Toughening mechanisms for the attachment of architectured materials: The mechanics of the tendon enthesis

Architectured materials offer tailored mechanical properties but are limited in engineering applications due to challenges in maintaining toughness across their attachments. The enthesis connects tendon and bone, two vastly different architectured materials, and exhibits toughness across a wide range of loadings. Understanding the mechanisms by which this is achieved could inform the development of engineered attachments. Integrating experiments, simulations, and novel imaging that enabled simultaneous observation of mineralized and unmineralized tissues, we identified putative mechanisms of enthesis toughening in a mouse model and then manipulated these mechanisms via in vivo control of mineralization and architecture. Imaging uncovered a fibrous architecture within the enthesis that controls trade-offs between strength and toughness. In vivo models of pathology revealed architectural adaptations that optimize these trade-offs through cross-scale mechanisms including nanoscale protein denaturation, milliscale load-sharing, and macroscale energy absorption. Results suggest strategies for optimizing architecture for tough bimaterial attachments in medicine and engineering.

Buckling and postbuckling of architectured materials: A review of methods for lattice structures and metal foams

Recent advances in manufacturing and material science have given rise to numerous architectured materials (archimats), which are tailored for multifunctionality and improved performance. Specifically, lattice structures and metal foams are usually lightweight optimized structural morphologies, which are prone to non-linear instability phenomena, leading to collapse or to a different stable state. This article offers an extensive review of analytical, numerical and experimental methods for investigating buckling and postbuckling in such materials. In terms of analytical modelling, linear elastic and geometrically non-linear models are presented. In numerical analysis, discrete and continuum models are presented, highlighting how numerical modelling can inform design of such materials and finally, experimental methods across different scales are reported, highlighting their merits, depending on the aim of the investigation.

Interface of a Al6061/Ti Composite Prepared by Field Assisted Sintering Technique

Architectured heterogeneous metallic composites consist of two dissimilar materials with a particular focus on spatial arrangement of constituents. This experimental study describes the application of Field Assisted Sintering Technique (FAST) for manufacturing of composite materials by sintering of a bulk reinforcement with a powder metal. Simple structure made of Ti wire (Ti Grade 2) was sintered with Al6061 alloy powder at 560 °C for 10 min. Successful material bonding and evolution of diffusion layer was thoroughly studied by scanning and transmission electron microscopy. Diffusion layer and adjacent precipitates are described as ternary Ti-Al-Si τ1 and τ2 phases. Si, as an alloying element in the Al6061 alloy, significantly affects the formation of the diffusion layer at the material interface due to its high inter-diffusion coefficient in both Al and Ti. Detailed TEM analysis also showed a modulated τ1/τ2 structure resembling a long-period stacking order (LPSO) phase, which has not been previously reported in the Ti-Al-Si ternary compounds. FAST is capable to manufacture composites from dissimilar constituents, which opens new possibilities for design and manufacturing of architectured materials.

Properties and role of interfaces in multimaterial 3D printed composites

In polyjet printing photopolymer droplets are deposited on a build tray, leveled off by a roller and cured by UV light. This technique is attractive to fabricate heterogeneous architectures combining compliant and stiff constituents. Considering the layer-by-layer nature, interfaces between different photopolymers can be formed either before or after UV curing. We analyzed the properties of interfaces in 3D printed composites combining experiments with computer simulations. To investigate photopolymer blending, we characterized the mechanical properties of the so-called digital materials, obtained by mixing compliant and stiff voxels according to different volume fractions. We then used nanoindentation to measure the spatial variation in mechanical properties across bimaterial interfaces at the micrometer level. Finally, to characterize the impact of finite-size interfaces, we fabricated and tested composites having compliant and stiff layers alternating along different directions. We found that interfaces formed by deposition after curing were sharp whereas those formed before curing showed blending of the two materials over a length scale bigger than individual droplet size. We found structural and functional differences of the layered composites depending on the printing orientation and corresponding interface characteristics, which influenced deformation mechanisms. With the wide dissemination of 3D printing techniques, our results should be considered in the development of architectured materials with tailored interfaces between building blocks.