On the progressive fatigue failure of mechanical composite joints

In this study, a novel holistic progressive damage model for mechanical fiber-reinforced polymer (FRP) joints under static and fatigue loading is presented. The model is implemented as a user-defined subroutine in the finite element software ABAQUS/Implicit. First, the theoretical basis of both the static and the fatigue damage model are explained in detail. Here, special emphasis is put on the introduction of the FRP fatigue damage model (FDM), which is based on a physically-motivated hypothesis enabling the consistent coupling of static and fatigue damage properties. Furthermore, detailed insights concerning the experimental calibration of the FDM are presented for the first-time. Subsequently, the presented damage model is validated using first-hand experimental results for standard bolt bearing, as well as T-bolt bearing, test setups. The experimental bearing setups are tested and analyzed until ultimate failure, applying static and fatigue loading. It is shown that the model prognoses are in close accordance with experimental measurements and observations in terms of static joint strength, cyclic stiffness degradation and cycles to failure. The rich information provided by the damage model concerning the progressive damage evolution under static and fatigue loading conditions allows for its application within virtual test rigs for mechanical FRP joints. In that context, this work demonstrates the promising abilities and features of the energy hypothesis applied for the FDM for use-cases of significant relevance in the composite industry for the first time in literature.