受負載頻率與溫度影響的疲勞裂紋成長模式研究

The Study of Fatigue Crack Growth Models with the Influence of Loading Frequency and Temperature

陳建忠(Jien-Jong Chen)

指導教授 ： 施延欣

中原大學/工學院/機械工程研究所/博士(2001年)

https://doi.org/10.6840/cycu200100321

摘要

在裂紋疲勞成長過程中，負載頻率及溫度對疲勞裂紋的成長有一定程度的影響，而且也是設備、結構的實際工作條件中必須經常面對的問題。因此，James對於奧斯田系列的不銹鋼，執行一系列的疲勞裂紋成長實驗，並透過實驗數據的回歸分析提出一套可靠的評估方法；目前這套評估方法已被美國機械工程師學會的規範採用作為奧斯田系列裂紋成長的評估。然而，由於James僅是利用數值回歸分析，並且為了更精確的吻合實驗數據，故其係數項顯得較為繁雜。本文則是以304不銹鋼為對象，應用其材料機械性能，建立的機械性能與溫度及應變率的關係式，並據此探討溫度及負載頻率對於疲勞裂紋成長的影響。
透過降伏應力與應變率的關係式及疲勞裂紋成長數據的分析，可建立以應變率為參數的無因次降伏應力函數，並以此函數反應負載頻率對疲勞裂紋成長速率的影響；透過降伏應力及楊氏係數與溫度的關係式及對疲勞裂紋成長數據的分析，也成功的運用以溫度為參數的無因次降伏應力及楊氏係數函數，表示溫度對疲勞裂紋成長速率的影響；在探討合併溫度及負載頻率對對疲勞裂紋成長速率的影響時更發現兩者相互之間存在關係。最後並以導入材料機械性能所建立的疲勞裂紋成長關係式對所蒐集的實踐數據進行回歸分析，證明本文所建立的疲勞裂紋成長模式，可相當準確的預測304不銹鋼的疲勞裂紋成長。

關鍵字

疲勞裂紋成長 ； 304不銹鋼 ； 負載頻率 ； 溫度

並列摘要

Under cyclic loading condition, the fatigue crack growth rate governed by range of stress intensity factor and stress ratio is well known. Paris’ law, Forman’s equation and Elber’s equation are all the typical formula of this type. However, the effects of loading frequency and temperature on fatigue crack growth rate have also play an important role from many of experimental test. Although, the power law relationship has been used to characterize the effect of loading frequency on fatigue crack growth rate, and thermal activated process has also been used to interpret the effect due to temperature, but, it fail to using a single value of activation energy for lower and higher range of stress intensity factor. James had performed a lot of experiments, through the data regression analysis, an evaluation equation is suggested. In the present study, the mechanical behavior of material is successfully introduced to illustrate the combined effect of loading frequency and temperature on fatigue crack growth rate. By defined dimensionless yielding stress function and dimensionless Young’s modulus, A new FCG rate model that considers the effect of loading frequency and temperature on fatigue crack growth rate for wide-range of temperature and loading frequency has been proposed. By modifying the modified Forman’s equation which was used in the NASGRO and NASGRO 2.0 programs, the effect of loading frequency and temperature can then be taken into account. By comparing with the experimental data and James model, except some of susceptible data, the proposed model shows a good agreement with the experimental results and only a very small difference from James’ predicted value.

並列關鍵字

Fatigue crack growth ； 304 stainless steel ； temperature. ； frequency

參考文獻

Andresen, P.L. (1993), Effects of temperature on crack growth rate in sensitized type 304 stainless steel and alloy 600, Corrosion Science, Vol. 49, No. 9, pp. 714-725.

ASME (1998), ASME Boiler and Pressure Vessel Code Section II, Table TM-1, 1998.

Bathias, C. and Pelloax, R.M. (1973), Fatigue crack propagation in Martensitic and Austenitic steels, Metallurgical Transactions of ASME, Vol. 4, pp. 1265-1273.

Carpenter Steel Company (1969), Technical Data of Carpenter stainless steel Type 304.

Forman, R.G., Kearney, V.E., Engle, R.M. (1967), Numerical analysis of crack propagation in cyclic-loaded structures, Journal of Basic Engineering, Transactions of the ASME, Series D, Vol. 89, pp. 459-464.