Optical evaluation of the buckling behavior of stiffened composite laminates

Digital fringe projection profilometry (FPP) is suitable to inspect the surface profiles of objects with some apparent advantages such as being non-contact, making full-field measurement, using simple apparatus, being of high precision and enabling real-time profile automation. With our technique, four phase-shifted sinusoidal fringe patterns were circularly projected onto the surface of a composite laminate panel reinforced with crossed ribs. A phase shifting method was applied to inspect the surface profile variations during compression. The profile results revealed that different deflection directions of local buckling appeared at different crossed ribs, with the wave valleys located at the middle and the wave peaks occurring at the composite panel ends. From the details of the deflection analysis, it has been seen that the local buckling couple with the whole bending of the composite panel. The local buckling deflections agree well with finite element method (FEM) simulations.