Compressive Strength Parallel to Grain Variation of Different Clones of Populus deltoides Marsh.

In order to explore the differences in the compressive strength parallel to grain （CSPG） between different clones and individual woods of Populus deltoides Marsh., the CSPGs of 5 15-year-old P. deltoides clones were determined and analyzed. The results showed that there were significant differences in CSPG of wood between different clones of P. deltoides . The CSPG of the tested clones reached more than 41 MPa, which was higher than the average compressive strength of P. deltoides （32.94 MPa）. Similar to the changes of stem height, the CSPG of the clones gradually increased with the increase of stem height. However, there were significant differences in CSPG of an individual plant at different tree heights. The CSPG of P. deltoides clones was related with their growth traits, but not significantly. Therefore, it is expected to achieve simultaneous and independent improvement on CSPG and the growth of P. deltoides , so as to get excellent individuals with fast growth and high CSPG.

Compression Behaviors of Parallel Bamboo Strand Lumber Under Static Loading

In order to investigate the influence of length and compression directions upon behaviour of parallel bamboo strand lumber(PBSL)specimens,240 axial compression tests have been performed.With three similar one different typical failure modes,the mechanical performance for PBSL specimens under compression parallel to grain and perpendicular to grain are different as a whole.From the point of the characteristic values,the compression strength parallel to grain is 2.1 times of the compression strength perpendicular to grain.The elastic modulus for compression parallel to grain is 3.64 times of the compression strength perpendicular to grain.While the compression ratios along two compression directions are equal to each other.The bigger Poisson ratios for one typical side surface is 3.93 times of that for another typical side surface for PBSL specimens under compression perpendicular to grain,and the bigger value is equal to that for PBSL specimens under compression parallel to grain.Length can influence the mechanical properties of the PBSL specimens.The size 50 mm×50 mm×100 mm should be good choice for the standard or code to measure the compression strength.PBSL materials have better ductility under compression parallel to grain than that under compression perpendicular to grain.Stress-strain relationship models were proposed for PBSL specimens under compression parallel to grain and perpendicular to grain,respectively.These proposed models gave a good agreement with the test results.

Analysis of Factors Affecting Solidification Strength of Sludge in a Landfill Area of Shenzhen

Parallel and orthogonal tests are used to explore the influence law of the dosage and age of curing agent on the strength of solidified sludge. The test results show that: 1) The strength of solidified sludge is mainly related to the cement content and dry soil content, and presents a good linear relationship. The influence of gypsum content is not significant. As the age increases, the strength is greatly affected by the cement content. 2) At different ages, the unconfined compression strength of solidified sludge presents a linear relationship, and the change law of later strength can be predicted by early strength. 3) Degree of influence of curing agent dosage: cement dosage > gypsum dosage > dry soil dosage. The optimal mixture ratio is 8% of cement content, 30% of gypsum content (proportion of cement content), and 4 times of dry soil content (multiple of cement content).

Plato热处理工艺对云杉木材顺纹抗压性能的影响

采用Plato水热-常压过热蒸汽联合热处理工艺对云杉木材进行热处理,对不同温度水平处理前后云杉木材的顺纹抗压强度进行了测试。结果表明,未处理云杉木材的顺纹抗压强度为65.75 MPa,经130、145及160℃水热-常压过热蒸汽热处理后云杉木材的顺纹抗压强度分别为70.86、68.07和64.15 MPa,并运用化学成分分析法对热处理工艺对云杉木材顺纹抗压强度的影响进行了分析。

Experimental Study on Uniaxial Compressive Strength of Reservoir Ice

Uniaxial compression experiments on horizontal and ervoir were conducted at different temperatures and strain rates vertical samples of first-year freshwater ice in a res- with an electronic universal machine equipped with low temperature cabinet. The results show that there is no difference between the strengths of two horizontal samples with grain sizes ranging from 1 to 4 mm and 4 to 14 mm, while the strength of the 1--4 mm vertical samples is 1.4 times higher than that of the 4--14 mm vertical samples because of the change of crystal structure. For different load- ing directions, the strengths of the horizontal samples do not differ from those of the vertical samples with the same grain sizes. The relation among the uniaxial compressive strength, strain rate and temperature was established through data analysis in both the ductile and brittle regions.

Characterization of some Egyptian serpentinites used as ornamental stones

Egypt is characterized by wide occurrence of serpentinites, particularly in the central and southern parts of Eastern Desert. There are several cooperate factors that affect the serpentinites used as ornamental stones. These factors involve mineralogical characteristics (including mineral composition and microstructure parameter), physical properties and mechanical properties. Antigorite is an essential serpentinite mineral, with a minor amount of chrysotile. Talc, carbonates (magnesite and dolomite) and tremolite are the main associated minerals. Quality and quantity of associated minerals such as talc and carbonates (dolomite and magnesite) affect the properties of serpentinites used as ornamental stones. Carbonates are resistant to weathering but suffer from acidic cleaning agents in interior use, whereas serpentinites with a high content of talc used on external faces undergo an increase in volume and a consequent rapid degradation. Studied serpentinites are characterized by relatively small grain size with foliated texture, low water absorption, low porosity, and high abrasion resistance. In the samples studied the uniaxial compressive strength (UCS) varies between 89 and 189 MPa, with an average of 152 MPa. According to the classification of Bell (1992), sample No. B8 is very high in strength while the rest high in strength.

密度和含水率对重组竹顺纹抗拉强度的影响

【目的】探究不同密度和含水率下重组竹顺纹抗拉强度的变化规律,提出重组竹顺纹抗拉强度与密度、含水率的相关模型,为推进重组竹在工程中的应用提供依据。【方法】参考ASTM D143—14《木材无疵小试样的标准试验方法》,选取不同密度(1.1、1.2、1.3 g·cm^(-3))和含水率(4%、8%、12%、16%、20%)的重组竹试件进行正交抗拉试验,分析重组竹顺纹抗拉的主要破坏形态;采用线性模型和抛物线模型拟合重组竹顺纹抗拉强度随密度的变化规律,采用线性模型和ASTM模型拟合重组竹顺纹抗拉强度随含水率的变化规律,提出重组竹顺纹抗拉强度在密度和含水率双因素影响下的耦合模型。【结果】重组竹顺纹抗拉的主要破坏形态为平口破坏和斜口破坏,重组竹密度越大,平口破坏概率越大;重组竹含水率越大,斜口破坏概率越大。基于试验研究和数据拟合提出重组竹顺纹抗拉强度的单因素影响模型和双因素耦合模型,理论结果与试验结果吻合良好。【结论】在本研究密度范围内,重组竹顺纹抗拉强度随密度增加而增大、随含水率升高而减小。线性组合模型和ASTM组合模型均能较好预测重组竹顺纹抗拉强度在密度和含水率双因素影响下的理论值,线性组合模型计算更为简便,在实际预测中建议直接使用线性组合模型。

密度与含水率双因素作用下重组竹顺纹弹性模量的预测与分析

本研究选取3组不同密度(1.10、1.20、1.30 g/cm^(3))和5组不同含水率(4%,8%,12%,16%,20%)的重组竹试件进行顺纹抗拉、抗压试验,分析不同密度和含水率作用下重组竹顺纹抗拉、抗压弹性模量的变化规律。结果发现,重组竹顺纹抗拉、抗压弹性模量随密度的增大而增大,随含水率的升高而减小并趋于平衡;通过试验研究和数据拟合提出重组竹顺纹抗拉、抗压弹性模量的双参数耦合模型,线性组合模型和ASTM组合模型均能较好地预测重组竹顺纹抗拉、抗压弹性模量随密度和含水率变化后的理论值,顺纹抗拉弹性模量的实测值与线性组合模型和ASTM组合模型预测值之间最大误差为5.28%和8.20%;顺纹抗压弹性模量的实测值与线性组合模型和ASTM组合模型预测值之间最大误差为8.91%和8.67%,因线性组合模型计算更为简便,建议在实际应用中优先选用。

油污泥热解残渣改良粗粒硫酸盐渍土力学性能试验研究

为探究油污泥热解残渣改良粗粒硫酸盐渍土的力学性能,试验研究了残渣掺量和盐渍化程度对粗粒硫酸盐渍土回弹模量以及无侧限抗压强度的影响规律。结果表明:粗粒硫酸盐渍土的回弹模量和无侧限抗压强度均随残渣掺量的增加呈先提高后下降的趋势。当残渣掺量为10%时,各项力学性能提升最显著。此时回弹模量最大为245.52 MPa,无侧限抗压强度最大为0.48 MPa。随着含盐量增加,改良粗粒硫酸盐渍土的力学性能先提高后下降,且随残渣掺量的增加,非盐渍土较盐渍土的力学性能提升更加明显。根据X射线衍射(X-ray diffraction,XRD)和扫描电镜(scanning electron microscope,SEM)试验微观分析,油污泥热解残渣改良粗粒硫酸盐渍土主要由物理和化学两个因素共同作用,颗粒间的嵌挤摩擦和离子间的置换反应促就了改良盐渍土强度的提高。

Correlation of mechanical anisotropy with fine grain strengthening for Sm_(2)Co_(17)-type sintered permanent magnets

The as-solution-treated Sm_(2)Co_(17)-type magnets exhibiting a single 1:7 H phase with different average grain sizes(D) were designed.Anisotropy of bending strength(R_(bb))and compressive strength(R_(mc)) of the magnets were investigated.Moreover,the R_(bb) increases from 86 to 173 MPa with D decreasing from~52 to~18 μm for group c//h samples.The Hall-Petch correlation was employed to reveal the effect of grain size on mechanical properties of the magnets,giving deep understanding of the mechanical anisotropy characteristics.The relatively high Hall-Petch coefficient K^(Rbb)(0.79 MPa·m^(1/2)) gives rise to the largest R_(bb)(173 MPa) for group c//h samples.The mechanical anisotropy of the samples is well explained based on crystal structure and grain size features(grain boundaries).Grain refinement is an effective way to enhance the mechanical properties of Sm_(2)Co_(17)-type sintered magnets.

高强钢多道次热压缩晶粒尺寸模型

为准确描述300M高强钢在多道次热压缩过程中的晶粒尺寸演变行为,解决晶粒尺寸在不同再结晶过程之间不连续的问题,提出了包含15个待定参数的晶粒尺寸演化模型。在温度950~1150℃、应变速率0.01~10 s^(-1)、应变0~0.9、道次间保温时间0~600 s的范围内开展了双道次热压缩实验,结果表明,随着温度的升高和应变速率的降低,平均晶粒尺寸呈增加趋势;亚动态再结晶和静态再结晶在变形后保温大约3 min就发生地比较完全,在后续的保温过程中,晶粒长大非常缓慢。随着应变的增加,再结晶体积分数增加。基于实验结果,通过参数识别获得模型参数,平均相对误差为6.90%,平均相对偏差为3.3μm。将模型集成在DEFORM中,模拟了Ф90 mm×200 mm的圆柱形试样的平均晶粒尺寸变化,并在模锻压力机上开展了验证实验,结果表明所建立的双道次压缩晶粒尺寸演化模型能很好地预测300M高强钢平均晶粒尺寸的演化。

晶体粒径对花岗岩力学特性影响规律的试验研究

岩石晶体尺寸在空间分布上具有变异性,不同晶体尺寸岩石具有不同的力学特性。为研究晶体尺寸对岩石力学特性的影响规律,选取怒江拥巴段浅层弱风化花岗岩为研究对象,根据晶体尺寸将花岗岩分为粗粒、中粗粒、中细粒和细粒共4组;采用三轴压缩试验研究不同晶体粒径花岗岩的应力-应变响应特征,并在此基础上分析了花岗岩强度、刚度及破坏特征随晶体粒径的变化规律;最后结合花岗岩微观结构图像讨论了晶体粒径对其宏观力学特性的影响。研究表明:(1)同一地区晶体粒径较小的花岗岩具有较大的峰值抗压强度及对应的轴向压缩应变,细粒花岗岩的峰值抗压强度及其对应的轴向压缩应变分别为粗粒花岗岩的1.5~2.2倍和1.6~2.1倍;(2)晶体粒径从粗粒逐渐减小到细粒的过程中,花岗岩的抗剪强度和刚度均逐渐增大,其中黏聚力从13 MPa增加至32 MPa,内摩擦角从45.2°增加至52.5°,变形模量从1.0(归一化)增加至1.7~2.5,泊松比从0.29减小至0.22;(3)不同粒径花岗岩的微观结构具有显著差异,细粒花岗岩晶体颗粒的致密程度及晶体之间的胶结程度显著优于粗粒花岗岩。

某矿细粒级全尾砂充填材料性能研究及配比优化

为了确定某矿细粒级全尾砂充填的最佳工艺参数,进行了充填试验研究。试验过程中,分别开展了细粒级全尾砂物理化学性质试验、流动性试验、流变试验及充填体强度试验,获得了符合该矿的最佳充填配比参数。研究结果表明:当料浆浓度为68%时,料浆泌水率较低,且流动性和充填强度可以满足矿山充填要求;当胶凝材料为水泥时,一步骤充填推荐砂灰比为4∶1,二步骤充填推荐砂灰比为8∶1;当胶凝材料为细尾砂专用胶材时,一步骤充填推荐推荐砂灰比为8∶1,二步骤充填推荐砂灰比为12∶1。

不同海拔高度对毛竹主要物理力学性质的影响

就不同海拔高度对毛竹主要物理力学性质影响的研究,为竹材资源合理开发、高效科学加工利用有着十分重要的意义。结果显示:(1)气干密度、基本密度,都随毛竹自身轴向高度及海拔高度增加而增加。山脚与山顶的毛竹基本密度分别为0.699、0.715g.cm-3;气干密度分别为0.798、0.827g.cm-3,在0.05水平上经T-检验差异显著。(2)山脚与山顶毛竹的抗弯弹性模量、顺纹抗压强度、抗弯强度分别为12368.28、11934.07,55.858、59.840和183.203、196.293MPa,海拔高度对顺纹抗压强度、抗弯强度影响,在0.05水平上经T-检验差异显著。

荔枝树枝力学特性的试验研究

为获取荔枝树枝的力学特性参数,以糯米糍品种荔枝树枝为试验材料,在精密型微控电子式万能试验机上进行了压缩特性和剪切特性试验。测得荔枝树枝顺纹抗压强度平均值为32.77MPa,顺纹抗压弹性模量平均值为1068.02MPa,顺纹压缩能平均值为56.57N.m;树枝横纹抗压比例极限应力平均值为8.02MPa,横纹抗压弹性模量平均值为422.84MPa,横纹压缩能平均值为1.25N.m;树枝剪切强度平均值为9.52MPa,剪切功平均值为17.59N.m。采用统计软件对树枝力学特性参数进行相关性分析,结果表明:顺纹抗压强度和顺纹压缩能之间呈指数函数正相关关系;横纹抗压比例极限应力和横纹压缩能之间呈弱对数函数正相关关系;峰值剪切力、剪切功都与树枝横截面面积呈强线性正相关。试验结果为研制果树修剪机具提供了依据。

竹楠木顺纹力学性能试验研究

目的分析比较几种胶合木材料,研究竹楠木拉、抗压基本力学性能,给出基于木材强度设计值的计算方法为基础的竹楠木拉压强度设计值建议值.方法按照《木材物理力学性能试验方法》和《木材无疵小试样的试验方法》对竹楠木材顺纹抗拉和抗压进行试验研究,测得竹楠木顺纹抗拉、抗压强度.结果试验结果表明竹楠木抗压经历了弹性、弹塑性和破坏3个阶段,发生塑性破坏;抗拉经历了较长的弹性阶段后发生脆性破坏.试验得到竹楠木顺纹抗拉强度可达98.1 MPa,顺纹抗压强度可达73.3 MPa.结论竹楠木顺纹强度具有离散性,抗拉强度的离散性要高于其抗压强度.竹楠木胶合竹材能够满足建筑结构对材料抗拉压力学性能的要求,试验结果对竹楠木的合理利用和深入研究提供理论依据.

不同颗粒级配的某火山灰的力学性质试验研究

以吉林省靖宇县的红色火山灰为原材料,配制了5种不同级配的试样,通过比重、直剪和一维压缩试验测试了该火山灰材料的相对密度、剪切强度、压缩性等物理与力学特性,分析了颗粒级配对该火山灰的剪切和压缩力学特性的影响,为该材料的进一步应用提供参考。试验发现,所配制的火山灰试样的剪切特性与干砂土的抗剪性质类似,压缩特性都属于中压缩性土。

3种无损检测方法评估巨尾桉木材抗弯和抗压强度性质

为探讨不同无损检测方法评估木材强度性质的可行性及可靠性,该文分别运用纵向基频振动、超声波和应力波3种无损检测方法,对由广西东门林场采集的34株14年生巨尾桉人工林加工的191个无疵小试样进行了抗弯和抗压强度性质预测。首先采用3种无损检测设备获得无疵小试样的动态弹性模量,然后进行抗弯弹性模量(MOE)、抗弯强度(MOR)和顺纹抗压强度(σc)的测定,并分析3种无损检测结果与木材强度性质的关系。结果表明:纵向基频振动法、超声波法和应力波法获得的动态弹性模量Efr、Eus和Esw与静态MOE的相关系数分别为0.8166、0.7889和0.6347,均在0.001水平上显著相关;与MOR的相关系数分别为0.6940、0.6830和0.5673,均在0.001水平上显著相关;与σc的相关系数分别为0.8103、0.8093和0.6489,均在0.001水平上显著相关;其中应力波法测得的动态弹性模量Esw与木材强度性质的相关系数均为最低。可见,纵向基频振动法和超声波法能够比较精准地预测国标无疵小试样的MOE、MOR和σc,但应力波方法对无疵小试样进行测定时具有一定局限性。

考虑层理方向效应煤岩巴西劈裂及单轴压缩试验研究

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马尾松人工林木材主要材性家系间的变异

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