微波预处理对杨木流变性能影响研究

发布时间：2018-05-05 02:45

本文选题：杨树木材 + 微波处理　；参考：《中南林业科技大学》2017年硕士论文

【摘要】：本文紧密结合国家自然科学基金项目(杨木高强度微波膨化与重构机制研究,31370564)以速生杨树木材为研究对象,利用微波处理技术对杨木进行预处理,观察杨木宏观和微观结构的变化。探讨了微波处理对杨树木材常规力学性能的影响,在此基础上测试了杨树木材在不同微波处理条件,不同荷载水平下的蠕变曲线,并以流变学理论为指导,利用Burgers流变模型对实验曲线进行了拟合,同时讨论了模型的改良,论文主要工作和创新性成果如下:(1)简要介绍了微波处理技术及电镜工作原理。从宏观上来看,当微波辐射强度较低时,可以看到试件表面仅覆盖了一层水蒸汽;当微波辐射强度较高时,某些试件表面发生了明显的开裂现象,试件已经被破坏。从微观上来看,未经微波处理的杨木内部截面孔洞和孔道壁比较完整光滑。经过微波处理的杨木横、纵截面显得更粗糙,孔洞边缘形成的毛糙变多,变细,形成网状结构;部分孔洞破裂扩大和周围的孔洞贯通形成更大、更不规则的新孔洞,甚至形成一条贯穿通道。经过力学试验后的杨木孔洞呈现出方向性使得材料的各向异性更趋明显。(2)不同的微波辐射强度和微波辐射时长对杨树木材的力学性能均有不同程度的影响。当辐射强度低于5kW和辐射时长少于50s时,其抗弯弹性模量和弯曲强度均有所降低,降低幅值在8%-13%之间。当微波辐射强度加大或辐射时长加长时,其抗弯弹性模量和弯曲强度均有所上升。18kW高功率时弹性模量的增幅达到52.6%,弯曲强度提高近20%。(3)杨树木材在不同微波处理条件和不同荷载下的蠕变曲线遵循相似的规律,都可以观测到减速蠕变阶段和稳态蠕变阶段,但未出现蠕变第三阶段(加速蠕变阶段)。荷载的改变会对各组蠕变的改变量造成较大的差异。荷载增大时,杨树木材瞬时弹性变形和总蠕变量也会增大。微波处理强度和处理时长对杨木蠕变性能均有不同程度的影响。试验结束时,同一辐射强度,不同辐射时间的各组杨木试件在50%破断强度水平下的蠕变总量相比于30%破断强度水平下的蠕变总量增幅在25%至69%之间;而同一辐射时间,不同辐射强度的各组杨木试件在50%破断强度水平下的蠕变总量相比于30%破断强度水平下的蠕变总量增幅均在46%以上,在65s,15kW微波处理工况下,50%破断强度下的蠕变总量增幅甚至达到100.3%,远超不同微波辐射时间下的最高增幅68.5%。利用Origin软件对各组在不同荷载水平下实验曲线进行拟合,拟合得到的曲线决定系数R2均可达到0.99以上。这说明在该实验条件下,Burgers流变模型在短期内可以很好的描述杨树木材的蠕变行为。但在预测长期蠕变的过程中发现Burgers流变模型数学表达式在后期变的过于线性,与实际不符。为此,在Burgers流变模型的本构关系式基础上引入λ参数,可以基本解决模型长期预测值过于线性的问题,且新模型能在实验时间内更好的模拟杨树木材的蠕变。本文的研究成果为杨树木材经过微波处理后流变性能研究提供了基础数据,也为木材设计中避免由于蠕变变形过大导致构件失效等问题提供了理论和实验依据。
[Abstract]:This paper closely combines the National Natural Science Fund Project (Yang Mugao strength microwave expansion and reconstruction mechanism research, 31370564) to study poplar wood by microwave treatment technology and observe the changes of macro and micro structure of poplar wood by microwave treatment technology. The influence of microwave treatment on the conventional mechanical properties of poplar wood is discussed. On this basis, the creep curves of poplar wood under different microwave treatment conditions and different load levels were tested. Based on the rheological theory, the experimental curves were fitted with the rheological model of Burgers, and the improvement of the model was discussed. The main work and innovative results of the paper were as follows: (1) the microwave treatment technology was briefly introduced. On the macroscopic point of view, when the microwave radiation intensity is low, it can be seen that the surface of the specimen is covered with only one layer of water vapor. When the microwave radiation intensity is high, the surface of some specimens has been obviously cracked and the specimen has been destroyed. From the microcosmic point of view, the inner section holes and channels of the poplar wood without microwave treatment The wall is more complete and smooth. The longitudinal section of the poplar section, after microwave treatment, appears more rough, and the roughness of the hole edge becomes more rough and finer, forming a network structure; the rupture of some holes expands and the surrounding holes are formed to form larger, more irregular holes and even a penetration channel. The poplar holes after the mechanical test are presented. The anisotropy of the material is more obvious. (2) the microwave radiation intensity and the length of microwave radiation have different effects on the mechanical properties of poplar wood. When the radiation intensity is lower than 5kW and the radiation length is less than 50s, the flexural modulus and bending strength of the wood are reduced, and the amplitude is reduced to 8%-13%. When the intensity of wave radiation is increased or the length of radiation is long, the flexural modulus of elasticity and flexural strength of its flexural modulus and flexural strength are all increased by.18kW, the modulus of elasticity increases by 52.6%, and the bending strength increases by nearly 20%. (3). The creep curves of poplar wood following different microwave treatment conditions and different loads follow similar laws, and the deceleration creep can be observed. At the stage and steady creep stage, there is no third stage of creep (accelerated creep stage). The change of load will make great difference to the change of creep. When the load increases, the instantaneous elastic deformation and the total creep variable of poplar wood will also increase. The microwave treatment strength and the treatment length have different degrees of shadow on the creep property of poplar wood. At the end of the test, the total creep amount of the poplar specimen under the 50% breaking strength level was increased from 25% to 69% at the 30% breaking strength level at the same radiation intensity and different radiation time, while the same radiation time, the total creep total phase of the poplar specimens with different radiation intensity at the level of 50% breaking strength was at the same radiation time. The increase of the total creep rate at the 30% breaking strength level is above 46%. Under the condition of 65s, 15kW microwave treatment, the increase of the total creep of the creep under the 50% breaking strength is even 100.3%. The maximum increase of 68.5%. under different microwave radiation time is obtained by using Origin software to fit the experimental curves of each group under the same load level. The curve determination coefficient R2 can reach more than 0.99. This shows that under this experimental condition, the Burgers rheological model can describe the creep behavior of poplar wood in a short time. But in the process of predicting long term creep, it is found that the mathematical expression of the Burgers rheological model is too linear in the later period and does not agree with the reality. For this, Burgers On the basis of the constitutive relation of the rheological model, introducing the parameter of lambda, it can basically solve the problem that the long-term prediction value of the model is too linear, and the new model can better simulate the creep of poplar wood in the experimental time. The research results of this paper provide the basic data for the study of the rheological property of poplar wood after microwave treatment, and also for the wood. It provides theoretical and experimental evidence for avoiding failure of components due to excessive creep deformation.

【学位授予单位】：中南林业科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU531.1

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