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論文中文名稱:分離元素法於擬脆性岩材微觀破裂機制之初探 [以論文名稱查詢館藏系統]
論文英文名稱:Distinct Element Approach on Mesoscopic Fracture Mechanism in Quasi-brittle Rock [以論文名稱查詢館藏系統]
院校名稱:臺北科技大學
學院名稱:工程學院
系所名稱:土木與防災研究所
中文姓名:張家銓
英文姓名:Chia-Chuan Chang
研究生學號:93428027
學位類別:碩士
語文別:中文
口試日期:2007-01-29
論文頁數:85
指導教授中文名:陳立憲
口試委員中文名:陳堯中;倪至寬;彭嚴儒
中文關鍵詞:分離元素法擬脆性微裂叢聚正/切向勁度比粒間剪/張微裂增量比加載比
英文關鍵詞:distinct element methodquasi-brittlemicro-cracklocalizationnormal/shear stiffness ratioshear/tensile cracks increment ratioloading level
論文中文摘要:土木結構物受不同應力場,引致受力材料雖未達尖峰荷載水準但卻於內部產生微裂之叢聚,可能造成往後突然失穩而脆性破壞之情事,因此微觀尺度之裂縫監測對於整體結構穩定行為之研究日趨重要。
本研究以分離元素法(Distinct Element Method)之三維數值軟體PFC3D模擬圓形顆粒元素間之微觀非連體力學行為,嘗試建立顆粒微觀參數與整體材料巨觀參數相互關聯性之敏感分析。再以三軸試驗(含單壓)及巴西試驗為例,作為微、巨觀參數之核驗;進而探討擬脆性岩材受到剪力或拉力等不同應力路徑之微觀行為。模擬受載過程中,輒以顆粒元素間產生微裂之破壞型態,與聲射實驗文獻之結果作定性比較。由此局部式微觀開裂機制與傳統全面式巨觀材料破壞行為之校核探討,應有助於預測相關擬脆性材料結構之破壞演化(時間特徵);並提供另一種研判局部至全面破壞區域之定位方法(空間特徵)。
透過幾何參數(顆粒元素粒徑與數量)之設定,進行PFC3D模擬結果發現,顆粒元素粒徑大小對於巨觀材料參數(彈性模數、柏松比、單壓強度)之影響甚鉅;又由電腦合理運算範圍內之參數敏感分析顯示,元素顆粒數量約在7000顆後,巨觀材料參數方較穩定而趨於定值。而就材料微、巨觀參數校核之關聯性探討,得知顆粒元素之微觀彈性模數與粒間鍵結強度;分別與材料巨觀彈性模數和單壓強度約成正比關係;觀顆粒元素之正/切向勁度比則與另一材料巨觀參數柏松比成正相關;微觀之粒間摩擦係數亦與巨觀摩擦角呈正面影響,但會因試驗方式或受試材料之不同而有所差異。
依巨、微觀參數之敏感度分析結果,選擇三軸(含單壓)試驗與數值模型調準(model fitting)作比對而推估具物理意義之諸微觀材料參數。經求算顯示出PFC3D模擬三軸(含單壓)試驗所輸入之微觀材料參數;確可適切反應出實驗過程之巨觀彈、塑性參數。另就其局部微觀破裂演化之觀察得知,稍早於尖峰強度的粒間剪/張微裂增量比之變化趨勢;暨不同加載歷程之粒間微裂位置,可定性判知單壓破壞時主要為局部之粒間剪裂所控制。再以相同之微觀參數代表相同岩材進行巴西試驗之模擬,仍可由其峰前之剪/張微裂增量比的變化趨勢;暨不同加載歷程之粒間微裂位置,來判知破壞乃為局部之粒間拉裂所控制;惟所求之巨觀間接張力強度較文獻之實驗值有高估現象。最後就數值求算之粒間微裂位置與試驗文獻之聲射微裂的叢聚位置與發生時機作比較,二者於單壓試驗所生成之微裂叢聚分別發生於加載比為61%及51%時;而巴西試驗則各發生於加載比為65%及61%時,二者之比較,顯示PFC3D可定性預測微裂叢聚現象之發生位置與時機。
論文英文摘要:Due to the growth of microcracks leading to localization within quasi-brittle materials, the engineering structure subjected to different stress paths would be caused an unexpected damage prior to peak load. Therefore, it is more important to understand the evolution of microcracks for the stability of structural materials.
This study presents a numerical simulation of displacement discontinuity behavior by using Particle Flow Code in three dimensions(PFC3D)which bases on the principle of distinct element method(DEM). First of all, we proceed the sensitivity of parametric studies to calibrate the consistency of micro-to-macro material properties during both triaxial including unconfinement case and Brazilian test, and discuss mesoscopic behavior of quasi-brittle rock under different stress paths. Secondly, the numerical results in terms of the development of micro crack as well as the failure type of cracks between particles were compared with experimental data of acoustic emission qualitatively. It evolves the failure characteristic of quasi-brittle materials by viewing mesoscopic fracture behavior and conventional global failure criterion, and provides an option to identify the location of damage zone under certain stress level.
This numerical simulation shows that, by setting proper micro-geometrical parameters, a significant influence of particle radius on some macroscopic material parameters such as E, υ, qu. In this study, 7000 balls of particle numbers were used to conduct a series of parametric studies. Furthermore, the relation between micro- and macro- material properties: micro elastic modulus versus macroscopic elastic modulus, and bond strength versus confinement strength are found the existence of linear relation. In addition, there is a fair correlation between the normal/ shear stiffness and Poisson’s ratio. Macroscopic friction angle is also controlled by micro friction coefficient in spite of the upper bound of friction angle may not be controlled well with respect to different material and stress path.
According to analysis of sensitivity parametric, numerical model fitting is able to match through triaxial test including unconfing case. It shows that the micro-properties of PFC3D indeed response a good agreement with laboratory results in terms of both elastic and plastic parameters. By monitoring shear/ tensile cracks increment ratio and localization of particle cracks corresponding different load level, local shear cracking somehow dominated the damage around peak in uniaxial compression test. On the other hand, by simulating Brazilian test with same micro-properties, relatively tensile crack in element which dominates damage was found. However the estimation of tensile strength is higher than laboratory experiment value about 3 times. Finally, appearance of localization are obtained about 61% and 51% for numerical simulation and experimental AE data under uniaxial test respectively, and about 65% and 61% under Brazilian test. It shows that PFC3D could be used to verify the growth of micro cracks as well as its localization qualitively.
論文目次:中文摘要 i
英文摘要 iii
謝誌 v
目錄 vi
表目錄 ix
圖目錄 x
符號對照表 xiii
第一章 緒論 1
1.1 研究動機與目的 1
1.2 研究方法與範圍 1
1.3 論文架構與分章概述 2
第二章 文獻回顧 5
2.1 分離元素法之沿革與相關文獻扼述 5
2.2 微裂破壞機制之應用-數值模擬 7
2.2.1 以單壓試驗為例 7
2.2.2 以巴西試驗為例 9
2.2.3 微觀參數分析之應用 10
2.3 微裂縫之非破壞檢測-聲射試驗 11
2.3.1 聲射技術之原理 11
2.3.2 聲射定位理論 12
第三章 數值模擬方法 18
3.1 分離元素法 18
3.1.1 分離元素法之理論 18
3.1.2 分離元素法之假設 19
3.1.3 分離元素法之運算邏輯 19
3.2 力與位移法(Force-Displacement Law) 20
3.3 數值模擬軟體-PFC(Particle Flow Code) 24
3.3.1 PFC之概說 24
3.3.2 PFC之模擬流程及自撰式之輔助程式語言FISH 25
3.4 PFC之微觀參數 27
3.4.1 顆粒元素參數 27
3.4.2 鍵結力參數 29
3.4.3 邊界參數 31
3.4.4 微觀參數檢核之步驟 32
3.5 PFC之接觸組合律模式 33
3.5.1 接觸勁度模式 33
3.5.2 滑動模式 34
3.5.3 鍵結力模式 35
3.5.4 特殊替代模式 38
第四章 數值分析、驗證與結果 39
4.1 幾何參數之敏感度研析 41
4.1.1 顆粒粒徑對彈性參數之影響 41
4.1.2 顆粒粒徑對塑性參數之影響 43
4.1.3 顆粒粒徑對間接張力強度之影響 47
4.2 材料參數敏感度分析 49
4.2.1 微觀材料參數對彈性模數之影響 49
4.2.2 微觀材料參數對柏松比之影響 50
4.2.3 微觀材料參數對尖峰強度之影響 52
4.2.4 微觀摩擦係數對摩擦角之影響 54
4.3 剪控式驗證案例:單壓試驗 58
4.3.1 數值模型之建立 58
4.3.2 數值環境之建置:圍壓、軸差壓之模擬 61
4.3.3 數值材料之描述:彈、塑參數之輸入 63
4.3.4 微裂發展位置及粒間剪/張微裂增量比於全程加載歷史之演變 65
4.3.5 數值粒間微裂行為與實驗聲射之比對:單壓試驗為例 69
4.4 拉控式驗證案例:巴西試驗 70
4.4.1 數值模型之建立 70
4.4.2 間接張力試驗之抗張強度 71
4.4.3 微裂發展位置及粒間剪/張微裂增量比於全程加載歷史之演變 73
4.4.4 數值粒間微裂行為與實驗聲射之比對:巴西試驗為例 77
第五章 結論與建議 79
5.1 結論 79
5.2 建議 80
參考文獻 82
附錄
附錄A 簡易PFC3D指令 A-1
附錄B 微裂發展與破壞特徵之測試 B-1
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論文全文使用權限:同意授權於2007-02-13起公開