Investigation of crack growth in functionally graded materials using digital image correlation

The crack growth resistance behavior of functionally graded materials (FGMs) was investigated using the full-field measurement technique of digital image correlation (DIC). Model FGMs were manufactured using ultraviolet irradiation of a photosensitive polyethylene co-polymer. Edge crack FGM fracture specimens were loaded such that stable quasi-static crack growth occurred. A DIC code, generated and tested in-house, was used to obtain the in-plane displacement field surrounding the propagating crack. The results were then used to extract stress intensity factors and generate resistance curves for the FGM. A crack growth resistance behavior of continually increasing toughness with crack extension was observed. The full-field optical technique also allowed for the investigation of regions of K-dominance in the FGM (i.e. areas where the theoretical asymptotic fields well describe the near tip deformation). The results were compared to stress intensity factor values obtained using crack face profile shape measurements and good agreement was found.