非织造土工布应力松弛性能的模拟及应用探讨

对短纤针刺非织造土工布的研究表明 :标准线性固体力学模型和欧林三元件模型均能较好地描述非织造土工布的应力松弛性能。     

土工布力学性能的模型及其应用初探

对不同类型的土工布研究表明 :线性和非线性的简易三元件模型的模拟应力松弛曲线相同 ,欧林三元件模型在引入一个时间滞后常数后能很好地模拟土工布的应力松弛特性。     

氨纶包芯纱和棉纱粘弹性力学性能的研究

本文通过对氨纶包芯纱和纯棉纱的粘弹性力学性能的测试，选择了三元件力学模型对其应力松弛进行模拟，建立了相应拟合方程，探讨了氨纶包芯纱的预牵伸倍数与纱线的强伸性以及应力松弛间关系。     

氨纶包芯纱和棉纱粘弹性力学性能的研究

本文通过对氨纶包芯纱和纯棉纱的粘弹性力学性能的测试,选择了三元件力学模型对其应力松弛进行模拟,建立了相应拟合方程,探讨了氨纶包芯纱的预牵伸倍数与纱线的强伸性以及应力松弛间关系.     

PVC 压延柔性复合材料应力松弛的力学模型

根据黏弹性材料力学模型的假设,选取线性黏弹性力学模型中四元件模型的等效模型和非线性黏弹性力学模型中的欧林模型,基于材料相同但增强织物组织结构不同的3 种试样进行的应力松弛试验,通过MatLab 软件计算,拟合出四元件模型的等效模型及欧林模型的方程参数,并采用MatLab 软件计算机画图显示实测点和拟合曲线,从而进一步比较、分析得出最适合压延类柔性复合材料松弛性能的力学模型,证明PVC 压延类柔性复合材料具有非线性黏弹性的力学特征,属于非线性黏弹性的范畴,且增强织物的组织结构对这一属性影响不明显。     

非织造土工布应力松驰性能的模拟及应用探讨

对短纤针刺非织造土工布的研究表明：标准线性固体力学模型和欧林三元件模型均能较好的描述非织造土工布的应力松驰性能。     

基于图像处理技术的非织造土工布的泊松比测试

非织造土工布是随机分布各向异性纤维网经机械加工、热黏合或化学黏合固结而得到的一种产业用纺织品,广泛应用于土木工程建设中,主要结构特征是纤维的不连续且随机分布。作为材料的一个基本力学指标,泊松比影响材料的剪切模量、变形特性、断裂韧性等力学性能。由于非织造土工布在拉伸过程中存在严重的"颈缩"现象,因此,有必要研究泊松比的非接触式测试方法。提出应用图像处理技术测试非织造土工布的泊松比并进行实验验证,该方法为实现泊松比的自动、实时测试提供了理论基础和实践可能,对非织造土工布力学性能的研究和应用有着重要的科学意义。     

7种淀粉凝胶应力松弛特性研究

将7种淀粉采用相同方法制备出凝胶块作为实验试样,经质构仪进行压缩和应力松弛实验得到流变学特性参数。利用统计分析软件进行非线性回归拟合,建立了广义Maxwell力学模型。结果表明:淀粉凝胶具有良好的压缩黏弹性力学性质,五元件广义Maxwell模型适用于模拟淀粉凝胶的应力松弛现象。通过主成分分析,应力松弛参数可归纳为两类,即凝胶粘弹特性和凝胶松弛时间。     

酱牛肉应力松弛特性实验

以5个品牌酱牛肉为试样,从压缩试验及应力松弛试验研究中获得力学-流变学性质参数,利用SPSS软件进行非线性回归拟合,建立了广义Maxwell流变模型。结果表明:酱牛肉具有良好的压缩黏弹性力学性质,属黏弹性材料,五元件广义Maxwell模型适用于模拟酱牛肉的应力松弛现象。对应力松弛参数做主成分分析,应力松弛试验的7个参数可以分为两个主成分,归纳为2类,即黏弹特性和松弛时间。     

木材应力松弛特性及其影响因素概述

在总结木材应力松弛力学模型的基础上,主要分析了温度、水分等因素对木材应力松弛的影响规律,并对相应温湿度条件下的应力松弛机理进行了总结。     

An improved method to analyze the tensile behavior of carpet yarn

Since the strain, friction, and vibration of carpet yarn have direct impact on the quality of tufted carpet, mechanical properties of yarn play an important role in carpet weaving. An improved method based on Boltzmann superposition principle for describing mechanical behavior of carpet yarn is presented in this paper, which greatly reduces the amount of calculation and further improves the fitting precision. To estimate the performance of the model, we carry out some experiments on carpet yarn specimens, and compared with a nonlinear viscoelastic model widely used in studying nonlinear material. The results showed that the improved method and the nonlinear viscoelastic model perfectly fit the stress relaxation experimental curves when the deformation of the specimens is small, however the improved method is more accurate than the nonlinear viscoelastic model based on single integral constructive equation when the models are used to predict the stress relaxation responses.     

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.     

Interpretation of viscoelastic behaviour of sweet cherries using rheological models

Viscoelastic behaviour of some commercial sweet cherry cultivars of Iran has been studied in current research. For this purpose, stress relaxation test was conducted on five cultivars of sweet cherry including Siah Mashhad, Abarde, Victoria, Dovom Ras and Tak Dane. Two common models (Generalised Maxwell model and Peleg model) were fitted to the experimental data. Both models could describe stress relaxation behaviour of cherries (R² = 0.99), but Generalised Maxwell model had lower root mean square error (RMSE) than Peleg model. Based on analysis of stress relaxation data using models constants, Tak Dane exhibited more solid properties, while Victoria showed less elastic behaviour than other cultivars. The results revealed that relaxation ratio (R%) and the area under the stress relaxation curve could be effective alternative to models with easier mathematical procedure.     

COMPARISON OF MECHANICAL TESTS FOR EVALUATING TEXTURAL CHANGES IN POTATOES DURING THERMAL SOFTENING

The changes in the texture of cylindrical samples of potato tissues immersed in water at 60, 70, 80 and 90C for up to 80 min were monitored at each temperature in terms of tangent modulus of elasticity in axial and radial compression tests, and elasticity and viscosity parameters in creep and stress relaxation tests. The magnitude of all mechanical test parameters decreased with an increase in heating time and temperature. The creep and stress relaxation responses of individual potato samples were adequately represented by respective mechanical models (R²= 0.94 to 0.99). The mechanical test parameters followed apparent first-order degradation kinetics due to the effect of thermal softening, and the rate constant was used as an index of the sensitivity of a mechanical test. The radial compression test was relatively more sensitive than the axial test. Based on an overall comparison, the parameters from creep and stress relaxation tests were found to be the most sensitive in describing the textural changes during thermal softening of potatoes.     

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.     

The influence of two bar warp-knitted structure on the fabric tensile stress relaxation Part II: (locknit,satin, loop raised)

When strain is applied constantly, there is a decreased stress with time in viscoelastic materials, which is called stress relaxation. During the manufacture and application of clothing and footwear, materials experience various long-lasting deformations, and relaxation process in materials arises. Thus, with theoretical and experimental study of the factors affecting stress relaxation, the ability to design and produce appropriate clothes will be increased. In the first part of this research, we studied the stress relaxation behavior of warp-knitted structures which have longer underlaps in back bar (reverse locknit, three- and four-needle sharkskin, and queens’ cord). Following the previous research, the aim of this study was to investigate the effect of fabric structure, strain percentage, and course density on the stress and stress relaxation of the warp-knitted structures which have longer underlaps in front bar (locknit, three- and four-needle satin, and loop raised). The results reveal that the fabric structure, strain value, and fabric density are important factors affecting the stress and stress relaxation percent of the fabrics. By increasing the strain and the length of underlap in the front guide bar, stress and stress relaxation percent will be increased. Also, fabrics with higher course density show higher stress and stress relaxation percent. Among the mechanical models used to describe the stress relaxation behavior of the fabrics, the three-component Maxwell’s model with parallel-connect nonlinear spring showed the best agreement with the experimental stress relaxation curves of the analyzed fabrics.     

猪软革的应力松驰行为研究

从猪软革的应力松驰行为方面研究了其粘弹性 ,建立了猪软革应力松驰行为的理论力学模型 ,圆满地描述了这种粘弹性行为。     

Stress relaxation characteristics of low-fat chicken sausages made in Argentina

Low-fat sausages were prepared with fresh chicken breast meat and formulated with different levels of added fat, whey protein concentrate, and hydrocolloids (xanthan and guar gums) to study the effect of composition on the stress relaxation behavior of the products. Stress relaxation experiments were conducted on precooked sausages at 25°C. Generalized Maxwell and empirical Peleg models were used to predict the stress relaxation behavior of the material. A model with seven maxwellian elements in parallel with a pure elastic element showed a very good agreement with experimental data. Results show that the proposed model satisfactorily fits the experimental data better than Peleg's model or Maxwell models with less elements. The relaxation time distribution functions were obtained. The characteristic relaxation time was shorter (2500s) for the formulations with no added fat which produced a less elastic product while the sausages with added fat showed longer characteristic relaxation time (5000s). The stress relaxation experiment differentiated the viscoelastic nature of different formulations due to reduction of fat content.     

Modeling of Coupled Water Transport and Large Deformation During Dehydration of Apple Tissue

Water loss of fruit during storage has a large impact on fruit quality and shelf life and is essential to fruit drying. Dehydration of fruit tissues is often accompanied by large deformations. One-dimensional water transport and large deformation of cylindrical samples of apple tissue during dehydration were modeled by coupled mass transfer and mechanics and validated by calibrated X-ray CT measurements. Uni-axial compression–relaxation tests were carried out to determine the nonlinear viscoelastic properties of apple tissue. The Mooney–Rivlin and Yeoh hyperelastic potentials with three parameters were effective to reproduce the nonlinear behavior during the loading region. Maxwell model was successful to quantify the viscoelastic behavior of the tissue during stress relaxation. The nonlinear models were superior to linear elastic and viscoelastic models to predict deformation and water loss. The sensitivity of different model parameters using the nonlinear viscoelastic model using Yeoh hyperelastic potentials was studied. The model predictions proved to be more sensitive to water transport parameters than to the mechanical parameters. The large effect of relative humidity and temperature on the deformation of apple tissue was confirmed by this study. The validated model can be employed to better understand postharvest storage and drying processes of apple fruit and thus improve product quality in the cold chain.