梨果实压缩特性的研究

以内蒙古河套地区盛产的完整形态的苹果梨和早酥梨为实验材料,在不同压缩速率下针对果实不同部位进行了准静态压缩实验.结果表明:果梗部位受压时的生物屈服极限和破坏极限所对应的压力值均比赤道部位压缩时的大.相同的压力作用下,赤道部位受压时的变形量比果梗部位受压时的大;梨果实各压缩特性参数随压缩速率的增加而增大,其中,苹果梨各压缩特性参数值均大于早酥梨;品种、压缩部位和压缩速率对梨果实的生物屈服极限、变形能、破坏极限、破坏能和杨氏模量均呈极显著影响;梨果实的各压缩特性之间均呈正相关关系(不相关概率≤0.005).     

绿豆挤压力学特性的实验研究

为降低绿豆种子在收获、贮藏、运输过程中所产生的机械损伤,掌握绿豆籽粒的挤压粉碎加工机理,通过选取含水率为9.3％～12.8％的绿豆籽粒,在不同加载速度下对不同放置方式的绿豆籽粒在材料力学实验机上进行静态挤压实验.实验结果表明,绿豆籽粒的弹性模量为153.4～247.7MPa,屈服强度为0.23～0.98MPa,破碎负载为42.62～81.72N,最大应变为0.25％～0.61％;绿豆籽粒随着含水率的增加,其弹性模量、屈服强度、破碎负载均有明显下降但最大挤压变形量却升高;在同一含水率下,立放与侧放挤压时绿豆的屈服强度、破碎负载较大,平放挤压时较小;对于弹性模量变化而言,立放与平放挤压时较大,侧放时较小;在实验参数选取范围内加载速率对绿豆籽粒抗挤压能力影响不显著,绿豆籽粒在3种不同放置方式下,受压面生成挤压裂纹的形状、部位及规律不同.     

不同采摘期对库尔勒香梨静压损伤影响规律研究

为探究不同采摘期对库尔勒香梨静压损伤影响,本文利用万能材料试验机对不同采摘期下库尔勒香梨进行静压损伤试验,研究不同成熟度库尔勒香梨机械特性参数,建立不同成熟度库尔勒香梨变形量与静压损伤面积关系的数学模型,研究采摘期内硬度变化规律.结果表明:采摘期内果实各机械特性参数均随采摘期的后延而减小,采摘期内果实极限屈服力变化范围...     

体育防护用品的压力舒适性及运动功能性探讨

本文探讨服装压对体育防护用品运动功能及穿着舒适性的影响。通过实验得出以下结论:1.人体皮肤对服装压的主观感受随着受压强度、作用时间、受压部位及运动状态的不同而异;2.人体在通常状态下,前臂、小腿及腰部等部位所需要的舒适服装压较小(490～2600帕),但在剧烈运动时所需舒适压力要比一般状态下大1980帕左右;3.人体各部位都有其舒适压力范围和最大可承受的压力极限,故服装压的大小直接影响体育防护用品的运动功能及穿着舒适性。     

枸杞深加工产品开发现状及研究进展

枸杞作为一种药食同源的经济林果,富含多糖、类胡萝卜素、类黄酮、甜菜碱、牛磺酸等多种功能性成分,具有增强免疫调节、抗衰老、预防癌症和肿瘤生长、降低血糖和血脂水平等多种功效,消费者对枸杞相关产品的需求也日益增加。枸杞生长性状属无限花序,果实成熟期较长为每年6～10月份;然而,枸杞果实在成熟后期快速软化,使其极易受到机械损伤和病原微生物侵染,限制果实的贮藏和运输;因此,在果实成熟期为降低枸杞果实的损耗和迎合消费者对枸杞保健功能的需求,需要在成熟期内对果实进行深加工处理。阐述了枸杞的主要营养价值和保健功效,并提出传统加工产业与现代消费升级引起的供需矛盾;介绍了枸杞深加工产品和配套技术设备的相关产业现状,分析了枸杞产业精深加工的市场需求和产品研发的未来发展趋势,并指出了枸杞深加工产品和新技术、新装备在枸杞深加工产业的应用前景以及面临的难题和挑战,为枸杞深加工产业的发展提供理论参考。     

钢筋锈蚀对其力学性能退化规律的影响研究

文章采用外加直流电法对四种常用直径的HRB400带肋钢筋进行加速锈蚀,对锈蚀后钢筋采用除锈剂进行除锈,钢筋除锈后进行拉伸试验,最后对试验数据进行统计拟合分析。研究发现:钢筋的名义屈服强度、名义极限强度随着钢筋质量锈蚀率的增大呈线性退化规律;同一直径钢筋的名义极限强度退化速率要明显快于名义屈服强度退化速率;大直径钢筋的名义屈服强度、名义极限强度退化速率比小直径钢筋要快,名义屈服强度退化速率随钢筋直径变化较为敏感,名义极限强度退化速率随钢筋直径变化不敏感。从而为混凝土结构的承载力、耐久性评估提供理论依据,为今后项目建设提供一定的参考与建议。     

高强钢扭转力学性能测试

国产X80管线钢制成的扭转试样在一个方向作用转矩,使得产生一定的预塑性变形后,再反向加载时屈服转矩就会降低.对国产X80管线钢的试样进行了初次加载实验,得到试样的转矩-应变曲线.随后对存在一定预塑性变形的圆轴试样进行反扭.测试的结果表明,试样在初次加载时,其曲线有明显的线弹性阶段和屈服平台;反向加载时,加载曲线无明显的屈服平台,低于初次加载曲线,且预塑性变形越大,反向加载曲线越低,即反向加载时材料的屈服强度随预塑性变形的增大而降低,也就是出现了包申格效应.从理论上对反向加载时屈服转矩进行了计算,结果和试验测试能较好的吻合.     

机械搅拌对凝胶状油脂质构、流变及微观形态的影响

以精炼一级大豆油(RBDSBO)加入体积分数5%全氢化棕榈硬脂(FHPST)制备凝胶状油脂,探讨了不同的机械搅拌速率(0~10 000 r/min)对凝胶状油脂质构、流变性质及微观形态的影响,同时探讨了其微观结构与物理特性的关系。实验结果表明:搅拌速率小于500 r/min时,样品的硬度、凝聚性,储能模量(G’)、损耗模量(G")及不规则碎片维数Db均随着搅拌速率的增大而增大,其中搅拌速率为0~200 r/min时增大最明显;但当搅拌速率大于500 r/min时,其质构、流变学等参数没有显著差异。因此,机械搅拌速率500 r/min时凝胶状油脂的网络强度、质构及流变等机械性质为最佳。     

薄板梁腹板超临界屈曲强度的研究

本文研究一种估算剪切负载下簿板梁的总屈服负载的简捷方法。所得公式在英国谢菲尔薄大学机械工程系实验室内以小范围的极限负载试验作了验证。一、概述簿板梁的设计有各种标准,例如,在英国有BS449、153、5400,在美国有A.I.S.I.(美国     

1-MCP处理延缓采后机械伤青圆椒的衰老进程

为了探究1-MCP处理对采后机械损伤青圆椒果实生理生化的影响,本实验采用10 μL/L 1-MCP处理机械损伤的青圆椒果实。在贮藏期间分析了1-MCP处理对机械损伤青圆椒果实的品质、细胞膜损伤以及丙二醛（MDA）含量、叶绿素含量和活性氧清除酶如超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、过氧化物酶（POD）、抗坏血酸过氧化物酶（APX）活性和基因表达水平的影响。实验结果显示：在20 ℃的贮藏条件下,用1-MCP处理机械损伤青圆椒果实,可以有效保持其贮藏期品质。与对照组相比,10 μL/L 1-MCP处理有效减缓了青圆椒果实中叶绿素的降解和维生素C含量的降低,抑制了青圆椒果实MDA含量的积累,维持了细胞膜的完整性。同时,用1-MCP处理的机械损伤青圆椒的抗氧化酶类POD、CAT、APX的活性和基因相对表达量均显著高于对照组。以上结果表明,1-MCP处理可以有效延缓采后机械伤的青圆椒的衰老进程,保持果实的贮藏品质,延长青圆椒果实的货架期。     

辣根过氧化物酶催化淀粉接枝丙烯酸甲酯浆料制备及其上浆性能

为改善淀粉浆液对涤棉混纺纱的黏附性和浆膜的力学性能,采用辣根过氧化物酶(HRP)/乙酰丙酮(ACAC)/过氧化氢(H2O2)引发体系,催化酸解淀粉接枝丙烯酸甲酯。通过傅里叶红外光谱、扫描电子显微镜和X射线衍射对接枝淀粉进行表征,并分析其流变特性。结果表明,在HRP酶催化作用下丙烯酸甲酯与未糊化酸解淀粉发生接枝共聚反应,且对酸解淀粉结晶度影响不大;淀粉接枝改性后浆液黏度增大,黏弹性增加,呈现更具弹性的流体特征;相比于酸解淀粉,含有柔性接枝支链的淀粉浆液对涤/棉黏附性有明显提高,浆膜断裂伸长率和断裂强度均有增加,力学性能得到改善。     

Effect of storage time and temperature on structure,mechanical and barrier properties of chitosan-based films

The mechanical (tensile strength, elongation at break, mechanical work of deformation) and barrier (water vapor permeability and water vapor uptake) properties of chitosan films produced with acetic and lactic acids have been studied as a function of storage time, molecular weight of chitosans, concentration of plasticiser and the storage temperature. It was demonstrated that mechanical properties of chitosan-based films can be improved to a great extent during storage at low temperatures in freezer and refrigerator. Transition of chitosan molecules during storage in the solid state to more extended conformations and free volume changes are considered as mechanisms for the improvement of mechanical and barrier properties of chitosan films. The best mechanical properties are achieved for chitosan films produced with acetic acid and plasticized by the addition of 20% of glycerol. Sharp decrease in water vapor permeability has been demonstrated for thinner chitosan films and related to more dense packing and orientation of linear chitosan macromolecules.     

EVALUATION OF CERTAIN PHYSICAL PROPERTIES OF MEAT USING A UNIVERSAL TESTING MACHINE

ABSTRACT— The Instron tester served to evaluate physical properties of uncooked rabbit and beef muscle including work of rupture, breaking strength, break elongation elasticity and stress relaxation. These methods measure variations in muscle type, aging and post-mortem treatments comparably with shearing instruments. Shank showed higher tensile properties than tenderloin, less elasticity and lost more applied stress. With rabbit, the breaking force of longissimus dorsi unrestrained during rigor was .237 Ib/g ± 7.5% for samples 5.0 cm by 0.2–0.5 cm² while restrained muscle gave .168 ± 9.9% and also exhibited higher elasticity and break elongation. Post-mortem aging decreased tensile properties and elasticity. Psoas muscle, characterized by more coextensive fibers, had higher tensile properties than longissimus dorsi.     

A new instrumental setup for determination of small amplitude viscoelastic properties of dough during fermentation

In this study, the working principles and the theoretical background of a new method to measure the viscoelastic properties of dough in the fermentation process are presented. During measurements, the dough sample was placed between a stationary bottom plate and an oscillating top plate and squeezed at random frequencies ranging from 10 to 100,000 rad/s. By measuring the required force and velocity of oscillations, the mechanical impedance of the samples, defined as the ratio of the force to oscillation velocity, was determined during fermentation. The measured mechanical impedance was used to calculate viscoelastic properties such as elastic and loss moduli of the dough samples. The nondestructive quick measurements and data covering a wide range of frequencies are some of the main advantages of the method. Furthermore, the described instrument can be easily affixed to the commonly available texture analyzer type equipments.     

Functional Properties of Myofibrillar Protein-based Biopackaging as Affected by Film Thickness

Fish myofibrillar protein-based biopackagings were developed from a film-forming solution cast on plates. Film thickness was modulated by variations in “apparent thickness” of the cast solution to evaluate effects on the main functional properties. The thickness variations seemed to have no influence on optical properties (apparent opacity) or on percent solubility in water. Study of mechanical properties revealed that elongation at break and relaxation coefficient were not dependent on film thickness, while force at break was directly proportional to film thickness. This could be interpreted by variations in the number of potential intermolecular interactions in the films. Analysis of water vapor transport showed that the biopackaging did not behave as an ideal material according to Fick's and Henry's laws.     

含变异结构的三维机织复合材料的轴向拉伸性能

为克服加纱或减纱造成三维机织预制体交织结构的局部变异,进而对复合材料的力学性能产生一定的影响,采用加纱和减纱相结合的方法分别制备了4种三维机织石英纤维树脂基复合材料,结合拓扑方法建立了加减纱区域的路径,利用数字图像相关技术研究了拉伸过程中全场纵向应变变化。结果表明:引入加、减纱变异结构试样的拉伸强度和拉伸模量的保留率分别大于93.0%和88.0%,断裂伸长率无明显差异,且与未引入加、减纱试样在拉伸过程中的力学响应规律、断裂失效模式基本一致;应变云图表明损伤起始于交织点,引入加减纱的试样其高应变集中在加减纱“点”处,同时存在富树脂低应变区域与之对应。     

刺辊锯齿螺旋倾角与分梳质量关系的理论研究

针对梳棉机刺辊分梳时刺辊锯齿的螺旋倾角使得锯齿倾斜分梳纤维层,易加重纤维损伤的问题,以单个锯齿为研究对象,对嵌入式和自锁式刺辊锯齿的分梳过程进行深入的理论分析,采用建立力学模型的方法对螺旋倾角为0°和θ 时纤维的受力情况进行研究。通过显式动力学模块对倾角为0°、1°、2°时锯齿的运动进行仿真。结果表明：当倾角为0°时,被梳纤维束所受的摩擦阻力及应力、应变均最小,且随着倾角的增大,摩擦阻力、应力及应变逐渐增大,束中纤维损伤越严重,纤维断裂概率越大;螺旋倾角的存在使得锯齿分解能力降低,易导致束纤维比例增大,分梳质量下降。     

6×29Fi+FC-52mm钢丝绳的生产

介绍 6× 2 9Fi+FC - 5 2mm钢丝绳的试生产过程 ,提出该钢丝绳生产的技术要求 ,并对制绳钢丝的生产工艺和材质进行了介绍 ,给出制绳钢丝、股、芯的规格和力学性能及捻制参数。该钢丝绳的破断拉力达到 192 7kN ,使用表明该钢丝绳可满足用户要求 ,可替代进口钢丝绳     

Classification,modeling and prediction of the mechanical behavior of starch-based films

The starch-based film properties database was created with 8 variables and 322 observations collected from the literature. The selected variables were: (1) the starch origin (potato, cassava (tapioca), corn (maize), wheat, yam), (2) the starch concentration, (3) the amylose content, (4) the glycerol concentration, (5) the ambient relative humidity during storage, (6) the aging time of films and two mechanical properties of the starch films at break, (7) tensile strength at break (s_b) and (8) strain at break (e_b). The main objective of this work was to classify the data set and to predict mechanical properties (tensile strength (s_b) and strain at break (e_b) of starch-based films using a Rival Penalized Competitive Algorithm to find the clusters and, for each class, an artificial neural network (ANN) model from 6 parameters (starch origin, starch concentration (%), amylose content (%), glycerol content, ambient relative humidity (RH) and the aging of films). Each ANN was optimized using a genetic algorithm. The root-mean square error (RMSE) and the coefficient of determination B allowed to choose the best ANN. The results showed that it was possible to distinguish five classes where the composition of each class C_i could be described accurately and connected with the mechanical behavior of the films. This work also showed that it was useful firstly to classify the database before attempting to predict the mechanical properties of the starch-based films.     

EFFECT OF SAMPLE THICKNESS ON THE BITE FORCE FOR APPLES

The thickness of a piece of food and its mechanical properties affected the bite force. A multiple-point sheet sensor was used to measure the bite force applied to apple specimens of various thicknesses during the first bite with incisors. The results of wedge penetration tests on the same samples were compared with results of the bite measurements. The maximum bite force increased with the sample thickness for two apple varieties, though the maximum load measured by the wedge penetration test did not change. Therefore, it is important to consider that not only the mechanical properties but also the thickness of the sample affects the required bite force.