Phase-field modeling of fracture in fused filament fabricated thermoplastic parts and experimental validation

In this work, a phase-field fracture model is formulated specifically for thermoplastic parts manufactured by fused filament fabrication (FFF). Due to their layered nature, FFF parts present an orthotropic fracture behavior, with their interfaces representing energetically favorable crack paths. The proposed phase-field model relies on the introduction of two damage variables, one for cross-layer and one for inter-layer crack propagation, allowing to capture the distinct fracture behavior of the thermoplastic filaments and the interfaces. The model is applied to the three-point bending of single-edge notched bending (SENB) FFF specimens with six different material orientations. The comparison with the experimental results shows that the proposed phase-field model can predict the experimentally observed peak load for the six material orientations with a maximum error of ≈ 11%. Furthermore, the model can also accurately predict the crack path and the softening behavior observed experimentally. To validate the capacities of the phase-field model, an experimental campaign on FFF compact-tension (CT) specimens modified with holes was performed. Comparing the numerical prediction with the experimental results for the modified CT specimens shows that, although the model features some limitations, it is still able to accurately capture the location of crack initiation and predict the peak load with a relative error of ≈ 2%.