Evaluation of a Crack-Growth Gage for Monitoring Possible Structural Fatigue-Crack Growth
Final rept. May-Sep 1977
SYSTEMS RESEARCH LABS INC DAYTON OH
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The results of an experimental and analytical investigation on the use of a precracked coupon mounted onto a structure for monitoring the effect of service loads upon fatigue crack growth in the structure are discussed. The precracked coupon of gage is a simple device which provides a convenient means for determining the potential damage in a structure since the gage takes into account the mechanics of crack growth. Experimental results are reported for gages made from two aluminum alloys and having two types of crack geometries. These gages contained either a center crack or a single crack at the edge of a hole. The effect of the load amplitude upon the growth of the crack in the gage as a function of the crack growth in the structure was investigated. All tests were conducted under constant-amplitude cyclic load. The theoretical model is developed to predict the correlation between the growth of the cracks in the gage and in the structure. Two areas of major importance in the analysis are the load transfer from the structure through the ends of the crack gage and the crack-propagation law for the crack growth in the gage and in the structure. Comparison of the analyses and the experimental results is made.