Fracture assessments of blunt V-notches using the coherent gradient sensing (CGS) method

In this paper, the coherent gradient sensing (CGS) method is extended to study the local stress fields and fracture behavior of a blunt V-notch tip. First, the optical governing equations of the CGS method are derived based on Filippi's stress equation for blunt V-notches and the concept of the notch stress intensity factor (NSIF). Moreover, the CGS fringe patterns in the vicinity of the blunt V-notch tip with different opening angles and notch radii are theoretically synthesized. Next, the fracture property of a blunt V-notch is experimentally studied using a series of three-point-bending polymethyl methacrylate (PMMA) specimens with different geometrical configurations. Finally, the generalized NSIFs up to the initiation of a fracture are evaluated using the proposed CGS method. The CGS fringe patterns in the experimental results exhibit a reasonable agreement with the theoretical fitted fringes, and the NSIFs and notch fracture toughness at the blunt V-notch tip are consistent with those obtained in previous theoretical studies and finite element simulations.