A micromechanical damage characterization and the modeling of a mineral filled epoxy adhesive

• An experimental study of the failure process of an epoxy adhesive has been undertaken.
• The mineral fillers contribute to a deterministic failure process.
• SEM observations of the damage evolution has been used to evaluate its kinetics.
• A physically based damage model is proposed and its performance assessed.

Current structural adhesives can be used to assemble a variety of similar and dissimilar materials, usually with minimal surface preparation and sometimes even without degreasing. This kind of performance is obtained by using filled structural polymers which, as a consequence, lead to complex multi-phased composite material microstructures. Nevertheless, the use of mineral fillers such as talc also affects the adhesive mechanical behavior which is of major importance for structural applications. In order to study this type of material, a multi-axial mechanical characterization of an epoxy structural adhesive has been undertaken using a modified Arcan setup. An unfilled and not marketed formulation of the epoxy adhesive has also been tested to emphasize the role of the mineral particles on its mechanical behavior. As a first step, this paper reports the mechanical differences that have been observed between the filled and the unfilled versions of the adhesive, and proposes possible explanations related to microstructural processes. Contribution of the mineral fillers leads to a deterministic failure process. This is suggested, most significantly, by microstructural observations which have revealed useful information concerning the damage evolution and its kinetics. Indeed, the applied mechanical load provokes an exfoliation of talc flakes leading to a pattern of micro-cracks. In a subsequent step in the study, based on both macro and micro experimental results of the adhesive, a damage model has been derived from the vectorial description of cracking modes and its performance has been assessed.