Chromatic DIC-Assisted Fringe Projection Profilometry for Shape, Deformation, and Strain Measurement With Intensity-Chroma Space Analysis.

The recently emerging digital image correlation (DIC)-assisted fringe projection profilometry (FPP) has been demonstrated to be superior in shape and deformation measurement on complex structures. But the contradictory demands on the reflectivity of tested surface between FPP and DIC extremely limit its measuring accuracy. In this work, chromatic DIC-assisted FPP is proposed to achieve accurate 3-D shape, deformation measurement, and strain analysis. First, colorful fluorescent pigment is introduced to fabricate speckle patterns, and the optimal fluorescent color is solved to simultaneously ensure high fringes intensity modulation and speckles' chroma difference; then, the intensity-chroma space analysis method is presented to modulate and demodulate the projected fringe and fabricated speckle information in intensity and chroma space without interference. High-quality fringe and speckle patterns can be simultaneously obtained for accurate shape, deformation, and strain measurement. To the best of our knowledge, for the first time, it essentially overcomes inherent contradictions between FPP and DIC on the requirement of surface reflectivity. Finally, the chain rule is introduced to further complete strain analysis with less computational cost. Experimental results demonstrated that the proposed method could simultaneously guarantee shape and deformation measurement accuracy. Meanwhile, both complete and fine surface geometry and its strain distributions can be obtained with simple convolution and algebraic operations, which can provide an alternative method for bridging 3-D geometric structures and the mechanical state of complex specimens.