Three-dimensional crack tip deformation measurement using combined Moire-Sagnac interferometry

A combined Moire-Sagnac interferometry method is developed for in-plane (u and v) and out-of-plane (w) surface deformation measurement. The combined o ptical setup is used to measure three-dimensional crack tip deformations of Al 2024-0 and Al 2024-T4 specimens at room temperature and an Inconel 909 specimen at 570 degreesC. Measured displacements near the crack tie region of the Al 2024-T4 specimen are used as input nodal displacements to determi ne stress intensity factors based on two-dimensional and three-dimensional Jacobian derivative method. The values compare favorably with theoretical c alculations. The extent of the three-dimensional crack tip deformation zone is also discussed.