Damage and fracture mechanisms of polyoxymethylene: Multiscale experimental study and finite element modeling

This work deals with the deformation and damage of a semi-crystalline polymer (polyoxymethylene) into which a metallic screw is screwed. The micro-mechanisms were investigated by using the Synchrotron Radiation Tomography technique. Penny shaped damage/crazes were revealed. The maximum damage location was found to be dependent on the initial notch root radius of the specimen. The X-ray laminography technique highlighted the extent of the damaged/crazed volume within a flat CT specimen. Thanks to an understanding of these micro-mechanisms, the local approach of fracture was applied to model the screw penetration operation. To this end, a dedicated damage based constitutive model was implemented in a FE code. After calibration of the material parameters, the FE simulations were able to describe the net stress versus opening displacement curves, as well as the evolution of void volume fraction distribution along the remaining section, as a function of increasing load.