Identification of a cohesive zone model from digital images at the micron-scale

We present a new methodology for the identification of a zone cohesive model that describes material failure. The material under consideration fails by crazing. The study is conducted at the micron scale in order to capture and analyze the fracture mechanism. The crack tip displacement fields are measured optically by Digital Image Correlation. The local stress intensity factors (mode I and II) and the location of the equivalent elastic crack tip are calculated during the loading. The variation of the location of the equivalent crack tip is used to track the initiation and growth of the process zone, up to the onset of crack propagation. These experimental measurements are used to define the appropriate parameters in a cohesive zone model. The methodology addresses the onset of crazing, the traction–separation profile and the maximum opening corresponding to the local nucleation of a crack. The cohesive parameters that are derived from the experimental data are consistent with results available in the literature. In addition, the model enables the characterization of the normal and tangential mode of the cohesive model.

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► Fracture experiments on PMMA sample with sharp initial crack are carried out.
► Digital images with sub-micron resolution of the sample surface are analyzed.
► Cohesive zone features are derived from fracture mechanics elastic fields.
► Numerical simulations of the experiment using a cohesive zone model are carried out.
► Cohesive zone parameters are adjusted within the proposed theoretical framework.