摘要
本研究主要是以連體損壞力學方法配合有限單元技法探討缺口板件在受到拉應力之持續作用下所產生的潛變破裂行為。吾人首先根據一複雜之單維潛變損壞律導出一完全由潛變量控制的損壞律，並依最大主張應變法則將此律通化成多維之潛變損壞律，用以計算潛變機件的損壞量。而求解步驟則是對所探討之邊界值問題以有限單元技法重覆地求取機件內部之應力與應變，並據之求得損壞量。機件之潛變破裂過程可分成兩個階段。在第一階段，機件內之潛變損壞尚未達臨界值，亦即是屬於破裂之醞釀期。至於在第二階段，機件內之局部區域其損壞量已達臨界值而開始生成“裂痕”，進而向機件內部延伸成長，直到機件完全破裂。在有限單元技法之求解過程中，單元破裂之處理是當單元之損壞量達到臨界值時即予以除去，並將其原有之剛性自整體結構中略去不計，而這種處理方式基本上乃是模擬機件之實際破裂行為。分析結果顯示，缺囗板件之初始裂痕首先發生於缺口端附近，隨即逐漸地朝板件內部延伸，使得其涵蓋區域逐漸擴大，最後便分成數條裂痕各自傳播，直到板件完全破裂。
並列摘要
In this work, the creep rupture behaviors of externally-notched plates, subjected to constant boundary stress, are investigated by means of local continuum damage mechanics approach in conjunction with the finite element technique. First of all, a one-dimensional strain-controlled creep damage law is derived from a more complex strain-dependent creep damage law in which creep strain is the only variable that determines the amount of creep damage. Then, based on a postulate of maximum principal tensile strain criterion this one-dimensional creep damage law is generalized and subsequently used to evaluate the creep damage under more general stress states. The continuum damage mechanics approach for creep rupture process essentially involves a repetitive solution for the associated boundary-value problem and a determination of the development of the continuously accumulated creep damage. The creep rupture process may be separated into two stages. In the first stage, which is called the incubation period, the creep damage everywhere has not yet reached a critical value. As for the second stage, initial local rupture occurs where the creep damage has reached a critical value and then propagates throughout the structure. In the finite element procedure, rupture of an element is assumed to have occurred when its creep damage has reached a critical value. The ruptured elements and their associated stiffness are then removed from the overall structural model to form a new boundary-value problem. This procedure continues until the whole structure has completely ruptured. The analysis for the externally-notched plates indicates that the initial rupture zones develop in the neighborhood of the notch tips and then propagate slowly into the plates. These rupture zones gradually spread out over somewhat wide area and develop into a number of crack-like regions propagating simultaneously.