Bio-inspired 3D-printed microstructure for crack arresting in bio-based epoxy matrix
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Zhiyuan XU (NETHERLANDS), Ran TAO (NETHERLANDS), Sofia TEIXEIRA DE FREITAS (NETHERLANDS)Abstract :
The demand for greater sustainability in load-bearing materials in aerospace and automotive engineering, with low carbon emission and safety requirements, drives the need for the replacement of fossil fuel-based materials by bio-based materials. Despite their eco-friendly and sustainable properties, bio-based epoxies for example face limitations in engineering applications due to their low mechanical properties such as fracture resistance. Through evolution over millions of years, natural materials provide a wealth of sophisticated and hierarchical structures with high fracture resistance at low environmental costs, including spider silk, bone, and nacre. One of the key features that contribute to the high fracture resistance of these biological materials is the presence of sacrificial bonds and hidden length (SBHL) in their microscale organic structures.
Drawing inspiration from these biological structures, this work presents a bio-inspired microstructure named overlapping curl (OC) to mimic SBHL features for the purpose of arresting crack propagation in a bio-based epoxy matrix and improving their intrinsic poor fracture resistance. Fused filament fabrication 3D printing was adopted to fabricate OC with polylactide (PLA) material and its mechanical behavior was first characterized through tensile tests. Subsequently, the OC microstructures were embedded into a bio-based epoxy. Compact tension (CT) tests were performed to assess the mode I fracture toughness of the bio-based epoxy under quasi-static opening displacement. Utilizing a 3D Digital Image Correlation together with a microscope, the crack advancement was monitored and the evolution of the process zone was analysed.
The OC experimental results revealed a typical saw-tooth curve attributed to the continuous break of sacrificial bonds and the corresponding unfolding of hidden length, ultimately leading to the failure of the straightened OC filament. A higher energy absorption was obtained in OC thanks to the rupture of sacrificial bonds and extension of hidden length in comparison with the straight fiber. Observations from the CT experiments confirm the crack propagation arrest capability of the integrated OC through extrinsically toughening mechanisms. By partially bearing the load as the hidden length unravels, the OC effectively transferred stresses between the crack surfaces and redistributed the stress field around the crack tip, thereby delaying the crack propagation. As a result, the modified bio-based epoxy exhibited enhanced fracture toughness compared to the pure epoxy. The findings in this work lay the foundations for developing novel bio-based epoxy and composite materials with desired mechanical properties and open new opportunities for safer and more sustainable applications in load-bearing structures.
Drawing inspiration from these biological structures, this work presents a bio-inspired microstructure named overlapping curl (OC) to mimic SBHL features for the purpose of arresting crack propagation in a bio-based epoxy matrix and improving their intrinsic poor fracture resistance. Fused filament fabrication 3D printing was adopted to fabricate OC with polylactide (PLA) material and its mechanical behavior was first characterized through tensile tests. Subsequently, the OC microstructures were embedded into a bio-based epoxy. Compact tension (CT) tests were performed to assess the mode I fracture toughness of the bio-based epoxy under quasi-static opening displacement. Utilizing a 3D Digital Image Correlation together with a microscope, the crack advancement was monitored and the evolution of the process zone was analysed.
The OC experimental results revealed a typical saw-tooth curve attributed to the continuous break of sacrificial bonds and the corresponding unfolding of hidden length, ultimately leading to the failure of the straightened OC filament. A higher energy absorption was obtained in OC thanks to the rupture of sacrificial bonds and extension of hidden length in comparison with the straight fiber. Observations from the CT experiments confirm the crack propagation arrest capability of the integrated OC through extrinsically toughening mechanisms. By partially bearing the load as the hidden length unravels, the OC effectively transferred stresses between the crack surfaces and redistributed the stress field around the crack tip, thereby delaying the crack propagation. As a result, the modified bio-based epoxy exhibited enhanced fracture toughness compared to the pure epoxy. The findings in this work lay the foundations for developing novel bio-based epoxy and composite materials with desired mechanical properties and open new opportunities for safer and more sustainable applications in load-bearing structures.