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应力波木材无损检测信号采集系统 总被引:3,自引:2,他引:3
应力波木材无损检测技术可在不破坏木材使用性能的前提下,快速的检测出木材的尺寸、规格和基本物理性质等,基于此优点,应力波无损检测技术近几年越来越受到青睐。应力波在木材中传播时,如遇到裂缝、孔洞、裂纹等界面不连续处,就会发生反射、折射、散射和模式转换,对缺陷有很高的敏感性。基于应力波的这种敏感性,本文对应力波在木材中传输时的信号进行采集,通过对采集信号进行频谱分析、小波变换等处理,可进一步得到应力波在木材中的传播速度等参数,从而为鉴别木材的缺陷提供更多的信息。 相似文献
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木材干燥应力的研究对丰富和完善木材干燥理论、建立和完善干燥工艺、提高干燥质量和经济效益具有重要意义,许多研究者从不同角度对木材干燥应力应变进行了试验测定及数值计算.本文对其中的主要研究方法进行了较详细的归纳,并对今后的研究提出了看法和建议. 相似文献
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木材干燥应力测试的一种新方法 总被引:3,自引:0,他引:3
木材干燥应力的研究是木材干燥工作中一个重大课题,在木材干燥工作中占有重要地位。自三十年代以来,国内、外许多专家和学者致力于这一课题的研究,先后出现了不少木材干燥应力的理论和测试方法,特别是测试方法在不断改进和发展,有简单易行的切片法和梳 相似文献
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木材无损检测的现状及展望 总被引:2,自引:0,他引:2
无损检测在木材分等到木材构件机械性能的现场评估范围得到广泛应用。本文阐述了无损检测的基本概念,记述了无损检测在林产品中的早期研究成果,以及无损检测在现代工业中的应用及其研究工作状况。 相似文献
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无损检测在木材分等到木材构件机械性能的现场评估范围内得到广泛应用。本文阐述了无损检测的基本概念,记述了无损检测在林产品中的早期研究成果,以及无损检测在现代工业中的应用及其研究工作状况。 相似文献
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Causes of color changes in wood during drying 总被引:3,自引:0,他引:3
The forest industry operates in a dynamic and global market where change and competition are the rule rather than the 相似文献
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《Scandinavian Journal of Forest Research》2012,27(3):234-240
Proanthocyanidins (PAs), which are common phenolic compounds in plants, are considered to be mainly defensive compounds against different kinds of stress, e.g. herbivory. In addition to increasing after stress, they may condense and/or oxidize to form coloured compounds when cells die, which may affect both the resistance of xylem to rot and its colour. This is important in the mechanical wood industry. The effects of some biological factors (growing site, sampling date, wood location in the trunk) on the concentration of soluble PAs (sPAs) were studied in fresh and dried birch wood. Those factors that affected sPA concentration most were sampling date and radial location. Drying method also had a great effect on the sPA concentration, which in turn correlated with the colour of the wood. 相似文献
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Effects of pressure and temperature in the chamber during vacuum drying on the relative humidity and evaporation of wood surface were investigated by using the vacuum chamber. The setting temperature during vacuum drying included dry-bulb temperature td, the wet-bulb temperature tw and the temperature difference between the air in the vacuum chamber and the cooling water in the condenser. Results indicated that relative humidity during vacuum drying was affected by the dry-bulb temperature td, the wet-bulb temperature tw and the temperature difference between the air in the vacuum chamber and the water in the condenser. Relative humidity of wood decreased with the increase in temperature at the given temperature of the water in the condenser. The relative humidity was affected slightly by pressure in the vacuum chamber pA, and it decreased from 70% to 65% with pA increased from 50 kPa to 101 kPa. Moreover, there was nearly no evaporation under the vacuum without external heating. 相似文献
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A new method for monitoring moisture content during radio-frequency (RF)/vacuum drying was developed by measurement of temperature
and pressure in wood. Temperature and pressure inside the wood were measured simultaneously during RF/vacuum drying at the
same point. The relative humidity (RH) and moisture content (MC) below the fiber saturation point (FSP) were calculated based
on temperature and pressure, and the relationship between the temperature, RH, and equilibrium moisture content (EMC) at the
measurement point. When the moisture content was below the FSP, the calculated MC was slightly greater than the value given
by oven drying. The absolute error was within 0.8% near the open cross side, and was within 1.8% at another measurement point.
Thus, we concluded that it was practicable to monitor the moisture content below the FSP according to the temperature and
pressure inside the wood.
Part of this study was presented at the 15th Annual Meeting of the Chugoku Shikoku Branch of the Japan Wood Research Society,
Higashi-Hiroshima, Japan, September 2003 相似文献
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现代热泵木材干燥技术的发展 总被引:1,自引:0,他引:1
论述了现有热泵木材干燥技术的发展,现代热泵木材干燥技术吸收了常规木材干燥技术的某些优点,具有木材干燥周期越来越短、被干燥木材质量和节能效果明显等特点。 相似文献
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In this study heartwood from a Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantation was treated using a high-temperature drying (HTD) method at 115°C, a low-temperature drying (LTD)
method at 65°C, and freeze vacuum drying (FVD), respectively. The dynamic viscoelastic properties of dried wood specimens
were investigated. The measurements were carried out at a temperature range of −120 to 250°C at four different frequencies
(1, 2, 5, and 10 Hz) using dynamic mechanical analysis (DMA). We have drawn the following conclusions: 1) the storage modulus
E′ and loss modulus E″ are the highest for HTD wood and the lowest for FVD wood; 2) three relaxation processes were detected in HTD and LTD wood,
attributed to the micro-Brownian motion of cell wall polymers in the non-crystalline region, the oscillations of the torso
of cell wall polymers, and the motions of the methyl groups of cell wall polymers in the non-crystalline region in a decreasing
order of temperatures at which they occurred; and 3) in FVD wood, four relaxation processes were observed. A newly added relaxation
is attributed to the micro-Brownian motions of lignin molecules. This study suggests that both the HTD and the LTD methods
restrict the micro-Brownian motion of lignin molecules somewhat by the cross-linking of chains due to their heating history.
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Translated from Journal of Beijing Forestry University, 2008, 30(3): 96–100 [译自: 北京林业大学学报] 相似文献
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An improved technique, cheaper and less time-consuming, to measure standing wood volume by using an electronic theodolite was tested, by which greater information from the forest could be acquired accurately and non-destructively. This was achieved by recording the diameter at breast height and ground-level diameter of a tree as well as the included angle between the electronic theodolite and the left and right tangents of the stem at any point. The standing wood volume then was computed precisely by section. In addition, the factors that influence the precision of the method (observable distance and number of segments) were also analysed. In the study, 175 Larix gmelinii (Rupr.) Kuzen. trees and 190 Populus tomentosa Carrière trees chosen randomly for sampling were measured with the electronic theodolite, and then were cut down for measurement of the average cross-section volume. Based on the data acquired from 100 sample trees, a standard volume table was compiled, and then the data for the remaining random 10 sample trees in each group were selected for a comparison test. The results indicated that the optimal distance for indirect observation should be as high as the sample tree, and the optimal visual distinguished section was about 2?m. The correlation coefficient between the value measured non-destructively and the value of the felled trees of L. gmelinii was 0.97, with an average relative error of 1.62%. With regard to P. tomentosa, the correlation coefficient between the two values obtained by the two methods was 0.905 with an average relative error of 8.40%. It was concluded that the standard volume model based on the non-destructive measurement technique meets the requirements for precision in forest surveys. The precision of the standard volume model for L. gmelinii (a coniferous tree) was superior to that of the model for P. tomentosa (a broad-leaved tree). The electronic theodolite method provides an alternative technique for measuring trees without destructive sampling and is widely applicable for forest surveys. 相似文献
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Li Xian-jun Li Wen-jun Zhang Bi-guang 《中国林学(英文版)》2007,9(1):63-67
Microwave-vacuum (MV) drying characteristics of plantation Masson pine (Pinus massoniana) were studied experimen-tally for various levels of microwave radiation time, initial moisture content (MC), vacuum level and wood thickness. The results show that the process of MV drying for wood can be significantly divided into a short accelerating rate drying period, a long constant rate drying period and falling rate drying period, and the second drying period can extend to levels of mean MC below the fiber satu-r... 相似文献