A Comparative Study of FEM Modelling Strategies for the Fibre Composite Adherend to Predict the Strength of Bonded Joints

The increasing importance of lightweight construction in aviation to enhance fuel efficiency has brought fiber reinforced composite structures back into focus. To fully leverage the potential of these structures, adhesive bonding is particularly suitable, as it enables uniform load transfer without weakening the material through drilling. However, adhesive bonds in aviation are subject to a complex certification process. Precise progressive damage analyses, particularly for predicting static strength, are therefore essential for understanding and potentially certifying bonded fiber-reinforced composite structures. The aim of this study is to evaluate FEM modelling strategies to accurately predict the progressive damage behaviour of Carbon Fiber Reinforced Polymer (CFRP) laminates in bonded joints. As damage may not only occur in the adhesive but can also arise within the adherend, it is necessary to model the intra- and interlaminar (damage) behavior of the laminate. Especially with regard to the modelling of fibre composite laminates, many different approaches can be found in the literature. This work aims to provide an overview of the strategies suitable for adhesive joints and to give recommendations for a computationally efficient and precise numerical prediction. The intralaminar behavior of CFRP laminates is modeled using either 2.5D continuum shell elements or fully 3D solid elements, coupled with a material model capable of capturing the matrix’s plasticity. This material model incorporates extended 3D formulations of failure criteria and damage evolution based on Cuntze’s Failure Mode Concept (FMC), providing a robust framework for damage initiation and progression. Interlaminar behavior is analyzed using either cohesive zone modeling (CZM) with surface-based contacts or cohesive elements, or by neglecting interlaminar effects entirely for comparative evaluation. To evaluate the various modelling strategies, these are compared with various experimental results. This involves comparing samples from material characterisation to single lap shear specimens. This study provides an overview of the quality, advantages and disadvantages of different modelling strategies of fibre composite adherends in bonded joints. In combination with an equivalent study on the modelling of adhesives, this work serves as a basis for further investigations with more complex requirements. Possible applications of these strategies could be bonded fuselage segments, stringer-skin joints or investigations of bonded joints on CFRP hydrogen tanks, as well as many others.