共查询到20条相似文献，搜索用时 31 毫秒
1.
Yoshiyuki Yanase Yoshihisa Fujii Shogo Okumura Yuji Imamura Tsuyoshi Yoshimura 《Journal of Wood Science》2000,46(3):243-247
To examine the feasibility of using plate-type waveguides for effective detection of acoustic emissions (AEs) from termite attacks in wood, AEs generated by breaking pencil leads or by termite attacks were detected using an AE sensor with a resonant frequency of 140kHz with steel plates of four different sizes and thickness and three AE sensors without them. The larger plates were associated with larger amplitudes of the artificial AEs. The amplitudes of AEs detected by an AE sensor with a steel plate larger than 30×30mm were greater than the average amplitude of the artificial AEs detected by three AE sensors. When detecting AEs generated by the feeding activity of workers,Coptotermes formosanus Shiraki, the cumulative AE events detected by the sensor with a steel plate were much larger than those of the three AE sensors without a plate. Because AE waves are attenuated much less in a steel plate than in wood, it is more effective to attach the AE sensor to wood with a steel plate rather than directly to the wood. These findings suggest that it is feasible to use an AE sensor with a plate-type waveguide for the nondestructive detection of termite attacks in wood. 相似文献
2.
Summary The acoustic emissions (AEs) under partially compression were monitored with two softwood and one hardwood specimens in very eary stages of decay by a brown- and a white-rot fungus. Even slightly decayed specimens emitted AEs immediately after beginning of loading, typically when partial compression stress was applied to brown-rotted wood with the flat-headed attachment. With sound specimens of three wood species, only a few AEs were generated until the load reached at the proportional limit. These results suggest that AE monitoring will be one of the feasible means to detect the incipient stages of decay in a field test.The authors thank the Weyerhaeuser Research Grants Program for its aid in this investigation 相似文献
3.
Acoustic emission from softwoods in tension 总被引：3，自引：0，他引：3
M. P. Ansell 《Wood Science and Technology》1982,16(1):35-57
Summary Acoustic emission (AE) monitoring is a non-destructive testing technique widely used to detect flaw development and crack propagation in metals, ceramics, polymers and composite materials.This paper relates the AE-strain characteristics from three softwoods tested in tension to mechanisms of deformation observed by scanning electron microscopy. All wood specimens are identical in size and radial-longitudinal in orientation, enabling the path of failure through planes of earlywood and latewood to be examined.It is found that the proportion of earlywood to latewood in each species has a marked effect on the shape of the AE-strain curves. Parana pine, containing very few latewood tracheids, exhibits a close to linear relationship between log cumulative emissions and strain until close to failure when the count rate increases rapidly. Douglas-fir, which has well-defined earlywood-latewood boundaries generates many AEs at low strain and there is greater variation in the shape of the AE characteristic between samples.Parana pine and Douglas-fir are tested at 20 °C (12.5 % EMC). Scots pine is also stressed at 20°C (12.5%EMC), 20°C (0.7%EMC) and 80°C (0.7%EMC), to assess the effect of moisture content on AE.Values of Young's modulus, stress at failure and work of fracture for the three softwoods are compared with the AE-strain data. Although the work of fracture is related to the total AEs to failure, no direct proportionality exists between the two parameters.Finally, the AE-strain data for plywood and glass-reinforced plastic (GRP), both man-made composite materials, are compared with those of wood, the natural composite material.S.R.C. support for this work under grant No. GR/A/13257 is gratefully acknowledged. The support of Professor Bryan Harris of the School of Materials Science, University of Bath and Dr. J. M. Dinwoodie of the Building Research Establishment, Princes Risborough is greatly appreciated. Mr. B. Dobraszczyk performed the impact tests. 相似文献
4.
Acoustic emission (AE) monitoring was used to trace directly the fracture intensity in cylinders of lime wood subjected to
variations in temperature and relative humidity (RH) in their environment. High-frequency components produced by mechanical
fracturing were extracted from the raw AE signals using the wavelet transforms. The accumulated energy of these components
depended on the magnitude and rate of the RH variations. The AE activity correlated well with predictions of the numerical
modeling carried out as the first part of the present investigations. In particular, the AE activity became negligible below
the allowable magnitude for the rapid RH variation predicted by the simulation, or when the time interval allowed for the
RH variation was long enough. Furthermore, AE proved capable of tracing the progressive evolution of damage at the microlevel,
which preceded failure of wood discernible from the macroscopic perspective. 相似文献
5.
The mechanism for radial compression of coniferous wood was examined from the viewpoint of the porous structure of wood. The compressive test was carried out in a wet-type scanning electron microscopy (WET-SEM) chamber to observe continuously the deformation process of wood. The initial stress-strain relation of the cellular solids or single cell was measured with image analyses of SEM photographs. The first fracture occurred in one tangential row of earlywood tracheids just after the load-displacement curve exceeded the proportional limit. The fracture occurred because of abrupt breaks of the radial cell walls. The first fractured cells had a tendency to have the smallest percentage of cell wall within an annual ring, and the cells suffered shearing deformation in a radial direction until the occurrence of the first fracture. On the basis of the results of image analyses, it was concluded that this shearing deformation of cells was almost linearly related to the compressive load.Part of this work was presented at the 47th annual meeting of the Japan Wood Research Society at Kochi, April 1997 and at the 1997 meeting of the Research Society of Rheology in the Japan Wood Research Society at Tsukuba, December 1997 相似文献
6.
7.
Hiroshi Yoshihara 《Journal of Wood Science》2001,47(1):8-12
The influence of the span/depth ratio when measuring the mode II fracture toughness of wood by endnotched flexure (ENF) tests was examined. Western hemlock (Tsuga heterophylla Sarg.) was used for the specimens. The ENF tests were conducted by varying the span/depth ratios; and the fracture toughness at the beginning of crack propagation GIIc was calculated by two equations that require the load-deflection compliance or Young's modulus. Additionally, the influence of the span/ depth ratio on the load-deflection compliance was analyzed by Timoshenko's bending theory in which additional deflection caused by the shearing force is taken into account. The following results were obtained: (1) When the span/depth ratio was small, the fracture toughness calculated with the data of load-deflection compliance was large. In contrast, the fracture toughness calculated with the equation containing Young's modulus tended to be constant. (2) In the small span/depth ratio range, the load-deflection compliance was estimated to be larger than that predicted by Timoshenko's bending theory. (3) To obtain the proper fracture toughness of wood with a single load-deflection relation, the span/depth ratio should be larger than that determined in several standards for the simple bending test method of wood, 12:16. 相似文献
8.
Summary Acoustic emission (AE) signals were collected during fracture tests in order to analyze them for characteristics that could be used as parameters in a reactive control system for the wood drying process. Ponderosa pine and California black oak single edge notch tensile specimens were tested in the TR, TL, and mixed mode configurations, at 12 and 18 percent moisture content and at temperatures of 20, 40 and 60 °C. AE was observed in both opening mode and mixed mode tests, but cumulative events to maximum load in mixed mode were 7.4 times greater than in opening mode for oak and 3.4 times greater in pine. It was concluded that mixed mode AE signals were most promising for pattern recognition analysis, which will be the subject of Part II of this study.This research was supported in part by USDA Grant No. 90-37291-5762 相似文献
9.
The relationships among rate of ultrasound acoustic emission (AE), xylem water potential and transpiration rate were investigated in 5-year-old potted saplings of Picea abies Karst. after cycles of water stress. Water-stressed plants displayed minimum xylem water potentials of -3.9 MPa, near-zero transpiration rates and up to 45 AE counts per minute. After rewatering, water-stressed plants no longer produced AEs. Well-watered control plants produced only a small number of ultrasonic AEs. After three cycles of water stress (lasting 24 days in total), it was estimated that about two-thirds of the functional tracheids were embolized. The concomitant reduction in hydraulic conductance was about 70%. 相似文献
10.
Bruna Ugulino 《Wood material science & engineering》2018,13(2):64-72
Sanding is the most common machining process used to prepare wood surfaces prior to coating. Hence, to improve surface quality and coating performance during this process, an optimal set of machining parameters should be established according to wood species and its final use. The effects of grit size and feed speed on surface properties and coating performance of red oak wood were studied. Surface quality was assessed by surface roughness, scanning electron micrographs, and wetting analyses. Coating performance was evaluated using pull-off adhesion tests on coated surfaces before and after an accelerated weathering. The results showed that smoother surfaces are obtained as the grit size number of the abrasive increased. On the other hand, minor differences were observed on cell damages and surface roughness as feed speed changed. Also, there was little difference among treatments concerning wetting behavior and surface energy. Pull-off strength was more affected by changes in grit size than feed speed. A P100-grit size program with a feed speed of 7 m/min resulted in a suitable roughness which provided good adhesion and high pull-off strength after aging test. 相似文献
11.
The effect of aging on the ultrastructure of wood 总被引：1，自引：0，他引：1
Summary Wood samples varying in age from 900 to 4400 years were investigated with the electron microscopes (TEM, SEM) and polarized light microscopy as well as by analysis of the mechanism of fracture. The weakest parts of the structure, and therefore the most susceptible to failure, are the middle lamella/S1 region and the interfibrillar matrix. Parts of the wall exhibit fissures, cracks and loss of adhesion, not found in recent wood. Studies of the fractured surfaces confirm a change in the micromorphology of the old wood samples. In spite of the breakdown of certain elements at ultrastructural level the samples had retained almost their normal macroscopic appearance and properties. As long as the main reinforcing structural elements, the microfibrils, remain intact, the major properties of wood do not apparently undergo drastic changes. 相似文献
12.
13.
南方型黑杨无性系木材材性的研究 总被引：3，自引：1，他引：2
在48个7—8年生南方型黑杨无性系对比试验林中,选择生长量达中等以上水平的19个新、老无性系,开展木材基本密度、纤维素含量、纤维形态的分析研究。纤维素含量和纤维长度在19个无性系中无显著差异,基本密度只在中汉17等几个无性系间有显著差异。基本密度和纤维长度在不同年龄间都存在显著差异。1～3年生的纤维长度在0．9mm以下,属短纤维;4—7年生的纤维长度在0．91mm以上,达到中级纤维长度标准。因此,杨树纸浆材超短轮伐期可以确定为3a或3a以上。 相似文献
14.
不同含水率云南松声发射信号特征 总被引：1，自引：0，他引：1
【目的】研究不同含水率条件下云南松试件声发射信号的传播规律,探讨含水率对声发射信号波形的响应,为云南松声发射源定位提供依据,为木材内部缺陷无损检测提供基础数据。【方法】以云南松为试验材料,采用NI高速数据采集设备和LabVIEW软件构建云南松试件声发射信号采集平台,利用铅芯折断模拟声发射源,对绝干、气干、生材和饱水4种含水率状态下的试件表面进行声发射信号采集,通过时差法计算信号在4种含水率状态下的平均传播速率,并运用小波分析对声发射信号波形进行分解和重构,根据软阈值量化方法消除各通道系数和经阈值量化后的各高频层系数,去除非主能量信号以便从噪声中析取微弱的声发射信号。【结果】试验中传感器均以接收表面波信号为主;随着含水率增加,云南松试件表面声发射信号波形和平均声速均大幅度衰减,绝干状态下声发射信号时域波形幅值达到±5.2 V,平均声速可达4 208.77 m·s^-1 ,而饱水状态下信号时域波形幅值仅为±0.6 V,平均声速降至1 414.07 m·s^-1 ,气干和生材状态下信号时域波形幅值和平均声速分别为±4、±2 V和 3 331.79 、 2 328.73 m·s^-1 ,且各含水率状态之间平均声速差在876.98~1 003.06 m·s^-1 范围内;小波变换能有效将“淹没”在噪声中的声发射信号析取出来,4种含水率状态下试件声发射信号频域波形范围在40 ~150 kHz之间,且气干状态下波形峰值出现在110 kHz左右,其余3种均在50 kHz左右达到峰值。【结论】含水率增加可显著改变云南松声发射信号和传播特征,其信号波形和平均声速均与含水率降低呈正比;小波变换在信号降噪处理方面具有明显优势,不仅可去除信号中的大量噪音,而且不会破坏有用信号,保证信号完整性,能更大程度降低对不同含水率云南松试件声发射信号的分析误差,为云南松表面声发射源定位研究及内部无损检测给予试验数据支持;作为一种木材声发射信号采集与分析平台,研究结果可为不同含水率云南松受压变形破坏全过程的声发射特征分析提供必要的基础理论依据。 相似文献
15.
16.
为了研究苏鲁两省杨树木材变色、变色真菌和造成的损失,于2005—2010年分别对9个县市杨木加工厂进行了调查和定点观察。结果表明,在杨树砍伐后,在露天存放22～80天杨原木和单板存在不同程度边材变色,其变色程度与在露天存放时间有密切关系。春夏之交砍伐的杨木比冬季砍伐的杨木更易变色;3～5年生杨木比8—9年生杨木更易变色;剥皮杨木比带皮杨木更易变色;单板变色比原木更明显,致使单板的经济价值可降低25％～30％。鉴定出引起杨木变色的真菌有23属32种,其中危害最严重的变色菌主要有可可球二孢、交链孢、球孢枝孢。其中不高双孢菌、红紫球二孢、青琐龙孢球二孢在杨木上属于首次报道。 相似文献
17.
Noriko Tamura 《Journal of Forest Research》2001,6(3):187-190
Walnuts,Juglans ailantifolia Carriere, are large and the shell is difficult to open. Thus, seed predators in Japan are restricted mainly to the Japanese
squirrel (Sciurus lis Temminck) and the wood mouse (Apodemus speciosus Temminck), which can shave away the hard shells with their sharp incisors. Previous work indicated that the squirrels are
not only predators, but also disperse walnuts. In this study, 95 walnuts in Period1 (September 1996–February 1997) and 80
walnuts in Period 2 (September 1999–February 2000) each attached to a miniature radio transmitter, were placed in a feeding
box, and 93 and 53 of them were transported by free-living wood mice in the respective periods. Most of the walnuts provided
from September to November were scatter-hoarded in the litter layer, while from December to February, the mice fed immediately
and seldom scatter-hoarded on the ground surface. In all, 66 walnuts were hoarded and 80 were eaten soon after discovery,
although walnuts were eaten more frequently in Period 1 than in Period 2, which may be related to annual differences in seed
crop size in the study site. The mean transport distance of hoarded seeds was 6.2 ± 5.0 m (mean ± SD,n=66). The fate of hoarded walnuts was followed from September 1996 to May 1997; 21 (75%) of the scatter-hoarded walnuts were
recovered, but 7 (25%) were left uneaten. Consequently, the Japanese wood mouse also plays a role in seed-dispersion of the
walnut, but the transport distance for mice was shorter than that for squirrels. 相似文献
18.
Hermann Pleschberger Alfred Teischinger Ulrich Müller Christian Hansmann 《Wood material science & engineering》2014,9(2):92-101
Effects of different thermal treatments (maximum treatment temperatures of 200, 210 and 220°C for 2.5 hours) on solid spruce (Picea abies L. Karst.) and ash (Fraxinus excelsior L.) were investigated in this study. The fracture behaviour in radial/longitudinal as well as in tangential/longitudinal and the change of the wood colour (CIEL*a*b* colour space) on all principal anatomical surfaces (cross sectional, radial and tangential) were analysed. The specific fracture energy and the maximum breaking load decreased almost significantly after all thermally treated samples in comparison to the untreated (standard dried) sample. The wood colour changed also significantly, in particular the lightness decreased with increasing intensity of thermal treatment on all investigated surfaces. A comparison of the percentage loss of the different fracture and colour values has shown a strong correlation between the maximum breaking load and the lightness after several thermal treatments, in both investigated crack propagation systems, on all measured surfaces and for both analysed species. 相似文献
19.
在蓝桉、直干桉子测林中各抽3个家系，从不同的区组按径阶等距抽样测定木材的密度，研究家系内木材密度的变异；在种子园中抽取蓝桉30株、直干桉36株作试材研究木材密度株内变异。结果表明蓝桉家系内不同径阶的木材密度差异不显著，直干桉极显著；蓝桉的木材密度在区组和家系间的差异都显著，而直干桉都不显著。株内不同方向的木材密度差异两树种均不显著，而不同高度和不同年龄的木材密度差异都极显著；在亲缘关系混杂的群体中两树种的树高和胸径与木材密度均呈负相关，而在3个蓝桉家系内，胸径与密度呈正相关，直干桉3个家系中两个呈正相关，1个呈负相关，但都不显著。为将这两个树种纸浆材的主伐年龄定为6年提供了充分的科学依据,且在2年生时对蓝桉、直干桉作早期选择可取得满意的效果，对直干桉尤为明显。 相似文献
20.
Alberto Santini Alessia Pepori Luisa Ghelardini Paolo Capretti 《Forest Ecology and Management》2008,256(3):502-506
The persistence of Sphaeropsis sapinea, Leptographium serpens and Heterobasidion annosum s.s. in artificially inoculated pine branch pieces (S. sapinea and L. serpens) and wood blocks (L. serpens and H. annosum s.s.) was investigated in order to discuss the alternative of leaving coarse woody debris in stands of Italian stone pine (Pinus pinea). Also, natural colonization by S. sapinea of pine cones of different ages was assessed. Methods used for inoculating branch pieces and wood blocks were highly effective for all fungi. Type of a forest stand in which branch pieces and wood blocks have been incubated did not affect the persistence of the pathogens in the inoculated samples. For branch pieces, the success of re-isolation of L. serpens dropped as the sample incubation time increased, while S. sapinea was always successfully (100%) re-isolated (even 12 months after the inoculation). L. serpens and H. annosum s.s. were re-isolated from most of the buried wood blocks (from more than 95% samples) up to 3 months following the inoculation. Of the observed P. pinea cones (in most cases, more than 2 years old), 74% were naturally infected byS. sapinea. All three investigated pathogens were able to survive in dead plant tissues for long periods of time (at least for several (3–12) months). The persistence of these pine-pathogenic species in dead plant material questions the feasibility of leaving coarse woody debris in managed Italian stone pine forests meant for landscape conservation and leisure activities. 相似文献