马铃薯渣应力松弛模型的建立及参数分析

为改善马铃薯渣机械处理方式及效果,在不同喂入量下进行了薯渣应力松弛试验.获取了应力松弛曲线并分析了弹性模量随时间变化的规律,建立了3种广义Maxwell模型用于描述薯渣应力松弛行为,得到了应力松弛时间、平衡弹性模量、衰变弹性模量、松弛时间比率等特性参数;同时分析了3种喂入量对薯渣应力松弛特性参数的影响.结果表明:可用五...     

非热诱导猪肉盐溶蛋白凝胶力学特性研究

以超高压技术和TGase协同诱导猪肉盐溶蛋白凝胶形成,利用压缩试验和应力松弛试验,研究压力水平和TGase对其凝胶力学特性的影响。结果表明:最大力、滞后损失和永久弹性模量随压力水平的不断增大呈上升趋势,弹性度先增大后稳定;凝胶最大力、滞后损失和弹性度随TGase添加量的增加都呈现先增大后稳定的趋势,永久弹性模量则呈现直线上升趋势;可以采用Maxwell三元件模型来表达猪肉盐溶蛋白凝胶的松弛流变特性。     

单轴多级循环加载下聚氯乙烯膜材料的力学行为与能量耗散

为研究建筑用膜材料在多级循环加载下的力学行为与能量耗散,对聚氯乙烯(PVC)膜材料进行单轴多级循环加载实验测试,分析了变形行为、能量耗散与损伤特性。研究结果表明:相对于单轴拉伸强度,经向试样的循环加卸载峰值强度较低,而纬向试样的循环加卸载强度较高;多级循环加载条件下,加载与卸载弹性模量呈现逐渐增加的变化趋势,且卸载弹性模量高于加载弹性模量;小载荷水平下,相对于经向试样,纬向试样表现出较高的总吸收应变能、弹性应变能和耗散能,但在高载荷水平下较低;在逐级循环加载过程中,PVC膜材料均表现为黏-弹-塑性,基于塑性变形累积来定义损伤变量较为合理。     

压缩速度与压缩方位对大豆籽粒压缩特性的影响研究

按照美国农业与生物工程师协会ASAE S368.4DEC2000(R2006)标准,使用Brookfield质构仪测定了黑龙江大豆籽粒(2011年产)的表观弹性模量、最大破坏力、最大破坏力能、破坏时的变形量。试验选定压缩速度为:0.02、0.1、0.5、1.0 mm/s,选定压缩方位为长轴(X轴)、中轴(Y轴)、短轴(Z轴)。由质构仪软件,得到了加载载荷与对应变形量的关系曲线,运用spass软件对数据进行分析处理,得到大豆的表观弹性模量、最大破坏力、最大破坏能、破坏时的变形量。试验结果表明:随着压缩速度的增加,大豆籽粒沿长轴(X轴)、中轴(Y轴)、短轴(Z轴)压缩的最大破坏力增大,最大破坏能增加,压缩变形量增大,表观弹性模量减小。     

棉纤维蠕变与应力松弛行为分析

研究基于黏弹性的棉纤维蠕变回复与应力松弛规律。建立棉纤维蠕变与应力松弛的本构模型。在不同压缩载荷作用下测试棉纤维蠕变量与应力变化量。结果表明:棉纤维蠕变与应力松弛体现了非线性黏弹性;非线性黏弹性模型能较好地表征棉纤维蠕变回复、应力松弛的力学行为。在本研究范围内,施加载荷增加,棉纤维蠕变回复量增加,蠕变回复力学指标增大;棉纤维应变量增加,应力松弛的力学指标增大。     

契达干酪应力松弛特性与成熟度相关性研究

测定了契达干酪不同成熟期样品的应力松弛时间、弹性模量和成熟度指数,分析了其与干酪成熟度之间的相关性。结果表明,弹性模量随成熟期呈降低趋势。应力松弛时间随成熟期先增大后降低,并在7出现最大值。7~90d样品应力松弛时间呈单调递减。各成熟期样品的应力随测试时间的衰减规律符合对数规律。随成熟期的增加,可溶性氮质量分数pH4.6-SN和12%TCA-SN均呈增大趋势,增大幅度分别为18.07%和8.2%。弹性模量和应力松弛时间与成熟度指数分别呈极显著和显著线性相关。     

循环应力松弛下黄麻织物/聚乙烯复合材料能量耗散演化规律

为探讨麻纤维增强热塑性复合材料在复杂受力条件下的能量耗散特性,以黄麻织物为增强体,聚乙烯膜为基体,采用热压法制备了黄麻织物/聚乙烯复合材料,并对其在循环应力松弛下的力学性能进行测试,分析应力松弛时间、循环应力峰值、循环次数对应变能(总应变能、弹性应变能、塑性应变能)和应变能系数(可恢复与不可恢复应变能系数)的影响规律。结果表明:经、纬向试样的变形规律与能量演化机制一致,应变能与应变能系数不仅与应力松弛时间、循环应力峰值密切相关,同时还与循环次数密切相关;循环应力松弛下的弹性应变能变化趋势迥异于无应力松弛过程的简单循环加载。     

烟丝压缩过程中应力松弛模型的建立

为了揭示烟丝压缩后应力松弛规律及获得烟丝的流变学参数,以烟丝为研究对象,利用烟丝流变测试仪对烟丝进行蠕变-应力松弛试验,构建表征堆积烟丝应力松弛过程的数学模型,分析了不同条件下烟丝被压缩后的应力松弛行为,并求解了该过程中烟丝的流变学参数。结果表明：(1)堆积烟丝具有良好的压缩黏弹性力学性质,在应力松弛过程的前5 s松弛速率最快,松弛过程持续约60 s后应力衰减速率变缓,最终存在平衡应力。(2)烟丝压缩过程中堆积烟丝流变特性可用五元件广义Maxwell模型描述,相关系数R2>0.994。(3)考察样品量和压缩载荷对烟丝应力松弛行为的影响,对获得的流变特征进行分析发现,随着样品量和压缩载荷的增大,平衡应力呈增大趋势。样品量越大,应力松弛时间比率α越小,压缩载荷越大,应力松弛时间比率α越大。该规律的表达为进一步研究不同条件下烟丝应力松弛特性与宏观烟支质量间的关系提供了基本方法。     

刀豆脱壳力学特性的实验研究

利用万能试验机对刀豆的力学特性进行压缩实验。选择破壳力、破壳变形量和破壳能量为实验指标,以刀豆宽度、厚宽比、含水率、加载位置和试验机的施压速率为因素进行了混合水平正交实验和回归分析。结果表明,当沿荚果纵脊面平行压缩时,破壳效果理想,为脱壳的有效加压方向。含水率对破壳力和破壳能量的影响极显著,呈非线性正相关关系,降低含水率有利于提高脱壳率和减少设备能耗。加载位置、宽度和厚宽比对破壳变形量有显著影响,破壳变形量总体上随宽度和厚宽比的增大而减小。刀豆破壳力和破壳能量的综合最优水平组合:加载位置为中部,含水率为14.6%,施压速率为20mm/min。      

小台农芒果力学特性及其贮藏期预测模型的研究

为了研究不同贮藏温度下芒果的力学特性随贮藏期的变化,对芒果的应力松弛、蠕变特性等力学指标进行了测试,并结合Maxwell模型以及动力学模型对所得实验结果进行拟合,以此建立基于力学特性的小台农芒果贮藏期预测模型。结果表明:在10、20、30℃的贮藏温度下,芒果的坚实度、主松弛时间以及弹性模量均随着贮藏时间的增加而呈现显著的下降趋势;且在较高温度段的贮藏环境下,小台农芒果的弹性模量变化速率系数高于在较低温度段的贮藏环境下芒果的弹性模量变化速率系数;采用最大形变量作为评价芒果贮藏期模型指标更能显著表征芒果在不同贮藏温度下其贮藏期的变化趋势。     

鲜枣整果力学特性研究及其有限元分析

为预测鲜枣在收获、贮运过程中的机械损伤,对甘肃靖远产小口大枣进行整果压缩特性研究及仿真分析。通过压缩实验,获得了不同加载速率条件下（10～30 mm/min）整果在横向和纵向上的弹性模量、破裂负载和破裂相对变形量：横向分别为：8.23～9.70 MPa、227.52～305.97 N、16.07%～17.46%;纵向分别为：10.05～11.44 MPa、288.50～383.17 N、16.33%～20.12%。通过观察鲜枣破裂特征,建立鲜枣压缩力学有限元模型,比较鲜枣在横向和纵向受压的模拟值和实验值,最大差异为11.4%。结果表明：鲜枣的抗挤压能力具有各向异性（相同压力下,鲜枣横向放置时的变形量大于纵向放置;相同压缩位移下,纵向承载压力大于横向）。在验证了仿真数值可行的基础上,利用有限元法可分析鲜枣内部应力应变的分布情况。研究结果可为鲜枣的作业装备设计以及减少其机械损伤提供理论依据。     

The influence of two bar warp-knitted structure on the fabric tensile stress relaxation Part I: (reverse locknit,sharkskin, queens’ cord)

Time-dependent mechanical behavior of textiles has particular importance. One of such behaviors is the stress relaxation. If a fabric is under tension over a period of time, some of the stresses in it will be relieved. During the manufacture and application of clothing and footwear, materials experience various long-lasting deformations, and relaxation process in materials arises. For example, if medical pressure garments such as compression stockings are under tension over a long period of time, some of their stresses will be relieved, with a consequent reduction in the skin and garment interfacial pressure. Thus, with theoretical and experimental study of the factors affecting stress relaxation, the ability to design and produce appropriate clothes will be increased. The aim of this study was to investigate the effect of fabric structure on the stress relaxation of two bar warp-knitted fabrics (reverse locknit, sharkskin, queens’ cord), as well as to find the effect of strain value and loading direction on the stress relaxation of the fabrics. The results reveal that the fabric structure, strain, and loading direction are important factors affecting the stress and stress relaxation percent of the fabrics. By increasing the strain and the length of underlap in the back guide bar, stress will be increased, but stress relaxation percent will be decreased. Also, stress relaxation percent in wale direction is more than course direction for reverse locknit and sharkskin3, but this is reversed for sharkskin4 and queens’ cord. Finally, among the mechanical models used to describe the stress relaxation behavior of the fabrics, three-component Maxwell’s model with parallel-connect nonlinear spring showed the best agreement with the experimental relaxation curve of the analyzed fabrics.     

南美白对虾虾肉流变学模型的建立

为了研究在真空微冻状态下南美白对虾虾肉流变学特性的变化,以南美白对虾虾肉为原料进行应力松弛实验,基于虾肉应力实验曲线特征提出了Burgers模型表征其黏弹性的流变模型,获得其黏弹塑性模型参数,并研究其变化趋势。结果表明：Burgers模型对实验曲线拟合的决定系数达到0.99以上,能够较准确地表示南美白对虾虾肉的应力松弛现象。在贮藏后期,虾肉的黏性和弹性模量有了明显下降,且松弛时间（τ）具有规律性变化,反映出虾肉随贮藏时间改变其肌肉组织状态及品质发生变化,能够为其快速检测提供一种方法。     

Storage time effect on the rheology of refrigerated potato tissue (cv. Monalisa)

 Potato tubers were held in refrigerated storage and their firmness periodically sampled over a period of 140 days. At each sampling, the rheological properties uniaxial compression, shear, uniaxial tension, successive cycles of stress relaxation, creep compliance and texture profile analysis were determined, as was moisture content. Compression energy, maximum shear force, longitudinal tension stiffness and maximum tension deformation, stress relaxation parameters and moisture content were all significantly affected by storage time. Relaxed forces decreased consistently and linearly with time over a 140-day storage period, reflecting the decrease in cell turgor pressure resulting from the predominance of water loss through evaporation over water production. Longitudinal tension stiffness and maximum shear force increased linearly in the early stages, reflecting the increase in cell wall stiffness and elastic tissue behavior. Maximum tension deformation increased linearly with time reflecting the plastic deformation of the cell wall caused by growth in cell turgor pressure at early stages. Changes in the trends of rheological parameters over 140, 64 and 28 days evidenced the importance of extending the time period considered for rheological parameters of potato tissue. Received: 28 December 1999     

Mechanical strength and rheological behaviour of barley kernels

Basic mechanical and rheological properties (stress relaxation behaviour) of single barley kernels under uni-axial compression were studied. The mechanical properties studied were the modulus of elasticity, yield and ultimate compressive strength, and the modulus of toughness as influenced by the moisture content. The stress relaxation experiments also included the effect of deformation rates and strain levels.
Results indicated that with an increase in moisture content, the strength of the barley kernels decreased while the energy required to cause rupture in the kernel increased initially and then decreased. The stress relaxation behaviour of barley kernels was described by a threeterm Maxwell model with a Maximum Relative Difference (MRD) ≤5%, when compared with one- and two-term Maxwell models. The elastic component (E¹) and relaxation time constant (τ¹) of the first term of the three-term Maxwell model decreased linearly with increase in moisture content. Of the different variables studied, moisture content had a significant influence on both of these parameters.     

Deformation and Dehulling of Sponge Gourd (Luffa aegyptiaca) Seeds

This work presents the compressive strength properties of sponge gourd (Luffa aegyptica) seeds to facilitate the design or adaptation of an appropriate dehuller. The sizes and shape indices of the seed and kernel, and the clearance of the kernel from the seed coat were determined. The seed samples were subjected to uni-axial quasi-static compression tests at 1.0 mm min^?1 along the minor and the major axes. The fracture resistance, stiffness modulus, modulus of elasticity, toughness, and maximum elastic deformation of the seed were obtained from the force-deformation curve. The geometric mean diameters varied from 4.0 to 4.5 mm for the seed and 1.6 to 3.9 mm for the embedded kernel; while their corresponding sphericities were 0.64 and 0.62, respectively. The compressive strength of the seed varied with loading orientation. The seed exhibited larger deformation but lower stiffness along the major axis than the minor axis. The force required for rupturing the hull were 95 N along the major axis and 81 N along the minor axis; while the corresponding energy required were 95 and 40 mJ.     

BRUISING AND SPLITTING OF APPLE FRUIT UNDER UNI-AXIAL COMPRESSION AND THE ROLE OF SKIN IN PREVENTING DAMAGE

Whole apples were compressed uni-axially with the core at right angles (horizontal compression) and parallel (vertical compression) to the direction of force. Under horizontal compression, the apple begins to bruise as soon as force is applied. The energy absorbed is proportional to the volume of bruise produced. Resistance to bruising varies with variety. In this orientation the fruit does not deform elastically, bruises easily, and the skin is not important in preventing bruising. Under vertical compression the apple is a much more elastic structure and can expand laterally. It can withstand greater deformation without damage. Rock Pippin can elastically absorb up to 0.5 J before damage. In this orientation, skin plays an important part in preventing cracking under tension. Any damage to the skin greatly reduces the structural strength of the fruit and renders it much more susceptible to cracking. Apples stacked in boxes seldom experience energies greater than 0.5 J. Storing apples in a vertical orientation can therefore reduce risk of bruising.     

在压缩载荷下银杏果核破壳参数优化

利用LDS-W10A型微机控制的电子材料实验机对我国西南地区银杏果核进行了压缩实验,并以杏壳破裂力、破裂能耗、杏仁的破损率为目标参数,以施压部位、加载速率、含水率为因素进行了多目标的正交实验。同时,采用隶属度法的综合评分以及最小显著差值法（LSR法）优化出银杏果核脱壳的最佳工艺参数组合。通过对实验数据分析,得到相应的数学模型。实验表明:不同含水率的杏核在沿三个不同方向被压缩时,均出现明显的弹性变形,而且没有明显的生物屈服点;杏核施压方向、施压速率、含水率与综合评分指标均为显著相关（p<0.05）。要使银杏果核脱壳质量最佳,其最优水平组合为杏核施压方向为Y轴、挤压速率为55mm/min、含水率23.72%。