A NOTCH ROOT RADIUS TO ATTAIN MINIMUM FRACTURE LOADS IN PLATES WEAKENED BY U-NOTCHES UNDER MODE I LOADING

Abstract The paper deals with the minimum value of a fracture load, with respect to the notch root radius, in plates weakened by U-notches under Mode I loading. It has been found that the fracture load has a minimum value at a critical value of the notch root radius ( ρ ), using four criteria, namely, Mean Stress (MS), maximum tangent stress or Point Stress (PS), Critical Strain-Energy (CSE) and Averaged Strain-Energy Density (ASED). Using a characteristic length ( l c h ), which is a function of material properties, the results showed that the dimensionless critical notch root radius ( ρ / l c h ) c r depended on w / a ratio (the specimen width to the notch depth), Poisson ratio, and loading condition (tensile or bending loading) under Mode I loading. In other words, according to these criteria, a notch root radius different from zero exists, providing a minimum fracture load. Therefore, a crack is not more dangerous rather than a U-notch under Mode I loading. This critical notch root radius is important for a quasi-brittle material, but may not be significant for brittle ones in practical engineering situations. Good agreement was found between theoretical predictions and experimental results on Al356-T6.

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