[pt] Após identificar que uma trinca de fadiga permanecia fechada durante parte do ciclo, Elber assumiu que o dano era induzido apenas pela fração do carregamento acima da carga necessária para abrir a trinca. Diversos modelos foram propostos utilizando o Delta Keff como força motriz da propagação, como os modelos da faixa plástica (strip-yield), que são amplamente utilizados para prever vida residual de componentes trincados. Embora o fenômeno do fechamento da trinca esteja provado, sua real importância na propagação da trinca de fadiga ainda é controversa. Outros mecanismos, além do fechamento da trinca, foram utilizados na tentativa de explicar os efeitos de sequência do carregamento na propagação em amplitude variável como o campo de tensão residual à frente da trinca. Mesmo após mais de 50 anos de pesquisas desde a proposição da primeira regra de propagação por Paris ainda não há consenso nem sobre o mecanismo nem sobre a modelagem. Esse trabalho tem como objetivo apresentar uma modelagem para prever propagação da trinca de fadiga com base na hipótese de que o dano acumulado por deformação plástica seria a força motriz para propagação. A modelagem proposta se diferença de outros modelos de acúmulo de dano por permitir que o contato existente entre as superfícies da trinca exerça influência sobre as deformações plástica à frente de sua ponta. Os resultados mostram que a modelagem proposta possui capacidade de reproduzir curvas de propagação semelhante ao modelo strip-yield. / [en] After identify that a fatigue crack remains closed during part of the load cycle, Elber assumed the damage was induced only by the cycle part over the load required to open the crack. Several models were developed based on Delta Keff as the strip-yield ones, which are widely used to predict residual lives of cracked components. Although the crack closure phenomenon is well proven its actual significance for the propagation is still controversial. Others mechanisms, beyond the crack closure, were used in trying to explain the sequence effects on variable amplitude crack propagation like the residual stress field ahead of the crack tip. However even after more than 50 years of research since the first propagation rule proposed by Paris there is no neither about the mechanism neither about modelling. This work has the aim of present a modelling to predict fatigue crack growth based on the hypothesis that the damage accumulated by cyclic plastic strain would be propagation the drive force. The modelling proposed differs from others damage accumulation models by allowing the existed contact between the crack surfaces to exercise its influence on plastic strain ahead of the crack tip. The results show that the proposed model is able to reproduce propagation curves similar to the model strip-yield.

One of prominent issues related to failures in nuclear power components is attributed to material degradation due the aggressive environment conditions, and mechanical stresses. For instance, reactor core support components, such as fuel claddings, are under prolonged exposure to an intense neutron field from the fission of fuel and operate at elevated temperature under fatigue loadings caused by start up, shut down, and unscheduled emergency shut down. Additionally, exposure to highluence neutron radiation can lead to microscopic defects that result in material hardening and embrittlement, which significantly affects the physical and mechanical properties of the materials, resulting in further reduction in fatigue life of reactor structural components. The effects of fatigue damage on material deterioration can be further exacerbated by the presence of thermal loading, hold-time, and high-temperature water coolant environments. In this study, uniaxial fatigue models were used to predict fatigue behavior based only on simple monotonic properties including ultimate tensile strength and Brinell hardness. Two existing models, the Bäumel Seeger uniform material law and the Roessle Fatemi hardness method, were employed and extended to include the effects of test temperature, neutron irradiation fluence, irradiation induced helium and irradiation induced swellings on fatigue life of austenitic stainless steels. Furthermore, a methodology to estimate fatigue crack length using a strip-yield based model is presented. This methodology is also extended to address the effect of creep deformation in a presence of hold- times, and expanded to include the effects of irradiation and water environment. Reasonable fatigue life predictions and crack growth estimations are obtained for irradiated austenitic stainless steels types 304, 304L, and 316, when compared to the experimental data available in the literature. Lastly, a failure analysis methodology of a mixer unit shaft made of AISI 304 stainless steel is also presented using a conventional 14-step failure analysis approach. The primary mode of failure is identified to be intergranular stress cracking at the heat affected zones. A means of circumventing this type of failure in the future is presented.

已實現投資報酬率與無風險利率之差、被稱為超額報酬，而股票的預期報酬率超過無風險利率的部份則為股票風險溢酬，是許多資產評價模型的重要依據，例如資本資產定價模型。有不同的理論架構解釋說明風險溢酬值，例如；股票風險溢酬的迷思、短期損失的憎惡、生還存留因素和回歸與偏離平均值等等。 研究台灣股市的超額報酬與股票風險溢酬，有助投資大眾和企業理性面對股市的預期報酬和風險，對台股才有合理的期望報酬值。分析1967年迄2003年的台灣金融市場，計算過去37年長期的幾何平均年報酬率，以臺灣證券交易所發行量加權股價指數為台股市場報酬率，已實現台股實質年報酬率為6.71%。無風險報酬率使用第一銀行的一年期定期存款利率，實質台幣存款年利率為3.07%，消費者物價指數年增率則為4.80%。以年資料計算的台股實質超額報酬，算術和幾何值分別為12.48%和3.63%(年)，計算月資料算術平均和幾何平均值分別為0.77%和0.25%(月)。過去37年長期的台股超額報酬現象未較歐美市場的情況更加明顯，也比一般市場的預期報酬率低。 因資料取得的限制、台股的理論超額報酬方面，1991年迄2003年的近十三年來，經固定股利成長模式和盈餘成長模式的兩種計算方式，台股的實質超額報酬分別為 0.6%和-4.3%，此時期台股的投資報酬率比起台幣存款並不突出、且是低超額報酬。同期的已實現的實質超額報酬值；算術平均1.69%和幾何平均-3.35%。評估目前台股風險溢酬，將十分接近過去37年長期歷史資料得到的超額報酬數值，算術年均值為12.48%(年)和0.77%(月)，幾何平均分別為3.63%(年)和0.25%(月)，低風險溢酬是當前台灣股票市場的一般現象。 / The difference between the observed historical investment return and the risk-free interest rate is the excess return. The equity risk premium, ERP is the expected rate of return on the aggregate stock market in excess of the rate of risk-free security. ERP is one of important factor of many asset-pricing models, including Capital Asset Pricing Model, CAPM. There were many theories and factors to explain the equity risk premium; equity premium puzzle, myopic loss aversion, survivorship bias, mean reversion & aversion and etc. Studying the value of Taiwan equity excess return and risk premium is fundamental for investors and institutions evaluating the expected market investment return and risk. Analyzing the data from year 1967 to 2003 for thirty-seven years long holding period, Taiwan Stock Exchange Capitalization Weighted Stock Index as Taiwan stock market return, the realized real return was 6.71%. One-year bank time deposit rate as NT dollars risk-free asset rate and real interest rate was 3.07% and consumer price index, CPI annual growth rate was 4.80%. The historical real yearly excess return was 12.45% for arithmetic mean and 3.63% geometric mean; the historical real monthly excess return was 0.77% for arithmetic mean and 0.25% geometric mean. Taiwan realized equity excess returns were not higher than the returns in the developed countries and were also lower than the market's expectation. Due to the limits of available data, the theoretical equity excess returns that were calculated on two theoretical models; Constant Growth Dividend Discount Model (dividend yield model) and earnings yield model were 0.6% and -4.3% from year 1991 to year 2003. Comparing the same period of historical realized excess returns of 1.69% for arithmetic mean and -3.35% geometric mean, Taiwan stock market returns were not spectacular. The current equity risk premium of Taiwan stock market is low and should be near the level of the long historical realized equity excess return.