Micro-mechanical characterisation of 3D-printed composites via nano-indentation and finite-element homogenization techniques: overcoming challenges in orthotropic property measurement

Abstract Mechanical characterisation of 3D-printed composite materials using conventional methods, such as tension and compression tests, faces several challenges, including precise machining of complex geometries, difficulties in testing materials with time-dependent properties, and extensive sample preparation to account for varying build orientations and raster angles. Accurately characterising the mechanical properties of composite constituents is further complicated by their anisotropic nature, visco-plastic behaviour, and phase interactions at the micro-scale. Traditional nano-indentation techniques often suffer from inaccuracies due to pile-up effects and time-dependent deformations in polymer matrices. To overcome these challenges, this study introduces an innovative methodology that integrates nano-indentation and micro-mechanical analysis of a representative volume element (RVE) to determine orthotropic engineering constants. Experimental nano-indentation, coupled with atomic force microscopy, is used to obtain load–displacement curves and residual indentation marks, whilst an inverse finite-element method accounting for neighbouring phase effects and polymer matrix creep properties enhances prediction accuracy. The stiffness properties of composite constituents derived from this method are employed in an RVE-based micro-mechanical model, with effective orthotropic engineering constants validated through experimental tensile and shear tests using the Digital Image Correlation technique. This approach not only enhances micro-mechanical characterisation accuracy but also reduces the need for extensive experimental testing, offering a cost-effective and scalable solution for evaluating 3D-printed composite materials. Additionally, it bridges the gap between microstructural and bulk property measurements, reducing test sample manufacturing costs and minimising the need for repetitive experimental trials.