Optimization of the phase demodulation algorithms for investigating the optical properties of the polymer fibre during mechanical deformations interferometrically

The mechanical deformations in polymer fibres play an essential role for understanding the mechanism of fracture in this material. These deformations were examined interferometrically. The optical phase map of the deformed fibres has the key information about their structural features. So, the main core of this paper is to find an optimal algorithm for analyzing the interference fringe patterns of deformed fibres and demodulating their phase maps. For performing this task, two beam interference patterns for crazed and fractured polypropylene (PP) fibres were captured using the non-duplicated Pluta interference microscope. The phase map for each deformation demodulated using the spatial carrier frequency, the one- dimensional continuous wavelet transform (1D CWT) and the phase shifting fringe pattern analysis algorithms. The performance of each algorithm for finding the optimal phase map was evaluated using the contour line method. A refined method for calculating the areal craze density of a crazed pattern is presented. Based on the optimal extracted phase values of PP fibre for each type of deformation, the 3D birefringence values were calculated.