Effects and recommendations of crack tip modelling on compliance solutions

•For blunt crack tips, as the radius increases, the specimens’ compliance also increases.•For sharp crack tips, as the element size of the crack tip increases, the specimens’ compliance decreases.•Similar compliance results are obtained for both meshes when the radius or element size of the crack tip are low enough.•Two models were created that show the crack tip radius or the element size impact on the elastic unloading compliance.•A parameter that normalizes the crack tip radius or the element size with the specimens’ width is proposed. Elastic unloading compliance is a common technique to determine instantaneous crack size in fracture mechanics properties such as resistance curves (R-curves) and fatigue crack growth. This technique uses a polynomial, developed using finite elements models, to correlate compliance with crack depth. In these models, crack tip is usually modeled with a blunt mesh (with a crack tip radius ρ) or a sharp mesh (with element size in the width direction l), and neither are standardized in the literature. This paper shows that both affect compliance, therefore potentially impacting results of fracture mechanics properties acquired from simulations. This paper focuses on how those parameters affects compliance in SE(B) models. Finally, a parameter φ that normalizes ρ or l with the width was developed and recommended values based on compliance convergence are suggested. Controlling φ may help to ensure reliable results in fracture mechanics models where compliance needs to be determined.