盧少微, 馮春林, 聶 鵬, 王曉強(qiáng), 熊需海, 馬克明
(1.沈陽航空航天大學(xué)遼寧省通用航空重點實驗室,沈陽110136;2.沈陽航空航天大學(xué)航空航天工程學(xué)部,沈陽110136;3.沈陽航空航天大學(xué)機(jī)電工程學(xué)院,沈陽110136)
聚合物基復(fù)合材料具有強(qiáng)度高、耐腐蝕及結(jié)構(gòu)可設(shè)計性等一系列優(yōu)異性能,廣泛應(yīng)用于航空航天、船舶、汽車等領(lǐng)域。然而其結(jié)構(gòu)易產(chǎn)生裂紋、纖維脫粘或斷裂、分層等多種形式內(nèi)部損傷,這些損傷隱蔽性強(qiáng),損傷類型和程度難以判斷,因此復(fù)合材料的實時檢測已變得越來越意義重大。近年來,國內(nèi)外研究人員開發(fā)了多種用于復(fù)合材料結(jié)構(gòu)損傷周期性連續(xù)檢測的原位結(jié)構(gòu)健康監(jiān)測技術(shù)[1~6],包括金屬導(dǎo)線應(yīng)變傳感器、光纖傳感器、壓電傳感器、聲發(fā)射法、聲-超聲法等,但都沒有得到大規(guī)模的工程應(yīng)用,主要因為在監(jiān)測過程中需要大量布線、引入缺陷、監(jiān)測量程小,數(shù)據(jù)分析復(fù)雜,影響使用。考慮上述原因,開發(fā)一種既不影響原有復(fù)合材料結(jié)構(gòu)完整性,又具備結(jié)構(gòu)健康監(jiān)測能力的傳感器成為結(jié)構(gòu)健康監(jiān)測技術(shù)的關(guān)鍵問題,而碳納米管(CNTs)的出現(xiàn),解決了上述問題。
1991年CNTs被Iijima[7]發(fā)現(xiàn)后,引起大批科研工作者的研究興趣,CNTs主要通過化學(xué)氣相沉積法[8~10]、電弧放電法[11,12]和激光蒸發(fā)法[13,14]獲得。大量的研究工作表明CNTs是目前世界上剛度和強(qiáng)度較大的材料之一[15],其優(yōu)異的力學(xué)性能,比如高剛度與強(qiáng)度、特殊的回彈性、低密度、高長徑比的纖維結(jié)構(gòu),加之高電導(dǎo)與熱導(dǎo)性,使CNTs作為納米尺度的增強(qiáng)體以提高聚合物基復(fù)合材料的電性能成為可能[16~18]。CNTs的尺寸比復(fù)合材料纖維小三個數(shù)量級,其電阻變化可用來監(jiān)測非傳導(dǎo)性聚合物基體的損傷。CNTs具有特別高的電流承載能力[19,20],能夠在低體積含量時在聚合物內(nèi)形成電流傳導(dǎo)網(wǎng)絡(luò),同時由于CNTs相對于增強(qiáng)纖維體積較小,能夠在纖維附近形成電傳導(dǎo)網(wǎng)絡(luò)并滲透到基體層間區(qū)域,這種應(yīng)變傳導(dǎo)網(wǎng)絡(luò)可監(jiān)測基體間的損傷產(chǎn)生和累積[21]。
本工作綜述CNTs在聚合物基復(fù)合材料健康監(jiān)測方面的研究進(jìn)展,同時展望其在聚合物基復(fù)合材料健康監(jiān)測領(lǐng)域的研究前景。
目前飛行器的大部分結(jié)構(gòu)件均由聚合物基復(fù)合材料制作而成,這些結(jié)構(gòu)件的應(yīng)變損傷直接影響到其服役壽命,同時還威脅到飛行器的飛行安全[22,23],故精確監(jiān)測聚合物基結(jié)構(gòu)件的應(yīng)變損傷具有十分重要的意義。近幾年,學(xué)者開始考慮將CNTs作為納米級填充物添加到聚合物基體內(nèi)形成導(dǎo)電網(wǎng)絡(luò),使得絕緣的聚合物基體具有一定的導(dǎo)電性,當(dāng)基體發(fā)生形變時,通過測量電阻變化,即可實現(xiàn)基體的應(yīng)變損傷的檢測[24~30]。
Kuronuma等[31]報道多壁碳納米管(MWCNTs)/聚碳酸酯復(fù)合材料中MWCNTs拉伸應(yīng)變傳感特性的研究結(jié)果。該研究小組對MWCNTs含量為0.8%,1.0%,2.5%,5.0%(質(zhì)量分?jǐn)?shù))的聚碳酸酯基復(fù)合材料進(jìn)行拉伸試驗,同時測量其MWCNTs網(wǎng)絡(luò)的電阻變化,根據(jù)電子隧道效應(yīng)理論,建立分析模型(見圖1),分析微/納尺度下CNTs與CNTs之間的形變狀況,并討論微/納結(jié)構(gòu)形變的發(fā)生對MWCNTs網(wǎng)絡(luò)電阻變化的影響。研究表明建立的模型與實驗結(jié)果有著較好的相關(guān)性,將MWCNTs加入到聚碳酸酯基體內(nèi)形成導(dǎo)電網(wǎng)絡(luò),利用電阻對應(yīng)變的響應(yīng)來監(jiān)測聚合物基體的拉伸損傷是可行的。
圖1 復(fù)合材料中MWCNTs網(wǎng)絡(luò)[31]Fig.1 A network of carbon nanotubes in the composite[31]
Gao等[32,33]將少量CNTs加入纖維增強(qiáng)復(fù)合材料內(nèi)沿樹脂基體形成電傳導(dǎo)網(wǎng)絡(luò),利用CNTs網(wǎng)絡(luò)對累積損傷的電響應(yīng)和聲發(fā)射技術(shù)一起監(jiān)測復(fù)合材料結(jié)構(gòu)的損傷產(chǎn)生和擴(kuò)展,并提出用電阻變化相關(guān)的ΔR/L-ΔRE/L和ΔRD/L等參數(shù)來表征結(jié)構(gòu)損傷階段的方法。同時,其還利用電傳導(dǎo)網(wǎng)絡(luò)的電阻變化來監(jiān)測厚平織玻璃纖維環(huán)氧樹脂基體的沖擊損傷。Costa等[34]把原始CNTs和功能化CNTs分別作為填充物填充到苯乙烯-丁二烯-苯乙烯聚合物中形成復(fù)合材料進(jìn)行拉伸測試(見圖2),研究表明,當(dāng)試樣發(fā)生形變時,其電阻發(fā)生改變,加入原始CNTs的復(fù)合材料樣件的滲流閥值約為1%(質(zhì)量分?jǐn)?shù)),顯示出良好的機(jī)電響應(yīng)特性,響應(yīng)靈敏度約為2~8,而加入功能化CNTs的復(fù)合材料樣件的滲流閥值約為8%(質(zhì)量分?jǐn)?shù)),阻礙其導(dǎo)電性,從而影響應(yīng)變傳感特性。又因苯乙烯-丁二烯-苯乙烯聚合物拉伸應(yīng)變可達(dá)400%,Costa等認(rèn)為加入原始CNTs的復(fù)合材料可作為大應(yīng)變傳感器,用于聚合物基復(fù)合材料的健康監(jiān)測。
圖2 復(fù)合材料的帶有電學(xué)測量的應(yīng)力-應(yīng)變實驗裝置示意圖[34]Fig.2 . Schematic representation of the experimental configuration of the clamps for the stress-strain experiments with simultaneous electrical measurements for electromechanical response evaluation of the composites[34]
研究人員把CNTs混入到聚合物中,利用其導(dǎo)電網(wǎng)絡(luò)對應(yīng)變的電學(xué)響應(yīng)來監(jiān)測基體的拉伸應(yīng)變損傷,傳感系數(shù)在2~45之間[34~37],CNTs除拉伸應(yīng)變傳感特性外,還具有壓縮應(yīng)變傳感特性[38~44]。Ferrreira等[39]在聚偏二氟乙烯中添加不同含量的CNTs形成復(fù)合材料作為壓阻傳感器使用,研究表明在聚偏二氟乙烯中CNTs的滲流閥值在2%(質(zhì)量分?jǐn)?shù))左右,結(jié)構(gòu)形變會引發(fā)聚合物中CNTs導(dǎo)電網(wǎng)絡(luò)強(qiáng)烈的和可逆化的電學(xué)響應(yīng)(見圖3),壓阻傳感系數(shù)最大值為6.2,同時他們還討論溫度對CNTs導(dǎo)電網(wǎng)絡(luò)的影響,在100℃以下CNTs導(dǎo)電網(wǎng)絡(luò)電學(xué)響應(yīng)具有較好的可逆性。Hwang等[43]把CNTs和石墨烯片雜化后添加到聚碳酸酯復(fù)合材料中,實現(xiàn)應(yīng)變傳感靈敏度的可控制備,從而通過監(jiān)測彎曲載荷下的電阻變化來監(jiān)測復(fù)合材料的彎曲變形損傷。Ku-Herrera等[45]用CNTs和乙烯酯制作成復(fù)合材料,利用CNTs網(wǎng)絡(luò)的電阻變化來監(jiān)測復(fù)合材料的在拉伸/壓縮變形中的應(yīng)變損傷。在拉伸載荷下,其CNTs導(dǎo)電網(wǎng)絡(luò)的電阻變化與應(yīng)變呈線性關(guān)系并具有較好的重復(fù)性,而在壓縮載荷下,其電阻變化與應(yīng)變成非線性關(guān)系,當(dāng)電阻發(fā)生永久變化時,則預(yù)示著復(fù)合材料也發(fā)生不可逆的損傷。
圖3 2%CNTs試樣的時間-應(yīng)變-電阻變化曲線(a)和應(yīng)變-電阻變化曲線及擬合曲線(b)[39]Fig.3 Strain applied to a sample with 2%CNTs and the corresponding resistance variation with time(a),and relative change in electrical resistance due tomechanical deformation(b)[39]
許多科研人員致力于探索聚合物基CNTs應(yīng)變傳感特性,取得一定的成果。Kim等[46]將0.5% (質(zhì)量分?jǐn)?shù))的MWCNTs加入到三維編織纖維復(fù)合材料中形成導(dǎo)電網(wǎng)絡(luò),利用復(fù)合材料發(fā)生應(yīng)變時,導(dǎo)電網(wǎng)絡(luò)電阻的變化來檢測基體的微損傷的出現(xiàn)及其累積損傷,但其電阻變化與應(yīng)變的線性度不高。Hu等[47]制作出一種CNTs/聚合物基復(fù)合材料作為應(yīng)變傳感器來檢測復(fù)合材料的應(yīng)變損傷,研究表明基體內(nèi)隧道電阻(率)與應(yīng)變傳感器的靈敏度成正比,而高的隧道電阻(率)意味著CNTs的含量高,會影響CNTs聚合物的成型工藝。Liu和Choi[48]制作CNTs/二甲基硅氧烷彈塑性復(fù)合材料,建立電阻變化與應(yīng)變的關(guān)系,導(dǎo)電網(wǎng)絡(luò)對拉伸大應(yīng)變(>45%)有著顯著的響應(yīng),可以用來監(jiān)測基體的大應(yīng)變損傷。Naghashpour和 Hoa[49]在玻璃纖維環(huán)氧復(fù)合材料中混入CNTs,對復(fù)合材料層壓板在厚度方向上施加壓縮載荷,同時測量其導(dǎo)電網(wǎng)絡(luò)電阻變化,來實現(xiàn)對復(fù)合材料在厚度方向壓縮變形損傷的監(jiān)測。Wang等[50]將不同含量CNTs加入到聚酰亞胺復(fù)合材料中,使復(fù)合材料具有一定的導(dǎo)電性,以利用應(yīng)變發(fā)生過程中電阻的變化情況監(jiān)測復(fù)合材料的應(yīng)變損傷,同時其對0~265℃內(nèi)的溫度變化也有比較線性的電學(xué)響應(yīng)關(guān)系。Ferreira等[51]在偏二氟乙烯內(nèi)加入CNTs形成復(fù)合材料,研究其在壓縮變形過程中CNTs網(wǎng)絡(luò)的電阻變化,建立應(yīng)變-電阻變化關(guān)系曲線,傳感系數(shù)達(dá)3.9,并討論CNTs的滲透閥值對其電學(xué)響應(yīng)的影響。
將CNTs分散到聚合物內(nèi)形成導(dǎo)電網(wǎng)絡(luò),作為應(yīng)變傳感器來監(jiān)測自身的應(yīng)變損傷,為聚合物基復(fù)合材料健康監(jiān)測提供一種新型的監(jiān)測手段,對聚合物基復(fù)合材料的自檢測應(yīng)用具有重要意義。利用CNTs導(dǎo)電網(wǎng)絡(luò)進(jìn)行損傷監(jiān)測面臨的主要挑戰(zhàn)是如何在黏性的樹脂體系內(nèi)分散CNTs的問題,因為CNTs含量較高時具有較強(qiáng)的自團(tuán)聚趨勢。但是當(dāng)樹脂內(nèi)CNTs含量較低(1%)時,雖然大于滲透閾值,但 CNTs的傳導(dǎo)網(wǎng)絡(luò)的電阻率并不高,影響CNTs網(wǎng)絡(luò)的電導(dǎo)性。如果要使混合物擁有良好的CNTs導(dǎo)電性,通常需要在工程樹脂內(nèi)添加3%左右的CNTs,這時樹脂黏度的增加會影響復(fù)合材料的成型工藝[52,53]。
為解決CNTs在黏性樹脂體系內(nèi)難分散問題,國內(nèi)外學(xué)者開始考慮用其他方法在復(fù)合材料體系內(nèi)添加CNTs電傳導(dǎo)網(wǎng)絡(luò)。其中,將CNTs涂層涂覆在纖維表面,嵌入到復(fù)合材料體系中形成導(dǎo)電網(wǎng)絡(luò)是一種常用的方式[54,55]。
Fan等[56]研究出一種CNTs-熱塑性聚氨基甲酸酯(TPU)涂層纖維,將CNTs經(jīng)過超聲波處理嵌入或滲入到熱塑性聚氨基甲酸酯(TPU)多纖絲的表面,得到導(dǎo)電、可彎曲的CNTs-TPU纖維(見圖4),當(dāng)復(fù)合纖維應(yīng)變增加時,導(dǎo)電網(wǎng)絡(luò)的電阻會增加,反之亦然。實驗還發(fā)現(xiàn):CNTs含量為10%(質(zhì)量分?jǐn)?shù))時,電導(dǎo)率可穩(wěn)定在100s/m,CNTs-TPU纖維電阻會隨應(yīng)變增加而增加,循環(huán)拉伸應(yīng)變在400%以前,電阻變化可逆。Fan等認(rèn)為這種敏感性來源于穩(wěn)定固定在多纖絲表面的CNTs網(wǎng)絡(luò),其不同于其他彈性體粒子填充物,CNTs網(wǎng)絡(luò)在發(fā)生拉伸應(yīng)變高達(dá)1000%時還未完全喪失導(dǎo)電性,保證其在較大應(yīng)變范圍內(nèi)的傳感特性。Rausch等[57]開發(fā)出一種CNTs涂層玻璃纖維紗,然后將其埋入聚丙烯基體內(nèi)制成傳感器,CNTs在玻璃纖維紗表面形成電導(dǎo)網(wǎng)絡(luò),通過對比界面破壞、纖維紗斷裂與電阻變化之間的關(guān)系就可以實現(xiàn)對玻璃纖維增強(qiáng)復(fù)合材料的健康監(jiān)測。Sebastian等[58]用CNTs覆蓋于玻璃纖維上作為應(yīng)變傳感器,與聚合物基復(fù)合材料一體成型,用于復(fù)合材料大面積結(jié)構(gòu)和傳統(tǒng)傳感器難以測量的位置的應(yīng)變損傷監(jiān)測,取得與傳統(tǒng)應(yīng)變傳感器類似的監(jiān)測效果,在健康監(jiān)測領(lǐng)域有著較好的應(yīng)用前景。Zhuang等[59]報道將CNTs涂在黃麻纖維表面,并加入環(huán)氧樹脂制成復(fù)合材料,研究其自身對溫度、濕度和應(yīng)力/應(yīng)變的電學(xué)響應(yīng),建立相應(yīng)的關(guān)系曲線,利用其電阻變化可以實現(xiàn)對復(fù)合材料的應(yīng)變損傷監(jiān)測。
圖4 CNTs-TPU纖維的電鏡照片[56]Fig.4 Images of the CNTs-TPU fibers[56] (a)surfacemorphology of the CNTs-TPU fibers with 4.3%(mass fraction) CNT loading(Up-right insert shows themagnified image of the same sample.);(b)cross-sectionalmorphologies of CNTs-TPU fibers with 2.3%(mass fraction)CNT loading;(c)cross-sectionalmorphologies of CNTs-TPU fibers with 10%(mass fraction)CNT loading
除將CNTs涂層涂覆在纖維表面方式之外,不少學(xué)者將CNTs制作成碳納米線之后,加入到聚合物基體內(nèi)形成導(dǎo)電網(wǎng)絡(luò),來實現(xiàn)其應(yīng)變損傷監(jiān)測[60,61]。Alexopoulos等[62,63]首次提出在玻璃纖維增強(qiáng)復(fù)合材料中埋入CNTs纖維來進(jìn)行絕緣復(fù)合材料的結(jié)構(gòu)健康監(jiān)測,電阻對拉伸變形和壓縮變形表現(xiàn)出較好的響應(yīng);而后,采用聚乙烯醇-碳納米管(PVA-CNTs)纖維埋入玻璃纖維增強(qiáng)的塑料復(fù)合材料監(jiān)測復(fù)合材料的損傷,建立PVA-CNTs纖維的電阻變化與表現(xiàn)復(fù)合材料損傷的已知參數(shù)之間的函數(shù)關(guān)系曲線,但其關(guān)系隨加載次數(shù)的增加而改變。Abot等[64,65]首次將CNTs紡成碳納米線(見圖5)并埋入層壓復(fù)合材料中作為應(yīng)變傳感器監(jiān)測復(fù)合材料的應(yīng)變損傷,特別是復(fù)合材料的分層損傷,這種自感知復(fù)合材料對損傷十分敏感,有望實現(xiàn)層壓復(fù)合材料結(jié)構(gòu)損傷的實時監(jiān)測;而后,又對單獨的碳納米線進(jìn)行施加壓縮應(yīng)變,測量其電學(xué)響應(yīng),建立了應(yīng)變-電阻變化曲線,曲線呈拋物線狀,說明碳納米線可以作為壓阻傳感材料使用。
圖5 碳納米線的電鏡圖片[64]Fig.5 Image of the carbon nanotube yarn[64] (a)CNT being pulled and twisted from a CNT forest; (b)a CNT thread;(c)two strands twisted simultaneously to form a yarn;(d)a CNT ribbon
如今,用CNTs涂層涂覆在纖維表面或制成碳納米線埋入聚合物內(nèi)形成導(dǎo)電網(wǎng)絡(luò),利用其對應(yīng)變的電學(xué)響應(yīng)來監(jiān)測復(fù)合材料的健康狀況,成為復(fù)合材料健康監(jiān)測的重要方法。將CNTs涂層纖維、碳納米線埋入聚合物基復(fù)合材料結(jié)構(gòu)內(nèi),形成CNTs傳感網(wǎng)絡(luò),提高了CNTs含量,同時保持了原有結(jié)構(gòu)的完整性,然而上述材料與本體結(jié)構(gòu)間在大變形時存在協(xié)同變形問題,影響監(jiān)測精度,同時上述方法較難實現(xiàn)復(fù)合材料的全結(jié)構(gòu)健康監(jiān)測。
為解決CNTs涂層及碳納米線的協(xié)同變形和全結(jié)構(gòu)監(jiān)測等問題,國內(nèi)外學(xué)者提出碳納米紙用作傳感器以監(jiān)測復(fù)合材料的健康狀況的思路[66,67]。碳納米紙是依靠CNTs與CNTs之間的范德華力相互交錯搭接而成的三維網(wǎng)狀互聯(lián)結(jié)構(gòu)薄膜。
Lee等[66]采用SWCNTs薄膜制成的高精度應(yīng)變傳感器(見圖6),在0%~400%應(yīng)變范圍內(nèi)具有非常高的線性特征,其靈敏度系數(shù)高出傳統(tǒng)金屬箔應(yīng)變傳感器約30倍,可以用于聚合物基復(fù)合材料的健康監(jiān)測。Luo和Liu[67]制備一種單壁碳納米管(SWCNTs)薄膜作為壓阻傳感器,其傳感系數(shù)為5左右,研究發(fā)現(xiàn)其傳感系數(shù)與薄膜的厚度及其SWCNTs的長徑比有關(guān),并得出傳感系數(shù)和SWCNTs束的已占體積成反比關(guān)系。Rein等[68]利用真空吸濾法制備碳納米紙,并封裝在環(huán)氧樹脂基體作為應(yīng)變傳感器使用的相關(guān)研究,研究表明碳納米紙導(dǎo)電網(wǎng)絡(luò)對應(yīng)變的電學(xué)響應(yīng)十分敏感,單壁碳納米紙與脆性材料復(fù)合時表現(xiàn)出較高的應(yīng)變傳感靈敏度;應(yīng)變較低時,多壁碳納米紙和單壁碳納米紙電阻變化均具有較好的重復(fù)性和可逆性;在0%~30%應(yīng)變范圍內(nèi),相比于單壁碳納米紙,多壁碳納米紙電學(xué)響應(yīng)更靈敏。Li等[69]制作兩種高度敏感的對齊CNTs網(wǎng)絡(luò)應(yīng)變傳感器,一是通過氣溶膠將電極噴射印刷在CNTs網(wǎng)絡(luò)上,二是將電極噴射在聚酰亞胺基質(zhì)上,應(yīng)變變化時,CNTs網(wǎng)絡(luò)電阻也會變化,兩種類型傳感器的傳感系數(shù)分別為20和40,傳感器的高性能和靈活性特征使其在聚合物基復(fù)合材料健康監(jiān)測方面具有較大的應(yīng)用前景。
圖6 碳納米紙應(yīng)變傳感器[66]Fig.6 CNT paper strain gauge[66]
Karimov等[70]利用壓片工藝將MWCNTs成型在彈性聚合物梁上,在壓縮變形的同時測量CNTs片層的電阻變化,得到電阻-應(yīng)變曲線,傳感系數(shù)在50~80范圍內(nèi),可以監(jiān)測彈性聚合物梁的壓縮變形損傷。Su等[71]利用化學(xué)氣相沉淀法將SWCNTs和MWCNTs共同生長在懸臂梁上(見圖7),測量CNTs層的電阻變化,監(jiān)測懸臂梁的彎曲應(yīng)變損傷,識別應(yīng)變精度達(dá)0.00099%,最大壓阻傳感系數(shù)為744,對彎曲變形有著較高的敏感度。Li等[72]采用化學(xué)氣相沉積法在SiC微片上合成垂直定向排列的CNTs層作為應(yīng)變傳感網(wǎng)絡(luò),研究表明在復(fù)合材料彈性形變階段,導(dǎo)電網(wǎng)絡(luò)電阻隨應(yīng)變單調(diào)增加,而在塑性形變區(qū)域電阻開始下降。Li等認(rèn)為可以利用其電阻變化特征來識別SiC-CNTs復(fù)合材料的彈性及塑性變形。除直接測量碳納米紙導(dǎo)電網(wǎng)絡(luò)的電阻變化來進(jìn)行形變監(jiān)測,研究人員還開發(fā)出一種無接觸應(yīng)變傳感器用于聚合物基復(fù)合材料的健康監(jiān)測。Qin等[73]應(yīng)用微拉曼光譜法使碳納米紙作為無接觸應(yīng)變傳感器,通過定量評估CNTs薄膜獨立區(qū)域?qū)φw拉曼光譜的影響,建立碳納米紙的應(yīng)變傳感模型,以此來監(jiān)測平面部件在微尺度下的應(yīng)變情況。
關(guān)于碳納米紙在聚合物基復(fù)合材料健康監(jiān)測方面的應(yīng)用,盧少微項目組也進(jìn)行了相關(guān)的研究,設(shè)計出一種基于碳納米紙的應(yīng)變傳感器[74,75],可通過測量與復(fù)合材料一體固化成型的碳納米紙傳感器電阻變化來監(jiān)測復(fù)合材料在靜動態(tài)拉伸狀況下的變形損傷。其運用研體研磨、磁力攪拌、超聲分散、高速離心法等機(jī)械融合法將CNTs和表面分散劑的混合物(如曲拉通TX-100)制備成CNTs的單分散水溶液后,將其倒入真空吸濾裝置的容器抽濾成膜,高溫固化后剝離濾膜得到碳納米紙,埋入復(fù)合材料內(nèi)部特定位置,按復(fù)合材料固化工藝成型,制備出碳納米紙應(yīng)變傳感器,來監(jiān)測聚合物基復(fù)合材料的健康狀況。研究表明發(fā)生拉伸形變時,碳納米紙傳感器對應(yīng)變具有良好的電學(xué)響應(yīng),靈敏度系數(shù)分別為10.21(0~39000με)和524.79(39000~55000με),完全可以滿足復(fù)合材料結(jié)構(gòu)健康監(jiān)測需要。碳納米紙使復(fù)合材料具備結(jié)構(gòu)自健康監(jiān)測功能,可以用于結(jié)構(gòu)的應(yīng)變損傷監(jiān)測。
圖7 二維應(yīng)變傳感器插圖[71]Fig.7 Illustration of the two-dimensional strain sensors[71] (a)top-view;(b)sensing element;(c)sensing element design 1(short cantilever beam);(d)sensing element2(long cantilever beam)
以上介紹了CNTs在聚合物基復(fù)合材料健康監(jiān)測中的研究進(jìn)展,目前主要利用CNTs微觀導(dǎo)電網(wǎng)絡(luò)對宏觀形變的優(yōu)異電學(xué)響應(yīng)特性來實現(xiàn)對聚合物基復(fù)合材料的健康監(jiān)測,但仍處于科研初期。從CNTs到CNTs涂層纖維、碳納米線,再到碳納米紙,研究人員致力于將CNTs推向工程化應(yīng)用,未來CNTs聚合物基復(fù)合材料的工藝兼容性和工程實用性將得到更好的解決。將CNTs與其他先進(jìn)技術(shù)(如微機(jī)電系統(tǒng)(MEMS)技術(shù),無線通訊技術(shù)和集成電路設(shè)計等)結(jié)合起來,有可能帶來其他產(chǎn)業(yè)的革命性變化。隨著難題的不斷攻克,CNTs將在聚合物基復(fù)合材料健康監(jiān)測領(lǐng)域得以更廣泛的應(yīng)用。
[1]LEUNG C K Y,YANG Z L,XU Y,et al.Delamination detection in laminate composites with an embedded fiber optical interferometric sensor[J].Sensors and Actuators A:Physical,2005,119(2):336-344.
[2]XU D Y,CHENGX,HUANGSF,etal.Identifying technology for structural damage based on the impedance analysis of piezoelectric sensor[J].Construction and Building Materials,2010,24(12):2522-2527.
[3]RABIEI M,MODARRES M.Quantitative methods for structural healthmanagementusing in situ acoustic emission monitoring[J].International Journal of Fatigue,2013,49:81-89.
[4]HAMDISE,DUFF A L,SIMON L,etal.Acoustic emission pattern recognition approach based on Hilbert-Huang transform for structural health monitoring in polymer-compositematerials[J].Applied Acoustics,2013,74(5): 746-757.
[5]OLIVEIRA R D,MARQUES A T.Health monitoring of FRP using acoustic emission and artificial neural networks[J].Computers&Structures,2008,86(3/5):367-373.
[6]RATHOD V T,MAHAPATRA D R.Ultrasonic lamb wave based monitoring of corrosion type of damage in plate using a circular array of piezoelectric transducers[J].NDT&E International,2011,44(7):628-636.
[7]IIJIMA SH.Microtubules of graphitic carbon[J].Nature,1991,354:56-58.
[8]JOURDAIN V,BICHARA C.Current understanding of the growth of carbon nanotubes in catalytic chemical vapour deposition[J].Carbon,2013,58:2-39.
[9]MEYSAMISS,KOóS A A,DILLON F,et al.Aerosolassisted chemical vapour deposition synthesis of multi-wall carbon nanotubes II:an analytical study[J].Carbon,2013,58:159-169.
[10]CASTRO C,PINAULTM,PORTERATD,etal.The role of hydrogen in the aerosol-assisted chemical vapor deposition process in producing thin and densely packed vertically aligned carbon nanotubes[J].Carbon,2013,61:585-594.
[11]ZHANGY L,HOUPX,LIUC,etal.De-bundling of singlewall carbon nanotubes induced by an electric field during arc discharge synthesis[J].Carbon,2014,74:370-373.
[12]HUANG L P,WU B,CHEN JY,et al.Synthesis of single-walled carbon nanotubes by an arc-dischargemethod using selenium as a promoter[J].Carbon,2011,49(14): 4792-4800.
[13]KOKAIF,NOZAKI I,OKADA T,et al.Efficient growth ofmulti-walled carbon nanotubes by continuous-wave laser vaporization of graphite containing B4C[J].Carbon,2011,49(4):1173-1181.
[14]SCHAUERMAN C M,ALVARENGA J,LANDI B J,et al.Impact of nanometal catalysts on the laser vaporization synthesis of single wall carbon nanotubes[J].Carbon,2009,47(10):2431-2435.
[15]SALVETAT-DELMOTTE J P,RUBIO A.Mechanical properties of carbon nanotubes:a fiber digest for beginners[J].Carbon,2002,40(10):1729-1734.
[16]COLEMAN JN,KHAN U,BLAUW J,et al.Small but strong:a review of the mechanical properties of carbon nanotube-polymer composites[J].Carbon,2006,44(9): 1624-1652.
[17]TREACY M M J,EBBESEN T W.Exceptionally high Young'smodulus observed for individual carbon nanotubes[J].Nature,1996,381(6584):678-680.
[18]YU M F,LOURIE O,DYER M J,et al.Strength and breaking mechanism ofmulti-walled carbon nanotubes under tensile load[J].Science,2000,287(5453):637-640.
[19]THESSA,LEER,NIKOLAEV P,etal.Crystalline ropes of metallic carbon nanotubes[J].Science,1996,273 (5274):483-487.
[20]POHLS JH,JOHNSONM B,WHITEM A,etal.Physical properties of carbon nanotube sheets drawn from nanotube arrays[J].Carbon,2012,50(11):4175-4183.
[21]SRIVASTAVA R K,VEMURU V SM,ZENG Y,et al. The strain sensing and thermal-mechanical behavior of flexible multi-walled carbon nanotube/polystyrene composite films[J].Carbon,2011,49(12):3928-3936.
[22]POLIMENO U,MEO M.Detecting barely visible impact damage detection on aircraft composites structures[J]. Composite Structures,2009,91(4):398-402.
[23]DIAMANTI K,SOUTIS C.Structural health monitoring techniques for aircraft composite structures[J].Progress in Aerospace Sciences,2010,46(8):342-352.
[24]SHINDO Y,KURONUMA Y,TAKEDA T,et al.Electrical resistance change and crack behavior in carbon nanotube/polymer composites under tensile loading[J].Composites Part B:Engineering,2012,43(1):39-43.
[25]NOFAR M,HOA SV,PUGH M D.Failure detection and monitoring in polymermatrix composites subjected to static and dynamic loads using carbon nanotube networks[J]. Composites Science and Technology,2009,69(10):1599 -1606.
[26]LIC Y,CHOU TW.Modeling of damage sensing in fiber composites using carbon nanotube networks[J].Composites Science and Technology,2008,68(15/16):3373-3379.
[27]ZHAO JH,DAI K,LIU C G,et al.A comparison between strain sensing behaviors of carbon black/polypropylene and carbon nanotubes/polypropylene electrically conductive composites[J].Composites Part A:Applied Science and Manufacturing,2013,48:129-136.
[28]OLIVA-AVILéSA I,AVILéSF,SOSA V.Electrical and piezoresistive properties of multi-walled carbon nanotube/ polymer composite films aligned by an electric field[J]. Carbon,2001,49(9):2989-2997.
[29]KANG I,KHALEQUE M A,YOO Y,et al.Preparation and properties of ethylene propylene diene rubber/multi walled carbon nanotube composites for strain sensitivematerials[J].Composites Part A:Applied Science and Manufacturing,2011,42(6):623-630.
[30]KANGM H,CHOIJH,KWEON JH.Fatigue life evaluation and crack detection of the adhesive joint with carbon nanotubes[J].Composite Structures,2014,108:417-422.
[31]KURONUMA Y,TAKEDA T,SHINDO Y,et al.Electrical resistance-based strain sensing in carbon nanotube/polymer composites under tension:analytical modeling and experiments[J].Composites Science and Technology,2012,72(14):1678-1682.
[32]GAO LM,THOSTENSON E T,ZHANG ZG,etal.Coupled carbon nanotube network and acoustic emission monitoring for sensing of damage development in composites[J].Carbon,2009,47(5):1381-1388.
[33]GAO LM,CHOU TW,THOSTENSON E T,et al.In situ sensing of impact damage in epoxy/glass fiber composites using percolating carbon nanotube networks[J].Carbon,2011,49(10):3382-3385.
[34]COSTA P,SILVA J,ANSóN-CASAOSA,etal.Effectof carbon nanotube type and functionalization on the electrical,thermal,mechanical and electromechanical properties of carbon nanotube/styrene-butadiene-styrene composites for large strain sensor applications[J].Composites Part B: Engineering,2014,61:136-146.
[35]KARIMOV K S,CHANIM T S,KHALID F A,et al. Strain sensors based on carbon nanotubes-cuprous oxide composite[J].Physica E:Low-Dimensional Systems and Nanostructures,2012,44(4):778-781.
[36]PHAM G T,PARK Y B,LIANG Z Y,et al.Processing and modeling of conductive thermoplastic/carbon nanotube films for strain sensing[J].Composites Part B:Engineering,2008,39(1):209-216.
[37]NJUGUNA M K,YAN C,HU N,et al.Sandwiched carbon nanotube film as strain sensor[J].Composites Part B: Engineering,2012,43(6):2711-2717.
[38]VEGA A D L,KINLOCH IA,YOUNG R J,etal.Simultaneous global and local strain sensing in SWCNT-epoxy composites by Raman and impedance spectroscopy[J]. Composites Science and Technology,2011,71(2):160-166.
[39]FERRREIRA A,ROCHA JG,ANSóN-CASAOS A,et al.Electromechanical performance of poly(vinylidene flu-oride)/carbon nanotube composites for strain sensor applications[J].Sensors and Actuators A:Physical,2012,178:10-16.
[40]ZHANG R,DENG H,VALENCA R,etal.Strain sensing behaviour of elastomeric composite films containing carbon nanotubes under cyclic loading[J].Composites Science and Technology,2013,74:1-5.
[41]WANG L H,XU CG,LIY L.Piezoresistive response to changes in contributive tunneling film network of carbon nanotube/silicone rubber composite under multi-load/unload[J].Sensors and Actuators A:Physical,2013,189: 45-54.
[42]OLIVA-AVILéSA I,AVILéSF,SEIDELG D,etal.On the contribution of carbon nanotube deformation to piezoresistivity of carbon nanotube/polymer composites[J].Composites Part B:Engineering,2013,47:200-206.
[43]HWANG SH,PARK HW,PARK Y B,etal.Electromechanical strain sensing using polycarbonate-impregnated carbon nanotube-graphene nanoplatelet hybrid composite sheets[J].Composites Science and Technology,2013,89:1-9.
[44]LIM A S,AN Q,CHOU TW,et al.Mechanical and electrical response of carbon nanotube-based fabric composites to Hopkinson bar loading[J].Composites Science and Technology,2011,71(5):616-621.
[45]KU-HERRERA J J,AVILéS F.Cyclic tension and compression piezoresistivity of carbon nanotube/vinyl ester composites in the elastic and plastic regimes[J].Carbon,2012,50(7):2592-2598.
[46]KIM K J,YUW R,LEE JS,et al.Damage characterization of3D braided composites using carbon nanotube-based in situ sensing[J].Composites Part A:Applied Science and Manufacturing,2010,41(10):1531-1537.
[47]HU N,KARUBE Y,ARAIM,etal.Investigation on sensitivity of a polymer/carbon nanotube composite strain sensor[J].Carbon,2010,48(3):680-687.
[48]LIU C X,CHOI JW.Analyzing resistance response of embedded PDMS and carbon nanotubes composite under tensile strain[J].Microelectronic Engineering,2014,117:1-7.
[49]NAGHASHPOUR A,HOA S V.In situ monitoring of through-thickness strain in glass fiber/epoxy composite laminates using carbon nanotube sensors[J].Composites Science and Technology,2013,78:41-47.
[50]WANG Y Z,WANG A X,WANG Y,et al.Fabrication and characterization of carbon nanotube-polyimide composite based high temperature flexible thin film piezoresistive strain sensor[J].Sensors and Actuators A:Physical,2013,199:265-271.
[51]FERREIRA A,MARTINEZM T,ANSóN-CASAOSA,et al.Relationship between electromechanical response and percolation threshold in carbon nanotube/poly(vinylidene fluoride)composites[J].Carbon,2013,61:568-576.
[52]CHEN H Y,JACOBSO,WUW,et al.Effect of dispersion method on tribological properties of carbon nanotube reinforced epoxy resin composites[J].Polymer Testing,2007,26(3):351-360.
[53]SANDLER JKW,KIRK JE,KINLOCH IA,et al.Ultra-low electrical percolation threshold in carbon-nanotubeepoxy composites[J].Polymer,2003,44(19):5893-5899.
[54]ZHANG R,DENG H,VALENCA R,etal.Carbon nanotube polymer coatings for textile yarns with good strain sensing capability[J].Sensors and Actuators A:Physical,2012,179:83-91.
[55]LIU L,MA P C,XU M,et al.Strain-sensitive Raman spectroscopy and electrical resistance of carbon nanotubecoated glass fibre sensors[J].Composites Science and Technology,2012,72(13):1548-1555.
[56]FAN QQ,QIN ZY,GAO SL,etal.The use of a carbon nanotube layer on a polyurethanemultifilamentsubstrate for monitoring strains as large as 400%[J].Carbon,2012,50(11):4085-4092.
[57]RAUSCH J,M?DER E.Health monitoring in continuous glass fibre reinforced thermoplastics:tailored sensitivity and cyclic loading of CNT-based interphase sensors[J]. Composites Science and Technology,2010,70(13):2023 -2030.
[58]SEBASTIAN J,SCHEHL N,BOUCHARD M,et al. Health monitoring of structural composites with embedded carbon nanotube coated glass fiber sensors[J].Carbon,2014,66:191-200.
[59]ZHUANG R C,DOAN T T L,LIU JW,et al.Multifunctional multi-walled carbon nanotube-jute fibres and composites[J].Carbon,2011,49(8):2683-2692.
[60]CRAVANZOLA S,HAZNEDAR G,SCARANO D,et al. Carbon-based piezoresistive polymer composites:structure and electrical properties[J].Carbon,2013,62:270-277.
[61]MISAK H E,ASMATULU R,SABELKIN V,et al.Tension-tension fatigue behavior of carbon nanotube wires[J]. Carbon,2013,52:225-231.
[62]ALEXOPOULOSN D,BARTHOLOME C,POULIN P,et al.Structural health monitoring of glass fiber reinforced composites using embedded carbon nanotube(CNT)fibers[J].Composites Science and Technology,2010,70(2): 260-271.
[63]ALEXOPOULOSN D,BARTHOLOME C,POULIN P,et al.Damage detection of glass fiber reinforced composites using embedded PVA-carbon nanotube(CNT)fibers[J]. Composites Science and Technology,2010,70(12):1733 -1741.
[64]ABOT JL,SONG Y,VATSAVAYA M S,et al.Delamination detection with carbon nanotube thread in self-sensing compositematerials[J].Composites Science and Technology,2010,70(7):1113-1119.
[65]ABOT JL,ALOSH T,BELAY K.Strain dependence ofelectrical resistance in carbon nanotube yarns[J].Carbon,2014,70:95-102.
[66]LEE D,HONG H P,LEE M J,et al.A prototype high sensitivity load cell using single walled carbon nanotube strain gauges[J].Sensors and Actuators A:Physical,2012,180:120-126.
[67]LUO S,LIU T.Structure-property-processing relationships of single-wall carbon nanotube thin film piezoresistive sensors[J].Carbon,2013,59:315-324.
[68]REIN M D,BREUER O,WAGNER H D.Sensors and sensitivity:Carbon nanotube buckypaper films as strain sensing devices[J].Composites Science and Technology,2011,71(3):373-381.
[69]LI S,PARK JG,WANG S K,et al.Working mechanisms of strain sensors utilizing aligned carbon nanotube network and aerosol jet printed electrodes[J].Carbon,2014,73:303-309.
[70]KARIMOV K S,KHALID F A,CHANIM T S.Carbon nanotubes based strain sensors[J].Measurement,2012,45(5):918-921.
[71]SU C C,LIU T,CHANG N K,et al.Two dimensional carbon nanotube based strain sensor[J].Sensors and Actuators A:Physical,2012,176:124-129.
[72]LIW K,YUAN J K,DICHIARA A,et al.The use of vertically aligned carbon nanotubes grown on SiC for in situ sensing of elastic and plastic deformation in electrically percolative epoxy composites[J].Carbon,2012,50 (11):4298-4301.
[73]QIUW,LIQ,LEIZ K,et al.The use of a carbon nanotube sensor formeasuring strain by micro-Raman spectroscopy[J].Carbon,2013,53:161-168.
[74]盧少微.一種基于碳納米管三維網(wǎng)絡(luò)薄膜的應(yīng)變傳感器制備方法:中國,201210436811.7[P].2012-11-06. (LU SW.A preparationmethod of the strain sensor based on three dimensional network carbon nanotubes film:China,201210436811.7[P].2012-11-06.)
[75]盧少微,馮春林,聶鵬,等.噴射吸濾成型法制備碳納米紙及其應(yīng)變/溫度傳感特性研究[J].航空學(xué)報,2014. doi:10.7527/S1000-6893.2014.03071. (LU SW,F(xiàn)ENG C L,NIE P,et al.Fabrication ofmultiwalled carbon nanotube buckypaper by spray-vacuum filtrationmethod and characterization of its strain and temperature sensing properties[J].Chinese Journal of Aeronautics,2014.doi:10.7527/S1000-6893.2014.03071.)