| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 92 === A program of experimental and analytical tasks has been conducted to discuss the relationship between corrosion environment(immersion NaCl solution and open flow NaCl solution) and fatigue crack propagation（FCP）in an aluminum aerospace alloy 7050.We observe the influence of environmental change for the accelerating of crack growth rate,too.
The experiment was investigated via different heat treatments, corrosion environments, frequency, stress intensity factor range, crack length of add corrosion solution condition and load ratio. The influence of fatigue crack propagation was characterized and analyzed by using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Instron Model 8800 Testing System. The basis of airframe structural application is the result of experiment combining with tensile properties and stress corrosion cracking effect.
The result indicate that the alloys received homogenuzation-H470×24h have bigger plastic zone, more rough in crack surface and oxide debris then Step-homogenuzation (StepH) when load ratio (R) are 0.1 and 0.8. So homogenuzation-H470×24h have higher resistance to fatigue crack growth with the crack closure effect. And the accelerating of crack growth rate is changed by stress intensity factor range.
Keyword：Aluminum alloy 7050, immersion NaCl solution, open flow NaCl solution, accelerating of crack growth rate, crack closure.
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