Evaluation of stress intensity factors of rounded V and U notches under mixed mode loading, using the experimental method of caustics

• The theory of caustics was developed for rounded V and U notches.
• The caustic curve was calculated by applying formulas in terms of stress intensity factors and geometrical properties.
• Stress intensity factors were determined by measuring specific lengths in image plane.
• Reliability of the caustic method for determination of stress intensity factors in rounded V and U notches was established.

The caustic method has proven to be a useful optical method to determine stress intensity factors. In this paper, the theory of caustics was developed for rounded V and U notches. The caustic curve was calculated by applying stress and optic formulas in terms of stress intensity factors and geometrical properties of V and U notches and the specimen. In this study, stress intensity factors were determined by measuring specific lengths in image plane. The models were subjected to bending and experiments were conducted as a function of applied load, notch length to notch width ratios, notch tip radiuses, and notch opening angles. The results compared well with the FEM method. The paper finally establishes the reliability of the reflected caustic for determination of stress intensity factors in rounded V and U notches under mixed mode loading.