Uniform Arrays of Unequal-Depth Cracks in Thick-Walled Cylindrical Pressure Vessels—Part I: Stress Intensity Factors Evaluation

The influence of the unevenness of crack lengths on the mode I stress intensity factors (SIF) for large uniform arrays of radial cracks of unequal depth in thick-walled pressurized cylinders is investigated applying the previously proposed “two-crack-length level model.” Using the finite element method, SIFs are evaluated for numerous configurations of crack arrays bearing a wide range of crack lengths. The interaction range for various combinations of crack arrays and crack lengths is then determined. The numerical results anticipate that any statistical unevenness of the initial crack lengths, prevailing in the pressurized cylinder, will be amplified during the process of fatigue crack growth. Thus, while the fatigue life of the vessel is determined by a large number of cracks, its final failure, which is governed by a small number of the largest cracks, is likely to be caused by one major crack, as is usually the case. This sequence of events results from the particular nature of the inter-crack stress field, which is analyzed and discussed in detail in Part II of the paper.