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毛竹不同种源竹材物理力学性质初步研究 总被引：3，自引：0，他引：3
通过对来自福建建瓯试验地16个毛竹种源竹材的密度、顺纹抗压强度、顺纹抗剪强度、顺纹抗拉强度和弦向抗弯强度及其弹性模量等物理力学性质的初步研究,结果表明:竹材物理力学性质在各种源之间存在一定的差异,其中湖南株洲的毛竹竹材物理力学性质比于其它种源的毛竹要好,而安徽霍山的毛竹竹材的物理力学性质较差,测量的各指标中有基本密度、抗剪强度、抗拉强度三项指标都达到最低;竹材密度的大小、抗拉强度的高低随种源纬度的降低而呈降低的趋势,而竹材的抗剪强度呈与之相反的趋势。 相似文献
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在浙江平阳竹木混交林内,采集3年生大木竹,按标准制成试样,测定了丛生竹种大木竹竹材的各力学性质,并以材性优良的毛竹为参比进行分析.结果发现:大木竹竹材的顺纹抗拉、顺纹抗压、抗劈力和抗弯弹性模量分别为238.0 MPa、75.1 MPa、45.6 N·mm-1和12.6 GPa,比毛竹材的相应值大或与毛竹相当,顺纹抗剪和抗弯强度较毛竹材为低.大木竹的各力学性质间有较密切的相关性,顺拉强度:顺压强度:顺剪强度:抗劈力:抗弯强度为3.2:1.0:0.2:0.6:1.8.该研究结果可为大木竹的合理开发利用提供理论依据. 相似文献
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安徽霍山县靠近毛竹天然分布的北部边缘,其独特的地理位置及气候条件影响着毛竹材的各项特性,其中海拔是影响毛竹材力学性质的重要因子。以安徽霍山不同海拔（设120、230、370、510和600 m 5种海拔处理）的毛竹材为试验材料,研究了海拔因子对竹材力学性质的影响。结果表明：海拔因子对霍山毛竹的竹材密度有一定影响,随海拔升高,竹材的气干密度和全干密度呈增大趋势,但差异不大;海拔因子对竹材的顺纹抗压强度和顺纹抗剪强度有显著影响,但对顺纹抗拉强度影响不大。霍山毛竹材的各项力学特性接近传统的建筑用木材,经过合理加工可以替代传统木质建筑材料。 相似文献
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以麻竹、毛竹、小叶龙竹和粉单竹为研究对象,考察了竹龄(1~6年生)对竹材物理性质和力学性能的影响规律,并探究了竹材的结构构造,以期为广东省原竹的合理采伐和加工利用提供依据。研究结果表明:随着竹龄的增大,竹材的密度、顺纹抗压性能、顺纹抗弯性能、抗冲击性能和径向环刚度均呈先上升后下降的趋势,然而干缩率变化并不明显。4个竹种中,有竹节的麻竹拥有优异的环刚度性能;毛竹拥有优异的顺纹抗压强度和横纹抗压强度;小叶龙竹拥有优异的顺纹抗压弹性模量和抗冲击性能;粉单竹拥有优异的顺纹抗弯性能。4~6年生小叶龙竹的节间长度虽短,但其直径、壁厚和径厚比略显优势,且其纤维体积分数呈明显的径向梯度分布。 相似文献
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毛竹顺纹抗拉性质的变异及与气干密度的关系 总被引：4，自引：0，他引：4
将毛竹轴向分段(4段)、径向分层(6层)取样,研究其顺纹抗拉弹性模量和顺纹抗拉强度的变异规律,顺纹抗拉性质与气干密度之间的关系.结果表明:毛竹的顺纹抗拉弹性模量和顺纹抗拉强度的径向变异很大,不同位置竹材的顺纹抗拉弹性模量为8.49～32.49 GPa,最外层竹材的顺纹抗拉弹性模量约是最内层的3～4倍;不同位置顺竹材顺纹抗强度在115.94～328.15 MPa之间,最外层竹材的顺纹抗强度是最内层的2～3倍.用直线方程预测毛竹顺纹抗拉性质的效果略优于曲线方程的效果. 相似文献
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《中南林业科技大学学报(自然科学版)》2017,(10)
为进一步发掘麻竹材加工利用潜力,通过对不同竹龄、不同部位麻竹材的气干密度、力学性质、燃烧性能及其相关关系进行分析。结果表明:(1)竹龄对麻竹材气干密度、顺纹抗压强度、抗弯强度、抗弯弹性模量、点燃时间、释热速率、质量损失率、释烟总量及60、180、300 s比消光面积均有显著影响,而对抗拉强度无显著影响;(2)竹材部位对气干密度、顺纹抗拉强度、抗弯强度有显著影响,而对顺纹抗压强度、抗弯弹性模量无显著影响;(3)麻竹材顺纹抗拉强度:顺纹抗压强度:抗弯强度:抗弯弹性模量=3.06∶1.00∶2.63∶164.28;(4)麻竹材气干密度与顺纹抗压强度、抗弯强度、抗弯弹性模量、点燃时间、释烟总量、60 s比消光面积和300 s比消光面积呈显著正相关,且相关系数达到0.899~0.958。4 a生麻竹材的气干密度、力学性质及燃烧性能等指标渐趋基本稳定,利用简单易测的麻竹材气干密度能较准确预测评价麻竹材部分力学性质与燃烧性能。 相似文献
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《Scandinavian Journal of Forest Research》2012,27(5):427-435
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. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(3):206-217
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. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(1):53-61
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. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(1):15-27
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. 相似文献
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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. 相似文献
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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。 相似文献
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Astra Zaluma Lauma Bruna Darta Klavina Natalija Burnevica Kristine Kenigsvalde Andis Lazdins Talis Gaitnieks 《Forest Pathology》2019,49(6)
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. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(2):118-130
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. 相似文献
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Steven Maranz Amadou Niang Antoine Kalinganire Djeneba Konaté Bocary Kaya 《Agroforestry Systems》2008,72(3):231-239
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. 相似文献
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《Wood material science & engineering》2013,8(2):76-84
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. 相似文献