Effect of compressive load on the dimensional changes of the Japanese larch dried in a radio-frequency/vacuum drier

This study investigated the effect of a compressive load of 0.092 MPa on the dimensional changes of Japanese larch in a humidity chamber after continuous radio-frequency/vacuum drying. The dimensional changes in the loading directions were significantly increased while those perpendicular to the loading directions were decreased. The shrinkages showed higher values in continuous drying than in intermittent drying. For the specimens loaded on their tangential sections, the radial shrinkages were even higher than the tangential shrinkages; thus, the tangential/radial shrinkage ratio was decreased by 0.27. The transverse hygroscopicity was reduced for the specimens loaded on their cross sections, but increased for the specimens loaded on their tangential sections.     

Strength properties of glued laminated timber made from edge-glued laminae II: bending,tensile, and compressive strength of glued laminated timber

The purpose of this study was to investigate the strength properties of glued laminated timber composed of edge-glued laminae and to investigate the influence of edge gluing on the strength properties. Glued laminated timber composed of multiple-grade laminae (symmetrical composition, strength grade E95-F270, 10 laminations) was produced from karamatsu (Larix kaempferi) edge-glued laminae according to the Japanese Agricultural Standard. The bending, tensile, and compressive strengths of the glued laminated timber were measured. The average bending, tensile, and compressive strengths were 33.4, 24.5, and 35.9 MPa, respectively, and these values are almost equal to those of glued laminated timber composed of karamatsu single-piece laminae. It was determined that finger-joints and knots in the edge-glued laminae played a significant role in the failure of specimens. However, the use of glued edge-joints did not appear to affect the failure of specimens.     

Comparison of moisture distribution along radial direction in a log cross section of heartwood and mixed sapwood and heartwood during radio-frequency/vacuum drying

The purpose of this study was to compare the distribution of moisture contents (MCs) along the radial direction during radio-frequency/vacuum (RF/V) drying of log cross sections of heartwood (HLC) where sapwood was removed from a green log cross section and log cross section of mixed sapwood and heartwood (MLC) prepared with debarked logs of Japanese larch (Larix leptolepis) and locust (Robinia pseudoacacia). For Japanese larch, an even distribution of MC was observed over the entire cross section in HLC not only at the initial stage of drying but also up to the completion of drying. Furthermore, the moisture gradient between the outermost slice and the adjacent inner slice was more gradual compared with that in MLC. For locust, the moisture gradient between the outermost slice and the adjacent inner slice became severe as drying progressed. It decreased after reaching the maximum during the middle stage of drying but continued until the late stage of drying. Furthermore, despite the fact that the average initial MC of mixed slice within MLC was higher compared with that in heartwood slice, this trend reversed immediately after drying started. It was suggested that the possibility of formation of border checking would be high during drying the MLC, since it would be so complicate that the sapwood and heartwood reach fiber saturation point together because of differences in their green MCs and permeability between them.     

原木截面形状的二次B样条曲线拟合

描述了一种模拟原木截面形状的新方法。用自行研制的MQK3102原木形状识别机测得原木截面上的有限离散样点,利用二次B样条参数曲线拟合方法对这些点进行拟合。该方法能较好地模拟出原木截面的真实形状,样点数量要求不多,计算速度快,前一段曲线的计算结果不影响后面的计算,避免了由累计误差引起的图形失真。将其运用到原木长度方向上的多个采样截面,可近似模拟出原木的整体外形,从而为原木的优化下锯提供参考模型。图4参9。     

Effect of end-taping and removal of sapwood on radial distribution of moisture content and tangential strains during radio-frequency/vacuum drying of <Emphasis Type="Italic">Cedrela sinsensis</Emphasis> log cross sections

This study was carried out to investigate the effects of end-taping of sapwood (ETS) and removal of sapwood (ROS) treatments of log cross sections on the radial distributions of moisture content (MC) and tangential strain, according to the circumferential slicing method (CSM), during radio-frequency/vacuum (RF/V) drying of log cross sections. The MC of control and ETS samples showed an even distribution around the center but decreased closer to the periphery side. In ROS samples, the MC decreased closer to the periphery side when above the hygroscopic range but showed an even distribution at the late stage of drying. Tangential strain in ETS samples showed slight compressive stress or tensile stress through the entire area of the cross section during the initial stage of drying, although the periphery side was in tensile stress from an area starting at a relative radius of 0.7. ROS samples showed tensile stress in the heartwood around the center and the heartwood of the periphery side and showed no stress or slight compressive stress in the middle area at the initial stage of drying, after which it showed an even distribution of tensile stress throughout the entire end surface. About 90% of the total checks contained in ETS and ROS samples were observed on the periphery side starting from a relative radius of 0.7.     

The effect of taper on the MOE of log stringers

Load sharing between the stringers in gravel-decked log bridges is an important design factor when small- diameter stringers are used with thin gravel decks. In order to estimate the load sharing between the stringers, it is necessary to consider the deflection of the stringers; therefore, accurate estimates of the apparent modulus of elasticity (MOE) for full-size log stringers are required. In this paper, load and displacement data from the full- size bending tests are used to demonstrate that taper near midspan has the greatest effect on the MOE used in common log bridge design methods, where the logs are assumed to have constant cross sections. This paper proposes a method to estimate a MOE that can be used in a constant cross-section model given the geometry of the particular log of interest, and the MOE from full-size bending tests calculated when considering actual log geometry.     

A determination method of compressive design value of dimensional lumber

The objective of this study was to develop a determination method of compressive design value of dimensional lumber for its safety design and rational application as a green building material. A total of 1049 full-size 2?×?4 samples of Chinese larch (Larix gmelinii) dimensional lumber, including visual grades Ic, IIc, IIIc, and IVc, were tested by static compressive tests. Compression strength parallel to grain (UCS) of different grades were summarized. By the least square method, the fitted parameters and results for UCS were obtained under different probability distribution models (normal, lognormal and 2-P-Weibull) and test data points (100, 75, 50, 25, and 15%). Based on reliability analysis method, relationships between the reliability index and partial factor were investigated under different probability distribution models, fitting data points, load combinations and load ratios. Finally, this study suggested that the lognormal distribution, 25% data points, load combination of dead load plus residential live load, and load ratio of 1.0 be selected for the determination of compressive design value of Chinese larch dimensional lumber. For Chinese larch dimensional lumber, the compressive design values of grade Ic, IIc, IIIc and IVc were 22.9, 18.3, 14.6 and 13.8 MPa, respectively.     

Numerical and experimental study of moisture-induced stress and strain field developments in timber logs

When solid wood dries from a green condition to a moisture content used for further processing, moisture-induced fracture and stresses can occur. The drying stresses arise because of internal deformation constraints that are strongly affected by the cross-sectional moisture gradient differential shrinkage and the inhomogeneity of the material. To obtain a better understanding of how stresses develop during climatic variations, the field histories of stresses (and strains) in cross sections in their entirety need to be studied. The present paper reports on experiments and numerical simulations concerned with analysing the development of strains and stresses during the drying of 15-mm-thick discs of Norway spruce timber log. The samples were dried at 23 °C and relative humidity of 64 % from a green condition to equilibrium moisture content. The moisture gradient in the longitudinal direction was minimised by use of thin discs simplifying the moisture history of the samples studied. The strain field history was measured throughout the drying process by use of a digital image correlation system. Numerical simulations of the samples agreed rather well with the experimental strain results obtained. The stress results also indicated where in the cross section and when fractures could be expected to occur during drying. More optimal drying schemes showed markedly reduced stress generation.     

Derivation and application of an equation for calculating shear modulus of three-ply laminated material beam from shear moduli of individual laminae

In a detailed study of the relation between the deflection caused by shear force and the constitution of a laminated material beam, we derived an equation for calculating the shear modulus of a laminated material beam from the shear moduli of individual laminae. The validity of the derived equation was investigated using crosslaminated wood beams made with five species. The calculated shear moduli parallel to the grain of face laminae ranged from 48.3 MPa to 351 MPa, while those perpendicular to the grain of face laminae ranged from 58.0 MPa to 350 MPa. The calculated shear moduli increased markedly with increasing shear modulus in a cross section of perpendicular-direction lamina of a cross-laminated wood beam. The calculated apparent modulus of elasticity (MOE) of cross-laminated wood beams agreed fairly well with the measured apparent MOE values. This fact indicated that the apparent MOE of cross-laminated wood beam was able to be calculated from the true MOE values and shear moduli of individual laminae. The percentage of deflection caused by shear force obtained from the calculated apparent MOE (Y _sc) was close to that obtained from the measured apparent MOE (Y _s) and there was a high correlation between both values. From the above results, it was concluded that the derived equation had high validity in calculation of shear modulus of a cross-laminated wood beam.     

旋切原木六点定心理论的研究

在单板旋切中 ,选择最佳的定心点是旋切优化的最关键技术。本文在原木三、四点定心理论的基础上 ,提出了旋切原木六点定心理论。该理论是在原木的任意截面上取 6个点 ,由这 6个点回归出原木内包络圆柱的最佳圆心轴线 ,为高精度原木定心机的数控化提供先进的基础理论 ,提高原木的定心精度和单板的出材率及成品单板的合格率。使原木的定心理论提高到一个新的水平。     

Estimating the equilibrium position by measuring growth stress in weeping branches ofPrunus spachiana Kitamura f.spachiana cv.Plenarosea

The equilibrium position of a current-year branch of the weeping Japanese cherry,Prunus spachiana Kitamura f.spachiana cv.Plenarosea, was estimated by measuring the released strains of growth stresses. In current-year branches that were supported with wires to prevent weeping as soon as the branches first budded, tensile growth stresses on the upper side were smaller than those of the control branches. Gelatinous fibers were rarely found on the upper part of the cross section of the supported branches, whereas the control branches had many gelatinous fibers on the upper part. The upright orientation of the supported branches was closer to the equilibrium position than the weeping orientation of the control branches. The equilibrium position of the branches was thought to be in the initial bud direction, above the horizontal plane; and the weeping style of branch was not the preferred angular orientation forP. spachiana.     

Influence of stress level on compression deformation of wood in 170°C transient steam conditions

Abstract

Compression creep experiments of hybrid poplar (Populus deltoides×Populus trichocarpa) were performed in a pressurized vessel equipped with a heated hydraulic press. The viscoelastic response at various stress levels (2–7 MPa), a temperature of 170°C and transient steam conditions was studied. Moisture content and oven-dry density of compressed specimens were determined. While some recovery of compression strain occurred, compression resulted in permanent deformation and increased wood density. The influence of stress level on the amount of set recovery of compressive deformation was evaluated after 24 h water soaking. Applied stress level had a significant effect on the compression deformation. The initial strain, as well as creep strain, varied depending on the applied stress level. The highest oven-dry density was obtained at a stress level of 6.9 MPa. Lower stress levels resulted in lower moisture content after the compression process, while the equilibrium moisture content of compressed specimens was not significantly affected by stress level. Set recovery increased from 20% to 65% with increased stress level from 1.7 MPa to 4.1 MPa, then decreased to 53% for specimens compressed at 6.9 MPa. Moisture content after the compression process significantly affected the set recovery.     

Plastic deformation in small clear pieces of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis>) during densification with the CaLignum process

Specimens made of clear wood from Scots pine (Pinus sylvestris L.) were compressed semi-isostatically at 25°C in a Quintus press. Pressure ranged from 0 to 140MPa and the maximum decrease in the crosscut area was about 60%. Quarter-sawn and plain-sawn specimens were densified with the inside face (pith side) up or down. A laser-made dot grid on the crosscut area of the uncompressed specimen was used to calculate plastic strains by image analysis of the displacement of dots after compression. Multivariate models were developed to determine the causes of deformation. The lower face was restrained by the press table and remained flat whereas sides attached to the rubber diaphragm became more irregularly shaped when compressed. Most of the total compression occurred below 50MPa and was determined exclusively by pressure. Above 50MPa, wood density was more important and compression was lower in the interior of specimens and in heartwood. Plastic compressive strain occurred predominately in the radial direction and toward the rigid press table. Strains were dependent on the sawing pattern and orientation. The growth rings of quarter-sawn specimens oriented with the outer face (bark side) down tended to buckle.     

Strength properties of glued laminated timber made from edge-glued laminae I: strength properties of edge-glued karamatsu (Larix kaempferi) laminae

The object of this study was to investigate the strength properties of edge-glued laminae and to propose a suitable grading method based on the lamina modulus of elasticity (MOE). Edge-glued laminae composed of lumber with similar MOEs (uniform laminae) and edge-glued laminae produced by randomly gluing lumber independent of MOE (random laminae) were made from karamatsu (Larix kaempferi) lumber having the same thickness and length, but various widths. For both the uniform and random laminae, there was a strong correlation between MOE values measured using the longitudinal vibration technique, the static bending test, and a grading machine. The average values of bending, tensile, and compressive strengths of the uniform laminae were similar to those of the random laminae. On the other hand, the average strength of laminae without end joints was significantly higher than that of finger-jointed laminae for both uniform and random laminae. Finger-joints and knots played a significant role in the failure of specimens, but the edge-gluing and the difference in MOE within an edge-glued lamina did not appear to affect the strength properties. The bending, tensile, and compressive strengths of edge-glued laminae were strongly correlated to the lamina MOE.     

世界原木定心技术现状及发展趋势

原木定心技术在木材加工生产中广泛应用。精确定心,对提高木材利用率及经济效益是十分重要的。在分析现有定心技术的基础上,综合世界森林资源短缺及科学技术进步情况,提出原木定心技术向采用计算机扫描控制、提高精度、效益和效率方面发展是必然趋势。     

粉煤灰陶粒混凝土配合比的正交实验研究

针对大庆热电厂粉煤灰新型建材公司的粉煤灰陶粒,吉林省的鼎鹿牌水泥、大方牌减水剂,将水泥用量、净水用量、体积砂率和减水剂用量作为4个因素,每个因素取3个值,通过正交实验,测定试件的塌落度、7 d抗压强度、28 d抗压强度。实验结果分析,确定用以上材料可以配制强度为LC35级的轻骨料混凝土,其较佳配合比为C∶S∶G∶W∶减水剂=1∶1.60∶1.05∶0.34∶0.0065。此配合比下的新拌混凝土的塌落度为56 mm,7 d抗压强度均值33.2 MPa,28 d抗压强度均值40.1 MPa,标准差3.1 MPa。28 d抗压强度标准值为37 MPa。     

Predicting spiral grain by computed tomography of Norway spruce

Spiral grain is a feature of wood that affects the shape of the sawn timber. Boards sawn from logs with a large spiral grain have a tendency to twist when the moisture content changes. The aim of this study was to investigate the possibility of predicting spiral grain based on variables that should be measurable with an X-ray LogScanner. The study was based on 49 Norway spruce (Picea abies) logs from three stands in Sweden. The logs were scanned with a computed tomography (CT) scanner every 10mm along the log. Concentric surfaces at various distances from the pith were then reconstructed from the stack of CT images. The spiral grain angle was measured in these concentric surface images, and a statistical model for predicting spiral grain was calibrated using partial least squares (PLS) regression. The PLS model predicts the spiral grain of a log at a distance 50mm from the pith based on different variables that should be measurable with an industrial X-ray LogScanner. The result was a PLS model withR ²=0.52 for the training set andR ²=0.37 for the test set. We concluded that it should be possible to predict the spiral grain of a log based on variables measured by an industrial X-ray LogScanner. The most important variables for predicting spiral grain were measures of sapwood content, variation in the ratio between the heartwood and log areas, and the standard deviation for the mean log density in 10mm thick cross slices along the log. The accuracy when sorting the logs into two groups with spiral grain of 2.0° and of <2.0°, respectively, was 84% of the correctly sorted logs.     

Elastic strain at semi-isostatic compression of Scots pine (Pinus sylvestris)

Quarter-sawn and plain-sawn specimens of Scots pine were semi-isostatically compressed at 5, 15, 50, and 140 MPa in a Quintus press. Elastic strain was measured using a telescope device that was pushed together when wood was compressed and remained in this position at release of pressure. Delayed elastic and plastic strains were assessed through repeated callipering during 5 years after densification. At 140 MPa, wood reached an almost compact structure (ρ ≈ 1450 kg/m³) but as a result of elastic springback the density decreased to just below 1000 kg/m³. At 140 MPa, the elastic and delayed elastic strains were 14.6% and 1.8%, respectively, in quarter-sawn specimens, and were 13.1% and 0.8%, respectively, in plain-sawn specimens. The higher elastic strains in quarter-sawn specimens can be attributed to elastic springback in the tangentially deformed latewood bands.     

基于AMESim的树木移栽机负载敏感系统仿真研究

为了提高树木移栽机在不同工况下,达到最佳的工作效率,本文提出了针对树木移栽机工作原理中铲刀阻力所带来的问题,应用负载敏感系统作为整台机械的液压系统。在AMESim软件的仿真平台上,建立了负载敏感系统仿真模型图,设置了元件中的相应参数,为验证模型的正确性以及进行后续的动态特性分析做准备。选定的负载压力范围在0~30 MPa,仿真时间设置为1 s,采样时间为0.001 s,在节流阀全开的情况下,样本曲线压力增大时,流量有细微的下降;接着,验证阀负载压力分别为0、5、10 MPa、15、20时,泵的出口压力与节流阀出口压力之差始终保持在一个稳定的数值上,这就说明,依靠负载敏感系统就可以顺利解决了压力与外界负载变化无关这项课题。     

湿地松与马尾松人工林木材物理力学性质的比较研究

通过对湿地松和马尾松人工林木材物理力学性质的测定和比较分析,结果表明:湿地松人工林木材密度、干缩系数和除冲击韧性以外的力学强度均稍大于马尾松人工林木材,而冲击韧性则恰恰相反.经差异显著性t检验表明:湿地松和马尾松木材物理力学性质指标中顺纹抗压强度、抗弯强度、弦面顺纹抗剪强度和冲击韧性差异极显著,气干密度、基本密度、径面顺纹抗剪强度和端面硬度差异显著,除此之外的其余指标差异不显著.