的木质素能够在高温条件下热解碳化形成石墨化程度更高、导电性更好的炭材料,在热解温度为1 000℃、碳化时间为1 h时,PLC电阻率就能达到0.112Ω·cm。同时,PLC均为过渡态炭且含有少量氮元素,在高温条件下随着碳化保温时间增加,其无定形结构增加,有序性减小,导电性能和炭产率同步降低。因此,PLC能够充分地节省时间成本,从而提高工作效率。 相似文献
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木材高温炭化及导电功能木炭研究进展 总被引：1，自引：0，他引：1
木材经高温炭化生成的固体炭化物——木炭具有较高的导电性,以其作为导电功能单元可用于生产电磁屏蔽材料、抗静电材料、电热材料等新型功能材料。文中概述了木材的炭化机理,分析了木炭的基本性能及影响因素,系统地介绍了国内外导电功能木炭的研究进展,提出了今后的研究重点,旨在为开发利用新型功能材料提供科学依据。 相似文献
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Strength properties of thermally modified softwoods and its relation to polymeric structural wood constituents 总被引：3，自引：0，他引：3
Michiel J. Boonstra Joris Van Acker Bôke F. Tjeerdsma Edo V. Kegel 《Annals of Forest Science》2007,64(7):679-690
Thermal modification at relatively high temperatures (ranging from 150 to 260 °C) is an effective method to improve the dimensional stability and resistance against fungal attack. This study was performed to investigate the impact of heat treatment on the mechanical properties of wood. An industrially-used two-stage heat treatment method under relative mild conditions (< 200 °C) was used to treat the boards. Heat treatment revealed a clear effect on the mechanical properties of softwood species. The tensile strength parallel to the grain showed a rather large decrease, whereas the compressive strength parallel to the fibre increased after heat treatment. The bending strength, which is a combination of the tensile stress, compressive stress and shear stress, was lower after heat treatment. This decrease was less than the decrease of only the tensile strength. The impact strength showed a rather large decrease after heat treatment. An increase of the modulus of elasticity during the bending test has been noticed after heat treatment. Changes and/or modifications of the main wood components appear to be involved in the effects of heat treatment on the mechanical properties. The possible effect of degradation and modification of hemicelluloses, degradation and/or crystallization of amorphous cellulose, and polycondensation reactions of lignin on the mechanical properties of heat treated wood have been discussed. The effect of natural defects, such as knots, resin pockets, abnormal slope of grain and reaction wood, on the strength properties of wood appeared to be affected by heat treatment. Nevertheless, heat treated timber shows potential for use in constructions, but it is important to carefully consider the stresses that occur in a construction and some practical consequences when heat treated timber is used. 相似文献
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真空热处理改性马尾松木材物理性能研究 总被引：3，自引：0，他引：3
文章采用间歇抽真空法及利用木材自身含有的水分对马尾松木材进行热处理,并研究了热处理温度和时间对马尾松木材的尺寸稳定性（ASE值）和力学性能的影响。结果表明：处理温度和时间均显著影响着木材的力学强度和ASE。综合考虑处理温度和处理时间对ASE、顺纹抗压强度和抗弯强度的影响,较佳的真空热处理工艺为：压力-0.09 Mpa、处理温度200℃,处理时间1 h。 相似文献
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Mechanical behaviour of Eucalyptus wood modified by heat 总被引：4，自引：2，他引：2
J. A. Santos 《Wood Science and Technology》2000,34(1):39-43
Summary Eucalyptus wood (Blue gum) shows very high mechanical performances, presents very few knots and gives strong glued joints,
reasons that justify its interest for structural uses, carpentry and furniture components or even building construction. The
inconveniences of this species are its slow and difficult drying process and its low dimensional stability – with very high
swelling and shrinkage coefficients.
The drying process has been studied at INETI and the problem revealed to be solved with appropriate drying schedules and the
stresses released by a steam treatment. Heat treatment of Eucalyptus wood has been identified as one of the most promising
techniques to increase its dimensional stability. Studies in this area still proceed.
This paper presents some test results that show the influence of heat treatment in the strength properties of this wood, namely
the bending modulus of elasticity and tensile strength perpendicular to grain, in addition to the explanation of dimensional
stability evaluation and some results of dimensional stability treatments.
Received 15 June 1998 相似文献
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人工林杉木木材力学性质对高温热处理条件变化的响应 总被引：6，自引：0，他引：6
以人工林杉木为试材,分别用空气和菜子油为介质,在温度为180,200和220 ℃对其分别热处理1,3和5 h,研究试材的抗弯强度(MOR)、抗弯弹性模量(MOE)、顺纹抗压强度、表面硬度对高温热处理条件变化的响应,同时对处理材的主要化学成分进行分析,用扫描电镜对处理材横切面微观结构进行观察.结果表明:人工林杉木试材的4种主要力学性质对不同条件热处理的响应程度不同.无论是空气热处理还是油热处理,试材的MOR,MOE,顺纹抗压强度与对照比有不同程度的降低,且随处理温度升高、时间延长,下降幅度增大,相比于时间,温度的影响更显著;180 ℃热处理1,3和5 h时,试材的MOR,MOE与对照比未发生明显变化(降幅在3%以内),而顺纹抗压强度则明显低于对照,两介质中降低幅度分别在3.29%～9.58%和3.89%～7.18%;200 ℃以上处理时,不同时间处理的3种主要力学性质不仅显著或极显著低于对照,且各性质问的差异也达显著或极显著水平;对硬度的测试结果表明:180 ℃热处理时,试件的径面硬度和弦面硬度均随时间的延长而增大;200 ℃热处理3 h时,试件的硬度达最大,与对照差异达显著水平;随后热处理试件的硬度开始降低,220 ℃热处理5 h后试件的硬度又明显低于对照.在隔氧的油介质中进行热处理,4种主要力学性质的变化程度低于空气介质处理材,当温度高于200 ℃时,两介质处理间的差异达显著水平.而热处理过程中木材主要化学组成与横切面微观结构变化的差异,反映了4种主要力学性质对不同条件热处理时表现出的响应差异. 相似文献
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Heat treatment is an alternative to the chemical treatment in wood preservation, which has been used to some extent in improving timber quality. However, reduction in strength properties has been one of the major limitations in the use of this technique and therefore investigations on the use of various pre-treatment methods are highly essential. Wood samples from Scots pine were immersed in already boiling water (100°C) for 20 min followed by 2 h of heat treatment at 160 and 200°C. The acidity and strength properties were determined by measurement of pH and static bending test, respectively. There were no significant changes in pH due to preboiling in both heat-treated and untreated wood. Similarly, preboiling did not result in any appreciable differences in strength both before heat treatment and during heat treatment at 160°C. However, for 200°C heat treatment preboiling reduced significantly the degree of strength loss as indicated by 19.4% reduction in modulus of rupture in preboiled wood compared to 26.6% reduction in unpreboiled wood. From the results of this study it is evident that preboiling has a buffering effect on wood during heat treatment and the higher the intensity of heat treatment the higher the significance of the buffering effect of pre-boiling. 相似文献
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Variations in compression strength and surface roughness of heat-treated Turkish river red gum (Eucalyptus camaldulensis) wood 总被引：1，自引：0，他引：1
This article reports the effects of heat treatment on compression strength parallel to the grain, the surface roughness [average roughness (Ra)], and the air-dry den-sity of wood from the river red gum tree (Eucalyptus camaldulensis Dehn.) planted in Turkey. Eucalyptus wood was heat-treated at temperatures varying from 120° to 180°C for durations of 2–10 h. Samples cut from the heat-treated wood were tested for air-dry density, compression strength parallel to grain, and surface roughness properties. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Based on the findings in this study, the results showed that density, compression strength, and surface roughness values decreased with increasing treatment temperature and treatment times. Eucalyptus wood could be utilized by using proper heat treatment techniques without any losses in strength values in areas where working, stability, and surface smoothness, such as in window frames, are important factors. 相似文献
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Thermal conductivity and diffusivity of wood 总被引：5，自引：0，他引：5
Summary Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have been performed with the
plane source technique on oven-dry hardwood (birch) samples at room temperature and at 100 °C. The influences of temperature,
density, porosity and anisotropy on thermal conduction were investigated. The measurements were done in longitudinal (parallel
to the grain) and transverse (intermediate between radial and tangential) directions. As the temperature increased from 20
to 100 °C, the thermal conductivity of each sample increased slightly for both longitudinal and transverse directions. The
effect of density and porosity on the thermal conductivity may be related to the presence of other scattering mechanisms such
as voids and cell boundaries. It seems that the dominant mechanism of heat transfer across the cell lumina in these types
of wood is the heat conduction through the voids. An attempt was made to explain the behaviour of the effective thermal conductivity
by adopting a model based on the ratio between heat conduction in parallel and serial layers of gas, liquid, and solid phases.
Received 7 May 1997 相似文献
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高温热处理对樟子松板材物理力学性能影响的研究 总被引：1，自引：0，他引：1
分别采用170、190、210℃三组处理温度对樟子松板材进行了高温热处理工艺试验,并对处理材和对照样进行了物理、力学性能测试:高温热处理工艺使樟子松木材的绝干密度下降、吸湿性降低,对其抗弯强度亦有较大影响,且此影响随温度升高而增大;对于抗弯弹性模量、顺纹抗压强度、表面硬度三项指标则基本无影响.在常规使用环境下,由于处理材与对照样之间存在含水率差异,除了210℃处理材的抗弯弹性模量、顺纹抗压强度、表面硬度比对照样略小外,170℃和190℃处理材的三项指标均不同程度高于对照样. 相似文献
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蒸汽压力对热处理材力学性能影响的机理研究 总被引：2，自引：0，他引：2
通过对樟子松和柞木分别在常压和一定蒸汽压力下进行热处理,比较了不同热处理木材与常规对照材的力学性能差异。结果表明:热处理使木材的抗弯强度和冲击韧性出现明显下降,然而,就抗弯弹性模量和顺纹抗压强度而言,除樟子松的MOE指标外,经过热处理的试材的性能指标都高于对照材。和常压热处理相比,压力蒸汽热处理进一步降低了试材的力学强度,但这一差异并不显著。木材化学组分分析表明,热处理材力学性能的变化主要归因于热处理过程中木材半纤维素的降解以及木素在热处理过程中的化学变化。 相似文献