رسالة جامعية
以分子動力學研究臨界分解剪應力在BCC與HCP結構上的適用性 ; The examination of the applicability of CRSS theory in BCC and HCP structure by molecular dynamics simulation
| العنوان: | 以分子動力學研究臨界分解剪應力在BCC與HCP結構上的適用性 ; The examination of the applicability of CRSS theory in BCC and HCP structure by molecular dynamics simulation |
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| المؤلفون: | 邱韋倫, Qiu, Wei-Lun |
| المساهمون: | 機械工程學系碩博士班, 張怡玲, Chang, I-Ling |
| سنة النشر: | 2012 |
| المجموعة: | National Cheng Kung University: NCKU Institutional Repository / 國立成功大學機構典藏 |
| مصطلحات موضوعية: | 分子動力學, 奈米線, 差排, 雙晶, 臨界分解剪應力, molecular dynamics, nanowires, dislocation, twinning, critical resolved shear stress |
| الوصف: | 本文將以分子動力學方法研究兩種晶格結構（體心立方及六方最 密堆積）之奈米線的彈塑性行為，並以系統性的方式來觀察降伏時的 臨界應力值受晶格排列方向及尺寸的影響，以檢驗臨界分解剪應力理 論在奈米尺度下的適用性。 由模擬結果發現，體心立方結構奈米線的彈性性質、臨界應力與 臨界應變值都沒有明顯的尺寸效應，奈米線彈塑性性質與軸向晶格排 列方向有關，觀察降伏時奈米線的外觀與內部原子的滑動，發現不同 晶格方向的奈米線降伏機制不同，在[100]、[110]奈米線為雙晶現象， 而在[111]奈米線發現其塑性時產生的變形機制與[100]、[110]奈米線 截然不同，初步斷定為差排滑移所造成，且產生的滑移系統非常的雜 亂難以區分。經計算臨界分解剪應力發現其值差距非常大，因而推論 在奈米尺度下臨界分解剪應力理論不適用於預測雙晶現象的發生。 而六方最密堆積結構奈米線，除了[0001]奈米線的臨界應力有明顯 地隨著線寬尺寸加大而遞增的現象外，其餘在[01-10]、[2-1-10]奈米線 皆無明顯趨勢，觀察降伏時奈米線的外觀與內部原子的滑動，發現不 同晶格方向的奈米線降伏機制皆為差排滑移。而經由臨界分解剪應力 的計算，可發現除了[0001]奈米線因加載方向造成沿次要的滑移系統 滑動，其餘在[01-10]、[2-1-10]奈米線與作為驗證的[10-10]、[10-11]奈米 線所計算出的臨界分解剪應力值皆非常接近，誤差值皆在5%以內， 故推論臨界分解剪應力理論可用來預測六方最密堆積結構奈米線的 差排產生。 關鍵字: 分子動力學、奈米線、差排、雙晶、臨界分解剪應力 ; Molecular dynamics simulations were employed to investigate the elastic and plastic behaviors of nanowires (body-centered-cubic and hexagonal-closed-packed crystal structures) The size and axial crystal orientation effects on critical stress/strain at the yielding point of the nanowires were systematically studied to examine the applicability of critical resolved shear stress (CRSS) theory at nanoscale From simulation both elastic properties and critical stresses/strains of the body-centered-cubic (bcc) nanowires do not show noticeable size effect The elastic and plastic properties of bcc nanowires depend on the axial crystal orientations From the inspection of the atomic configuration at yielding it was observed that the yielding mechanism was different for various oriented nanowires It was twinning for [100] [110] nanowires and dislocation slip for [111] ones whose slip systems were complicated and difficult to distinguish The calculated critical resolved shear stresses for [100] and [110] nanowires deviated significantly which indicated that the CRSS theory could not apply to the prediction of twining behavior at nanoscale For hexagonal-closed-packed (hcp) nanowires only the critical stress of [0001] nanowires showed obvious size effect It is observed that dislocation slips were the yielding mechanisms for all crystal orientated nanowires The ... |
| نوع الوثيقة: | thesis |
| اللغة: | Chinese English |
| العلاقة: | http://ir.lib.ncku.edu.tw/handle/987654321/127922Test; http://ir.lib.ncku.edu.tw/bitstream/987654321/127922/-1/index.htmlTest |
| الإتاحة: | http://ir.lib.ncku.edu.tw/handle/987654321/127922Test http://ir.lib.ncku.edu.tw/bitstream/987654321/127922/-1/index.htmlTest |
| رقم الانضمام: | edsbas.20EF77DF |
| قاعدة البيانات: | BASE |
| الوصف غير متاح. |