Experimental study on lightweight expanded clay at particle level:Breakage of isolated grains

In this study,more than 1500 particles of lightweight expanded clay aggregate(LECA)are individually loaded up to breakage,following different patterns of contact(from 2 to 7)using a purpose-built apparatus.Consequently,a statistical model for predicting the number of fragments into which a grain breaks as a function of the number of contacts and their diameter is proposed.The number of fragments is found to follow a statistical binomial-type distribution function that depends on the number of contacts.In addition,a model based on Bayesian networks,capable of assessing the number of fragments and their size(measured as normalized weight)as a function of the number of contacts,is implemented.The proposed method is applicable when performing discrete element method(DEM)simulations on granular media in which grain breakage plays a relevant role.

Modeling for critical state line of granular soil with evolution of grain size distribution due to particle breakage

Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.

Particle breakage of sand subjected to friction and collision in drum tests

This paper presents a laboratory experimental study on particle breakage of sand subjected to friction and collision,by a number of drum tests on granular materials(silica sand No.3 and ceramic balls)to investigate the characteristics of particle breakage and its effect on the characteristics of grain size distribution of sand.Particle breakage increased in up convexity with increasing duration of drum tests,but increased linearly with increasing number of balls.Particle breakage showed an increase,followed by a decrease while increasing the amount of sand.There may be existence of a characteristic amount of sand causing a maximum particle breakage.Friction tests caused much less particle breakage than collision tests did.Friction and collision resulted in different mechanisms of particle breakage,mainly by abrasion for friction and by splitting for collision.The fines content increased with increasing relative breakage.Particle breakage in the friction tests(abrasion)resulted in a sharper increase but with a smaller total amount of fines content in comparison with that in the collision tests(splitting).For the collision tests,the fines content showed a decrease followed by an increase as the amount of sand increased,whereas it increased in up convexity with increasing number of balls.The characteristic grain sizes D_(10) and D_(30) decreased in down convexity with increasing relative breakage,which could be described by a natural exponential function.However,the characteristic grain sizes D50 and D60 decreased linearly while increasing the relative breakage.In addition,the coefficients of uniformity and curvature of sand showed an increase followed by a decrease while increasing the relative breakage.

筑坝堆石料颗粒破碎及分形特性试验研究

为探究筑坝堆石料颗粒破碎现象,选取不同粗粒含量和含水量的堆石料作为研究对象,开展室内击实试验,分析土体的压实特性、颗粒破碎特性及分形特征,并揭示其力学响应机理。试验结果表明:随含水量的增加,堆石料的干密度先增大后减小。而最大干密度和最优含水量分别与粗粒含量呈现正相关和负相关。堆石料中出现明显的颗粒破碎现象,随粗粒含量和含水量的增加其颗粒破碎率随之增大。粗粒含量与含水量分别与分形维数成反比和正比关系,相较于含水量,粗粒含量对分形维数的影响更显著。

基于连续级配方程的粗粒料压实密度缩尺效应试验研究

根据双江口心墙堆石坝堆石料的原型平均设计级配曲线,采用剔除法、等量替代法、相似级配法和混合法等4种不同缩尺方法得到室内最大干密度试验成果。结合土的连续级配方程,采用级配面积与小于5 mm的颗粒质量分数P5构建的函数式作为级配量化指标,拟合出最大干密度与试验前级配曲线面积、P_(5)及最大粒径之间的关系,据此可推求出原型级配的最大干密度。通过分析得到试验前后级配量化指标之间的拟合公式,并利用试验前后级配量化指标的相对变化量B_(w)作为颗粒破碎的定量指标,探讨了缩尺方法对压实过程粗粒料颗粒破碎的影响。结果表明,采用等量替代法缩尺,B_(w)随粒径的增大呈减小趋势;而采用剔除法、相似级配法和混合法缩尺,B_(w)随粒径增大呈增大趋势。

揉搓式高粱脱粒装置的设计与性能试验

为了提高高粱联合收获时脱粒分离的作业质量,设计了一种揉搓式高粱脱粒滚筒。通过纹杆滚筒和与之相配合的栅格滚筒的相互作用,加强对物料挤压、揉搓、翻转,实现高粱籽粒的脱粒与分离,降低损失率和籽粒破碎率;采用二次通用旋转组合设计,以籽粒破碎率和夹带损失率为主要指标,选取喂入量、纹杆滚筒转速、栅格滚筒转速为影响因素,对揉搓式高粱脱粒装置进行了试验。结果表明:随着喂入量的增加,夹带损失率和破碎率均为先降低后升高;随着纹杆滚筒转速的增大,破碎率逐渐增加,夹带损失率先降低后升高;当栅格滚筒正转时,随着转速的升高,破碎率和夹带损失率均呈先降低后升高的趋势;当栅格滚筒反转时,随着转速的升高,破碎率和夹带损失率均呈升高的趋势;通过回归方程在约束条件下求最优解,得到脱粒装置最优参数组合为:喂入量为0.76kg·s^(-1)、纹杆滚筒转速为403r·min^(-1)、栅格滚筒转速为35r·min^(-1),在最优参数组合下籽粒破碎率为0.21%,夹带损失率为1.03%。研究结果可为该装置的田间试验提供依据。

红砂岩粗粒土破碎性质及累积变形模型研究

红砂岩粗粒土具有易破碎性,在动力荷载反复作用下会发生颗粒破碎,导致路基产生明显的工后沉降。针对红砂岩粗粒土颗粒破碎的特点,采用室内动三轴试验仪进行了不同工况下的动力荷载试验,研究了动弹性模量、动弹性应变与粒径大小之间的关系,以及颗粒破碎率与颗粒形状系数变化率的关系。根据试验材料的动力破碎特性,构建了考虑颗粒破碎的累积变形模型,并对模型进行了修正。研究结果表明:颗粒粒径越大,动弹性应变越大,动弹性模量越小;动弹性应变先快速增大后逐渐趋于稳定,动弹性模量随着加载次数的增加不断减小,土体出现应变软化现象。颗粒形状系数变化率变化趋势与颗粒破碎率变化趋势相似,随着加载次数的增加,形状系数值趋近于1。此外,所构建的累积变形模型包含了应力状态参数、物理状态参数和拟合参数,能够较好地描述颗粒破碎状态下的红砂岩粗粒土的累积变形趋势。根据试验数据的反算结果,对累积变形模型的拟合参数进行了确定,便于在实际工程应用中对路基变形进行计算。由于室内试验与工程实践现场工况有一定区别,提出了模型修正系数ψ,提高了模型的预测精度。该研究结果可为红砂岩粗粒土路基设计、施工及运营提供理论依据和工程应用基础。

鲜食玉米果穗的物理力学特性

目的:针对鲜食玉米在机械脱粒过程中存在籽粒破损的问题,研究对籽粒造成挤压破坏的最小挤压力和实现玉米籽粒与玉米芯分离的最小轴向及径向剪切力。方法:采摘3个不同时期的果穗,利用万能拉压型试验机对果穗开展挤压及剪切试验。结果:结果表明,果穗的籽粒会经历3个阶段,即籽粒的形变、破损、爆浆阶段。在不同采摘期,含水率均值分别在71.51%±2.00%、64.96%±2.00%、50.21%±2.00%的条件下,籽粒破损临界点所对应的试验力的平均值分别为81.7、644.5、960.4 N;轴向剪切试验结果表明,果穗所受到的轴向剪切力的平均值分别在25.3、60.8、234.1 N时,第1、2排籽粒被完全切除;径向剪切试验结果表明,单籽粒果穗被径向切除的试验力的平均值分别为20.5、12.1、6.8 N。结论:本研究获得的重要物理力学参数可为鲜食玉米脱粒机关键部件的设计提供理论依据和参考。

Influence of broken kernels content on soybean quality during storage

Although it is recognized that the post-harvest system is most responsible for the loss of soybean quality,the real impact of this loss is still unknown.Brazilian regulation allows 15%and 30%of broken soybean for group I and group II(quality groups),respectively.However,the industry is not informed about the loss in the quality parameters of soybeans and its impacts during long-term storage.Therefore,the objective was to evaluate the effect of the breakage kernel percentage of soybean stored for 12 months.Content of 15% of breakage kernels did not affect soybean quality.However,content of 30% of breakage kernels affected significantly soybean quality,which was evidenced by the increase of up to 75% in moldy soybeans,72% in acidity,50% in leached solids,27% in electrical conductivity,and the decrease of up to 12% in soluble protein,6.4% in germination and 3.5% in thousand kernel weight after 8 months of storage.Although the legislation establishes a percentage limit,it is recommended to store soybeans with up to 15% breakage kernels.On the contrary,values higher than that can cause a significant reduction in soybean quality,resulting in commercial losses.

基于转速调控的玉米收获机脱粒装置优化研究

为进一步优化我国玉米收获机的综合作业效率,实现精准收获的智能化提升,以脱离装置为研究对象,进行转速调控的优化研究。以玉米收获机的组成及作业原理为基础,搭建过程参数与脱粒滚筒之间的转速调控数学模型,进行装置的控制优化与组件改进。同时,进行基于转速调控功能提升的玉米收获机整机作业试验,结果表明:经深度转速参数动态计算与架构式调控布局设计,玉米收获机的各项评价参数得到明显改善,籽粒破损率与平均含杂率可分别降低至0.58%与0.76%,在转速调控下果穗脱净率相对提升8.00%,整机运行稳定可靠,高于玉米收获机设计的各项农艺性指标要求。

铁路粗粒土填料蠕变及颗粒破碎特性试验研究

粗粒土被广泛用作铁路路基填料,其蠕变特性对路基的长期沉降与服役性能有重要影响。利用自制粗粒土填料单元模型试验系统,开展系列二维蠕变试验,探索竖向应力、降雨入渗等因素对蠕变及颗粒破碎的影响;试验后对试样进行颗粒分析,据此建立能同时考虑降雨入渗量、破碎率Bg和荷载的双曲线蠕变预测模型,并且基于确定的静力荷载分布模式及含水率分布公式,建立了粗粒土路基蠕变变形分析模型,分析不同轨道型式条件的路基蠕变变形。结果表明,在50~300 kPa荷载作用下,粗粒土填料蠕变稳定后应变为0.05%~0.101%,且呈衰减型增长趋势;在蠕变过程中颗粒破碎以大粒径颗粒破裂为主、研磨为辅,降雨入渗导致粗粒土填料的颗粒破碎,粒径发生改变;粒组含量的变化总量随荷载增大而显著增大,随降雨入渗强度增加呈先迅速增加而后缓慢增加的趋势;蠕变预测模型计算值与试验值较为吻合,降雨入渗引起路基蠕变变形增幅可以达到80%。研究结果可为高速铁路粗粒土路基变形分析提供参考。

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.

玉米亲本自交系及杂交种机械粒收质量相关指标分析

以玉米亲本自交系及杂交种为试验材料,于2019—2020年对玉米植株地上倒3—5节的折断力、节间长、节间粗及收获时籽粒含水率、破碎率、抗压能力、脱水速率等指标进行分析,并筛选茎秆强度强、籽粒机收质量好的玉米材料,为适宜机械粒收玉米新种质的培育奠定基础。结果表明,自交系E8501和杂交种郑单6122的茎秆折断力较大,自交系郑58、ZC1456和杂交种郑单958折断力较小;自交系郑682和杂交种先玉335的节间较长,自交系郑588和杂交种郑单1002的节间较短;自交系郑P6、PH6WC和杂交种DK517节间较粗,自交系郑682和杂交种郑单6098节间较细。聚类分析结果表明,玉米亲本自交系E8501、郑7541、郑H71、郑V89M、郑D58M、HCL1645和PH4CV及杂交种郑单6386、郑单6122、DK517、郑单6095、郑单6098、郑单1868和郑单1002的茎秆强度较强。杂交种郑单958的籽粒含水率较高,郑单6122较低;自交系郑H71和杂交种郑单958、郑单1868的籽粒破碎率较高,自交系PH4CV和杂交种DK517的籽粒破碎率较低;自交系PH4CV和杂交种郑单6122的籽粒抗压能力较大,自交系郑H71和杂交种郑单958的籽粒抗压能力较小。玉米收获时籽粒含水率≤26.87%就能够满足籽粒破碎率≤5%的机械粒收标准。在上述14个抗倒伏能力较强的玉米材料基础上,最终筛选出亲本自交系E8501、郑7541、郑H71、郑V89M、郑D58M、HCL1645和PH4CV以及杂交种DK517、郑单6122、郑单6386和郑单6098为抗倒伏较强且机械粒收质量佳(籽粒含水率≤26.87%且破碎率≤5%)的材料。

不同类型煤颗粒侧限压缩变形破碎特性试验研究

煤与瓦斯突出等动力灾害严重制约了矿井的安全生产,而不同类型煤颗粒的加载破碎特征反映了煤体结构、力学特性以及能量存储行为,对煤与瓦斯突出灾害研究具有重要的意义,但目前缺少煤颗粒的破碎特性研究。因此,选取了原煤和构造煤颗粒,开展了不同粒径级配和应力条件下的侧限加载实验研究。结果表明,加载过程依次分为滑移阶段、破碎阶段和压固阶段。在滑移阶段和破碎阶段构造煤抗变形能力均弱于原生煤,但是在压固阶段其应变硬化趋势明显强于原生煤。应力虽然会较大程度影响煤颗粒的相对破碎率,但是在压固阶段该影响较弱。加载过程中由于中粒径中部分煤颗粒结构不稳定,加载过后的煤颗粒存在明显粒径丢失现象。同时粒径级配也影响着煤颗粒的破碎,单一级配试样组中大粒径的试样相对破碎率更高,混合级配试样组的相对破碎率整体比单一级配的要低。相比于原生煤,构造煤的大、中粒径煤颗粒绝对破碎率更高,且破碎过程中更倾向于破碎成粒径更小的煤颗粒,构造煤颗粒破碎程度总高于原生煤。总体而言实验中构造煤颗粒应变硬化现象明显、破碎程度较高,甚至呈现流变特征,这是导致构造煤孔隙率小,渗透率更低的根本原因。且外界对构造煤颗粒输入的能量大都耗散在煤颗粒的摩擦、破碎以及塑性变形,因而储存在其本身的弹性能较低。

基于微积分理论的玉米收获机作业效率优化

为提升玉米收获机的作业效率,提出以微积分控制理论为优化主导,针对其核心结构与作业控制展开应用性研究。以通用型玉米收获机的主要作业流程为依据,结合整机作业过程特点,搭建用于收获机各环节的微积分控制优化模型,针对机体的核心结构及执行部件进行相适应性设计,给出微积分算法下的导向控制执行系统与干扰控制系统设计,并展开针对性的收获作业试验。试验结果表明:基于微积分理论的玉米收获机结构与控制设计,收获含杂率与籽粒破碎率明显降低,系统运行准确、平稳,整机的作业效率相对可提升9.26%,对于我国类似农用收获机械的持续创新有重要的参考价值。

红砂岩粗粒土动力试验及颗粒破碎模型研究

铁路路基建设需要经过泛红砂岩地区,红砂岩路基的稳定性对列车安全起到至关重要的作用。为研究列车荷载对红砂岩粗粒土动力特性以及颗粒破碎的影响,采用室内大型动静三轴试验系统,开展动力荷载下的红砂岩试样动力响应测试,分析了粒径大小、加载次数对轴向应变、动力软化以及颗粒破碎的影响。根据动力破碎三轴试验结果,构建了动力作用下的颗粒破碎模型,并对模型进行了验证。研究结果表明:在加载次数一定的条件下,颗粒粒径越大对应的轴向应变越大;颗粒粒径越小,越早完成颗粒破碎及土体结构调整。粗粒土软化曲线呈半对数关系,颗粒粒径越大,软化系数越小。动力荷载下,大粒径颗粒主要演化为下一级粒径颗粒和细小粒径颗粒,破碎形式为研磨,存在一个极限破碎级配。根据动力破碎试验建立了动力破碎的概率密度函数f,构建了动力条件下的颗粒破碎模型。该模型能够较好的模拟动力作用下的颗粒破碎过程。Marsal颗粒破碎率Br与颗粒破碎模型中的死亡率Ps-t呈线性关系。研究结果能为铁路路基工程相关设计提供一定的理论参考价值。

基于大直径三轴试验的钙质砂相对破碎率公式修正

钙质砂因特殊的成因,具有不规则形状和复杂孔隙等特征,容易发生颗粒破碎。本文对南海某岛礁天然钙质砂进行等向压缩试验和大直径三轴排水试验,同时测量颗粒相对破碎率,结果表明:钙质砂强度随轴向应变逐渐增大,达到峰值后明显软化,且峰值偏应力随围压增大而增大;颗粒破碎随着剪切逐渐发生,且围压越大破碎程度越大。采用描述颗粒破碎的SIMSAND模型预测排水条件下的三轴剪切试验,通过试验与预测结果的对比,揭示了模型对钙质砂预测的局限性。本文改进了SIMSAND模型,提出了围压不超过1 MPa时的颗粒相对破碎率公式,优化后的公式能更合理地预测峰值应力对应的轴向应变和颗粒破碎程度的演化。

A constitutive model for granular materials considering grain breakage

A particle breakage has a significant impact on the mechanical behavior of granular materials. In this paper, we present an elasto-plastic model with two yield surfaces to which the influence of particle breakage has been introduced. The main feature of this model is to incorporate the change in the critical state line (CSL) consequent to the grain breakage induced by isotropic and deviatoric stresses during loading. For this purpose we propose a breakage function which connects the evolution of the CSL to the energy consumed. Results from earlier studies on drained and undrained compression and extension triaxial tests were used to calibrate and validate the model. Comparison between earlier results and our simulations indicates that the model can reproduce with good accuracy the mechanical behavior of crushable granular materials and predict the evolution of the grain size distribution during loading.

静动力荷载作用下路基粗粒料力学特性试验研究

粗粒土因其良好的力学性能被广泛应用于路基建设中,但长期荷载作用下填料的变形严重影响了道路结构的安全运营。为了揭示典型路基应力水平及交通荷载条件下粗粒土的变形及强度演化,开展了一系列粗粒土填料静动力学特性试验,并进一步分析了静动力作用下填料破碎特征及差异。研究表明,低围压情况下,较小的轴向应变就可以使材料达到峰值应力状态,且围压的增加可显著提升填料峰值强度。不同围压下,填料在剪切过程中均出现剪胀现象,其中围压小于300 kPa试样的最终体应变均大于0。在动力试验中,填料轴向累积应变在相同加载次数下随着动偏应力的增加而增大,随围压的增加而减小,且前500次加载所造成的轴向应变占总应变的80%。静动力作用下的填料颗粒破碎形式存在差异,静荷载作用下的颗粒破碎主要以边角及整体断裂为主,而动荷载下主要以表面研磨和边角轻微断裂为主。

Evaluation of grain breakage sensitivity of maize varieties mechanically-harvested by combine harvester

A high grain breakage rate is the main problem that occurs during mechanical maize harvest in China.The breakage sensitivity of different varieties was significantly different,and the breakage resistance is heritable.Therefore,breakage resistant variety screening can help improve the field production efficiency and provide references for breeding work.In this study,42 varieties of maize were harvested with the same mechanical parameters and the same manipulator on a range of harvest dates at experimental stations in Xinxiang,Henan Province,in 2017 and Changji,Xinjiang Province,in 2018 to determine the sensitivity of grain moisture content on grain breakage rate during machine harvest for different varieties.The integral value of the grain breakage rate curve corresponding to the range of 15%to 30%grain moisture content was used as an index that expressed the sensitivity of maize grains to breakage depending on grain moisture content(BSW).Forty-two varieties were categorized as having weak,intermediate,or strong BSW.Among the same four varieties in the two stations,Lianchuang 825 and Lianchuang 808 were classified as sensitive and fragile varieties,Shandan 650 was classified as an intermediate variety,Zeyu 8911 was divided into weak sensitive and breakage-resistance varieties in Xinxiang and intermediate varieties in Changji.The BSW classification results at the two experimental sites were generally consistent,indicating that breakage sensitivity due to moisture content may be a relatively stable genetic characteristic.This study suggested that the integral method for determining BSW can be used to assess the resistance of different maize varieties to grain breakage during mechanical harvesting.The integral method was used to identify twelve breakage-resistant varieties in Xinxiang Station,and six breakage-resistant varieties in Changji Station.This study provides a method for screening maize varieties that are suited to mechanical grain harvesting and for studying the mechanisms of grain breakage resistance.