人造類岩在不同應變率條件下之宏觀力學特性與微觀力學機制探討

Abstract

綜合前人對於岩石材料在擬靜態及中應變率條件下的試驗，發現擬靜態條件下岩材破裂面多呈現傾斜的剪力破壞且破壞產狀為大塊狀，而中應變率加載下岩材則呈現粉碎性的破壞，兩者破壞模式有明顯的差異。而岩石的力學特性具應變率效應，主要反映在強度隨應變率的增加而有提升的趨勢，且增加的幅度又與岩性有關；目前已有研究透過SHPB單軸壓縮試驗前後的薄片觀察指出了不同應變率條件下，岩石存在沿晶與穿晶兩種微觀力學機制，但與宏觀力學特性的關係仍有待進一步的探討；為瞭解不同應變率下的破壞模式是否與岩石微組構有關，本研究嘗試以人造類岩，針對基質與顆粒不同含量(顆粒含量40%與60%)的組構型態，探討其在不同的應變率條件下，宏觀力學特性的變化與微觀破壞機制的差異。 本研究分別以石膏及人造岩石球作為基質與顆粒模擬材料，製作二種不同顆粒體積含量的人造岩材，進行不同應變率範圍的探討，單軸壓縮試驗分別採用MTS 810材料試驗機及SHPB試驗裝置；中應變率條件下的試體破裂面發展，將透過高速攝影機觀察；而為能釐清人造岩材經單軸壓縮試驗後發生穿晶破壞的顆粒含量，透過蒐集已破壞的試體進行篩分析篩出破壞的顆粒，計算穿晶破壞百分比。 結合以上試驗分析結果顯示：(1)相同顆粒體積含量下的試體其單壓強度會直接受到基質強弱的影響。(2)顆粒體積含量40%試體力學行為會受到基質材料特性的影響較大。(3)在中應變率加載條件下穿晶破壞會明顯對材料強度有影響，但基質含量少其穿晶破壞帶來的效應則相對較小。(4)當應變率超過102sec-1時開始產生穿晶破壞，且單壓強度此時會有劇烈的變化。

The influence of strain rate on mechanical behavior of rock is significant. The strain rate affects not only the strength of rock but also the failure modes. To understand the relationship of failure modes under different strain rates and micro-structure of rock, this study adopted rock-like material with different grain contents and performed a series of compression tests at different strain rates (static tests and spilt-Hopkinson pressure bar tests). The experimental results indicate that (1) The strength of matrix plays an important role on the strength of specimens with the same grain content. (2) For the specimens of 40% grain content, most failure modes are split failure, but for the specimens of 60% grain content, the shear failure occurs at low strain rate and the split failure could be observed at high strain rate. (3) When the trans-granular fracture percentage at high strain rate increases, the strength of specimen would increase.