Brittle fracture in polyoxymethylene plates

The fracture mechanics properties and dynamic crack propagation in polyoxymethylene plates are examined in this study. Experiments are carried out in terms of three-point-bending of beams with an initial central crack and also tensile testing of compact-tension test specimens. The test specimens were taken from plates that had been manufactured by injection-moulding. Test specimens were taken in different orientations in the test plates in order to investigate the possible influence of anisotropy. The influence of crack sharpness and loading rate was also investigated. The mechanical fields around the initial, stationary crack were analysed using a rate-dependent plasticity model and the standard finite element method. Dynamic crack propagation was modelled using an AT1-type phase-field model. In the phase-field model, the bulk material was modelled as a linearly elastic material, and the surface energy was taken to be the equivalent surface energy that also includes possible dissipative processes in the surrounding bulk material. In both of the test specimens, dynamic crack propagation would initiate at a critical external load. In the three-point-bending tests, the crack would just propagate straight-ahead as a single crack, whereas in the compact-tension tests, the crack would branch into two main cracks after a short distance of single crack propagation. The crack branches made an angle of about 40 ° to the initial crack plane, and the branched cracks reached speeds of up to 30% of the Rayleigh wave speed. The simulations suggested that the surface energy is much higher at quasi-static crack growth (about 3kJ/m 2 ) than during dynamic crack propagation (5-6 times lower). Also, the phase-field simulations were able to reproduce the crack branching observed in the CT specimens. • Experimental fracture mechanics testing of polyoxymethylene plates. • Phase-field simulations of dynamic crack propagation in polyoxymethylene.