Study on fracture behavior for sharp V-notched specimens combined with 3D-DIC and caustics

Abstract

In this paper, the fracture behavior of Three-Point Bending (TPB) beams with V-notch under mode I and mixed mode I-II loading is investigated. For this purpose, first, an experimental system combining three-dimensional digital image correlation (3D-DIC) and a new digital laser caustic is established. Then, based on displacement field for V-notch and the displacement extrapolation theory, a new method (3D-DIC) for measuring Notch Stress Intensity Factors (NSIFs) of V-notches under mixed mode loading is presented and verified. Furthermore, based on the established system, the effect of eccentric loading and the rotation angle of V-notches on the initiation and propagation for V-notch is analysed, and the SIF results for V-notched specimen from initiation to crack arrest are provided. Obtained results demonstrate that SIF increases rapidly at first, and then decreases with the decrease of energy at the initial stage of notch propagation. Under the action of eccentric load, V-notches initiate and propagate toward the load position. In addition, the values of mode I NSIFs (KIV) and the length of failure time of these specimens are ranked as: specimen B (notch rotation angle of 0°) > specimen D (notch rotation angle of −60°) > specimen C (notch rotation angle of 60°). However, the absolute value of mode II NSIFs (KIIV) and the distance of crack arrest in X direction of these specimens are ranked as: specimen C > specimen D > specimen B. Finally, the Maximum Tensile Stress (MTS) criterion suitable for V-notches under mode I or mixed mode loading is proposed, and the validity of the criterion is verified by experimental results.