'AN INVESTIGATION ON DEVELOPMENT OF A PREDICTION MODEL FOR FATIGUE LIFE OF OPEN HOLE SPECIMENS WITH DOUBLE THROUGH THE THICKNESS CRACKS USING RESPONSE SURFACE METHODOLOGY'S. Sohrab Heidari Shabestari and Altan Kayran 'In this study, a model for predicting the life of open hole specimens with a double through the thickness fatigue cracks emanating from the fastener hole walls is suggested. The model predicts the life of 2024-T3 aluminum alloy under constant amplitude loading for varying geometries and is valuable for basic experimental evaluations dealing with crack growth from fastener holes. For the experimental verification, experimental test data under constant amplitude loading with the load ratio R=0 was extracted from the work of Crews et al. [1] published in NASA Technical Reports Server. In the experimental tests, specimens were prepared from 2024-T3 aluminum alloy plate for double through the thickness cracks embedded in an open circular hole. Stress intensity factors for different crack lengths have been calculated using the Bowie?s [2] analytical solution for the available fatigue lifes in the Crew's report. Experimental data is fitted to the FORMAN equation [3] and material constants are extracted accordingly. Afterwards, using the calculated Forman equation constants of the material, the same geometry is modeled in AFGROW. Variable parameters tensile stress (s), the radius of the rivet hole (r), and crack length (c) are considered as the parameters affecting the fatigue and faced central composite design of experiments using the Response Surface Methodology (RSM) is implemented. Finally, analysis of variance (ANOVA) of the RSM designs led to a regression model with a good correlation to AFGROW and experimental results.' |