本研究以數值分析和實驗方法來證明最小二乘法（Least-Squares Method，LSM）決定應力強度因子應用在搭接構件的適用性。在數值分析部份，主要是利用有限元素法配合最小二乘法計算兩種常見的搭接構件（即：單搭接－雙填角銲搭接構件與雙搭接－雙填角銲搭接構件）裂縫尖端之剪力模式應力強度因子（KII）與所對應之形狀因子（MKII），並以控制變因的方式改變幾何形狀參數，進行參數分析，藉以瞭解搭接構件在不同幾何形狀參數下之剪力模式形狀因子（MKII）的變化情形，再利用迴歸分析將MKII以一包含重要幾何形狀參數的通式表示之。在實驗部分，本研究將非接觸式COD位移量測系統導入實驗中，以實驗方法決定搭接構件裂縫尖端之剪力模式應力強度因子，並驗證MKII迴歸通式的準確性與適用性。結果證明本研究提出之MKII迴歸通式具有極佳的適用性，同時也確定非接觸式COD位移量測系統可精確量測裂縫張開位移（COD）且實驗方法配合最小二乘法可準確決定複雜搭接構件裂縫尖端之應力強度因子。

This research is to verify the feasibility of determining the stress intensity factors of fillet-welded lap joints using Least-Squares Method numerically and experimentally. In numerical analysis, Least-Squares Method incorporated with finite element analysis was employed to compute the shear mode (mode II) stress intensity factors (KII) and the corresponding shape factors (MKII) of two common types of fillet welded lap joints (single lap joint and double lap joints). Parameter analysis was implemented to understand the variations of the shear mode stress intensity factors and the corresponding shape factors of fillet welded lap joints affected by the geometric shape factors. The results from parameter analysis were incoporated into the regression analysis to derive two general formulas of MKII for fillet welded single lap joint and double lap joints respectively. In experimental study, a non-contact COD measurement system was utilized to determine the shear mode stress intensity factors of the fabricated lap joint specimens. The results from experiments were in good agreement with the results from the regression formulas. In summary, this research proposes two general regression formulas for computing shear mode stress intensity factors of two common types of fillet welded lap joints respectively, and verifies the application of non-contact experimental method to determine the stress intensity factors for fillet welded lap joints.

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