Micromechanical finite element study of initial porosity in structural adhesives

Adhesive bonding is widely adopted in the aeronautic and automotive industries due to their ability to distribute loads uniformly and reduce stress concentrations. However, adhesives may exhibit manufacturing defects, notably porosity. Initial porosity can be introduced during mixing phase, curing process or application and can alter their mechanical behaviour. Nevertheless, this phenomenon is neglected in adhesives constitutive behaviour modelling. Understanding the elastic porous behaviour is crucial for the damage initiation assessment. The novelty of this work is to numerically study the effect of initial porosity on the elastic properties of epoxy adhesives at the microscale. A Representative Elementary Volume (REV) approach is newly proposed in this framework. Key parameters such as porosity rate, density, size and spatial distribution are investigated. Porosity rate increasing gives a decreasing in tensile and shear elastic moduli (e.g. a decrease of 50% is found at a porosity rate of 30%). Porosity density, spatial arrangement and size distribution have negligible effects. Comparisons with literature experimental data, in a multiscale approach, set the reliability of this REV model for the identification of macroscopic mechanical properties of adhesive joints. • A numerical REV model is proposed to analyze initial porosity in adhesives. • Negligible effects: pores spatial and size distributions, porosity density. • Homogenized tensile and shear elastic moduli decrease with increasing porosity rate. • A REV-based multiscale approach is used to identify joints macroscopic properties.