可破裂顆粒在單向度壓力及膨脹收縮 之力學行為

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Title:	可破裂顆粒在單向度壓力及膨脹收縮之力學行為
Authors:	邱國豪;Qiu,Guo-hao
Contributors:	機械工程學系
Keywords:	顆粒體壓縮;儲氫顆粒體;離散元素法;顆粒體排列;顆粒體力量傳遞;顆粒體粉碎;granular assembly;confined compression;expanding/contracting process;DEM;bonding theory;force transmission property;pulverization mechanism of particles
Date:	2016-01-25
Issue Date:	2016-03-17 20:48:45 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究使用離散元素法 (Discrete Element Method, DEM) 模擬可破裂顆粒受到單向度壓縮及儲氫顆粒體吸收與釋放氫氣(體積膨脹與收縮)作用下顆粒體的粉碎行為，本研究的主旨藉由兩種不同的負載模式施加在可破裂顆粒體，來觀察顆粒體粉碎對內部顆粒體的排列、力量傳遞及顆粒體施加在容器壁上壓力的影響，本研究主要分三部分：(1)可破裂顆粒體承受單向度壓縮作用下之粉碎性問題；(2)儲氫顆粒體在承受重覆的吸收與釋放氫氣下(體積膨脹與收縮)之粉碎性問題；(3)三種不同鍵接強度(50N、100N及150N)與三種不同膨脹率(0.03、0.05及0.07)對儲氫顆粒體粉碎行為的影響，第一部分結果顯示，顆粒體在承受單向度壓縮作用下，顆粒體的碎裂是由受壓區 (接近上壓板) 開始向下傳遞，內部接觸力的傳遞在垂直面上為異相性分佈、水平面上為均向性分佈，顆粒鍵接的斷裂影響力量鏈的分佈，第二部分結果顯示儲氫顆粒體在經歷重覆膨脹與收縮下，顆粒體因相互擠壓產生碎裂，且顆粒體碎裂越多時，顆粒粒子體積佔有率逐漸升高，容器壁承受的壓力會隨著粒子體積佔有率逐漸增加，尤其以容器底度最為明顯。第三部分結果顯示三種膨脹率(0.03、0.05及0.07)對三種鍵接強度(50N、100N及150N)造成三種不同的顆粒破裂情形，第一種為顆粒體的破裂程度沒有達到鍵接上限，第二種顆粒體的破裂在較短的回合就已達至鍵接數上限，第三種顆粒體的破裂回合數上升直達鍵接數上限，三種不同的破裂狀況對其粒子體積佔有率的影響為：第一種碎裂狀況的顆粒粒子體積佔有率在整體過程中呈現鬆散狀態；第二種與第三種碎裂狀況的顆粒粒子體積佔有率在整體過程中為緻密的狀況，此兩種顆粒體粒子體積佔有率差異在於緻密程度與整體回合數過程，第三種緻密程度在較短回合數就不再變化，第二種緻密程度是逐步增加，三種破裂狀況對容器壁所承受的壓力變化也會產生影響，第一種狀況的壓力累積小且變化不明顯，第二種狀況整體過程中容器所承受到的壓力變化在較短回合數內有大量累積，第三種狀況壓力變化則是逐漸隨著回合增加累積增加。;This thesis develops the DEM modelling technique with bonding theory to study the pulverization mechanism of particles. The study considers two loading scenarios:(1) pulverization mechanism of LaNi5 alloy particles under confined compression;(2)pulverization mechanism of LaNi5 hydrides subjected to hydriding/dehydriding process. In the latter loading scenario, the effects of bond strength and expansion ratio on the pulverization mechanism are also explored. This study considers three different bond strengths (50N, 100N and 150N) and three different expansion ratios (0.03, 0.05 and 0.07). The internal properties such as crack number, solid fraction, normal and shear stresses, and coordination number were evaluated. The chief conclusions are as follows: 1.The load-displacement response shows bi-linear relationship in confined compression of LaNi5 alloy particles and the cracks gradually form from the top to the bottom. 2.The contact forces in this compressed system exhibit an isotropic distribution on the horizontal plane, but also show a strongly anisotropic distribution on the vertical plane. 3.In the system of LaNi5 hydrides subjected to hydriding/dehydriding process, the crack number increases with hydriding/dehydriding cycle number and most contact bonds are broken due to shear failure. 4.The solid fraction in the assembly of LaNi5 hydrides generally increases with hydriding/dehydriding cycle number, showing the phenomena of particle densification. 5.The normal wall pressure on the cylindrical wall generally increases with cycle number, especially in the lower part of the cylindrical shell. This phenomenon is attributed to the increasing solid fraction. 6.According to the parametric study, the normal wall pressure on the cylindrical wall exhibits three regimes depending on the rupture degree of granules: (1) as the rupture degree of granules is small or insignificant, the normal wall pressure does not show pressure accumulation; (2) as the crack number shortly reaches the upper limit of bonds, the normal wall pressure quickly accumulates; (3) as the crack number gradually reaches the upper limit of bonds, the normal wall pressure accumulates with cycle number, especially in the lower part of the cylindrical shell.
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