In situ AFM investigation of slow crack propagation mechanisms in a glassy polymer. J. Mech. Phys. Solids 2018

George M., Nziakou Y., Goerke S., Genix A.C., Bresson B., Roux S., Delacroix H., Halary J.L. and Ciccotti M., 2018.
In situ AFM investigation of slow crack propagation mechanisms in a glassy polymer. J. Mech. Phys. Solids 112, 109–125.

A novel experimental technique based on in situ AFM monitoring of the mechanisms of damage and the strain fields associated to the slow steady-state propagation of a frac- ture in glassy polymers is presented. This micron-scale investigation is complemented by optical measurements of the sample deformation up to the millimetric macroscopic scale of the sample in order to assess the proper crack driving conditions. These multi-scale observations provide important insights towards the modeling of the fracture toughness of glassy polymers and its relationship with the macromolecular structure and non-linear rheological properties. This novel technique is first tested on a standard PMMA thermo- plastic in order to both evaluate its performance and the richness of this new kind of ob- servations. Although the fracture propagation in PMMA is well known to proceed through crazing in the bulk of the samples, our observations provide a clear description and quan- titative evaluation of a change of fracture mechanism towards shear yielding fracture ac- companied by local necking close to the free surface of the sample, which can be explained by the local change of stress triaxiality. Moreover, this primary surface necking mechanism is shown to be accompanied by a network of secondary grooves that can be related to surface crazes propagating towards the interior of the sample. This overall scenario is val- idated by post-mortem fractographic investigations by scanning electron microscopy.

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