固態氧化物燃料電池可靠度分析

Abstract

本論文主要目的在建立固態氧化物燃料電池片在溫度分佈不均勻狀態下的壽命預估分析，固態氧化物燃料電池是由電化學原理來達到產電的目的，其在正常運作下會有溫度分佈不均勻的情況而有內應力的產生，本篇論文便是要以此內應力來計算燃料電池的失效預估。 由於固態氧化物燃料電池的用材多為複合脆性材料，不同於延展性材料有明確的可承受應力，在探討脆性材料能承受的應力強度時我們採用統計機率的概念，而本文中我們採用的機率公式為韋布失效機率公式，然而韋布失效機率雖然告訴我們物體的失效機率，但卻未告訴我們失效機率隨時間而變化的關係。為了得到此一關係式，我們從應力強度因子著手，配合裂隙成長速度公式，推導出等效應力後，將此等效應力(與時間有關)代入韋布失效機率公式即可得失效機率與時間之關係圖。 而要計算等效應力則必須知道物體在某個溫度分佈下的應力狀態，由於燃料電池並非處於均勻的溫度分布狀態下，為了能夠計算在非均勻分布的情況下之應力大小，我們使用有限元素法建構應力狀態之模型，再將此應力狀態套用到韋布失效機率，即完成了本論文所要達成的目標。

The purpose of the paper is to construct reliability analysis of Solid oxide fuel cell under non-uniform temperature distribution. Because the operation of solid oxide fuel cell is based on complex electro-chemical reaction, it will generate thermal stress, thus the effect of the thermal stress on the life of fuel cell is the main part to analyze in this paper. Different from ductile material which has definitely yielding stress, we use the probability of failure instead of the allowable stress that fracture material can resist. We use weibull probability of failure as our probability function, but weibull function didn’t tell the relationship between the probability of failure and the time. In order to gain the failure -time relation, we derived the equivalent stress by using the stress intensity factor with the concept of slow crack growth, and substitute it into the weibull probability of failure to gain the failure-time relation graph. The equivalent stress is calculated from known stress state, in general, the temperature distribution is NOT uniform, in order to acquire the stress state, we use the Finite Element Method to construct the model of stress state under temperature that is non-uniform distribution, and using this stress state substituted into the weibull probability of failure to complete our goal, the time-dependent probability of failure.