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.

Grain crushing in geoscience materials-Key issues on crushing response,measurement and modeling:Review and preface

Grain crushing is commonly encountered in deep foundation engineering,high rockfill dam engineering,railway engineering,mining engineering,coastal engineering,petroleum engineering,and other geoscience application.Grain crushing is affected by fundamental soil characteristics,such as their mineral strength,grain size and distribution,grain shape,density and specimen size,and also by external factors including stress magnitude and path,loading rate and duration,degree of saturation,temperature and geochemical environment.Crushable material becomes a series of different materials with the change in its grading during grain crushing,resulting in a decrease in strength and dilatancy and an increase in compressibility.Effects of grain crushing on strength,dilatancy,deformation and failure mechanisms have been extensively investigated through laboratory testing,discrete element method(DEM)modelling,Weibull statistics,and constitutive modelling within the framework of the extended crushing-dependent critical state theory or the energy-based theory.Eleven papers summarized in this review article for this special issue addressed the above issues in grain crushing through the advanced testing and modelling.

Bounding surface plasticity model for stress-strain and grain-crushing behaviors of rockfill materials

Crushing of grains can greatly influence the strength,dilatancy,and stress-strain relationship of rockfill materials.The critical state line(CSL)in the void ratio versus mean effective stress plane was extended to the breakage critical state plane(BCSP).A state void-ratio-pressure index that incorporated the effect of grain crushing was proposed according to the BCSP.Rowe’s stress-dilatancy equation was modified by adding the breakage voidratio-pressure index,which was also incorporated into the formulations of the bounding stress ratio and plastic modulus.A BCSP-based bounding surface plasticity model was proposed to describe the state-dependent stressstrain behaviors and the evolution of grain crushing during shearing process of rockfill materials,and was shown to sufficiently capture the breakage phenomenon.

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。

Effects of particle size on crushing and deformation behaviors of rockfill materials

Strength and deformation behaviors of rockfill materials,key factors for determining the stability of dams,pertain strongly to the grain crushing characteristics.In this study,single-particle crushing tests were carried out on rockfill materials with nominal particle diameters of 2.5 mm,5 mm and 10 mm to investigate the particle size effect on the single-particle strength and the relationship between the characteristic stress and probability of non-failure.Test data were found to be described by the Weibull distribution with the Weibull modulus of 3.24.Assemblies with uniform nominal grains were then subjected to one-dimensional compression tests at eight levels of vertical stress with a maximum of 100 MPa.The yield stress in one-dimensional compression tests increased with decreasing the particle size,which could be estimated from the single-particle crushing tests.The void ratio-vertical stress curve could be predicted by an exponential function.The particle size distribution curve increased obviously with applied stresses less than 16 MPa and gradually reached the ultimate fractal grading.The relative breakage index became constant with stress up to 64 MPa and was obtained from the ultimate grading at the fractal dimension(a?2:7).A hyperbolical function was also found useful for describing the relationship between the relative breakage index and input work during one-dimensional compression tests.

Influence of some rock strength properties on jaw crusher performance in granite quarry

The influence of rock strength properties on Jaw Crusher performance was carried out to determine the effect of rock strength on crushing time and grain size distribution of the rocks.Investigation was conducted on four different rock samples namely marble,dolomite,limestone and granite which were representatively selected from fragmented lumps in quarries.Unconfined compressive strength and Point load tests were carried out on each rock sample as well as crushing time and size analysis.The results of the strength parameters of each sample were correlated with the crushing time and the grain size distribution of the rock types.The results of the strength tests show that granite has the highest mean value of 101.67 MPa for Unconfined Compressive Strength(UCS) test,6.43 MPa for Point Load test while dolomite has the least mean value of 30.56 MPa for UCS test and 0.95 MPa for Point Load test.According to the International Society for Rock Mechanic(ISRM) standard,the granite rock sample may be classified as having very high strength and dolomite rock sample,low strength.Also,the granite rock has the highest crushing time(21.0 s) and dolomite rock has the least value(5.0 s).Based on the results of the investigation,it was found out that there is a great influence of strength properties on crushing time of rock types.

干湿循环对不同粒径堆石颗粒破碎强度的影响研究

高心墙堆石坝在运行期库水位变化可达60 m以上,库水位变动范围内的堆石体受干湿循环作用易产生较大的后期变形,会导致坝顶出现纵向裂缝,影响高心墙堆石坝的安全稳定运行。干湿循环对堆石料长期劣化变形的影响已有大量的试验研究,然而干湿循环对不同粒径筑坝堆石颗粒破碎强度的影响研究相对较少。对不同粒径的板岩堆石颗粒进行了干湿循环作用后的单颗粒破碎试验,结果表明,板岩颗粒的荷载-位移曲线及其对应破碎模式可以分为4类,颗粒破碎时对应的峰值荷载和破碎强度均值随循环次数的增加而逐渐减小。不同粒径和循环次数下板岩颗粒的破碎强度均服从Weibull分布,特征破碎强度与循环次数间呈幂指数关系,表明板岩颗粒力学性质的劣化速度逐渐减慢。不同循环次数下板岩颗粒的特征破碎强度均有较为明显的尺寸效应,尺寸效应与循环次数呈负相关关系。

果穗大小对玉米机械粒收籽粒破碎率的影响

为明确不同大小果穗穗粒特性对玉米机械粒收籽粒破碎率的影响,以玉米品种先玉1171和正红505为试验材料,将果穗分大穗、中穗和小穗,测定不同收获时期玉米果穗的农艺性状、力学强度、籽粒含水率和籽粒破碎率等指标,探讨不同大小果穗玉米籽粒含水率和力学强度变化规律,分析果穗大小对玉米机械粒收籽粒破碎率的影响。结果表明:随收获期推迟先玉1171籽粒破碎率表现为先降低后略微上升的趋势,正红505表现为下降趋势,品种间籽粒破碎率差异逐渐缩小。各时期小穗机械粒收籽粒破碎率均显著低于中穗和大穗,正红505小穗籽粒破碎率较中穗、大穗分别降低16.98,20.96百分点,先玉1171小穗籽粒破碎率较中穗、大穗分别降低了18.63,22.43百分点。随收获期的推迟玉米籽粒含水率逐渐降低,各时期正红505籽粒含水率均显著高于先玉1711。先玉1171小穗籽粒含水率显著高于中穗和大穗,而正红505小穗籽粒含水率低于中穗和大穗。先玉1171小穗籽粒胚乳穿刺强度多显著低于中穗和大穗;正红505果穗大小间籽粒力学强度差异不显著。相关分析表明,籽粒破碎率与含水率、穗长、穗粗和果穗体积呈显著或极显著正相关,而与籽粒力学强度极显著负相关。适度降低玉米果穗穗长、穗粗和果穗体积,可显著降低机械粒收玉米籽粒破碎率。因此,生产上可通过选择小果穗玉米品种,或通过增密等栽培措施降低果穗大小,是降低机收籽粒破碎率有效措施。

不排水条件下颗粒破碎粗粒土的动力特性分析

地震荷载作用下堆石等土料会发生颗粒破碎,从而导致其动力特性与不发生颗粒破碎的土料有很大的区别。为了探讨破碎粒状材料在循环荷载作用下的力学特性,对人工制备的粒状破碎土料进行了频率为1.0 Hz的循环加载固结不排水(consolidation undrained,CU)三轴试验,试验围压为100、200、300、400 kPa。研究结果表明:试样均为压缩破坏,呈应变硬化型;且不同激振力下的轴向应变曲线分为三段,即初始骤升段、中间平衡段和最终破坏段,并且每一阶段的长短和试样的变化均有所不同;动孔压随循环振次增大而增大,且在相同围压下激振力越大动孔压上升得越快。对动强度曲线分析发现,应力比越小动强度曲线越低;阻尼比整体上随着动剪应变的增大而逐渐增大,并且相同围压下激振力越小则阻尼比越小。颗粒破碎的影响因素有激振力、围压和振次等共同作用,不同围压(激振力)下各因素的影响大小不一、此消彼长,且随着围压增大颗粒破碎程度均逐渐增大。

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。

木材试件长度对其顺纹抗压强度性能的影响

为探究试件长度对针叶材和阔叶材顺纹方向轴压力学性能变化规律的影响,基于白蜡、冷杉和云南松3种木材的不同尺寸试件开展轴心受压试验,采用Weibull最弱链理论计算3种木材抗压强度长度尺寸效应系数,使用测试参数借助有限元软件模拟木试件轴压力学行为。结果表明:木材顺纹抗压强度和峰值应变有显著尺寸效应,试件长度从40 mm增加至80 mm时,3种木材试件平均抗压强度下降幅度分别为4.10%、7.19%、5.78%,平均峰值应变下降幅度分别为46.38%、70.07%、33.49%;白蜡、冷杉和云南松抗压强度长度尺寸效应系数(分别为0.06、0.11、0.09)可实现测试尺寸不同时3种木材测试抗压强度相互转换,使用该系数调整长度为100 mm试件的抗压强度,误差仅为0.76%、1.9%、1.06%;基于OpenSees纤维截面模型,可较好地模拟木构件轴心受压时非线性行为,但需考虑尺寸效应对木材力学参数的影响。

新能源汽车用高强韧6063铝合金型材挤压工艺研究

研究了新能源汽车用6063铝合金型材挤压工艺对其晶粒组织和力学性能的影响。结果表明,在铸锭加热温度450℃、挤压速度9 m·min^(-1)的工艺条件下,6063铝合金空心薄壁型材的强度、塑韧性、折弯性能、压溃性能等综合性能最佳,材料的平均晶粒尺寸达到70μm,晶粒组织细小且均匀,6063铝合金的屈服强度(R_(p0.2))、抗拉强度(R_(m))及延伸率(A_(50))分别可达到221 MPa、253 MPa、16.9%,在弯曲试验及压溃试验后无明显裂纹,获得了满足应用要求的新能源汽车用高强韧铝合金型材。

基于不同规范设计的重组竹顺纹抗压强度对比分析

【目的】为了更好推进重组竹在工程中的应用。【方法】分别参考中国和美国木结构试验设计方法,对重组竹进行顺纹抗压试验,对不同规范设计下重组竹的强度标准值与强度设计值进行对比分析。【结果】中国规范设计的重组竹顺纹抗压试件典型破坏形态主要有局部屈曲破坏、斜向剪切破坏、混合破坏,美国规范设计的重组竹顺纹抗压试件破坏形态主要是剪切破坏。【结论】分别选取正态分布、威布尔分布、对数正态分布3种分布模型对试验结果进行拟合,基于参数法和非参数法分别确定中美规范下重组竹顺纹抗压强度标准值和设计值。中国规范下重组竹顺纹抗压强度标准值与设计值分别为61.69 MPa和21.84 MPa,分别是美国规范下的1.11倍和1.55倍。推算出重组竹顺纹抗压强度标准值尺寸效应系数S为0.019,并提出中美规范下重组竹顺纹抗压强度设计值转化公式。

煤矸石的强度特征试验研究

通过中型三轴试验及现场大型直剪试验对煤矸石的强度特性进行了系统研究,得到了煤矸石强度包线的形式和参数以及煤矸石抗剪强度随粗颗粒(粒径D>5.0mm)含量的变化规律,并对试验中最大主应力差及颗粒破碎量进行多元统计分析,得到围压、孔隙比及粗料含量的变化规律。

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。

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.

火炬松种源顺纹抗压强度的变异与木材密度的关系

同一环境１０年生火炬松种源试验林材性分析结果表明：①３ｌ个火炬松种源间顺纹抗压强度近似于正态分布，其均值幅度为２３．７～２９．７ＭＰａ，对照种源为２６．６ＭＰａ，处于中等水平。方差分析表明种源间顺纹抗压强度差异显著，但多重比较显示仅部分种源间有显著差异；顺纹抗压强度广义遗传力为０．６１８，种源内顺纹抗压强度差异大于种源间，说明在种源选择的基础上再进行个体选择，效果会更好。②基本密度、气干密度和绝干密度间相关极为显著，三者与高度相关，非破坏性取样测定基本密度可很好预估顺纹抗压强度值。③顺纹抗压强度值与胸径、材积负相关，顺纹抗压强度值与晚材率正相关，材性育种可选择生长快、晚材率高的种源、个体来解决“生长快强度稍低”矛盾。④原产地纬度与顺纹抗压强度正相关显著，高纬度种源引种到低纬度区域种植，其顺纹抗压强度值有增大的趋势。

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。

火炬松种源顺纹抗压强度变异及与树龄、晚材率、木材密度相关分析

福建引种火炬松种源试验结果表明:31个种源15年生木材顺纹抗压强度均值为39.89 MPa,变化范围为32.85～46.13 MPa;种源间木材顺纹抗压强度差异显著,其广义遗传率为hf＞0.429,且随株内年轮数的增加或树龄的增大而明显增大;种源内个体差异大于种源间变异,栽培环境对木材顺纹抗压强度有着显著的影响.31个参试种源木材顺纹抗压强度与其树高、木材密度、晚材率和生长轮年龄呈显著正相关,与其胸径呈显著负相关.株间相同生长发育阶段或相同树龄情况下,年轮宽度与顺纹抗压强度呈负相关,这种负相关系数随着树龄增大而逐渐减小.美国东部海岸地区原产地种源经度与其顺纹抗压强度呈显著负相关,其原产地夏季降水量及其与年降水量的比值与顺纹抗压强度为显著的正相关;南部墨西哥湾地区原产地种源经度与其顺纹抗压强度则呈显著正相关,夏季降水量及其与年降水量的比值与顺纹抗压强度为不显著的负相关.原产地纬度、经度、1月份平均最低温、年均温、6～9月份降水量、年降水量、6～9月份降水与年降水之比和无霜期8个因子中,种源原产地纬度对顺纹抗压强度影响多为负相关.

马尾松人工林木材主要材性家系间的变异

对25个家系马尾松人工林木材主要物理力学性能进行测定和比较分析。结果表明,马尾松人工林木材气干密度由大到小居前五位的家系依次为378、329、317、341、335,顺纹抗压强度值由大到小居前5位的家系依次是335、350、372、325、329;家系341和350马尾松人工林木材体积干缩系数和差异干缩均较小,尺寸性稳定均较好。方差分析表明,家系对马尾松人工林木材主要物理力学性能影响显著。多重比较分析表明,马尾松人工林木材气干密度、体积干缩系数、差异干缩以及顺纹抗压强度各家系间大都表现为差异显著或极显著。家系335、341、350、378可作为马尾松人工林木材品质选育的优良材料。