基于摩擦特性的榫接合节点抗拔力研究

通过创新的测量方法对椭圆榫接合节点的摩擦特性进行了研究,基于合理的条件假设,建立了椭圆榫接合节点抗拔力的数学模型,并通过椭圆榫接合T形构件的抗拔力试验对模型计算结果进行了检验。研究结果表明,基于本研究所采用的加工方式,木材在平面接触状态下,接触面纹理角度、接触面积以及接触压力对木材与木材间的摩擦系数无明显影响。各接触面粗糙度测量结果表明,横纹不同纹理角度和顺纹不同纹理角度下的粗糙度基本相等。通过创新的试验方法对不同纹理角度的椭圆榫接合节点摩擦系数进行测量,其结果与平面接触状态下的测量结果基本一致,平均摩擦系数约为0.54。试验验证阶段对采用椭圆榫接合的T形构件抗拔力进行了测量,得到抗拔力平均值为3 192.5 N,标准差为398 N,而通过本研究建立的数学模型计算所得的榫接合节点抗拔力为2 928.08 N。数学模型计算结果与试验结果的最大值及最小值的误差均在标准差范围内。因此,本研究所建立的力学模型可用于实木椭圆榫接合节点抗拔力的估算,并为榫接合节点在胶合状态下的力学特性研究,以及实木榫接合家具结构设计提供依据。     

有限元法在实木榫接合家具结构设计中的应用

文中从实木榫接合家具节点、构件和整体框架3个层面，总结、分析有限元法在实木榫接合家具结构设计中的应用现状，并对该领域存在的主要问题及未来研究趋势进行了阐释。目前主要存在以下问题:1）未形成系统性的有限元分析方法，不同研究者之间存在较大差异；2）分析准确度不高，大多研究仅为有限元软件的模拟分析，缺乏试验验证；3）未建立合理的榫接合节点有限元模型，通常将榫接合节点视为刚性节点处理。未来研究可围绕以下几方面开展:1）榫接合节点有限元模型的建立方法及简化方法；2）实木榫接合家具疲劳寿命的有限元分析方法；3）基于有限元法的实木榫接合家具结构优化设计方法；4）二次开发，在有限元分析软件的基础上，建立实木榫接合家具结构设计模块；5）实木榫接合家具智能设计与制造系统开发。将有限元法应用于实木榫接合家具的结构设计中，将有助于实木榫接合家具的结构优化设计、智能设计与制造。     

辐射松处理材制备实木家具节点性能研究

为探讨改性辐射松应用于实木家具几种连接方式节点的接合强度,以辐射松树脂材与真空热处理树脂材为基材,采用力学试验方法测定"T"型与"L"型构件节点的破坏弯矩并分析其破坏特征。结果表明:相同条件下,树脂材节点接合强度大于热处理树脂材,贯通直角单榫双圆棒榫普通三合一连接件,"T"型构件节点接合强度大于"L"型构件,改性辐射松节点接合强度在一定条件下接近优质木材的节点接合强度。改性辐射松木材可满足实木家具对节点接合强度的要求,具备制造中高档松木家具的可行性。     

在实木家具结构中圆棒榫的强度分析

分析圆棒榫在实木家具结构中的主要力学指标,通过圆棒榫的抗拔力、抗弯强度与抗剪强度等指标的计算与比较,总结圆棒榫在实际应用中应注意的主要问题,以期对相关的设计与生产提供参考依据.     

黄荆木重组材家具结点性能分析

对黄荆木重组材家具结点强度进行测试,选用T型、L型结构,对L型结构进行抗弯强度测试,对T型结构进行抗弯、抗拔强度测试,分析试验结果以及试件在试验中、试验后的情况,探讨自攻螺钉接合、双圆榫接合、三合一连接件接合三种连接方式对黄荆木重组材家具结构的适用性。通过对三种连接方式的抗弯、抗拔强度进行综合分析,结果表明:自攻螺钉接合强度双圆榫接合强度三合一连接件接合强度。若是要使用三合一连接件连接时,要配合其他连接方式进行使用。     

速生松木家具几种节点接合方式的强度比较研究

以南方速生脱脂马尾松松木为基材,以"L"型和"T"型构件为基本构件形式,采用力学实验方法 ,对理想使用状态——即在外力垂直荷载匀速加载的作用下使构件节点发生破坏或变形,测试构件节点破坏强度值及其破坏或变形形式。实验针对8种不同框架节点接合方式(贯通直角单榫接合、不贯通直角暗榫接合、双圆榫接合、倒刺螺母连接件接合、双圆榫与倒刺螺母共同接合、三件式偏心连接件接合,以及45°双圆榫斜角接合和45°不贯通榫斜角接合)的接合强度进行测定。实验结果表明:(1)对于直角连接构件,采用贯通直角单榫接合时的节点接合强度最大;双圆榫与倒刺螺母共同连接的节点接合强度次之;然后强度值从高到低依次为双圆榫接合、倒刺螺母螺杆连接件接合、不贯通直角单榫接合,接合强度最小的是偏心连接件接合;(2)对于45°斜角连接构件,采用45°不贯通榫斜角接合的节点强度大于45°双圆榫斜角接合的节点强度;(3)在相同条件下,"T"型实木构件的节点接合强度总体上大于"L"型实木构件的节点接合强度。研究表明:节点处的基本构件形式("L"型或"T"型)、角部构件的连接形式(直角构件或斜角构件),以及节点的接合方式等都不同程度地影响着马尾松松木家具框架节点的接合强度。     

椭圆榫接口标准化研究与创新设计

基于现有实木家具构件椭圆榫接合形式,对其进行了评估与创新设计。依据家具产品的标准化原则,设计出一种"台阶式"椭圆榫,并对其制造工艺及接合方式进行探究。结果表明,"台阶式"椭圆榫较常规椭圆榫接口具有高加工效率及较低加工成本等优势。     

桉木单板层积材家具角部“L型构件”接合强度研究

以速生桉木单板层积材为基材,榫接合连接、螺钉连接的L型构件为研究对象,通过对桉木层积材家具接合构件进行抗拉和抗弯力学性能试验,观察、分析8种不同榫接合方式对"L型构件"接合强度的影响。研究结果表明,榫接合强度与接合面积有关,接合面积大则接合强度高;桉木单板层积材本身强度对榫接合无影响;采用偏心连接件、倒刺螺母螺杆连接件的接合强度较低,接合部位不够牢固,在家具的使用过程中容易产生松动。     

椭圆榫T型构件接合强度影响因素研究

以北美鹅掌楸为基材,探究椭圆榫T型构件接合强度的影响因素。采用单因素试验探究涂胶量、陈放天数对椭圆榫抗拔强度的影响;采用正交试验探究榫眼深度、长度和宽度三个因素对椭圆榫抗弯强度的影响。结果表明:涂胶量对椭圆榫T型构件抗拔强度的影响非常显著,陈放天数的影响比较显著。榫眼宽度是影响椭圆榫T型构件抗弯强度的主要因素,榫眼深度和长度次之,而深度的影响大于长度。     

家具构件旋转摩擦焊接接合性能研究

圆棒榫旋转摩擦焊接技术具有加工速度快,胶合强度高,且无需任何石化类胶黏剂的优势。以南方松为基材,以双圆榫旋转摩擦焊接和白乳胶胶合的"T"型、"L"型实木构件为研究对象,通过力学强度测试对比两种不同节点接合方式的接合强度以及不同插人深度对圆榫旋转摩擦焊接强度的影响。结果表明,圆棒榫旋转摩擦焊接技术是一种颇具潜力的家具构件连接方式。     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.