Insertion of large diameter through-thickness metallic pins in composites

Existing Through-Thickness Reinforcement (TTR) methods for laminated composites using semi or fully rigid reinforcing elements, like tufting, stitching, and z-pinning, present limitations on reinforcing element geometry, strength, and stiffness. Where these application envelopes are exceeded, TTR element insertion results in unacceptable levels of damage to both the composite and/or TTR elements. Here, we demonstrate that low-speed insertion of rigid reinforcements into heated prepreg preforms is a feasible and robust reinforcement process capable of providing accurate TTR element placement with minimal tow disturbance compared with existing methods for similar pin sizes. The insertion process is characterised with respect to insertion forces, and mesoscale laminate deformation/damage for carbon-benzoxazine prepreg preforms. The research investigates the influence of pin leading edge on insertion for a range of pin diameters (1.2, 1.5, and 2.0 mm) and preform consolidation states, describing low insertion forces and good quality laminate preforms. Insertion forces increase with pin diameter, typically resulting from increased pin-tow contact area and friction. Large diameter sizes and low insertion forces expand the range and forms of materials that can be inserted compared to existing TTR methods and show that this method can potentially be transferred to benefit work on composite hole creation, joining, and repair

Cathepsin B modulates lysosomal biogenesis and host defense against Francisella novicida infection

Lysosomal cathepsins regulate an exquisite range of biological functions, and their deregulation is associated with inflammatory, metabolic, and degenerative diseases in humans. In this study, we identified a key cell-intrinsic role for cathepsin B as a negative feedback regulator of lysosomal biogenesis and autophagy. Mice and macrophages lacking cathepsin B activity had increased resistance to the cytosolic bacterial pathogen Francisella novicida. Genetic deletion or pharmacological inhibition of cathepsin B down-regulated mechanistic target of rapamycin activity and prevented cleavage of the lysosomal calcium channel TRP ML1. These events drove transcription of lysosomal and autophagy genes via transcription factor EB, which increased lysosomal biogenesis and activation of autophagy initiation kinase ULK1 for clearance of the bacteria. Our results identified a fundamental biological function of cathepsin B in providing a checkpoint for homeostatic maintenance of lysosome populations and basic recycling functions in the cell

Z-direction heat transfer in composites hybridised with large diameter metallic pins

Continuous fibre reinforced polymer composites have a well-established track record of excellent structural performance but generally lack non-structural functionalities inherent in legacy materials like metals. As the range of applications for composites continues to expand beyond their traditional base in aerospace, and to meet ambitious ‘Net Zero’ targets, there is increasing demand for embedded functionality in composites, like electrical or thermal energy transfer, though which a multitude of other functionalities are derived. A particularly under addressed challenge is how to efficiently achieve significant z-direction (through-thickness) functionality, which is restricted by the planar nature of composite. Through- thickness reinforcement (TTR) is typically used to achieve improvements in outof-plane structural performance but can be applied to the integration of hybridising elements, like metallics, that can impart desired functionality. Here we demonstrate that composite hybridisation by the addition of large diameter (2 mm) metallic pins positively affects the z-direction transfer of thermal energy through carbon-benzoxazine composite without adverse effects on in-plane mechanical performance. This work conducts extensive mechanical and thermomechanical characterisation of the carbon-benzoxazine composite and the metal-composite hybridised system which feeds into the development of an experimentally validated macroscale (ply-level) representative volume element (RVE) finite element (FE) model. The FE model captures both thermal energy transfer and thermomechanical behaviour of the hybridised system during operation. Results show that highly conductive pins significantly improve the local thermal conductivity and act to accelerate heat flow through the hybridised system, reducing thermal lag through-the-thickness

An evaluation of large diameter through-thickness metallic pins in composites

There is increasing demand for functional through-thickness reinforcement (TTR) in composites using elements whose geometry exceeds limitations of existing TTR methods like tufting, stitching, and z-pinning. Recently, static insertion of large diameter TTR pins into heated prepreg stacks has proven a feasible and robust reinforcement process capable of providing accurate TTR element placement with low insertion forces and lower tow damage compared with existing methods for similar element sizes (>1mm diameter) like post-cure drilling. Local mechanical performance and failure mechanics of these pinned laminates are reported here. Laminates with a single statically inserted pins (1.2, 1.5, and 2.0 mm) can mostly retain their in-plane integrity alongside a local improvement in mode I delamination toughness in carbon fibre-benzoxazine laminates. Tensile strength is mostly unaffected by the pins resulting from delamination suppression, whereas there is up to a doubling of Young’s modulus. Compressive strength is significantly diminished (up to 42 %) in pinned laminates. Interlaminar toughness is improved, and peak toughness is pushed ahead of the crack as pin diameter increases. The lack of significant deterioration in in-plane tensile properties in pinned laminates produced using static insertion can expand the range and forms of materials that can be inserted compared to existing TTR.This work was supported by the SEER project which has received funding from the European Union's Horizon 2020 research and innovation programme (Grant agreement 871875)

Metabolic signaling directs the reciprocal lineage decisions of αβ and γδ T cells

Wiring metabolic signaling circuits in thymocytes Cell differentiation is often accompanied by metabolic changes. Yang et al. report that generation of double-positive (DP) thymocytes from double-negative (DN) cells coincides with dynamic regulation of glycolytic and oxidative metabolism. Given the central role of mechanistic target of rapamycin complex 1 (mTORC1) signaling in regulating metabolic changes, they examined the role of mTORC1 pathway in thymocyte development by conditionally deleting RAPTOR, the key component of the mTORC1 complex, in thymocytes. Loss of RAPTOR impaired the DN-to-DP transition, but unexpectedly also perturbed the balance between αβ and γδ T cells and promoted the generation of γδ T cells. Their studies highlight an unappreciated role for mTORC1-dependent metabolic changes in controlling thymocyte fates. The interaction between extrinsic factors and intrinsic signal strength governs thymocyte development, but the mechanisms linking them remain elusive. We report that mechanistic target of rapamycin complex 1 (mTORC1) couples microenvironmental cues with metabolic programs to orchestrate the reciprocal development of two fundamentally distinct T cell lineages, the αβ and γδ T cells. Developing thymocytes dynamically engage metabolic programs including glycolysis and oxidative phosphorylation, as well as mTORC1 signaling. Loss of RAPTOR-mediated mTORC1 activity impairs the development of αβ T cells but promotes γδ T cell generation, associated with disrupted metabolic remodeling of oxidative and glycolytic metabolism. Mechanistically, we identify mTORC1-dependent control of reactive oxygen species production as a key metabolic signal in mediating αβ and γδ T cell development, and perturbation of redox homeostasis impinges upon thymocyte fate decisions and mTORC1-associated phenotypes. Furthermore, single-cell RNA sequencing and genetic dissection reveal that mTORC1 links developmental signals from T cell receptors and NOTCH to coordinate metabolic activity and signal strength. Our results establish mTORC1-driven metabolic signaling as a decisive factor for reciprocal αβ and γδ T cell development and provide insight into metabolic control of cell signaling and fate decisions. Development of αβ and γδ T cells requires coupling of environmental signals with metabolic and redox regulation by mTORC1. Development of αβ and γδ T cells requires coupling of environmental signals with metabolic and redox regulation by mTORC1

Improved Energy Absorption in 3D Woven Composites by Weave Parameter Manipulation

3D woven composites show significantly improved out-of-plane properties over traditional 2D laminates. This high through-thickness reinforcement is desirable in crashworthiness applications where crushing energy can be increased by composites’ improved interlaminar toughness. However, their use in practical applications is stunted by the poor understanding of how small variations in weave parameters, whether intended or not, affect the performance of these materials. Here, we demonstrate that small changes in textile properties, in this case pick density and float length have a knock-on effect that can greatly improve or diminish the crush performance of a 3D woven layer-to-layer structural fabric. Quasi-static and dynamic energy absorption values up to approximately 95J/g and 92J/g respectively are achieved. Crush performance is investigated on omega-shaped coupons, under both quasi-static and dynamic loading conditions with crush rates between 2mm/min and 8.5m/s. The failure mechanisms present during progressive crush under quasi-static loading transitions between more expected brittle dominated failure and ductile dominated failure, which is more typical of metals under similar loading conditions. Whereas when dynamic loading is considered, the materials present a more typical splaying failure event. As a result, additional exploration of the three-point bending response of these varied architectures is presented as a means of further explaining the interplay between lamina bending and progressive folding/micro-buckling in these materials. The effect of the weave’s architectural alterations on physical composite properties such as weight, density and conformability to shape is also investigated

Energy Absorption Mechanisms in Layer-to-Layer 3D Woven Composites

3D woven composites provide improved out-of-plane performance over their two-dimensional counterparts. This sort of reinforced through thickness behaviour is desirable in crashworthiness applications where energy absorption can be increased by the composite material's resistance to delamination. The behaviour of these 3D materials in not well understood and fundamental data that can be used to validate and improve material models is not yet sufficiently comprehensive. Here we demonstrate that a modified layer-to-layer type 3D woven architecture can be effectively used in energy absorbing elements to produce repeatable and predictable progressive failure under axial crush conditions. Specific energy absorption (SEA) values in glass and carbon coupons of up to 62J/g and 95J/g respectively are achieved in the quasi-static regime; values up 93J/g to were achieved in the dynamic regime when carbon coupons are tested. Carbon specimens displayed uncharacteristic mixed mode failure with elements of ductile and brittle failure. The addition of a toughening agent showed mixed results in this study, providing quasi-static improvements (+8%) in SEA but significant diminishment in dynamic SEA (-22%). The failure modes present in all cases are explored in depth and the suitability of this material for industry crash applications is investigated