果蔬压缩破坏特性的试验研究

为探索不同种类果蔬的破坏特性,选取白萝卜、土豆和苹果为研究对象进行压缩试验,分别得到了3种试样的破坏力、破坏极限、破坏能和弹性模量值,方差分析结果表明:不同种类果蔬力学特性指标差异显著,白萝卜的特性参数值均显著高于土豆、苹果参数值。     

SENSORY AND MECHANICAL ATTRIBUTES OF GEL TEXTURE

Eighteen experienced judges evaluated the texture of gels varying in gelatin concentration (22-45 g/L) in terms of firmness by oral and manual shear and compression, cohesiveness, and extent of breakdown in the mouth. Manual compression and biting with the front teeth discriminated well across gel concentrations. All sensory measures except extent of breakdown increased with gelatin concentration. Instron (IUTM) measurements showed that increasing gelatin concentration resulted in an increase in maximum force and force/deformation, but had little effect on deformation at yield and rupture or in elasticity and cohesiveness. Results from mechanical measurements varied with the type of force applied (compression, shear or puncture), the loading rate (50 or 200 mm/min), and the extent of deformation attained (40–90%). The highest discrimination across gel concentrations was achieved with shear force at a rate of 200 mm/min and at greater deformations. Sensory responses correlated most highly with the following IUTM measurements: (1) Compression forces at yield and at deformations of 70 and 85% at the higher crosshead speed; (2) Compression forces below the yield point at the lower crosshead speed; and (3) Shear forces measured at maximum deformation (90%) at 200 mm/min.     

质构参数与花生物性测定的相关性

为明确花生在物性测定中与质构参数的相关性,本研究以两种表观差异较大的花生品种为样品,通过调控质构测定仪的关键参数进行研究。结果显示:不合适的质构测试参数能显著影响花生样品的物性特性结果并降低检测准确性。其中,压缩形变量对花生的硬度、弹性、内聚性、咀嚼性等物性特性造成显著影响,而压缩形变量为35%～50%之间时影响较小;测试速度与花生样品脆性成显著负相关性,拟定测试速度在40mm/min时脆性检测结果较为平稳;过高的剪切速率会严重影响剪切力结果的稳定性,造成系统误差扩大,控制剪切速率小于60mm/min能较好的稳定剪切力数据。不同种类花生之间物性测定结果不同,利用合适的测定参数就可以减小系统误差,进而更好的体现样品之间的物性差异。因此,花生样品在进行物性测定时,选择质构参数中压缩形变比在35%～50%范围,测试速度40 mm/min,剪切速率不高于60 mm/min对花生物性测定影响较小,这样的检测参数可以取得稳定数据。     

Mechanical and acoustic evaluation of potato chip crispness using a versatile texture analyzer

The crispness of different potato chip samples was evaluated by uniaxial compression using a widely employed instrument. Acoustic and mechanical events were measured simultaneously during deformation and fracture of the samples at a constant speed. We particularly focused on the mechanical and acoustic characteristics in the vicinity of the major fracture point to confirm the hypothesis that the crispness of potato chips is perceived when they are totally fractured. The results indicated a significant correlation between the magnitudes of the force drop at the fracture point and associated sound pressure. The magnitude of the force drops at the major fracture point differed significantly among the samples, however, the results did not perfectly reflected the perceived crispness of the potato chip samples.     

MEASURING TENDERNESS of MEAT PRODUCTS BY WARNER BRATZLER SHEAR PRESS

Tenderness of bologna, salami and pastrami was measured by Warner-Bratzler (W.B.) tests. Three sample diameters and three crosshead speeds were studied. the samples were ruptured under tension instead of shear; thus, shear force did not increase with the increase in sample diameter at the same cross-sectional area to applied force ratio. Crosshead speed did not affect results of bologna and salami, but affected many parameters of pastrami. Recommended test conditions are: sample diameter 20 mm at any crosshead speed for bologna; 10 to 20 mm sample diameter at any crosshead speed for salami; 15 mm sample diameter and 250 mm/min crosshead speed for pastrami.     

STIFFNESS OF COMPRESSION TESTING MACHINES

A ring test with six participating laboratories and rubber stoppers as reference material was performed to monitor the performance of commercial compression testing instruments. Testing conditions were chosen to be in the range of regular compression testing. Small, single screw instruments with a cantilever exhibited a significant deviation in the force/deformation-response compared with double-screw instruments with a crosshead. Additional tests made with an external device for displacement recording revealed that these differences have to be attributed to insufficient stiffness and some compliance in the cantilever of the tested single-screw instruments. Some consequences of the test results for experiments on soft, semi-soft and rigid food materials are discussed and an equation is developed to correct for the flexing of the cantilever beam in the single screw machine.     

籼米胶稠度测定方法的研究

为了建立籼米胶稠度测定新方法,采用物性仪测定了籼米胶的反挤压特性和蒸煮籼米的压缩特性,并分别探讨了压缩量、测试速度对测定结果的影响。试验表明,籼米胶反挤压法最佳测定条件为压缩量15mm,测中速度和测后速度为1 mm/s;5种籼米胶反挤压特性指标胶强度、稠度、黏度和硬度与国标法的胶稠度均呈极显著的相关性;蒸煮籼米的压缩法最佳条件为压缩量70%,测试速度0.2 mm/s,5种蒸煮籼米的最大压缩力和滞后损失与国标法的籼米胶稠度均呈显著的相关性;籼米胶反挤压法和蒸煮籼米压缩法均可用于籼米胶稠度的测定与评价,而蒸煮籼米压缩法优于籼米胶反挤压法。     

A STUDY OF FORCE-COMPRESSION CONDITIONS ASSOCIATED WITH HARDNESS EVALUATION IN SEVERAL FOODS

Abstract. The hardness of fourteen foods has been evaluated by panel tests and by compression tests with a table model Instron. Oral evaluation of hardness was correlated with instrumental force -% compression data obtained for compressions extending up to 80% and with crosshead speeds up to 20 cm min⁻¹. With soft foods, agreement between panelists' and instrumental data commences at lower % compressions and lower applied forces than with hard foods. As the Instron crosshead speed increases so does the force required to achieve a desired % compression. With very hard foods exhibiting a short relaxation time, e. g. toffee, stress relaxation may influence the registered force. Crosshead speeds exceeding 20 cm min^-1** cannot be utilised in conjunction with the standard Instron recorder because its response time is too long. It should be replaced by a fast response recorder such as a UV recorder. The procedure whereby panelists evaluate hardness during the first downstroke of mastication appears to change from compression to biting as hardness increases. A limited number of tests with Cheddar cheese and table jelly suggest that hardness evaluation by squeezing samples between the thumb and index finger involves lower % compression and lower forces than the oral evaluation of hardness with the same products.     

Instrumental evaluation of defective texture in dry-cured hams

In the first experiment, the effect of the stress relaxation time on texture evaluation of biceps femoris (BF) muscle from dry-cured hams was studied. The specimens were compressed to 25% of their original height and the crosshead speed was 5mm/s. The force decay versus time was recorded and Peleg's model was fitted with different relaxation times. Whatever relaxation time was used, Peleg's model did not describe simultaneously the initial fall of force and the asymptotic tendency of force decay correctly. The initial force and force decay at 2s and at 90s are proposed to assess texture in dry-cured ham. In the second experiment, stress relaxation (SR) and texture profile analysis (TPA) tests were performed on BF and semimembranosus (SM) muscles of 10 hams with abnormal softness and 10 hams with normal texture, at different assay conditions: sample temperature (4°C or 20°C); compression crosshead speed (1mm/s or 10mm/s). The instrumental texture test and the assay conditions that detected defective textures better depended on the muscle considered: for BF muscle the SR test at 4°C and at 1mm/s and for SM muscle the TPA test at 10mm/s at both 4°C or 20°C.     

CONSTANT STRAIN RATE COMPRESSION OF BIOPOLYMER GELS

Usually, uniaxial compression of food materials is performed at constant speed, which causes an increase of the true strain rate during experiments. By using a method described previously (Jaros and Rohm 1994) highly elastic biopolymer gels were compressed at standard conditions and with decreasing crosshead speed in order to maintain constant strain rate conditions during test. In the case of gels showing failure at a Hencky deformation of > 0.5-0.6, significantly lower values for apparent fracture strain were found in constant strain rate compression. Differences in stress at apparent fracture showed good agreement with respect to this critical value. Implications and consequences on interrelation between sensory and instrumental measurements as well as on relationships between rheological and fracture properties are discussed.     

UNIAXIAL COMPRESSION OF A HARD WHEAT FLOUR DOUGH: DATA ANALYSIS USING THE UPPER CONVECTED MAXWELL MODEL

The behavior of a hard wheat flour dough has been measured in lubricated uniaxial compression experiments at compressional rates (crosshead speeds) of 0.2, 2 and 20 cm/min. The appropriate differential equation, derived for an upper convected Maxwell model, while taking into account the changing strain rate during the compression at constant crosshead speed, was solved numerically. With a single choice of model parameters (a viscosity and a relaxation time) there was surprisingly good agreement between the experimental and calculated results. Best fits were obtained, however, when the parameters were allowed to vary with crosshead speed, reflecting the broad relaxation time distribution known to exist in doughs.     

Evaluation method for firmness and stickiness of porcine perirenal fat

The firmness and stickiness of chilled porcine fat at 4°C were evaluated with an Instron compression tester and compared with fatty acid composition. Firmness of cylindrical adipose samples was measured at a force producing a 70% deformation. Firmness values were correlated with refractive index data (r=-0.67), melting point data (r=0.77), and saturated fatty acids concentration data (r=0.72) of the extracted lipid, and with sensory scores data (r=0.89). The firmness value correlated with the concentration of C18:0 (r=0.73). The stickiness of comminuted fat samples was evaluated with the Instron using a fixed load at a compression force of 20N and crosshead speed of 1.5mm/s. Single regression analyses showed that the stickiness parameters, stretch and adhesiveness correlated negatively with the concentration of the saturated fatty acids data (r=-0.64, -0.52) but positively and weakly with the monounsaturated fatty acids data (r=0.28, 0.34). Multiple regression analysis improved their relationships. These results indicate that mechanical evaluation may be used to predict porcine fat texture and saturated fatty acids concentration.     

EVALUATION OF GOUDA CHEESE FIRMNESS BY COMPRESSION TESTS

Cheese maturity, test temperature, crosshead speed, sample shape, sample height and surface area influence the force-compression behaviour of Gouda cheese in an Instron Universal Testing Machine. Introducing mineral oil or Emery paper between the sample's surfaces and the compression plates affects the shape of the compressed samples. Cine-film records indicate that deformation is barrel-shaped (convex) with Emery paper and under normal test conditions, and concave with mineral oil. In the first two test situations friction prevents the cheese surfaces from spreading to the same extent during sample compression as when using mineral oil. Compression as modified by friction may be the principal factor associated with the subjective evaluation of firmness by squeezing samples between the fingers. Firmness evaluation by chewing involves still higher percent compressions which, in Instron tests, lead to sample breakdown and crack propagation.     

暖体假人软质模拟皮肤的研究及其应用

为改善目前现有硬材料暖体假人与真实人体表面弹性的差异性,提高特殊功能服装测试的精度,对暖体假人上使用的一种软质模拟皮肤进行研究。选择6种高分子弹性体,分别是热硫化硅胶、天然乳胶、医用硅胶、聚苯乙烯系弹性体TPR、聚烯烃系弹性体EVA和热塑性聚氨酯TPU,在拉伸、压缩、热性能等多项实验的基础上,研究高分子弹性体的综合性能,并通过模糊数学的模糊决策理论选出综合性能最优的暖体假人模拟皮肤材料。通过在稳定环境条件和变化环境条件2种状态下的暖体假人实验,证明这种模拟皮肤材料在提高暖体假人控制精度、稳定性和环境耐受性方面发挥了良好的效果。     

预应力钢绞线车间工艺设计

预应力钢绞线生产应用现状:市场用量以年均20%以上的速度增长,拥有进口预应力钢绞线生产设备的企业约30家,国产设备的企业50多家,一些钢铁企业开始尝试建设预应力钢绞线车间。从线材表面预处理、拉丝、绞线及稳定化处理等方面阐述预应力钢绞线车间工艺设计,以1×7和1×19结构钢绞线为例,介绍生产设备和工艺参数。生产1×19结构钢绞线拉丝机进线最大直径16.0mm,最大速度15m/s,出线抗拉强度2100MPa,卷筒直径1200mm,盘卷质量4t;中频回火炉感应加热功率800kW;张力轮直径2500mm,最大张力490kN;双收/放线机收线轮外径2900mm,内径1200mm,张力3920N,生产线最大速度135m/min。对车间的平面布置和环保提出要求。     

Analysis of the effect of traffic exposure on the recovery properties of cut pile carpet using analytical and viscoelastic modeling

Viscoelastic models composing of different combination of spring and dashpot are usually used to explain the mechanical behavior of textile materials. In this work, a viscoelastic model was presented to analyze the effect of traffic exposure on the compression and recovery performance of the pile carpet. Wear test, performed by a Hexapod tumbling machine, was conducted to simulate the traffic exposure. Using a tensile tester, adjusted in compression mode, one cycle of compression–decompression was applied to the samples. The standard nonlinear model was presented to fit the experimental data. Best curve fitting based on the least square method was then used to fit the model to the experimental curve. Different attributions of compression were then analyzed and discussed. The results showed that the standard nonlinear model was fitted to the experimental curves with an acceptable coefficient of regression (R²). The district model parameters, i.e. the spring and dashpot constants, were both decreased as the wear cycles increased. At the higher level of wear cycles, the model parameters showed some increment. The initial compression modulus showed the same trend. This may be explained by the more compactness of the carpet at higher wear cycles. The decompression modulus, compression and the decompression work also decreased with the increase of wear cycles. However, no significant increase of the formers was observed at the higher wear cycles.     

碾搓式橡胶果脱壳试验

为研究橡胶果脱壳效率随相关参数的变化规律,确定最佳脱壳条件,根据碾搓原理研制了橡胶果脱壳试验机。通过单因素试验和正交试验,分析不同的挤压压力、摩擦速度和摩擦材料对脱壳率指标的影响规律及机器的最佳工作参数。结果表明:随着摩擦速度增大,脱壳率先增大后降低;随着挤压压力的增加,脱壳率线性增加;摩擦材料依次取钢板、塑料板、木板、橡胶板时,脱壳率逐渐降低。对橡胶果脱壳率的影响因素从大到小依次为挤压压力、摩擦材料、摩擦速度。当挤压压力为700N、摩擦速度为46 mm/s、摩擦材料为钢板时,橡胶果的脱壳率达到81.8%。研究结果可为橡胶果脱壳机的整体设计提供试验依据。     

Analysis of the effect of UV radiation on the recovery properties of pile carpet after static loading through analytical and viscoelastic modeling

Different combinations of spring and dashpot systems are usually considered to model the mechanical behavior of textile materials. In this work, Jeffery’s mechanical model, which is a combination of spring and dashpot components, was used to model the recovery behavior of the pile carpet after static loading. The carpet samples were exposed to different levels of UV radiation. The short-term static loading was applied to the samples. The recovery response or thickness vs. time was then measured. By analyzing this model and using the best curve fitting based on the least square method, the viscoelastic parameters in each UV exposure time were calculated. Four attributes of compression were then studied. The results showed that the thickness loss and the maximum compression under a constant load were mainly dominated by the deterioration of the dashpot elements (Plastic part of deformation). The thickness loss and the maximum compression were both higher at longer UV exposure times. The thickness loss showed a good linear correlation with the inverse of the first dashpot constant, 1/η₁. In contrast, the speed of recovery and the potential stored energy were mainly dominated by the parameters of the Voigt–Kelvin body, i.e. the elastic part of the compression.     

新丰核桃的多因素压缩试验

通过对新丰核桃进行挤压试验,研究含水率、加载速度及加载方向对核桃压缩特性的影响,并对核桃挤压破壳建立有限元模型分析,运用ANSYS对核桃在不同加载方向下的力学特性进行仿真。结果表明,核桃在厚度方向进行挤压破壳时所需的破壳力最大,此时的核桃壳裂纹扩散面积也最大,核桃壳破裂发生的形变最小,易于取出较完整的仁。挤压式和击打式两种破壳试验表明,多次多范围的冲击式加载能使核桃壳裂纹扩散率更大更均匀,得到的整仁率越高,能达到更好的破壳取仁效果。     

高速线材生产中吐丝质量控制

针对高速线材生产线吐丝机存在的吐圈忽左忽右飘落、吐丝线圈大小不等以及线圈不圆问题进行分析,并提出控制措施。经过调整在轧制65钢Φ6.5 mm盘条时,轧制速度稳定在108 m/s左右;使用该线材生产钢丝断丝率由原来的0.5次/t下降到0.1次/t;拉丝模耗由原来的0.3个/t下降到0.17个/t,用户生产效率大幅度提高。