共查询到19条相似文献，搜索用时 471 毫秒
1.
2.
在众多环境因素中,温度是对木塑复合材料性能影响最显著的因素之一.在一定温度范围内,木塑复合材料的抗弯性能随温度的升高而降低. 相似文献
3.
木塑复合材料是一种具备环境友好性以及良好性能的复合材料。开发具备电磁功能的木塑复合材料有利于提升产品的附加值并进一步拓宽产品的应用范围,具有重要的研究意义和应用价值。文中在概述常用电磁功能助剂的类型、结构、性能及其电磁原理的基础上,总结了导电型、电磁屏蔽型和抗静电型木塑复合材料的研究现状以及目前电磁功能型木塑复合材料的应用领域及行业现状;针对现有研究中存在的助剂分散性差、导电机理不明确、界面结合受影响、产业化难推广等问题,展望电磁功能型木塑复合材料的研究方向,以期为电磁功能型木塑复合材料的进一步开发和利用提供科学依据。 相似文献
4.
木塑复合材料生产工艺与发展前景 总被引：1，自引：0，他引：1
木塑复合材料是一种既类似木材又优于木材的新型复合材料,其加工工艺与传统木质人造板产品有较大的差别.本文介绍了木塑复合材料的加工工艺与产品性能特点,论述了木塑复合材料的发展趋势及应用前景. 相似文献
5.
德国：英国《木材贸易杂志》报道,木塑复合材料大会于2009年12月2、3日在德国科隆召开。届时有30场关于木塑复合材料最新研发进展的演讲,涵盖新工艺过程、新材料、国际市场最新动向。中国的主导木塑复合材料厂家将介绍中国的最新进展,中国产品也将在26展台展出。 相似文献
6.
7.
8.
9.
温度对重组竹短期受压蠕变性能的影响 总被引：1，自引：0，他引：1
通过对重组竹受压试件进行短期蠕变试验,研究温度对重组竹受压试件蠕变特性及蠕变规律的影响。针对不同应力水平下温度对重组竹短期受压蠕变的影响,研究了在同一应力水平7.5%下,重组竹在5种不同温度下的24 h顺纹受压蠕变性能;进一步比较了重组竹在应力水平为7.5%,15%,30%且温度分别为25,50,75℃情况下的24 h顺纹短期受压蠕变特点。最后,采用Burgers模型对上述不同温度变量和不同应力水平变量下重组竹短期受压蠕变曲线进行拟合分析。结果表明:在重组竹顺纹受压蠕变中,温度和材料应力水平越高,瞬时弹性变形越大,重组竹蠕变应变总量越大,重组竹抵抗蠕变性能越弱,且较高温度和较高应力水平的同时作用会对重组竹构件产生不利影响;Burgers模型的拟合决定系数基本均在0.98以上,说明Burgers模型能够较准确地描述温度对重组竹短期受压蠕变曲线特性的影响。根据试验与拟合曲线特性可知,重组竹顺纹受压蠕变中弹性变形占80%以上,说明在不同温度下重组竹顺纹受压蠕变中弹性变形占主要部分,随着温度的升高,弹性变形有所下降,黏性变形逐渐增加。 相似文献
10.
11.
P. W. Bonfield J. Mundy D. J. Robson J. M. Dinwoodie 《Wood Science and Technology》1996,30(2):105-115
Summary The development of rheological models to predict creep has led to the derivation of quite complex equations that can predict creep reasonably accurately. However, these models are conceptual and are not based on a fundamental understanding of the actual deformation processes occurring within the material. The concept of modelling creep using a chemical kinetic approach is one that attempts to understand creep in wood at a molecular level and, from this, to develop models that more accurately predict creep deflections.This paper presents two models developed from chemical kinetic theory, that describe the time-dependant deformation of wood. The validity of applying these models to experimental data has been assessed by stress relaxation tests on thin samples of Sequoia sempervirens.
Two stages of experimentation were carried out. In stage 1, both models were applied to the results of stress relaxation tests on 6 samples. Similar values of activation energy and activation volume were calculated by both models and a single energy barrier was found to dominate the deformation process.In stage 2, the effect of varying the initial applied stress on activation energy and activation volume was assessed by carrying out stress relaxation tests at stress levels of 25%, 30% and 35% of the short-term strength. Values of activation energy and activation were found to increase as the applied stress level decreased.Both models describe the time-dependent behaviour of wood well, however their ability to predict long-term creep deflections may be limited. Future work will develop these models further in order to improve long-term creep prediction and then apply them to the results of both creep and stress relaxation tests at a variety of stress levels and moisture contents in order to test their validity. 相似文献
12.
Viscoelastic properties of maleated polypropylene (MAPP)-modified wood flour/polypropylene composites (WPC) were investigated by both a compression stress relaxation method and dynamic mechanical analyses (DMA). Three wood to polymer ratios (40:60, 60:40, and 80:20) and five MAPP loading levels (0, 1, 2, 4 and 8%) were used to study their effects on the viscoelastic properties of MAPP-WPC. The results show that: 1) higher wood to polymer ratio corresponds to higher stress relaxation levels for unmodified WPC. The modification with MAPP has an obvious effect on the stress relaxation of MAPP-WPC at higher wood to polymer ratios (60:40 and 80:20), but almost no effect at the 40:60 wood to polymer ratio. The optimal MAPP loading level for the wood to polymer ratio of 60:40 appears at 1%; 2) the storage modulus reaches its maximum at a MAPP loading level of 1% for wood to polymer ratios of 40:60 and 60:40, while for the 80:20 wood to polymer ratio, a higher storage modulus is observed at higher MAPP loading levels, which is quite consistent with the stress relaxation results. The results suggested that a suitable loading level of MAPP has a positive effect on the viscoelastic properties of WPC at higher wood to polymer ratios. Excessive MAPP loading would have resulted in adverse effects. 相似文献
13.
To verify master curves obtained based on time–temperature superposition principle for wood–plastic composites (WPCs), a 220-day long-term creep test was conducted under an unconditioned environment. In this study, WPCs were made by extrusion with various formulations; using mountain pine beetle-attacked lodgepole pine flour and high-density polyethylene as raw materials, as well as maleated polypropylene as coupling agent. The results showed that the effect of naturally elevated temperature during the summer months caused additional increases in creep strain. The information obtained from the conventional creep study method may be insufficient to reflect the practical application. Comparisons between long-term data and the master curves showed that the master curves tended to overestimate the real creep strain of large specimens and that the deviation increased with time. The prediction of the master curve agreed more reasonably with the long-term data for coupled WPC products, whereas the master curves showed considerable overestimation for the uncoupled ones. In general, the master curves cannot precisely predict the long-term creep strain, but merely provide conservative estimations. 相似文献
14.
We investigated the temporal changes in creep and stress relaxation behavior in both microscopic crystalline cellulose and macroscopic strain of wood specimen using Japanese cypress (Chamaecyparis obtusa Endl.) to understand the viscoelastic properties of wood cell walls. Specimens 600 µm in thickness were observed by the X-ray diffraction and submitted to tensile load. The crystal lattice strain of (004) plane and macroscopic strain of specimen were continuously detected during creep and stress relaxation tests. It was found that the creep compliance based on macroscopic strain showed a gradual increase after instantaneous deformation due to loading and then the parts of creep deformation remained as permanent strain after unloading. On the other hand, crystal lattice strain showed a different behavior for macroscopic strain; it kept a constant value after instantaneous deformation due to loading and then increased gradually after a certain period of time. These differences between macroscopic and microscopic levels were never found in the stress relaxation tests in this study. Relaxation modulus at the macroscopic level only showed a decreasing trend throughout the relaxation process. However crystal lattice strain kept a constant value during the macroscopic relaxation process. In addition, the microfibril angle (MFA) of wood cell wall has a role of mechanical behavior at microscopic level; crystal lattice strains were smaller with increasing MFA at both creep and relaxation processes. Creep compliance and stress relaxation modulus at the macroscopic level decreased and increased with increasing MFA, respectively. Our results on the viscoelastic behavior at microscopic level evidenced its dependency on MFA. 相似文献
15.
16.
J. M. Dinwoodie D. J. Robson B. H. Paxton J. S. Higgins 《Wood Science and Technology》1991,25(3):225-238
Summary Deflection under 4-point bending of a range of board types was measured for up to six months. Results were obtained under steady-state conditions of stress level (30%, 45%, 60%, 67.5% and 75% of the short term breaking stress), relative humidity (30%, 65% and 90% rh) and temperature (10°C, 20°C and 30°C). These results are presented in terms of relative creep and creep modulus. The relative creep for all board types increased with increasing stress level, increasing relative humidity and increasing temperature. An analysis of variance investigating variations between materials showed significant differences in relative creep. When the relative creep of all materials was compared over all conditions and all stress levels, plywood and waferboard had consistently low relative creep values. High alkaline cured PF chipboard and non-British Standard UF chipboard had consistently high relative creep values. The creep modulus of MUF bonded chipboard decreased with increasing log10 (time) under all conditions. Creep modulus also decreased with increasing stress level.The statistical analysis in this paper was performed by Anne Hasted and Laura New of the Statistical Services Centre, Reading University 相似文献
17.
18.