應用電子點紋干涉術探討岩石貫切過程之破壞演化及破裂特徵

Application of Electronic Speckle Pattern Interferometry to Monitor Failure Evolution and Fracture Characteristics under Rock Indentation Process

李昶佑(Chang-Yu Li)

指導教授 ： 陳立憲

國立臺北科技大學/工程學院/土木與防災研究所/碩士(2007年)

https://doi.org/10.6841/NTUT.2007.00070

摘要

晚近台灣採用機械式隧道工程開挖漸加頻繁，有效與失當之案例互見，因此於鑽掘機具與岩石破壞之互制行為顯得相形重要。本研究以正向楔型貫切破壞試驗（normal wedge indentation fracture test）搭配非破壞檢測之電子點紋干涉術（electronic speckle pattern interferometry, ESPI）進行試驗。於無圍壓條件下，以裂縫開口位移（COD）作為油壓伺服系統封閉迴路（close-loop）之回饋信號；或於具圍壓試驗時，改以傳統衝程位移行之，藉由兩者之控制始能穩定加載歷程之峰後（post-peak）行為，俾能繪製完整加載歷程曲線，進而探討單一楔型刀角施力於岩材產生面內（in-plane）延性變形或脆性張裂之影響。實驗係以台灣東部隧道開挖工程常須面對之大理岩作為擬脆性岩樣，藉由改變：(1)楔型刀角以模擬地下開挖機具之刀角幾何因素；(2)水平側向圍壓以模擬側向大地應力之影響而進行系列探討。
由傳統巨觀性之試驗結果可知，當楔型刀角越鈍或圍壓越大時，材料延性或脆性破壞所需之貫切力隨之增大。佐以較新式之微觀電子點紋干涉術所得動態連續之干涉影像，可知材料受楔型刀角貫入時，刀角下緣所產生之塑性區（延性破壞）隨楔型刀角之漸減（150°∼90°）或圍壓增大（0至10MPa）而有逐漸擴大之趨勢，此與文獻關於聲射（AE）之於貫切試驗之結果比對，獲得合理的一致性。由連續干涉影像檢視試驗過程之破壞演化：(a)加載初期之彈性行為乃至延性破壞 (b)間接受張產生初裂之脆性破壞 (c)初裂後續之裂衍行為等階段，皆可進行即時、全域之觀察。
再者，本文亦採用線彈性破壞力學（LEFM）之裂端局部位移公式，直接利用電子點紋干涉術之計測估算材料之破壞韌度（fracture toughness），根據干涉圖計算不同楔型刀角及側向圍壓下，大理岩之破壞韌度求得介於1.01∼1.26 。而貫入岩體之總能量可依不同之發生時機分為三分量：彈性(Ue)、塑性 (Up)及破壞分量(Uf)。利用加載歷程及電子點紋干涉術作初裂時機之判定，可簡易求得脆性初裂前，延性破壞的塑性分量Up約佔當時所施總能量之73%。而於初裂後，除原有Ue 及Up外，增加之脆性破壞分量Uf約僅為塑性分量Up的12%；即各能量分量比值Ue：Up：Uf＝0.33：0.60：0.07。以上二者之破壞參數與能量釋放估計均與文獻有相符之比對，而驗證微觀光學電子點紋干涉術檢測之適確性。

關鍵字

正向楔型貫切破壞試驗 ； 電子點紋干涉術（電子斑點干涉術） ； 裂縫開口位移 ； 塑性區 ； 破壞韌度

並列摘要

Extensive uses of full-faced mechanical boring method in recent years report both success and failure. In order to facilitate more successful application of the method, it is highly important to study the relationship between mechanical indenter and rocks. This study combines normal wedge indentation fracture test with electronic speckle pattern interferometry (ESPI) for nondestructive test. To control the post-peak stability to obtain a complete loading curve, and to examine the influences of single normal wedge indentation on the in-plane brittle tension crack of natural rocks, crack opening displacement (COD) is used to be a close-loop control unconfinement case, and conventional stroke displacement adopted in the presence of confinement case. Marbles which make frequent appearances in tunnel engineering projects in eastern Taiwan are used as the specimen of brittle rocks for the investigation. The angle of wedge indenter is changed to simulate mechanical boring, and various horizontal confinement are conducted to simulate far-field stress.
Traditional macroscopic testing data indicate that the indentation force needed to cause brittle/ductile fracture rises with the increase in the angle of the wedge indenter or the confinement. By observing the moving interferometry images obtained in micron scale by ESPI, the plastic zone (ductile, damage zone) under the wedge indenter expands with decrease in the angle of wedge indenter and increase in the confinement. This result is in fine agreement with the one presented in studies on nondestructive technique of acoustic emission (AE). The moving interferometry images further help to facilitate real-time and full-field observation on fracture evolution in terms of: (a). elastic behavior to ductile fracture during initial loading; (b). brittle fracture of crack initiation under indirect tension; and (c). the crack propagation after crack initiation.
This investigation further uses formula related to linear elastic fracture mode and ESPI to calculate fracture toughness of materials. Under different wedge indenters and lateral confinements, fracture toughness of marbles falls in the range of 1.01~1.26 ( ). The total energy inside rock mass can be divided into three major parts: elastic (Ue), plastic (Up) and fracture energy (Uf). Loading curve and ESPI can be adopted to decide crack initiation time. Before crack initiation, brittle energy Up is about 73% of total energy. After crack initiation, brittle fracture energy Uf is about 12% of plastic energy. Namely, the ratio Ue : Up : Uf = 0.33 : 0.60 : 0.07. Both this energy dissipation ratio and the fracture toughness mentioned earlier are compared to the findings in previous literature, and fine agreement testifies to the validity of using ESPI to investigate fracture evaluation and to calculate fracture parameter under indirect tension in rock.

並列關鍵字

Normal wedge indentation fracture test ； Crack opening displacement ； Electronic speckle pattern interferometry ； Plastic zone ； Fracture toughness

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