Grid method: Application to the characterization of cracks

In this paper we present an application of the grid method to the assessment of crack initiation and growth in brittle materials. It is shown that a grid deposited on the surface of a structure can be utilized to characterize the crack location and opening. Furthermore, one single picture only is required to carry out a control over a predefined area. First, the principle of the method is introduced, showing that a periodical pattern encoding a cracked surface can be analyzed by signal processing. The phase modulation of the grid can be calculated very accurately for any small deformation of the structure. Discontinuities due to cracks are easily detected on the phase field and the crack width is proportional to the amplitude of the discontinuity. Secondly, the performances of the method are presented, mainly depending on the spatial frequency of both the pattern and the sampling. It is shown that good results can generally be obtained with few setting difficulties and equipment investment. Finally, we sum up some basic recommendations for the practical use of the technique.