同步聲-光非破壞檢測於應變率對岩材動-靜力學之研探

Abstract

審視岩石力學與相關工程應用之關聯性時，多因簡化假設而先以擬靜態行為進行研究，惟實際案例如邊坡滑移、落石坍方等往往需要考量到較高應變率乃至是衝擊式之力學行為。關於國內應變率之研究，主要以巨觀尺度進行研探；故本研究藉由透過微觀非破壞檢測將巨-微觀力學行為作一驗證比對，以探求擬脆性岩材於不同應變率之破壞特徵。 本研究以非破壞檢測之聲射技術(Acoustic Emission, AE)進行受載試體產生微震裂源之監測；並同步搭配電子斑紋干涉術(Electronic Speckle Pattern Interferometry, ESPI)量測試體表面之變形場，以探討不同應變率對岩材加載歷程及其巨、微觀破壞機制之研析。實驗設計變數乃以：(1)岩材－人造類岩(水泥砂漿)與天然岩材(木山層砂岩)；(2)以MTS加載系統執行擬靜態區間之應變率10-5∼10-1 s-1；及高應變率102∼250 s-1之分離式霍普金森壓桿動態試驗；並於擬靜態應變率區段搭配聲-光非破壞檢測技術。 本研究內容計可研探：(1)巨觀力學行為－岩材峰前的單壓加載歷程，亦即壓應力-壓應變曲線之尖峰強度、楊氏模數、破壞應變及破壞型態；微觀力學行為－岩材之微觀破壞演化特徵：叢聚、初裂。 由試驗成果得知，於擬靜態行為下，兩種擬脆性材料之單壓強度、楊氏模數與破壞應變皆隨應變率提升而漸增，而試體破壞面亦由剪裂轉成劈裂型態；另於高應變率下，單壓強度與楊氏模數顯現陡增之趨勢，但破壞應變則呈遞減趨勢。微觀非破壞檢測發現，10-5∼10-3 s-1之應變率為合適觀察區段；當應變率由10-5 s-1增至10-3s-1，兩種岩材均顯示其微裂發展之叢聚時機，由加載比LL = 40~67％提前於LL =19~30％發生，而變形不連續之初裂時機更由LL = 83~93％提前至LL =35~56％，亦即微-巨觀破壞特徵隨應變率之增加而有提前發生之趨勢。本研究相關成果，建議可建置工程資料庫俾供不同應變率之工程佐參。

As examining the application of rock mechanics and engineering association, the behavior of quasi-static is used to study because of simplifying assumptions. Except for actual cases, such as sliding slope and falling rock, etc. are often required considering the higher strain rate even the impact of the mechanical behavior. The researches of strain rate in Taiwan are mainly in the macroscopic scale. Therefore, this study compares the mechanical behaviors of macro to the behaviors of micro by using nondestructive techniques in order to seek quasi-brittle rocks at different strain rates of failure features. This study uses AE (Acoustic Emission) and synchronizes ESPI (Electronic Speckle Pattern Interferometry) to locate micro-seismic activities and to measure the deformation of the surfaces of specimens. Several key factors are also considered: rock types – artificial (cement mortar) rocks and natural (Mushan sandstone) rocks, strain rates for quasi-static (10-5 - 10-1 s-1) by MTS loading system and high strain rate (102 - 250 s-1) by SHPB (Split-Hopkinson Pressure Bar). Meanwhile, in conjunction of nondestructive techniques at quasi-static strain rate. This research is about to explore: macroscopic – the loading curve until pre-peak, max. stress, Young’s modulus, failure strain and failure type; Microscopic – localization and initial crack. From the results, the maximum stress, Young’s modulus and failure strain of two kinds of quasi-brittle materials are rising with strain rate at the quasi-static. And the failure types are changed from shear failure to splitting failure. The high strain rate, the max. stress and Young’s modulus are extremely increasing, but the failure strain is decreasing. In this study, nondestructive techniques show that strain rate from 10-5 to 10-3 s-1 is appropriate for observation. When the strain rate increased from 10-5 to 10-3 s-1, the load level of localization also happened earlier from 40-67% to 19-30%, and the load level of initial crack occurred from 83-93% to 35-56%. It means the failure features of microscopic and macroscopic could both take place ahead of schedule with the increasing strain rate. To build a database of different strain rates for engineering to consult is advised.