含開孔之圓筒型壓力殼初始疲勞壽命估算之研究

The Study of the Crack Initiation Fatigue Life Estimation for the Cylindrical Pressure Hull with Holes

圓筒形壓力殼（cylindrical Pressure hull）常應用於鍋爐、壓力容器及管線等承受內壓力之工業設備或是水中潛水器等承受外壓力之相關結構上，此類結構往往處於高壓或高溫之環境，使得結構容易產生老化現象而產生疲勞問題；本論文建立一套客觀之疲勞壽命估算程序，作為評估是類壓力殼結構疲勞壽命（fatigue life）之用；首先使用有限元素法來確定高應力區及此區域承受循環靜水壓負荷時之應變時間歷程，其次應用Coffin-Manson非線陸經驗方程式，結合Miner累積損傷理論（Miner damage accumulation rule），建立應變壽命法（strain 1ife method）之研究方法，並配合高應力區域應變譜建構疲勞壽命估算程序；在求解過程中應用雨流計數法（Rainflow counting method）及Newton-Raphson Method等技巧進行負荷歷程之計數簡化及Coffin-Manson非線性經驗方程式之求解；所建立之疲勞壽命估算程序，除可作為工業用壓力容器、軍用潛艇或水下載具進行壓力殼疲勞壽限研究之用，並可提供壓力殼結構設計者設計時之參考。 The cylindrical pressure hull is often applied in the boiler, pressure vessel, piping system under internal pressure loading or the submarine pressure hull under external pressure loading. These structures are often in the condition of the high-pressure or high-temperature environment, so the fatigue problem occurred in it. For this reason, this work presents an objective estimating approach of the fatigue life for cylindrical pressure hull with holes. The finite element method is initially used to locate the area of high stress on the pressure hull with circular holes, and the strain spectrum of this area under cyclic hydrostatic pressure loading is obtained. The Coffin-Manson nonlinear experience equation under the strain-life method is then used with the Miner damage accumulation rule using the front strain spectrum. Thus the fatigue life estimation schedule is constructed. In this schedule, the Rainflow counting and Newton-Raphson methods are applied to simplify the cyclic pressure loading history and derive the Coffin-Manson nonlinear experience equation. The schedule proposed herein in addition to study the fatigue life for industrial pressure vessel, military submarine or submersible vehicle, it also provides the pressure hull structure designer with an effective tool for use in the design stage.