稻谷堆修正剑桥模型参数的测定及含水率对其影响

使用TSZ-6A应变控制式三轴仪对不同含水率的稻谷堆(镇稻18号)进行三轴压缩试验,根据修正剑桥模型理论及试验数据计算出稻谷堆该模型的五个参数:临界状态应力比M、对数硬化模量λ、等向膨胀指数κ、弹性模量E、泊松比υ;由粮食孔隙测定仪测定出稻谷堆修正剑桥模型的第6个参数:初始孔隙比e_0。试验结果表明:当稻谷堆含水率范围为9.21%～16.96%w.b.时,临界状态应力比M的范围是1.761 9～2.037 3;初始孔隙比e_0的范围是1.144 1～1.296 2;对数硬化模量λ的范围是0.165 8～0.174 7;等向膨胀指数κ的范围是0.130 6～0.138 5。其中e_0、λ、κ随着含水率的增加而增加,而含水率对M无显著影响。当含水率范围为9.21%～16.96%w.b.时,围压为30～100 kPa时,稻谷堆弹性模量E在9.91～25.67 MPa范围内,泊松比υ的范围为0.10～0.15。由弹性理论与实验数据推导出了弹性模量E与围压σ_3的关系式。     

小麦堆修正剑桥模型的参数研究

通过TSZ-6A应变控制式三轴仪对小麦堆(宁麦13号)进行三轴压缩试验,测定并计算出小麦堆修正剑桥模型的参数:临界状态应力比M、对数硬化模量λ、等向膨胀指数κ和弹性模量E。试验结果表明:小麦堆含水率为10.20%,12.46%,14.05%w.b.时,临界状态应力比M分别为0.924 9,1.013 1,0.978 5;对数硬化模量λ分别为0.067 7,0.061 3,0.073 3;等向膨胀指数κ分别为0.025 4,0.027 0,0.026 3。含水率对M、λ和κ无显著性影响,对试验数据进行分析,推导出弹性模量E与广义剪切力q和平均主应力p的关系式。     

基于有限元方法的平房仓中小麦堆的密度分布研究

选定剑桥修正模型作为小麦堆的应力与应变关系本构方程,使用有限元方法计算平房仓中小麦堆的应变分布值,由应变值计算出平房仓中小麦堆的密度分布值。结果表明：小麦储藏在平房仓中,其堆密度分布是不均匀的。在同一含水率下,小麦平均层密度随着粮层深度的增加而增加,增加率随粮层深度的增加而减小;在同一粮层下,小麦的堆密度随距仓壁的距离减小而减小,在粮仓的拐角处小麦堆密度达到该层的最小值,当粮层深度越深,小麦堆层密度分布越不均匀;平房仓内小麦的平均堆密度随着含水率的增加而减小,平均堆密度相对于无压缩密度的增加率随含水率增加而增大;由剑桥修正模型计算出的数据拟合了平房仓中小麦平均层密度与粮层深度、含水率之间的关系方程。实仓验证得到：该模型计算的平房仓中小麦的重量与实仓内账面小麦重量的误差小于1.64%。     

平房仓中稻谷密度的时空分布值及堆高沉降特性研究

使用粮食回弹模量仪测定出稻谷堆的压缩密度与最大主应力（竖直压应力）及储藏时间的关系模型。选定修正剑桥模型作为稻谷堆的应力与应变关系本构方程,使用有限元方法计算出装粮后瞬时平房仓中稻谷层的竖直压应力分布值。由平房仓中稻谷堆各层的竖直压应力和稻谷堆的压缩密度与最大主应力（竖直压应力）及储藏时间的关系模型计算出平房仓中稻谷层的密度与粮层深度及储藏时间的关系模型。结果表明：稻谷堆压缩密度随最大主应力的增加而增大,随储藏时间的增加而增大,稻谷堆压缩密度关于储藏时间和最大主应力的关系模型是 ;平房仓中稻谷层密度随粮层深度的增加而增大,随储藏时间的增加而增大,平房仓中稻谷堆密度关于储藏时间和粮层深度的关系模型是 ;平房仓中稻谷堆高随储藏时间的增加而降低,且堆高降低幅度越来越小,最后稻谷堆高趋于稳定值。     

带锥斗筒仓中稻谷的密度与应力分布模型

采用LHT-1粮食回弹模量仪测定稻谷堆的压缩密度,建立带锥斗筒仓中稻谷堆的密度、应力与粮层深度关系的微分方程组,用数值方法计算带锥斗筒仓中稻谷密度、应力与粮层深度关系,由积分法计算出筒仓中稻谷的储藏总质量。试验结果表明,淮稻5号(含水率为10.38%~18.30%w.b.)的密度随竖直应力(0.495~245.892 kPa)增大而增大(582.772~696.593 kg/m~3)。模型计算结果表明,在带锥斗筒仓的筒体部分,稻谷堆密度随着粮层深度的增加而增大;到锥斗部分,稻谷堆密度随着粮层深度的增加而逐渐减小。在带锥斗筒仓的筒体部分,稻谷堆的竖直应力随着粮层深度的增加而增大;在锥斗部分,稻谷堆的竖直应力则随着粮层深度的增加而减小。在带锥斗筒仓中的筒体部分,稻谷堆的侧向应力随着粮层深度的增大而增大;在筒体与锥斗结合处,稻谷堆的侧向应力突然增加;到了锥斗部分,稻谷堆的侧向应力随着粮层深度的增大先稍增大再逐渐减小。     

不同储藏条件下筒仓中大豆堆高安全域研究

建立筒仓中大豆分层压缩平衡微分方程,实验测定微分方程中的参数,数值求解压缩平衡微分方程得到筒仓内大豆堆应力分布值;建立筒仓中大豆籽粒堆放模型,求解大豆籽粒堆放模型得出筒仓内大豆堆应力与籽粒压力的关系;实验测定大豆籽粒压缩力与塑性应变关系;设定大豆籽粒产生0.4 %的塑性应变为籽粒损伤阈值,结合筒仓内不同深度大豆堆应力、籽粒压力与塑性应变,给出大豆的堆高安全域。计算与实验结果表明：含水率为8.58%～15.01% w.b.并且储藏时间为60 d～240 d的大豆,在半径为10 m的筒仓内安全堆高的范围是47.6 m～20.6 m;在半径为15 m的筒仓内安全堆高的范围是40.2 m～19.3 m;在半径为20 m的筒仓内安全堆高的范围是37.4 m～18.8 m;筒仓内大豆堆的安全堆高随着含水率的增大而减小,随着筒仓直径的增大而减小,随着储藏期的增大而减小。     

稻谷堆的修正莱特-邓肯模型参数研究

使用TSZ-6A应变控制式三轴仪对4个不同含水率的稻谷堆进行轴向压缩试验和各向等压压缩试验,由试验数据计算出稻谷堆的修正莱特-邓肯模型的14个参数。试验结果表明:含水率为12.35%、13.68%、15.09%、16.52%w.b.稻谷堆的弹性模量数K分别为167.65、182.98、196.79、199.66,弹性模量指数n分别为0.80、1.17、1.10、0.96,泊松比ν分别为0.204、0.214、0.221、0.268;塑性塌落模量C分别为0.001 2、0.002 7、0.001 0、0.002 3,塑性塌落指数p分别为1.53、1.37、1.64、1.30;塑性剪切屈服常数η1分别为223.31、382.82、207.59、494.54,塑性剪切屈服指数m分别为0.58、0.93、0.76、1.14,势参数S分别为0.334、0.398、0.351、0.306,势参数R分别为1.447、8.330、0.811、-2.016,势参数t分别为2.26、1.07、1.79、2.74,硬化功参数θ分别为0.53、0.48、0.45、0.47,硬化功参数l分别为0.67、0.55、0.63、0.49,硬化功参数α分别为0.30、0.09、0.09、0.12,硬化功参数β分别为0.08、0.28、0.25、0.16。且K、ν随含水率的增大而增大,ν随围压增大而减小,其他参数与含水率无显著性关系。     

稻谷堆的压缩密度与体变模量的测定与分析

利用应变控制式三轴仪对稻谷堆的压缩密度与体变模量进行了测定,并分析了围压对稻谷堆压缩密度的影响以及围压和含水率对稻谷堆体变模量的影响。结果表明:同一含水率(11.50%、13.14%、14.47%、15.86%、17.37%)下,稻谷堆的压缩密度随着围压(23~188 kPa)的增大而增大,其变化范围分别为0.664 6~1.067 9 g/cm3、0.670 8~1.081 5 g/cm3、0.678 1~1.084 2 g/cm3、0.681 4~1.142 3 g/cm3、0.686 1~1.168 8 g/cm3;稻谷堆的体变模量随着围压(23~188 kPa)的增大而增大,其变化范围分别为311.52~495.06kPa、294.73~487.80 kPa、291.61~450.05 kPa、210.34~430.04 kPa、160.16~301.07 kPa;同一围压下,稻谷堆的体变模量随着含水率的增大而减小,并可拟合出回归方程k=-aW2+bW-c,式中:W为含水率,k为体变模量,且a,b,c随着围压的不同而变化。     

筒仓中油菜籽堆高安全域的研究

建立筒仓中油菜籽分层压缩平衡微分方程,实验测定微分方程中的参数,得到筒仓内不同深度油菜籽堆应力分布;建立筒仓中油菜籽籽粒堆放模型,给出筒仓内不同深度油菜籽的应力与籽粒压力的关系;设定油菜籽籽粒产生0.5 %的塑性应变为籽粒损伤阈值,结合筒仓内不同深度油菜籽堆应力分布以及籽粒受力与应变,给出油菜籽的堆高安全域。数值计算结果表明：油菜籽含水率为7.11%～13.52% w.b.时,半径为10 m的筒仓内油菜籽堆高安全域为22.00～45.59 m,半径为15 m的筒仓内油菜籽堆高安全域为19.78～35.97 m,半径为20 m的筒仓内油菜籽堆高安全域为18.87～32.76 m;筒仓内油菜籽的堆高安全域随着含水率的增大而减小,随着筒仓半径的增大而减小。     

筒仓中稻谷的空隙率分布研究

采用LHT-1粮食回弹模量仪测定稻谷(南粳5055)堆的表层密度及压缩密度,建立筒仓中稻谷堆的密度、应力与粮层深度关系的微分方程组,用数值方法计算筒仓中稻谷密度与粮层深度关系。采用粮食孔隙率测量仪测定表层稻谷(无压缩)孔隙率,由表层孔隙率,表层密度及筒仓深处的密度计算出筒仓中稻谷孔隙率与粮层深度关系。计算结果表明:在直径20米的筒仓中,在30米的筒体部分,南粳5055空隙率变化范围为61.00%~56.32%,在10 m的锥斗中,空隙率变化范围为56.32%~59.77%;在带锥斗筒仓的筒体部分,稻谷堆孔隙率随着粮层深度的增加而减小;到锥斗部分,稻谷堆孔隙率随着粮层深度的增加而逐渐增大。在不同直径的筒仓的筒体部分,在同一深度,稻谷堆孔隙率随着筒仓直径的增大而减小。     

THE DETERMINATION OF POISSON'S RATIO BY COMPRESSION TESTS OF CYLINDRICAL SPECIMENS*

Theoretical basis is presented for determining Poisson's ratio in uniaxial compression tests of cylindrical specimens. A simplified measurement technique and instrumentation for obtaining the required parameters are described in detail. Experimental data for Centennial sweet potato flesh at 72°F and four moisture contents are provided and analyzed to give the time dependent master curve and the time-moisture shift factor; thus, the time and moisture influenced viscoelastic property of Poisson's ratio is completely specified.     

40—STUDIES OF ADHESIVE-BONDED NON-WOVEN FABRICS PART II: THE DETERMINATION OF VARIOUS PARAMETERS FOR STRESS PREDICTIONS

The prediction of the fabric stress–strain behaviour by the theoretical analysis derived in Part I requires a knowledge of several fibre, binder, and fabric parameters. Values for some of these, such as fibre linear density and the contents of fibre and binder materials, may in practice be readily available. Some others, however, invariably need to be determined experimentally; the stress–strain properties of both the binder and fibre components and the Poisson's ratio are in this category. The complex nature of the binder distribution in the fabric structure, on the other hand, necessitates the introduction of the bond lengths into the computations as an arbitrary value. In the present paper, various approaches to determine all the required parameters are discussed, the experimental techniques devised are described, and the results of tests on all the fabrics investigated are presented with special emphasis on the fabric Poisson's ratio and its dependence on various factors.     

Theoretical Determination of the Mechanical Response of Spun-bonded Nonwovens

A new theory is presented to predict the tensile behaviour of spun-bonded nonwoven fabrics from the knowledge of the stress–strain behaviour of its constituent fibers, their orientation angle distribution, the fabric's Poisson's ratio and their shear strains. A comparison of the predicted stress–strain curves and experimental results of two commercially available fabrics is made in two principle directions. The theory is shown to work very well for the fabrics under study. Theoretical curves are presented by using Poisson's ratio values calculated from methods based on biaxial and uniaxial testing. A comparison of two methods is described.     

Measurement of stress–strain behaviour of human hair fibres using optical techniques

Many studies have presented stress–strain relationship of human hair, but most of them have been based on an engineering stress–strain curve, which is not a true representation of stress–strain behaviour. In this study, a more accurate ‘true’ stress–strain curve of human hair was determined by applying optical techniques to the images of the hair deformed under tension. This was achieved by applying digital image cross‐correlation (DIC) to 10× magnified images of hair fibres taken under increasing tension to estimate the strain increments. True strain was calculated by summation of the strain increments according to the theoretical definition of ‘true’ strain. The variation in diameter with the increase in longitudinal elongation was also measured from the 40× magnified images to estimate the Poisson's ratio and true stress. By combining the true strain and the true stress, a true stress–strain curve could be determined, which demonstrated much higher stress values than the conventional engineering stress–strain curve at the same degree of deformation. Four regions were identified in the true stress–strain relationship and empirical constitutive equations were proposed for each region. Theoretical analysis on the necking condition using the constitutive equations provided the insight into the failure mechanism of human hair. This analysis indicated that local thinning caused by necking does not occur in the hair fibres, but, rather, relatively uniform deformation takes place until final failure (fracture) eventually occurs.     

Mechanical and fracture properties for predicting cracking in semi-sweet biscuits

Mechanical and fracture properties required for predicting crack development in semi‐sweet (‘rich tea’) biscuits have been experimentally determined. Pilot‐scale biscuits of different fat concentrations were prepared and studied with commercial biscuits at different moisture contents. Bending modulus, fracture stress and strain were measured using three‐point bending tests. All biscuit types showed considerable dependence on moisture content over a range of 4–12%. Young's modulus and failure stress showed a uniform decrease and failure strain showed an increase with increasing moisture content. For pilot‐scale biscuits of different fat concentrations, an increase in fat level caused a decrease in modulus and failure stress values; however, the failure strains were very similar for all the fat types. The testing of the samples with top surface up and top surface down revealed that the sample orientation does not affect the measured parameters. The measured parameters also did not show any directional dependence within the plane, thus assuring that the assumption of an isotropic material would be valid for modelling. The mechanical and fracture properties measured in this study will serve as a very useful set of data to predict the stress state and cracking of the checked biscuits.     

白腐真菌对玉米秸杆和餐厨垃圾堆肥效果的影响

利用白腐真菌降解过的玉米秸秆和未降解过的玉米秸秆分别与餐厨垃圾进行堆肥对比实验,研究生物预处理对秸秆堆肥效果的影响.在30d的堆肥过程中,通过测定堆体的温度、含水率、pH、有机质含量以及种子发芽指数指标评价其堆肥效果和腐熟程度.结果表明,预处理过的秸秆堆体A较未处理过的堆体B先达到55℃;堆体A含水率下降迅速、有机质含量减少快,可缩短堆肥周期;两堆体pH最终接近中性;堆体A种子发芽率为99%,比堆体B的种子发芽率高1%,堆体A的腐熟速度和程度优于堆体B.生物预处理可加快堆肥进程,有效缩短堆肥周期.     

仓储粮堆通风干燥湿热传递模型的研究进展

从古到今,治国理政的首要之务是粮食安全。粮食仓储安全尤为重要,关系到一个国家的国家安全。由于粮食干燥储存方法原始、干燥技术落后等原因,我国每年收获后会损失大量粮食。粮食中湿热分布不均不仅会降低粮食的品质,而且会因霉变、虫害等问题严重影响食品安全。因此,如何快速、均匀而又低能耗地降低粮堆含水率或者温度,保证粮食品质,同时节约能源,是粮食干燥储藏研究的一个重要方向,具有重要的理论及现实意义。通风干燥是保证储粮中湿热均匀分布的重要措施,建立干燥模型预测粮堆的湿热分布是研究粮堆干燥过程中湿热传递的重要手段。该研究综述了粮堆湿热传递的经验模型、连续模型和离散模型,其中经验模型容易获得,但是应用较少;连续模型应用较多,但不能反映粮堆的孔隙结构;离散模型可以很好的反应粮堆的孔隙结构,但其计算量大,并且难以理解和构建。最后该研究指出可以根据不同的湿热传递过程,结合先进的计算方法和处理技术,建立相应的模型,以满足不同的模拟要求,并对粮堆通风干燥湿热传递模型未来的研究方向进行了展望。     

EXTRUSION COOKING OF RICE: EFFECT OF AMYLOSE CONTENT AND BARREL TEMPERATURE ON PRODUCT PROFILE

The effect of amylose content (5.0–28.6%) of rice and barrel temperature (80–120C) on extrusion system parameters torque and net specific mechanical energy and extrudate characteristics extrudate bulk density (ED), water solubility index, expansion ratio (ER) and Warner–Bratzler shear stress were studied using a twin‐screw extruder. The feed rate (15 kgh^?1), moisture content (20.0% ± 0.2) of feed and the screw speed (400 rpm) were kept constant. ED and ER of the product suggested that a barrel temperature of 120C was desirable to generate an expanded extrudate rice product from low‐amylose rice cultivar. Experimental data on system parameters and extrudate characteristics fit to second‐degree polynomial regression equations (r ≥ 0.904, P ≤ 0.01) with the amylose content of rice and barrel temperature of the extruder.     

硫酰氟气体在不同品种粮堆扩散规律比较研究（网络首发、推荐阅读）

为了解硫酰氟在小麦、稻谷和大豆3种粮堆中的扩散和分布规律,通过6个实仓熏蒸的数据采集,对熏蒸气体在不同粮堆内的扩散速度、均匀性、以及衰减速度等参数进行比较分析。试验结果表明,硫酰氟气体在不同粮种中的扩散速度是大豆>稻谷>小麦;大豆粮堆最快在熏蒸后8 h后,可实现整仓气体均匀;平均气体浓度半衰期分别是大豆>小麦>稻谷;在5.0~12.7 g/m3的熏蒸药剂浓度下实现6个月无虫期的防护效果。