A fracture mechanics analysis of fatigue crack growth in a complex cross section

This paper describes research conducted to determine the fatigue crack growth behavior of corner cracks which occur in a beam with a complex “double-T” shaped cross section. Particular objectives were to determine the changes in crack shape as they grow from one leg of the double-T cross section into the wider portion of the specimen, and to determine whether crack growth could be delayed or arrested in this area. Since it is difficult, if not impossible, to obtain details of crack growth inside metal specimens, it was decided to test transparent polymer models which allow in situ photographs of the crack plane. Fatigue crack growth rates measured at various positions along the crack front were used to compute cyclic stress intensity factors from the baseline fatigue crack growth behavior of the test material. The results of these experiments do indicate that cracks may be delayed once they sever one leg of the double-T cross section, although crack arrest may be compromised if a second crack develops in the opposing leg.