- 學位論文
分離元素法於接觸破壞之刀刃磨耗與雙刀效應之模擬暨耦合有限差分法之數值初探
Distinct Element Approach to the Effect of Wear Flat and Doubled- indenters on Contact Fracture and the Study of Coupled Numerical Method Using Distinct/Finite Different Element
摘要
邇來台灣地區利用機械式開挖所遭遇之地質狀況愈趨困難、複雜且工程尺度規模日增，是故對於隧道機械式開挖之安全性與可行性亟需加強瞭解。故本研究以分離元素法（Distinct Element Method）之二維數值軟體PFC2D為本；進行模擬楔形刃口正向貫入岩材之接觸破壞行為，以數值耦合（PFC2D＆FLAC）之方式，先就單壓及巴西試驗作校驗，再應用於貫切破壞之模擬，並比對貫切行為之理論模式與相關實驗數據，俾能提供隧道工程與地下管道機械開挖之安全性與施工效率探討之佐證。 本研究採用高強度岩類之花崗岩進行數值模擬，求算貫切破壞之力學特徵，藉由改變：（1）楔形刃口之磨耗（Wear Flat）特徵，以模擬切削刀具之耗損現象；（2）雙楔形刃口之影響間距，以模擬雙削刀同時掘挖時之互制效應。本研究並於國內首次使用分離元素法軟體PFC2D與有限差分法軟體FLAC兩二維數值軟體進行貫切破壞之數值耦合運算，利用耦合概念加速分析之運算速度，兩軟體之連結透過力與速度之交換傳遞。先以（1）單壓試驗（Uniaxial Compression Test）；及（2）巴西試驗（Brazilian Test）校驗耦合機制之適確性後，始應用於（3）貫切試驗之解析。 由數值模擬之結果得知，當楔尖磨耗增加時，岩材產生脆性破壞之初裂貫切力隨之增加，而其對應之臨界貫入深度則亦微幅增加，故磨耗效應確會干擾岩材脆性破壞機制之形成；而由雙刀效應之模擬，可知兩貫切刀楔互制影響之破壞裂縫生、衍行為，當雙刀相對刀距 為 時，岩材之破壞特徵有明顯變化，即定義此為臨界相對刀距，並探討其產生脆性破壞所需初裂貫切力之變動範圍及應力重疊區，由此得知適當之刀距安排將有助於減少能量之耗損。 於數值耦合之部分，經由單壓與巴西試驗之模擬，並比對單一數值軟體PFC2D模擬之結果，求算得知單壓強度、張力強度皆相吻合；且具相符之裂縫生、衍趨勢，將此耦合機制運用於貫切試驗，並與理論解進行比對後亦得良好之對應，證實耦合機制之可行性。 此一實驗室尺度之貫切破壞模擬所建立之模組概念，未來應可進一步應用於工程尺度之隧道開挖實例，以期將此構想落實運用於地下開挖之實務。
並列摘要
Recently some cases of underground mechanical excavations encountered the complex structural geological conditions become of difficulty in Taiwan. To obtain both construction security and the feasibility in tunnel engineering, and to understand the contact mechanism in these complex cutting cases, this numerical approach simplifies normal wedge cutter(s) indented into intact rock for simulating the process of fragmentation using a two-dimensional tool of distinct element method, so-named PFC2D. This numerical simulation uses the high strength granite to carry on the indentation fracture process to investigate two key effects: (1) wear flat of indenter due to cutting abrasion, (2) doubled-indenters on the failure characteristics such as maximum indentation force, the critical elastoplastic radius as well as the crack initiation/propagation. To observe global/local failure in macro- and micro-scope respectively, and to speed up numerical approach for some cases, this research also tries to combine PFC2D software with the finite difference method of FLAC code to carry out three issues: (1) uniaxial test; and (2) Brazilian test to assess this linking/coupling numerical algorism, then (3) indentation fracture test in rock by a single-cutting tool. This analytical approach shows that, as increasing the wear flat of indenter, the maximum indentation force needed to develop critical plastic zone increases and its corresponding critical penetration depth also increases slightly, Note that the effect of wear flat will affect rock fracture behavior. In addition, regarding the simulation of the effect of doubled-indenters, result shows that two adjacent indenters may interact each other as reaching the transient/critical relative space between indenters (Sr,c) of 2~3. It dicpicts that a proper spacing arrangement between indenters may enhance a efficient mechanical cutting due to the less required maximum indentation force and energy dissipation. By coupling numerical approach of PFC2D and FLAC to simulate both uniaxial test and Brazilian test, the results are agree with theoretical solutions in terms of elastoplastic interface, and also match to the results performed from PFC2D simulation in terms of the comparison of the uniaxial compressive strength (qu) , tensile strength (σt), and the pattern of crack propagation. It means that the feasibility of this numerical coupling algorism to the indentation problem is verified in this study. To sum up, the numerical model to indentation fracture mechanism was established in the laboratory scale, future works to simulate tunnel excavation in field could be conducted following this conceptual numerical model in the future.