發(fā)布時間：2018-05-05 02:45

  本文選題：楊樹木材 + 微波處理　； 參考：《中南林業(yè)科技大學》2017年碩士論文

【摘要】：本文緊密結(jié)合國家自然科學基金項目(楊木高強度微波膨化與重構(gòu)機制研究,31370564)以速生楊樹木材為研究對象,利用微波處理技術(shù)對楊木進行預處理,觀察楊木宏觀和微觀結(jié)構(gòu)的變化。探討了微波處理對楊樹木材常規(guī)力學性能的影響,在此基礎(chǔ)上測試了楊樹木材在不同微波處理條件,不同荷載水平下的蠕變曲線,并以流變學理論為指導,利用Burgers流變模型對實驗曲線進行了擬合,同時討論了模型的改良,論文主要工作和創(chuàng)新性成果如下:(1)簡要介紹了微波處理技術(shù)及電鏡工作原理。從宏觀上來看,當微波輻射強度較低時,可以看到試件表面僅覆蓋了一層水蒸汽;當微波輻射強度較高時,某些試件表面發(fā)生了明顯的開裂現(xiàn)象,試件已經(jīng)被破壞。從微觀上來看,未經(jīng)微波處理的楊木內(nèi)部截面孔洞和孔道壁比較完整光滑。經(jīng)過微波處理的楊木橫、縱截面顯得更粗糙,孔洞邊緣形成的毛糙變多,變細,形成網(wǎng)狀結(jié)構(gòu);部分孔洞破裂擴大和周圍的孔洞貫通形成更大、更不規(guī)則的新孔洞,甚至形成一條貫穿通道。經(jīng)過力學試驗后的楊木孔洞呈現(xiàn)出方向性使得材料的各向異性更趨明顯。(2)不同的微波輻射強度和微波輻射時長對楊樹木材的力學性能均有不同程度的影響。當輻射強度低于5kW和輻射時長少于50s時,其抗彎彈性模量和彎曲強度均有所降低,降低幅值在8%-13%之間。當微波輻射強度加大或輻射時長加長時,其抗彎彈性模量和彎曲強度均有所上升。18kW高功率時彈性模量的增幅達到52.6%,彎曲強度提高近20%。(3)楊樹木材在不同微波處理條件和不同荷載下的蠕變曲線遵循相似的規(guī)律,都可以觀測到減速蠕變階段和穩(wěn)態(tài)蠕變階段,但未出現(xiàn)蠕變第三階段(加速蠕變階段)。荷載的改變會對各組蠕變的改變量造成較大的差異。荷載增大時,楊樹木材瞬時彈性變形和總?cè)渥兞恳矔龃�。微波處理強度和處理時長對楊木蠕變性能均有不同程度的影響。試驗結(jié)束時,同一輻射強度,不同輻射時間的各組楊木試件在50%破斷強度水平下的蠕變總量相比于30%破斷強度水平下的蠕變總量增幅在25%至69%之間;而同一輻射時間,不同輻射強度的各組楊木試件在50%破斷強度水平下的蠕變總量相比于30%破斷強度水平下的蠕變總量增幅均在46%以上,在65s,15kW微波處理工況下,50%破斷強度下的蠕變總量增幅甚至達到100.3%,遠超不同微波輻射時間下的最高增幅68.5%。利用Origin軟件對各組在不同荷載水平下實驗曲線進行擬合,擬合得到的曲線決定系數(shù)R2均可達到0.99以上。這說明在該實驗條件下,Burgers流變模型在短期內(nèi)可以很好的描述楊樹木材的蠕變行為。但在預測長期蠕變的過程中發(fā)現(xiàn)Burgers流變模型數(shù)學表達式在后期變的過于線性,與實際不符。為此,在Burgers流變模型的本構(gòu)關(guān)系式基礎(chǔ)上引入λ參數(shù),可以基本解決模型長期預測值過于線性的問題,且新模型能在實驗時間內(nèi)更好的模擬楊樹木材的蠕變。本文的研究成果為楊樹木材經(jīng)過微波處理后流變性能研究提供了基礎(chǔ)數(shù)據(jù),也為木材設(shè)計中避免由于蠕變變形過大導致構(gòu)件失效等問題提供了理論和實驗依據(jù)。
[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.

【學位授予單位】：中南林業(yè)科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TU531.1

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