Experimental–numerical phase-field modelling of ductile and fatigue fracture in short fibre-reinforced polymeric adhesives

Structural adhesives are essential in wind turbine blades, where bonded joints are subjected to complex static and cyclic loading and are prone to fatigue-driven failure. Recently developed short fibre-reinforced polymeric (SFRP) adhesives offer enhanced mechanical performance, but their fracture behaviour is strongly influenced by fibre orientation and anisotropy. This study presents an experimental-numerical framework for predicting quasi-static and fatigue fracture in SFRP adhesives using a phase-field approach. An experimental campaign, including quasi-static and tension-tension fatigue tests with full-field strain measurements, reveals pronounced anisotropic elasto-plastic behaviour, orientation-dependent fatigue life, and distinct damage mechanisms under monotonic and cyclic loading. Based on these observations, an anisotropic phase-field model for ductile fracture is developed and coupled with an invariant-based transversely isotropic elasto-plastic constitutive formulation with pressure sensitivity and non-associative plastic flow. Fatigue effects are incorporated through a thermodynamically consistent degradation of fracture toughness driven by accumulated energy dissipation. The model is implemented within a finite element framework and validated against experiments through simulations of dog-bone and single-edge notched specimens. The numerical results show very good agreement with experimental stress–strain responses, S-N curves, and crack initiation and propagation behaviour, demonstrating the capability of the proposed framework to predict the durability of SFRP adhesive joints under static and cyclic loading.