Analysis of fatigue crack growth from countersunk fastener hole

Jungjun Suh, Purdue University

Abstract

This research dealt with fatigue cracks that form at countersunk open holes and mainly focused on obtaining stress intensity factor solutions for countersunk holes employing both experimental and computational approaches. Cracks developing from countersunk holes are an extremely important issue for ensuring the structural integrity of many types of aircraft components, and are crucial to aircraft safety. ^ Four different crack shapes (single knee crack, single corner crack, two non-symmetric knee cracks and two non-symmetric corner cracks) were studied in this research. The locations of the cracks were chosen to represent the previous numerical and experimental study by C. Y. Park. A stress ratio (R = σminmax), 0.3 was used for all the specimens tested to minimize the crack closure effect. The use of transparent PMMA polymer specimens allowed for direct observation of changes in crack size and shape. ^ The stress intensity factor ranges along the crack front were determined using the back calculation method proposed by James and Anderson. Then, the stress intensity factor ranges were normalized as geometric factors to obtain non-dimensional stress intensity factors. ^ The geometric factors for a total of 36 crack fronts are determined for the single crack experiments, and the geometric factors for a total of 76 crack fronts are obtained for the two non-symmetric experiments. The geometric factors obtained in this research can apply to structural metals since the geometric factors only depend on crack geometry and not on material properties. ^ One of the objectives of this research was to assess the validity of finite element predictions of stress intensity factors. Thus, computational approach was conducted with StressCheck. Generally, StressCheck results agree reasonably well with the experimental results. The average percent differences in geometric factor are within 9.1% compared to the experimental results. ^

Degree

Ph.D.

Advisors

Major Professor: Alten F. Grandt, Purdue University.

Subject Area

Engineering, Aerospace|Engineering, Mechanical

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