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Matthew D. Aro Xiping Wang Dwight E. McDonald Marshall Begel 《Wood material science & engineering》2017,12(4):228-235
Laminated strand lumber (LSL) and laminated veneer lumber (LVL) were thermally modified as a post-treatment at 140°C, 150°C, 160°C, 170°C, and 180°C. The tension modulus of elasticity (MOE) of LSL was not significantly impacted by the treatments, with the 180°C treatment group exhibiting the highest tension MOE (11.8?GPa). The LVL also experienced minimal impacts, with the 150°C treatment group having the highest tension MOE (19.4?GPa) and the 160°C treatment group exhibiting the lowest (17.1?GPa). The maximum tensile strength (MTS) of the LSL and LVL significantly decreased with increasing temperatures, with the control and 180°C treatment groups experiencing the highest and lowest MTS, respectively. The lowest MTS for LSL was 10.8?MPa (180°C treatment), which was 70% lower than the controls. The lowest MTS of the LVL was 24.4?MPa (also at the 180°C treatment), which was a 49% decrease compared to the controls. These results suggest that thermal-modification post-treatments minimally impact tension MOE, but can significantly reduce MTS at higher treatment temperatures. Combined with previous work improving the moisture properties and equilibrium moisture content of thermally modified LSL and LVL, it may be possible to optimize the treatment technique(s) to yield products with desirable properties. 相似文献
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薄型单板层积材结构改进的研究 总被引:1,自引:0,他引:1
薄型单板层积材(LVL)可替代锯材,应用于木质门窗构件等轻载结构领域.由于单板全部顺纹组坯,导致产品存在横向翘曲变形的技术问题.为此,尝试采用"部分单板横纹组坯"和"纤维板与单板复合"两种方法进行改进,制造了15 mm厚LVL,包含1~2层单板横纹组坯或1~2层3 mm纤维板.测试结果表明:单板横纹组坯.显著降低了LVL的抗弯性能,但LVL的弹性模量仍能达到单板层积材国家标准中70E级别的要求,而静曲强度甚至超过180E级别优等品的限值;与此同时,改进结构的LVL吸水翘曲变形显著降低.横纹单板越靠近LvL表层,板子抗弯性能降低越显著,而翘曲变形改善越明显.采用纤维板与单板复合制造LVL,纤维板的内结合强度衰减明显,易受破坏. 相似文献
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桉木单板层积材生产工艺的优化 总被引:1,自引:0,他引:1
采用响应面法(RSM)和中心组合旋转设计(CCRD),研究了桉树单板层积材(LVL)的生产工艺条件,并对优化工艺所得的预测值进行了实验验证。方差分析结果表明:面粉添加量对桉木LVL的静曲强度(MOR)和弹性模量(MOE)有着显著影响,而热压温度和热压时间的影响不显著。通过回归分析,建立了相应的回归模型。回归模型的预测值与实验值的拟合良好,说明回归方程能用来预测和优化桉木LVL的力学强度性能。最佳工艺条件为:热压温度130℃,热压时间1.5 min/mm,面粉添加量5%(质量分数)。在此工艺条件下压制的桉木LVL垂直加载条件下的静曲强度(MOR⊥)和弹性模量(MOE⊥)分别为89 MPa和16 722 MPa,平行加载条件下的静曲强度(MOR∥)和弹性模量(MOE∥)分别为88 MPa和15 067 MPa,MOR和MOE分别达到了结构用单板层积材国家标准的优等品和140E级别。 相似文献
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Incorporating size effects in the Tsai-Wu strength theory for Douglas-fir laminated veneer 总被引:1,自引:1,他引:0
Summary This paper elucidates the need to consider the effect of volume on brittle material strengths when these strengths are used in a strength theory. Specifically, Weibull weakest-link theory has been implemented with the Tsai-Wu strength theory to predict the ultimate load carrying capacity of a center point off-axis bending member made from Douglas-fir laminated veneer. Weibull theory has been used in two distinct ways to account for size effects needed to evaluate brittle material strengths (ie. tension perpendicular and parallel to grain, and shear) for the strength criterion. The analytical methods assume linear elastic, plane stress states and have been described and evaluated using probability theory as a framework. Analytical results are in reasonable agreement with experimental findings substantiating the techniques proposed herein. 相似文献
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Until now we developed an estimation method for strength distributions of laminated veneer lumber (LVL) element by nonlinear least-squares method (NLM). Estimated strengths by this method were modulus of elasticity (MOE) and modulus of rupture (MOR) in the horizontal use direction and the vertical use direction, tensile strength and compression strength. But to use LVL for structural members, shear strength was also needed. Therefore, we tried to estimate the shear strength distribution of LVL element by NLM same as MOE and MOR in the horizontal use direction and the vertical use direction, the tensile strength of LVL and the compression strength of LVL in the previous reports. We conducted shear strength test for LVL and estimated element shear strength distribution by LVL strength data in the horizontal and vertical use direction. Next, we simulated LVL shear strength distribution using element shear strength distribution and compared with experimental ones in each use direction. They were overlapped in both use direction. Therefore, we could validate NLM for estimating element shear strength distribution. 相似文献
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杉木小径材制造单板层积材技术的研究开发 总被引:4,自引:0,他引:4
利用人工林杉木小径材制造单板层积材对于高效利用小径材资源和缓解结构用木材供需矛盾具有十分重要的意义。介绍了《杉木小径材制造单板层积材及应用研究》课题组利用杉木小径材制作单板层积材的研究过程、工艺开发、设备制造和产品应用方面所作的工作和研究成果。 相似文献
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Hirofumi Ido Hirofumi Nagao Hideo Kato Atsushi Miyatake Yasushi Hiramatsu 《Journal of Wood Science》2010,56(5):422-428
Tests of compression perpendicular to the grain were carried out on laminated veneer lumber (LVL) and timber. The species
tested were sugi, radiata pine, karamatsu, akamatsu, and dahurian larch; two sets of sugi specimens were tested, with the
sugi LVL products being manufactured in different plants. The strength properties of the materials for different loading directions
were compared for LVL and timber. At 5% compressive strain in the same materials, the average stress in the tangential direction
of timber was larger than that in the radial direction for all species except for radiata pine, and the average stress in
the edge-wise direction of LVL was larger than that in the flat-wise direction for all species except for radiata pine. When
the stress at 5% strain was compared in the same direction, the average stress of LVL in the edge-wise direction was larger
than that in timber in the tangential direction for all species, but there were no great differences between the average stress
of LVL in the fl at-wise direction and that of timber in the radial direction for all species except for radiation pine. There
was a close relationship between density and stress at 5% strain in LVL, especially in the edge-wise direction. For all results,
radiata pine did not follow the trend of the other species; The large annual ring width of radiata pine was considered to
have affected the results. 相似文献
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K. Frühmann E. K. Tschegg C. Dai S. E. Stanzl-Tschegg 《Wood Science and Technology》2002,36(4):319-334
Mode I and Mode III loading experiments were performed on side grooved CT specimens of two types of Laminated Veneer Lumber
(LVL). Steady state crack propagation was maintained in order to detect complete load displacement diagrams. Fracture behaviour
and influence of fiber orientation were studied and all important fracture mechanical values (stiffness/compliance, microstructural
damage, crack initiation energy, specific fracture energy etc) were determined. Much higher crack initiation energies and
specific fracture energies resulted in mode III loading than in mode I loading for both material types. Under external mode
III loading, crack initiation occurs in mode III and crack propagation however takes place under mode I owing to crack surface
interference. The influence of fiber orientation on fracture mechanical properties of LVL was discussed.
Received 15 September 1999 相似文献
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Tomoyuki Hayashi Atsushi Miyatake Feng Fu Hideo Kato Masahiko Karube Masaki Harada 《Journal of Wood Science》2005,51(5):486-491
To investigate the durability of structural laminated veneer lumber (LVL), outdoor exposure tests have been conducted since
1990 at a field-testing site at the Forestry and Forest Products Research Institute. This article is the second interim report
on the results after 9 years of exposure. Seven kinds of structural LVL with no preservative treatment were subjected to the
tests. Almost all the exposed specimens were decayed by a kind of brown rot fungi (Pseudomerulius aureus (Fr.) Julich). The degree of decay varied with wood species; grand fir and western hemlock LVL in particular showed weak
resistance against the decay. All the specimens were stored for more than 1 year in a testing room conditioned at 20°C and
65% relative humidity. We then measured the ultrasonic velocity of the specimens by the Pundit method, penetration depth by
the Pilodyn method, and bending strength by a conventional bending test. Correlation between nondestructive measurement factors
and the density was strong even on LVL with many adhesive layers. The nondestructive testing method was found to be applicable
to LVL as well as solid lumber. After the nondestructive measurements, each LVL was cut into three types of specimen (top:
T, middle: M, and bottom: B) for the bending tests. The bending strength varied with the type of specimens. Correlation between
modulus of elasticity and modulus of rupture was strong even in the decayed specimens. 相似文献
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This paper describes the development of a three-dimensional constitutive model for laminated veneer lumber (LVL) needed for new developments using this material. The LVL was manufactured in New Zealand from Radiata Pine. Experimental testing has been performed according to European timber testing standards. Block compression testing has resulted in modulus of elasticity values in the three material directions. Digital image correlation (DIC) technique has been used to determine the six Poisson’s ratios. Shear testing, whereby timber specimens were glued between two steel plates, has given stiffness values using DIC measurements. Experimental testing results have been compared with values found in literature. Results from this experimental testing programme have made it possible to create a three-dimensional elastic material model of LVL for the use in finite element analysis programmes. Although the material properties do not result in a symmetrical constitutive matrix, only minor adjustments are needed to gain the benefits of a symmetrical matrix. 相似文献
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Laminated veneer lumber joints made with metal plate connectors were protected with wood carbon phenolic spheres (CPS) sheeting and tested for creep under fire. The effects of the carbonizing temperature of charcoal, used as raw material for the CPS sheets, the thickness, and the location of the sheet on the joint regarding the fire-resistance performance of the joint were studied. The time to rupture of the joints covered with CPS sheets made from charcoal carbonized at 800°C (CPS800) was slightly prolonged compared with that of uncovered joints. On the other hand, the time to rupture of CPS sheets made from charcoal carbonized at 1600°C (CPS1600) was markedly extended. The changes in the charcoal properties due to increasing the carbonizing temperature might be the main reason the CPS1600 sheets had higher fire-resistance performance. The thickness and location of CPS1600 sheets have significant effects on the fire resistance of the joint. A highly fire-resistant laminated veneer lumber joint was obtained using a CPS1600 sheet. The CPS1600 sheet with a thickness of 3mm covering three sides of the joint prolonged the time to rupture 16-fold compared with that of unprotected joints.Part of this paper was presented at the 4th International Wood Science Symposium, Serpong, Indonesia, September 2002 相似文献
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Dimensional stabilization of compressed laminated veneer lumber by hot pressing in an airtight frame
《Wood material science & engineering》2013,8(3-4):119-125
Abstract The purpose of this study was to evaluate the dimensional stability and strength properties of compressed laminated veneer lumber (LVL) produced using a closed hot pressing system. LVL specimens were produced with varying number of veneers using either diphenylmethane diisocyanate (MDI) or a water-soluble phenol formaldehyde (PF) resin at varying temperatures (160–200°C), pressures (0.5–3 MPa) and hot-pressing times (2–16 min). Results show that the heating process decreases the recovery of compressive deformation in the veneers when subjected to cyclic moisture and heat conditions. Thickness swelling was approximately 5% after a drying, wetting and boiling cyclic test for LVL using the MDI resin and hot pressed at 200°C for 8 min. Modulus of elasticity and rupture increased for samples produced in both an open press and the closed press with an increase in the number of veneers and density, as did the absorbed energy in impact bending. 相似文献
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利用三层尾巨桉单板之间嵌入与两张性能相同的金属薄板组成五层尾巨桉单板/金属网层积复合材,并采用预实验优化的热压工艺参数压制成板。采用大型通用有限元分析软件ANSYS10.0构建了尾巨桉/金属网复合材料的有限元数值分析模型,模拟了尾巨桉/金属复合材料界面自由边附近与板材内部界面应力的分布规律,解明了最可能引起分层破坏的正应力的分布规律。主要结果与发现如下:(1)复合材料四层界面处三个正应力的二维应力场分布云图表明自由边附近出现奇异应力的分布特征,自由边处正应力σx的值最大,其最大值为99.72 MPa;(2)复合材料四层界面处三个正应力的三维应力场分布云图表明在四层界面处正应力的应力σx集中现象都最为明显,最大应力集中值可达280.0 MPa。 相似文献