Influence of Thickness and Hole Diameter on Mutual Interaction of Two Opposing Cracks at a Hole

摘要

Holes in structure are typical locations prone to fatigue cracking. Usually cracks will develop at both sides of a hole, such that for some period the two unequal opposing cracks, might grow simultaneously, interact and influence each other. This mutual interaction is such that the larger crack influences the smaller one to accelerate it for tendency to equal its length to the larger crack. In turn, the smaller crack influences the larger one to accelerate it, by lower factors, though not negligible. Comparing crack growth life analyses results for accounting of these mutual interactions vs. not accounting, by ratio the results for the "not accounting" to the "accounting", reveals crack growth life ratio factors that range from 1.3 for common structural configurations, up to a factor of 2 for infinite width dimensions. These results certainly mean that this mutual interaction effect cannot be ignored. This paper uses the state-of-the-art NASGRO computing code in evaluating the hole two opposing cracks mutual interactions. The thickness in which cracks are growing and the hole diameter parameters are being evaluated for their influence on the mutual interaction of two opposing cracks at a hole. The paper presents test results for two opposing cracks at a hole. The cracking growth data is acquired by Fractographic analyses done on coupon tests and is accompanied by cracking growth analyses that includes mutual interaction effects.