Numerical and Experimental Study on Optimization of Overload arameters for Fatigue Life Increase

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Sarkheil, Saeed | 2010

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Type of Document: M.Sc. Thesis
Language: Farsi
Document No: 40648 (08)
University: Sharif University of Technology
Department: Mechanical Engineering
Advisor(s): Saadat Foumani, Mahmoud
Abstract:
Fatigue life and crack growth retardation due to periodic tensile overload that superposed on constant amplitude cycles has been investigated. The tests were performed using C(T) specimens made of 7075 aluminium. All periodic overload tests were carried out at the same spacing between overloads and the effect of overload ratio on fatigue life has been investigated. Results of experiments revealed that the at low and high overload ratios, crack growth rate is relatively high and there is an optimum OLR that maximize interaction and thus minimize FCGR. Whit OCR-1=50, overload ratio of 1.85 led to maximum interaction and resulted in 219% increase in specimen's life relative to CA loading. Also whit OCR-1=500, overload ratio of 2 led to maximum interaction and resulted in 613% increase in specimen's life relative to CA loading. In addition experimental results showed that in periodic overloading da/dN versus delta K curves shift parallel to constant load amplitude data
Keywords:
Stress Intensity Factor ; Fatigue Crack Growth Rate ; Over Loads ; Periodic Overload ; Occurrence Ratio