兴安落叶松锯材动态弹性模量测试研究

为研究利用纵向振动法测试落叶松锯材动态弹性模量,探究动态弹性模量分布规律,评价落叶松的力学性能。以纵向振动法测试尺寸为4000mm×150mm×50mm和4000mm×100mm×50mm的兴安落叶松锯材A和B的动态弹性模量,对动态弹性模量测试结果进行三参数Weibull分布、正态分布、对数正态分布拟合检验,抽样测试锯材静态弹性模量,并评价锯材的力学性能。结果表明纵向振动法测试的落叶松动态弹性模量和静态弹性模量在0.01水平线性相关;经检验锯材A和B的尺寸对动态弹性模量无显著影响,锯材A和B的动态弹性模量平均值为15475MPa和15347MPa;落叶松锯材A和B的动态弹性模量都符合正态分布;锯材A和B的静态弹性模量设计值分别为15174MPa和15073MPa。验证了落叶松动态弹性模量和静态弹性模量具有相关性,可以利用纵向振动法并根据公式E_(静态)=0.7866E_(FFT)+3.002(R~2=0.8474)估计锯材的静态弹性模量并评价其力学性能;截面尺寸对落叶松锯材的动态弹性模量无影响;可以利用正态分布拟合落叶松的动态弹性模量且其准确性高于Weibull分布;本批次落叶松静态弹性模量达到北美地区进口2550Fb-2.1E等级规格材对弹性模量的要求。     

单板层积材力学性能研究

经三种不同的外部条件处理后,使用无损检测设备(FFT)和力学试验机对杉木单板层积材试件静曲强度和弹性模量进行测量。结果表明,试件含水率在纤维饱和点以下时,无损检测方法(FFT)测得的弹性模量和力学试验机测得的静曲强度和弹性模量具有较优的线性相关性;在试件纤维饱和点以上,无损检测方法测得的弹性模量和力学测得的弹性模量有较优的线性相关性,而与静曲强度无线性相关性;单板层积材的静曲强度和弹性模量随着含水率的增加而降低。     

非标准大气压下烟叶含水率测试结果的修正

为了修正高海拔地区(非标准大气压下)烟叶含水率测试结果与低海拔地区(近似标准大气压下)测试结果之间的系统差异,选择了9个实验样品在8个不同海拔高度的实验室[非标准大气压下7个实验室(1#~7#),和一个近似标准大气压下实验室(8#)],进行了含水率测试。分析了大气压与含水率测试值的相关性,及标准与非标准大气压下实验室烟叶含水率测试值的关系。利用LINEST回归函数,建立了非标准大气压下烟叶含水率的修正方程,并重新选择验证样品对修正方程进行了验证。结果表明:(1)烟叶含水率测定值与大气压力负相关,二者决定系数R2在0.519 6~0.917 5之间,9个样品的含水率与大气压的相关性均达显著或极显著水平。(2)通过含水率与大气压之间的相关性拟合了两者之间的优化结果,为三重多项式。(3)将非标准大气压下验证样品测试结果带入修正方程,将修正值与标准大气压下测定值进行了比较,两者最大偏差绝对值为0.668 9%。     

中密度纤维板的力学性能与含水率关系研究

中密度纤维板的含水率是影响其力学性能的重要因素。通过在不同含水率条件下进行静曲强度、弹性模量和内结合强度试验,研究了中密度纤维板的力学性能与含水率之间的关系。结果表明:中密度纤维板含水率对其力学性能有显著的影响,通过平衡处理中密度纤维板的含水率从6.5%上升至14.0%,含水率每增加1%,静曲强度下降约9.6%,弹性模量下降约11.2%;内结合强度下降62.7%。     

两种无损检测方法评估足尺杉木规格材动态弹性模量

利用纵向基频振动和应力波方法测量了不同规格足尺杉木的动态弹性模量,结果表明:不同尺寸的杉木规格材平均动态弹性模量变化不大;杉木规格材纵向基频振动法测得的动态弹性模量Efft在8.18~9.50GPa之间,应力波法测动态弹性模量Esw在9.02~10.38GPa之间,两者的相关性很好,相关系数可达0.9以上;杉木规格材动态弹性模量最大值和最小值差异较大,主要分布在7~11GPa之间。     

搅拌型酸乳触变特性的研究

以酸乳为研究对象,建立了通过上下行曲线间的面积法及弹性模量的恢复性表征触变性2种测试方法,同时,对7类市面上流行的搅拌型酸乳进行相应的测试。结果表明:上行曲线及下行曲线之间的面积以及设定恢复时间时弹性模量与扫描初始时弹性模量之间的差值,均可用于评价酸乳的触变性大小,2种表征手段存在高度相关性,上下行曲线间面积越大或弹性模量的恢复值越大,酸乳的触变性越强。对方法的试验参数也进行了优化,研究了上下行曲线的扫描时间以及上下行曲线间等待时间对触变特性的影响,研究了不同预剪切速率与预剪切时间对酸乳弹性模量的影响。     

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.     

三种无损检测方法预测四种桉树木材弹性模量的对比研究

以四种人工林桉树板材为研究对象,分别采用超声波、应力波和FFT分析方法检测四种试材的动态弹性模量,并与力学实验机测定的静态抗弯弹性模量进行比较.结果表明:三种检测方法存在差异,其中以FFT所测定的动态弹性模量与静态弹性模量相关程度最高;木材密度和静态弹性模量之间存在着相关关系,但相关程度小于三种无损方法检测的动态弹性模量与静态弹性模量的相关程度,说明三种检测方法比简单地根据木材密度预测木材弹性模量更具有普遍意义.     

纤维板的弹性模量及静曲强度的动态检测

利用振动无损检测法测得纤维板的动态弹性模量,并用一元和二元回归分析了纤维板的密度、静态弹性模量、动态弹性模量、静曲强度之间的相关性。结果表明:纤维板的静态弹性模量与动态弹性模量之间,或动态弹性模量与静曲强度之间均密切线性相关;以纤维板的动态弹性模量和密度为自变量与静曲强度建立二元回归方程,其相关程度较一元回归更为密切。密度及长度与横截面面积比值较大的纤维板,其动态弹性模量与静态值更为接近。     

平衡处理条件对刨花板物理力学性能测试结果的影响

为探索不同平衡处理条件对刨花板物理力学性能测试结果的影响规律,以16 mm厚刨花板为试验对象,以标准平衡处理条件（20℃,相对湿度65%）为基础,以2种温度条件（5℃和35℃）和2种相对湿度条件（30%和90%）作为对比,测试不同平衡条件下试件的各项物理力学性能。从结果来看,在本试验范围内平衡处理条件对刨花板物理力学性能测试结果有影响,其中湿度对测试结果的影响显著,而温度的影响较小。对比平衡处理后的试验结果可知,温度一定时,随着湿度的增加刨花板试件的含水率明显增加,其静曲强度、弹性模量、握螺钉力、内胶合强度、吸水厚度膨胀率的测试值随着含水率的增加而降低。     

Relationship of Water Content to Textural Characteristics, Water Activity, and Thermal Conductivity of Some Commercial Sausages

Mechanical properties from cyclic low strain testing, texture profile parameters and thermal conductivity were evaluated for 7 types of commercial sausage products ranging in moisture content from 27.7% to 62.4% and a_w from 0.857 to 0.993. Hardness, fracturability, the apparent moduli, stress al 20% compression, mechanical hysteresis loss, and strain energy all increased with decreasing moisture level, while springiness and the degree of elasticity decreased. Moisture had no significant effect on cohesiveness. A linear relationship was observed between the a_w and the effective mole fraction of water in the brine, the exact nature of which depended on the thermal process which the product had received. Thermal conductivity decreased with decreasing moisture in a linear manner.     

落叶松材生长特性对应力波传播速度的影响

通过对落叶松材试件进行的应力波检测试验,研究了木材节疤尺寸和数量、生长率等对应力波传播速度的影响,并对节疤尺寸等与应力波传播速度之间关系进行了回归分析.结果表明,应力波传播速度与节疤尺寸大小呈负相关,与生长率呈负相关.密度对应力波传播速度的影响在无疵试件和有节疤等试件中是不同的.     

Non-destructive grading of green Maritime pine using the vibration method

The purpose of this study is to estimate the modulus of elasticity of green lumber with unknown moisture content (MC) by non-destructive measurement. This paper reports the results and statistical analysis of a large number of experiments. They indicate that the dynamic modulus of elasticity (DMOE) can be determined without knowing the MC. Mechanical grading with DMOE determined in this way is reliable and efficient with a correlation coefficient of 0.44, compared with a coefficient of 0.45 between MOR and DMOE of dry specimens. Thus the possibility of strength grading of Maritime pine (Pinus pinaster) at an early step in the industrial process is demonstrated with success.     

氯吡苯脲对生长期‘徐香’猕猴桃光学参数及内部品质的影响及其关系分析

为了解氯吡苯脲(1-(2-chloropyridin-4-yl)-3-phenylurea,CPPU)对生长期‘徐香’猕猴桃光学参数和内部品质的影响以及光学参数与内部品质的关系，采用单积分球系统(950～1 650 nm)测定经不同质量浓度(0、10、20 mg/L)CPPU处理的生长期猕猴桃的光学吸收系数(μ_a)和约化散射系数(μ_s’)，并测定猕猴桃的内部品质(可溶性固形物含量(soluble solids content,SSC)、含水率及硬度)；分析光学参数与内部品质之间的关系，并建立预测内部品质的偏最小二乘回归(partial least squares regression,PLSR)模型。结果表明，CPPU处理使得猕猴桃的硬度降低，含水率升高，但对SSC无显著影响(P>0.05)，且CPPU处理导致猕猴桃的光学参数值发生变化；μ_a和μ_s’与猕猴桃同一种内部品质之间呈现不同的正负相关性，且相关系数随波长而变化，并在某一波段内有较好的相关性；基于μ_a谱建立的PLS...     

Data Mining-Based Wavelength Selection for Monitoring Quality of Tomato Fruit by Backscattering and Multispectral Imaging

The aim of this research was to predict quality factors of tomato fruit during storage using backscattering and multispectral imaging techniques. To gather the required information for developing prediction models, batches of 200 tomatoes (cv. Pannovy) harvested at two maturity stages, were stored at standard condition up to four weeks. During storage, the modulus of elasticity, moisture content, soluble solid content, titratable acidity, hyperspectral data, and backscattering images were acquired on 40 tomatoes at regular intervals of one week. After extracting the spectral data from 40 points on each sample, they were subjected to preprocessing operations. Several feature selection techniques, including filter (Relief F, Fisher-Score, and t-Score) and wrapper (genetic algorithm) methods were used to find the sensitive wavelengths for each fruit quality parameter. With the novel strategy used, the wavelengths found by the fusion of genetic algorithm and t-Score techniques showed good prediction performance for all considered qualitative parameters. In order to verify the usefulness of selected wavelengths, backscattering and multispectral imaging techniques were applied. The artificial neural network produced the calibration models which gave a reasonably good correlation for estimating the modulus of elasticity, soluble solid content, and titratable acidity at 660 nm and moisture content at 830 nm of tomato from backscattering images. The correlation coefficient between the multispectral and backscattering imaging prediction results and reference measurement results were 0.952 and 0.891 for modulus of elasticity, 0.727 and 0.539 for moisture content, 0.736 and 0.561 for soluble solid content, and 0.811 and 0.706 for titratable acidity, respectively.     

Effect of relative humidity on some physical and mechanical properties of different types of fibreboard

Equilibrium moisture content and strength properties as a function of relative humidity (RH) were measured in three types of commercial fibreboards with different densities. The measurements were made after specimens had been conditioned to equilibrium at 35, 50, 65, 80 and 95% RH and 20 °C. It was shown that the modulus of elasticity decreased slightly between 35 and 65% RH and markedly – at above 65% RH for all types of boards. A very strong decrease of modulus of elasticity was observed at about 80% RH (capillary condensation). A similar decreasing trend was observed in bending strength. Overall, high RH had a noticeably detrimental effect both on the MOE and the bending strength for all tested boards. Adequate correlation exists between bending MOE and bending strength with moisture content. The lower the density of boards the higher their equilibrium moisture content.     

NaCl对猪肉干燥过程中质构特性的影响

以猪背最长肌为研究对象,经不同浓度NaCl溶液腌制后,60 ℃下热风干燥后其质构特性参数随含水率和NaCl含量的变化规律。结果表明:随含水率降低,各样品的剪切力值、硬度及咀嚼性均逐渐增加,而弹性、内聚性则逐渐下降;在相同含水率下,腌制液NaCl浓度≤8%腌制样的剪切力值、硬度、咀嚼性随NaCl浓度的增大而增大,腌制液NaCl浓度＞8%腌制样的上述参数随NaCl浓度增大而减小,各腌制样的弹性随腌制液NaCl浓度升高而逐渐减小,内聚性受NaCl浓度的影响较小。由部分物理指标与质构特性参数之间的相关性分析可知:肉样的质构特性参数与样品的含水率、横向收缩比(LSR)、纵向收缩比(TSR)、体积变化率等极显著相关(p<0.01),而相关系数的大小与腌制液NaCl浓度有关。研究结果为腌制肉的品质控制提供参考。     

织物与皮肤动态接触下的湿感觉阈限与强度评价

为研究织物以不同速度与皮肤动态接触过程中对湿感觉的影响,分析了湿感觉绝对阈限与阈上强度的影响机制.通过向织物内添加定量的水,让受试者应用心理学标尺对湿感觉的阈上强度进行评分;然后通过注射泵向织物持续加水直至受试者感觉到湿,记录此时的加水量为绝对阈限;最后采用温度传感器记录测试皮肤区域的温度变化,计算皮肤冷却率.结果表明...     

Texture Changes During the Ripening of Port Salut Argentino Cheese in 2 Sampling Zones

ABSTRACT: Texture changes during ripening of Port Salut Argentino cheese for different sampling zones were studied. Compression relaxation tests were performed and results were analyzed using both Maxwellian and Peleg's models. Elastic equilibrium modulus obtained from the Maxwellian model decreased from 1.22 to 0.11 10⁴Pa during ripening. The constants derived from Peleg's model, k₁ and k₂, diminished with ripening time from 1.18 to 0.71 min and from 1.27 to 1.12, respectively. Asymptotic equilibrium modulus from Peleg's model decreased from 0.95 to 0.07 10⁴Pa during ripening. Rate parameters derived from a 1st order kinetics applied to both equilibrium moduli showed that the decrease was faster in the external zone (0.0846 d⁻¹) than in the central zone (0.0368 d⁻¹). The correlation between equilibrium moduli, salt concentration, moisture content, and maturation indexes was obtained with a determination coefficient of 0.76.     

Moisture-dependent orthotropic elasticity and strength properties of Chinese fir wood

Elastic and strength properties are very important material characteristics in mechanical modelling. Due to the anisotropic and hygroscopic nature of wood, a characterization of wood mechanical behavior will require knowledge of its moisture-dependent properties in relation to the three principal axes of anisotropy. The influence of moisture content (MC) on the elastic and strength anisotropy of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook) wood was examined in the present study. Selected parameters, including the anisotropic Young’s moduli, shear moduli, Poisson’s ratios, yield and ultimate stress values in the longitudinal, radial and tangential directions, were determined in compression and tension tests at different moisture conditions. The results indicated that a distinct moisture dependency is exhibited for the elastic and strength behavior of Chinese fir wood. With the exception of some Poisson’s ratios, all investigated elastic and strength parameters were shown to decrease with increasing MC, whereby individual moduli and strength values were affected by the MC to different degrees. The two- and three-dimensional representation of the compliance matrix and the two-dimensional visualization of a yield surface give a valuable overview on the moisture-dependent elastic and strength anisotropy of Chinese fir wood.