擬脆性岩材受力作用於不同應力路徑下，加載雖未達尖峰強度水準，但於材料內部所產生之微裂而至叢聚，可能已有導致後續破壞之先兆，故微裂發展趨勢對於巨觀結構穩定之研究相當重要。準此，本研究以實驗與數值分析兩種方式，探討擬脆性岩材在不同應力路徑下之破壞機理。
在實驗方面，單軸壓縮與巴西試驗選用純水泥漿、C190水泥砂漿、大理岩及蛇紋岩試體；而貫切試驗選用C190水泥砂漿與大理岩試體。試體於加載歷程中(時間特徵)，輔以非破壞聲射檢測技術，量測微觀裂縫之叢聚與分佈，並比對巨觀裂縫之初裂與延伸(空間特徵)。其結果顯示微、巨觀所得趨勢相符；同時，就實驗成果對應於相關理論解析，亦可得到良好之佐證。
在數值分析方面，則以大理岩為例，利用分離元素程式PFC3D模擬不同應力路徑(單軸壓縮與巴西試驗)之試驗過程，並以滿足物理意義之模型校準(model fitting) 。比對數值演算之粒間微裂與實驗過程之微裂聲射，驗證數值分析於微觀研究之適用性，再就叢聚之發生時機、正規化之粒間剪/張微裂增量比值(△S/△T)及破壞模式(failure mode)，進行深入之探討。
經由實驗與數值分析兩者進行破壞機理之分析、比對及驗證，並求整體彈性、塑性與破壞歷程演變之確立，將可建立非破壞聲射檢測技術之相關準則，與提供數值分析選用驗證合理之輸入參數，以作為岩石工程實務之應用。

When quasi-brittle rocks are loaded under different stress paths, fracture development led by the internal microcracks and localization may exist although the loading level has not reached the peak point. Therefore, studies on the correlations between microcrack development and the safety of macro-scale structure become rather important. Both the approaches of experimental and numerical analysis are adopted in this paper to investigate the fracture mechanism for quasi-brittle rocks under different stress paths.

In the experiments, ordinary Portland cement (OPC) paste, C190 cement paste, marble and serpentinite specimens are selected for uniaxial compression and Brazilian tests. As for the indentation test, C190 cement paste and marble specimens are used. Non-destructive acoustic emission (AE) technique is applied in the loading process for specimens (time characteristics) to measure the localization and distribution of microcracks and further on to compare the initial crack and propagation of macrocracks (space characteristics). Experimental outcomes show the trends of micro and macro scales are consistent. Meanwhile, theoretical solutions are proven matching very well with the experimental results.

For the numerical analysis, a discrete element code, PFC3D is used to simulate the testing processes of different stress paths (uniaxial compression and Brazilian tests) for marble specimen by the model fitting which satisfies physics meanings. Microfractures between particle contacts from numerical analyses are compared with AE microcracks in the experiments to verify the suitability of numerical analysis. Numerical analysis can assist more detailed studies of localization timings, normalized shear/tensile microcracks increment ratio (△S/△T) and failure mode.

Based upon the analysis, comparision and verification of fracture mechanism for experiments and numerical analyses and further to ensure the evolutions of the whole elastic, plastic and fracture processes, relevant guidelines regarding to non-destructive AE technique can be established. Moreover, input parameters verified reasonable in the numerical analysis can be provided for the application in the rock engineering practice as well.

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