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

• Local approach of fracture to investigate screwing of a semi-crystalline polymer.
• X-ray tomography to inspect in 3D the deformation and damage mechanisms.
• Characterization of penny shaped crazes within notched round bars and CT specimen.
• FE simulations with dedicated damage-based model capturing the micro-mechanisms.
• Durability of the assembly assessed by the damage set during the screwing process.

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.

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