Phase-separating resins for light-based three-dimensional printing of oxide glasses

Silica-based glasses can be shaped into complex geometries using a variety of additive manufacturing technologies. While the three-dimensional printing of glasses opens unprecedented design opportunities, the development of up-scaled, reliable manufacturing processes is crucial for the broader dissemination of this technology. Here, we design and study phase-separating resins that enable light-based 3D printing of oxide glasses with high-aspect-ratio features and enhanced manufacturing yields. The effect of the resin composition on the microstructure, mechanical properties and delamination resistance of parts printed by digital light processing is investigated with the help of printing experiments, compression tests and electron microscopy analysis. The chemical composition and microstructure of the cured resins were found to strongly affect the stiffness, delamination resistance, and calcination behavior of printed parts. These findings provide useful guidelines to enhance the reliability and yield of the DLP printing process of multicomponent silica-based glasses.Group Masani

Diamagnetic Composites for High-Q Levitating Resonators

Levitation offers extreme isolation of mechanical systems from their environment, while enabling unconstrained high-precision translation and rotation of objects. Diamagnetic levitation is one of the most attractive levitation schemes because it allows stable levitation at room temperature without the need for a continuous power supply. However, dissipation by eddy currents in conventional diamagnetic materials significantly limits the application potential of diamagnetically levitating systems. Here, a route toward high-Q macroscopic levitating resonators by substantially reducing eddy current damping using graphite particle based diamagnetic composites is presented. Resonators that feature quality factors Q above 450 000 and vibration lifetimes beyond one hour are demonstrated, while levitating above permanent magnets in high vacuum at room temperature. The composite resonators have a Q that is >400 times higher than that of diamagnetic graphite plates. By tuning the composite particle size and density, the dissipation reduction mechanism is investigated, and the Q of the levitating resonators is enhanced. Since their estimated acceleration noise is as low as some of the best superconducting levitating accelerometers at cryogenic temperatures, the high Q and large mass of the presented composite resonators positions them as one of the most promising technologies for next generation ultra-sensitive room temperature accelerometers.Dynamics of Micro and Nano SystemsAerospace Manufacturing TechnologiesQN/Steeneken La

Quantification of structural response and edge orientation of Chopped Tape Thermoplastic Composites in net-shaped specimens

Chopped Tape Thermoplastic Composites (CTTCs) offer high formability and performance for complex-shaped components in the aerospace and automotive industries. However, the mesoscopic discontinuity leads to spatial variabilities and correspondingly high scatter in the elastic properties of CTTCs due to the random orientations of chopped tapes and chopped tape-cavity edge interactions. Here we propose a new approach to investigate the effect of mould cavity edges on chopped tape orientation and hence the mechanical properties of CTTCs. Based on this approach, a Set Voronoi tessellation was implemented to represent the variability of local Young's Modulus and chopped tape-cavity edge interactions occurring during the manufacturing process. It was confirmed that the chopped tapes align along the edges, and progressively transition to a random orientation towards the middle of the specimen. The results were validated on moulded specimens and demonstrated the ability to deconvolute the edge interaction.Aerospace Manufacturing Technologie

3D Printing of Flow-Inspired Anisotropic Patterns with Liquid Crystalline Polymers

Anisotropic materials formed by living organisms possess remarkable mechanical properties due to their intricate microstructure and directional freedom. In contrast, human-made materials face challenges in achieving similar levels of directionality due to material and manufacturability constraints. To overcome these limitations, an approach using 3D printing of self-assembling thermotropic liquid crystal polymers (LCPs) is presented. Their high stiffness and strength is granted by nematic domains aligning during the extrusion process. Here, a remarkably wide range of Young's modulus from 3 to 40 GPa is obtained during by utilizing directionality of the nematic flow during the printing process. By determining a relationship between stiffness, nozzle diameter, and line width, a design space where shaping and mechanical performance can be combined is identified. The ability to print LCPs with on-the-fly width changes to accommodate arbitrary spatially varying directions is demonstrated. This unlocks the possibility to manufacture exquisite patterns inspired by fluid dynamics with steep curvature variations. Utilizing the synergy between this path-planning method and LCPs, functional objects with stiffness and curvature gradients can be 3D-printed, offering potential applications in lightweight sustainable structures embedding crack-mitigation strategies. This method also opens avenues for studying and replicating intricate patterns observed in nature, such as wood or turbulent flow using 3D printing.Aerospace Manufacturing TechnologiesGroup PeetersGroup Masani

Non-linear bending compliance of thin ply composite beams by local compression flange buckling

Passive spanwise bending shape-adaption has the potential to increase the efficiency and manoeuvrability of vehicles with wing-like structures. By utilisation of compression flange buckling, the in-plane stiffness can be tuned to design beams with contrasting pre-buckling and post-buckling bending stiffness. The investigated concept is experimentally validated using a thin-ply laminated composite four-point bending beam, which is designed to experience compression flange buckling in the span with constant moment. The bending stiffness was reduced by more than 41% after the onset of buckling which shows the effectiveness of compression flange buckling for non-linear bending compliance.Aerospace Manufacturing Technologie

Effect of fabric architecture, compaction and permeability on through thickness thermoplastic melt impregnation

To reduce the cycle time of structural, automotive thermoplastic composites, we investigated the potential of direct thermoplastic melt impregnation of glass fabrics using an injection moulding process. At the high pressures that occur during the process, the effect of the fabric architecture on the impregnation, compaction, volume fraction and permeability of two unidirectional fabrics was studied. Using impregnation experiments with a low viscosity PA6 melt, we identified a favourable processing window resulting in an impregnation time of 5 min. The impregnation experiments with thermoplastic melts demonstrate that textile architectures promoting dual scale flow during impregnation are favourable for complete filling. Based on our findings, thermoplastic compression resin transfer moulding is an efficient processing route for automated production of composite parts with a high fibre volume fraction, if the fabric architecture is adapted for higher processing pressures and by fully utilising dual scale flow.Aerospace Manufacturing Technologie

Gradient interphases between high-Tg epoxy and polyetherimide for advanced joining processes

Adhesive joining of carbon fibre reinforced polymer (CFRP) is cumbersome due to the careful surface preparation required and multiple validation steps to certify adhesion quality. Further these joints are often supplemented by mechanical fastenings add weight whilst also localising bearing stress. As an alternative technique, CFRP parts can be functionalized with thermoplastic surfaces during manufacture to enable cost-effective welding of composite structures. In the process of manufacturing the CFRP, curing an epoxy resin in the presence of the functionalising thermoplastic polymer can lead to local dissolution of the latter in the epoxy, followed by a reaction-induced phase separation. This results in a thermosetting-thermoplastic interphase featuring gradient concentrations and a multiphase morphology, which promotes load transfer between the thermosetting matrix and the thermoplastic joint. The aim of the work presented in this paper was to investigate interphase formation between high-Tg epoxy and polyetherimide (PEI) at different curing temperatures. The morphology was characterised using scanning electron microscopy and the composition of the interphase was quantified through Raman spectroscopy. The curing experiments indicated that temperature has a significant effect on the interphase morphology and led to two different biphasic morphologies which generally increased in size with increasing curing temperature. This suggests that the size of the gradient interphase can be tailored through the curing process, which is as a fundamental step in optimising the structural performance of welded joints with PEI-functionalized epoxy-based CFRPs.Aerospace Manufacturing TechnologiesStructural Integrity & Composite

Fabrication of Living Entangled Network Composites Enabled by Mycelium

Organic polymer-based composite materials with favorable mechanical performance and functionalities are keystones to various modern industries; however, the environmental pollution stemming from their processing poses a great challenge. In this study, by finding an autonomous phase separating ability of fungal mycelium, a new material fabrication approach is introduced that leverages such biological metabolism-driven, mycelial growth-induced phase separation to bypass high-energy cost and labor-intensive synthetic methods. The resulting self-regenerative composites, featuring an entangled network structure of mycelium and assembled organic polymers, exhibit remarkable self-healing properties, being capable of reversing complete separation and restoring ≈90% of the original strength. These composites further show exceptional mechanical strength, with a high specific strength of 8.15 MPa g.cm−3, and low water absorption properties (≈33% after 15 days of immersion). This approach spearheads the development of state-of-the-art living composites, which directly utilize bioactive materials to “self-grow” into materials endowed with exceptional mechanical and functional properties.Aerospace Manufacturing TechnologiesGroup MasaniaGeo-engineerin

Spin-Printing of Liquid Crystal Polymer into Recyclable and Strong All-Fiber Materials

Fiber-reinforced polymers are widely used as lightweight materials in aircraft, automobiles, wind turbine blades, and sports products. Despite the beneficial weight reduction achieved in such applications, these composites often suffer from poor recyclability and limited geometries. 3D printing of liquid crystal polymers into complex-shaped all-fiber materials is a promising approach to tackle these issues and thus increase the sustainability of current lightweight structures. Here, we report a spin-printing technology for the manufacturing of recyclable and strong all-fiber lightweight materials. All-fiber architectures are created by combining thick print lines and thin spun fibers as reinforcing elements in bespoke orientations. Through controlled extrusion experiments and theoretical analyses, we systematically study the spinning process and establish criteria for the generation of thin fibers and laminates with unprecedented mechanical properties. The potential of the technology is further illustrated by creating complex structures with unique all-fiber architectures and mechanical performance.Aerospace Manufacturing Technologie

Experimental and numerical investigation of ply size effects of steel foil reinforced composites

The effect of ply thickness on the notch sensitivity and bearing properties on carbon fibre reinforced polymer composites and their hybrid laminates with steel foils were studied. Laminates with ply thicknesses of 0.3 mm and 0.03 mm comprising of CFRP and hybrid laminates were manufactured and characterized using tension, open hole tension and double lap bearing tests. A 25% ply substitution was found to double the bearing load with extensive plastic deformation in the joint while maintaining high stress and maintaining constant cross-sectional thickness in the laminate. With a good agreement between the finite element predicted values and failure behaviour, the damage initiation and progression behaviour could be observed experimentally. We numerically captured (i) rapid failure of 0° plies in the thin ply CFRP hybrid and (ii) continuous delamination with significant plastic deformation for the thick ply CFRP hybrid. The numerical results significantly reduce future experimental work when designing hybrid laminates and could allow the laminate lay-up to be tailored for load cases. Both the experiments and numerical models underline the distinct size effects occurring with respect to the ply thicknesses when hybridising a very ductile metal with a brittle yet strong composite material.Structural Integrity & CompositesAerospace Manufacturing Technologie