木材断裂韧性测试研究

 讨论了线弹性断裂力学原理在木材中应用的特殊性；采用不同的 试样和方法测定了木材的顺纹断裂韧性KTLIC，并分析了不同试样厚度 和裂纹长度对木材断裂韧性的影响. 实验表明，顺纹断裂韧性KTLIC是 木材的基本属性.     

木材顺纹断裂韧度的研究进展

木材的缺陷会使其在低应力状态下发生顺纹断裂,本文总结了木材抵抗顺纹断裂的重要力学参数——顺纹断裂韧度的研究进展.介绍了木材顺纹断裂韧度的测试方法,并分析了不同试验方法与数据处理方法的优缺点.重点阐述了影响木材顺纹断裂韧度的主要因素,如木材的种类、密度、含水率、木质纤维桥接作用以及试件跨高比等的影响.此外,也总结了木材顺纹断裂韧度尺寸效应的研究成果.并结合工程木被广泛应用的现状,介绍了木材胶结面断裂韧度的研究进展.     

复杂应力状态下木材力学性能的数值模拟

针对木材复杂的各向异性材料特点,建立了能反映木材正交各向异性弹性、抗拉和抗压强度不等、抗拉或抗剪时发生脆性破坏而受压时发生塑性变形等特性的本构模型。将木材弹性应力—应变关系简化为正交各向异性;选用Yamada-Sun强度准则来判断木材抗压时是否屈服,抗拉或抗剪时是否发生应变软化;通过引入损伤因子和弹性应变能,建立了木材...     

Kink Band Formation in Wood Species Under Compressive Loading

The design of wood structures, such as columns and beams, requires the knowledge of the compressive behavior of wood. Several wood species, hardwoods and softwoods, are tested under compression parallel to grain to investigate experimentally the formation of kink bands and the relationship between this localized mode of failure and wood anatomy. In order to determine the correct test method for successful observation of kink banding, an experimental plan is first carried out. Then, several characteristics of kink bands, as well as the compressive behavior of the specimens, are comparatively analyzed for the various wood species. Based on these observations and some theoretical predictions corroborated by experimental data, it is shown that compressive kinking strength of wood is governed mainly by its yield strength in shear and by certain features of its anatomy related to the so-called ray cells.     

Mechanics of wood and trees: some new highlights for an old story

The main aspects of wood mechanics are approached through the role played by wood as the building material of the tree. The main concepts used by nature: progressive setting up of tree weight and architecture, multifunctional role of wood and adaptability to hazard and long-term evolution, are clarified together with their consequence on the multilayered, anisotropic nature of wood. The technological choices of the plant world as the cellular structure, the use of composite with oriented fibres and hydro-carbonated polymers, as well as the systematic prestressing of every new layer, bear obvious consequences on the type of mechanical behaviour of wood. The local control of the level of prestressing through minor modifications of the cell-wall biosynthesis allows the tree to adapt to conditions of light exploration that will evolve according to time and risk occurrence. This analysis of wood genesis process permits in return to improve our understanding of the mechanical behaviour of the material in relation with the parameters of the microstructure.     

高速侵彻弹体层合木靶脱壳

利用实验和数值模拟方法研究一种利用层合松木靶作为脱壳装置的机械式脱壳方法。首先讨论了一种正交各向异性材料模型用于高速侵彻木材的可行性及其参数变化规律,结合美军的高速侵彻实验数据对数值模拟方案进行了验证与确认。在此基础上,讨论了不同弹靶作用下含弹托弹体对松木靶的侵彻/贯穿规律。数值模拟与实验研究结果表明:在垂直入射条件下,通过合理的层合木靶设计可对次口径发射弹体有效脱壳,高速侵彻弹体可垂直入射靶板,弹体速度衰减可控;在初始攻角入射条件下,层合靶将使高速侵彻弹体攻角放大。随入射速度增加,弹体贯穿层合木靶消耗动能增加,体现了木材具有明显的应变率增强效应。     

木材Ⅰ/Ⅱ复合型断裂破坏研究进展

复合型应力状态是木材断裂破坏的主要受力模式,本文从复合断裂模型和试验方法两个方面回顾了木材复合断裂研究的发展历程.在介绍了木材复合断裂的经验模型和物理模型后,通过一组试验数据进行了这些断裂模型的比较,总结了各自的特点.同时,总结了确定这些模型而进行的各类试验方法,主要是Ⅰ/Ⅱ复合断裂模式,即断裂模式Ⅰ和断裂模式Ⅱ均存在的情况.最后阐述了木材复合断裂研究中的一些问题,并对今后的研究方向提出了建议.     

穿斗式木框架受力性能研究

为研究西南地区穿斗式木结构的承载能力和变形特征,设计了单榀足尺穿斗式木框架进行水平静力单调加载试验,获得了木框架水平荷载-位移曲线关系以及木框架的整体破坏形态等,并采用ABAQUS 软件对木框架进行数值分析．研究表明木框架破坏形式表现为框架整体的严重倾斜,柱与枋本身较为完好;木框架柱顶侧移随着加载位移的增加呈线性增长关系,对称的左右立柱和瓜柱柱顶侧移基本一致;不同节点榫头同步拔出,拔榫量峰值相差较小,表现出较好的协调性;暗销节点的变形主要表现为榫头的挤压凹陷,榫头横纹方向较早地进入塑性变形阶段．卯口受压变形较小,处于弹性变形阶段．     

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木材声发射信号与其内外部损伤情况存在一定的定量关系. 依据损伤理论和含有裂 纹以及缺陷的木材不同阶段的声发射特征,分别探讨并建立了受交变载荷和单向静载荷情况下以声发 射特征参数表示的木材损伤演变模型. 分析结果与木材的实际情况相一致,表明以声发射特 征参量建立的木材损伤演变模型对木材的损伤预测具有提前性与敏感性,而且木材的不均匀 性是其提前破坏的主要原因之一.     

Deformations and Stresses in Dried Wood

The deformations and the evolution of drying-induced stresses in wood are studied based on a model which takes into account the alteration of mechanical properties of wood in the course of drying. A two-dimensional initial-boundary value problem is solved with the help of the finite element method. An influence of wood anisotropy on the deformation and the stress distributions and evolution of maximal stresses is analysed.     

白桦材断裂韧度的各向异性性质

木材可视为正交各向异性材料，表征木材抵抗裂纹扩展能力的断裂韧度硒。是木材的基本力学性质之一，它具有明显的各向异性．对白桦材试样断裂韧度硒。测试结果表明，LT试样的断裂韧度明显高于TL，TR试样的断裂韧度，TL和TR试样的断裂韧度相接近．无论哪种试样类型，起裂均发生在裂纹尖端．TL，TR试样裂纹扩展方向与原裂纹初始方向一致，LT试样与前两不同，裂纹沿着几乎平行于纤维的方向扩展．并且含水率对各个方向木材断裂韧度的影响趋势是一致的．     

A study of viscoelasticity and extrudate distortions of wood polymer composites

Natural fiber composites exhibit a characteristic surface tearing and extrudate distortions upon exiting from extrusion dies. This type of defect is characterized by highly rough, cracked, and distorted extrudate surface. In this study, the extrudate distortions and viscoelastic nature of metallocene-catalyzed polyethylene (mPE)/wood flour composites have been investigated. As the wood flour loading increases the region of linear viscoelasticity shortens. The first normal stress difference decreases, while the storage modulus increases. It was observed that increasing the wood flour loading up to 50 wt% aggravated the surface tearing; however, 60 wt% wood flour in mPE completely eliminated the surface defect. It was also found that increasing the shear rate improved the surface appearance of the filled compounds. This is due to the increased wall slip velocity of the composites at high shear rates and wood filler loadings. Increasing the diameter of the die at the same aspect ratio generally provides more severe surface tearing. This paper was presented at the 3rd Annual Rheology Conference, AERC 2006, April 27–29, 2006, Crete, Greece.     

杨木的动态力学性能

应用分离式Hopkinson压杆（SHPB）研究了干、湿速生杨木在高应变率加载条件下的动态力学性能,并同准静态压缩实验的结果进行了比较,论述了干、湿杨木在高应变率载荷条件下破坏的机制。结果表明:杨木的应力应变曲线与多孔固体相似,经历弹性、屈服以及致密3个阶段;冲击后,干杨木试样纤维因胞壁坍塌而压实,湿杨木试样由于胞管内水的作用而产生垂直于纤维轴向的拉应力,使纤维沿轴向相互分离,并且应变率对杨木的力学性能的影响明显。     

中国古建筑木结构力学研究进展

中国古建筑木结构是我国乃至世界的宝贵文化遗产, 也是中华文明的重要组成部分. 随着时间的延续, 对这些价值连城、失而不可复得的历史文物的保护日益迫切. 本文从古木结构的木材力学性能、关键节点(斗栱、梁柱节点和柱脚节点) 受力机理、木构架整体受力性能研究、结构残损勘查、安全评估及修缮加固等方面, 总结了近30 年来结构学者对古代木结构建筑的研究进展, 以期为今后进行古木建筑的结构研究提供参考.      

CFD modeling and experimental validation of heat and mass transfer in wood poles subjected to high temperatures: a conjugate approach

In this article, a coupling method is presented in the case of high thermal treatment of a wood pole and a three-dimensional numerical simulation is proposed. The conservation equations for the wood sample are obtained using diffusion equation with variables diffusion coefficients and the incompressible Reynolds averaged Navier–Stokes equations have been solved for the flow field. The connection between the two problems is achieved by expressing the continuity of the state variables and their respective fluxes through the interface. Turbulence closure is obtained by the use of the standard k–ɛ model with the usual wall function treatment. The model equations are solved numerically by the commercial package ANSYS-CFX10. The wood pole was subjected to high temperature treatment under different operating conditions. The model validation is carried out via a comparison between the predicted values with those obtained experimentally. The comparison of the numerical and experimental results shows good agreement, implying that the proposed numerical algorithm can be used as a useful tool in designing high-temperature wood treatment processes. A parametric study was also carried out to determine the effects of several parameters such as initial moisture content, wood aspect ratio and final gas temperature on temperature and moisture content distributions within the samples during heat treatment.     

Analysis of tapered ENF specimen and characterization of bonded interface fracture under Mode-II loading

An engineering approach for evaluating the shear-mode (Mode-II) fracture toughness of wood–wood and wood-composite bonded interfaces is presented. A tapered beam on elastic foundation model is developed to analyze and design a linear tapered end-notched flexure (TENF) specimen for fracture tests of bonded interfaces. The elastic foundation model is verified numerically by finite element analysis and experimentally by compliance calibration tests, which demonstrate that the present model can accurately predict the compliance and compliance rate-change of the specimen, and with proper design, an approximate constant rate of compliance change with respect to crack length can be achieved. The proposed TENF specimen can be used for Mode-II fracture toughness evaluations with reasonable confidence in the linearity of compliance crack-length relationship. The fracture of wood–wood and wood-composite bonded interfaces under Mode-II loading is experimentally evaluated using the proposed TENF specimen, and the corresponding values of critical strain energy release rate are obtained. The modeling technique and testing method presented can be efficiently used for characterization of Mode-II fracture of bonded bimaterial interfaces.     

Non-linear Model for Wood Saturation

The paper presents a non-linear model of saturation with fluid of anisotropic capillary porous bodies and the results of experimental investigations of wood saturation with methacrylate. The obtained experimental curves illustrating the distribution of methacrylate in wood samples allow the estimation of material coefficients and verification of the theoretical model. The theoretical model is developed based on the balance equations of mass, momentum, and energy, and the thermodynamics of irreversible processes. The non-linear differential equation, describing the distribution of methacrylate content in wood and its evolution during the saturation is solved numerically. The theoretical curves obtained on the basis of both linear and non-linear models are compared with the experimental data and better agreement between them for the non-linear model is stated.     

常用实木地板的摩擦磨损性能研究

用UMT-2MT摩擦试验机测试了9种常用实木地板对橡胶和440C不锈钢的摩擦磨损性能.结果表明：橡胶对多数地板的摩擦系数大于0.5,满足安全标准,且均大于钢球对地板的摩擦系数.钢球对地板漆层的摩擦系数介于0.1～0.6之间,而钢球对地板木材的摩擦系数基本相同,处于0.55左右.橡胶对地板磨损试验未能得到可测的磨损量（试验时间为1 h）.钢球对地板漆层和木材层的磨损不同,漆层的抗磨损能力普遍高于木质层.每种地板都有临界载荷,载荷小于临界载荷时,随着载荷的增加磨损量几乎不变;载荷大于临界载荷后,随着载荷的增加磨损明显加快.     

Damping Properties of Sequoia, Birch, Pine, and Aspen under Shock Loading

Results of an experimental study of strength—deformation properties of sequoia, aspen, pine, and birch wood for various loading rates, temperatures, humidities, and orientation angles of wood fibers with respect to the loading direction are described. Stress—strain diagrams and an analytical dependence of strength on humidity, temperature, and loading rate are presented.