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This perspective details the grand challenges of designing and manufacturing multifunctional materials to impart autonomous property recovery. The susceptibility of advanced engineering composites to brittle fracture has led to the... more
This perspective details the grand challenges of designing and manufacturing multifunctional materials to impart autonomous property recovery. The susceptibility of advanced engineering composites to brittle fracture has led to the emergence of self-healing materials. This functionality has been demonstrated in bulk polymers and fibre-reinforced composites; most recently through the addition of vascular networks into the host material. These network systems enable the healing agents to be transported over long distances and provide a means by which both the resin and hardener can be replenished, thus overcoming the inherent limitations of capsule-based systems. To date, vascule fabrication methods include machining, fugitive scaffold processes, a lost-wax process and the vaporisation of sacrificial components, but recent developments in additive manufacturing (AM) technologies have paved the way for more efficient, bio-inspired vascular designs (VDs) to be realised. This perspective...
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Design and certification of novel self-healing aerospace structures was explored by reviewing the suitability of conventional deterministic certification approaches. A sandwich structure with a vascular network self-healing system was... more
Design and certification of novel self-healing aerospace structures was explored by reviewing the suitability of conventional deterministic certification approaches. A sandwich structure with a vascular network self-healing system was used as a case study. A novel probabilistic approach using a Monte Carlo method to generate an overall probability of structural failure yields notable new insights into design of self-healing systems, including a drive for a faster healing time of less than two flight hours. In the case study considered, a mature self-healing system could be expected to reduce the probability of structural failure (compared to a conventional damage-tolerant construction) by almost an order of magnitude. In a risk-based framework this could be traded against simplified maintenance activity (to save cost) and/or increased allowable stress (to allow a lighter structure). The first estimate of the increase in design allowable stresses permitted by a self-healing system is...
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Novel multi-stage adaptive morphing of a hydrogel cube has been achieved by combining multi-metal ionoprinting and redox chemistry of iron. A demonstration of the two-stage deployment has been shown for (1) the selective opening and... more
Novel multi-stage adaptive morphing of a hydrogel cube has been achieved by combining multi-metal ionoprinting and redox chemistry of iron. A demonstration of the two-stage deployment has been shown for (1) the selective opening and closing of the cube’s lid, where the hinge point has been ionoprinted with iron, and (2) the full unfolding and folding of the cube into its cruciform net, with remaining hinges ionoprinted with vanadium. The selective unfolding and folding is achieved by alternating the oxidation state of iron between +2 and +3. This is achieved using redox chemistry selective for iron. This approach could be applied, in principle, to more degrees of staging by adding additional redox responsive ionoprinted cations and appropriate selection of reducing agents.
Research Interests: Materials Science, Polymerization, Polymer, Morphing, Biomaterial, and 6 moreVanadium, MRS, Redox, Reducing Agent, Hinge, and Cruciform
A qualitative study on the influence of an embedded vascular network on the structural performance of a FRP composite laminate is presented. This study includes: methods of forming such vascular networks in laminates; characterisation of... more
A qualitative study on the influence of an embedded vascular network on the structural performance of a FRP composite laminate is presented. This study includes: methods of forming such vascular networks in laminates; characterisation of laminate cross-sections; FE analysis for failure initiation and validation of the FE results via mechanical testing.
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Incorporation of multifunctionality to fibre reinforced polymer composite materials delivers many benefits. One example includes improved longevity of components through increasing permissible temperatures of operation, which could be... more
Incorporation of multifunctionality to fibre reinforced polymer composite materials delivers many benefits. One example includes improved longevity of components through increasing permissible temperatures of operation, which could be achieved via in-situ cooling. As the temperature of composite components approaches the glass transition temperature (Tg) of the matrix, thermal stress induced ageing greatly increases [1], [2], thus the incentive for integrated cooling. In order to assess the damage, which could be caused by exposure to elevated temperatures, isothermal ageing was performed at a temperature 15°C lower than the materials Tg (2200 hours at 110°C). Material used in this study is a carbon/epoxy prepreg system (Gurit, SE70), with a Tg of 126°C when cured at 110°C. Results have shown a significant drop in Short Beam Shear (SBS) Strength starting after exposure for 1700h and increase in fibre bridging seen in mode I Double Cantilever Beam (DCB) testing. Fracture surface anal...
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The development of advanced fiber reinforced polymer’s (FRP’s) to achieve performance improvements in engineering structures focuses on the exploitation of the excellent specific strength and stiffness that they offer. However, the planar... more
The development of advanced fiber reinforced polymer’s (FRP’s) to achieve performance improvements in engineering structures focuses on the exploitation of the excellent specific strength and stiffness that they offer. However, the planar nature of an FRP’s microstructure results in relatively poor performance under impact loading. Furthermore, significant degradation in material performance can be experienced with minimal visual indication of damage being present, a design scenario termed Barely Visible Impact Damage (BVID). Current damage tolerant design philosophies incorporate large margins to account for reduction in structural performance due to impact events, resulting in overweight and inefficient structures. An alternative approach to mitigate impact damage sensitivity can be achieved by imparting an ability for these materials to undergo selfhealing. Selfhealing composites would allow lighter, more efficient structures and would also offer a potentially substantive reduction in maintenance and inspection schedules and their associated costs. This paper considers the development of autonomic selfhealing within CFRP, and demonstrates the strength recovery possible when a resin filled HGF system is distributed at specific interfaces within a laminate, minimizing the reduction in mechanical properties whilst maximizing the efficiency of the healing event.
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The concept of self-healing materials has gained widespread acceptance in the research community. Over recent years a diverse array of bio-inspired self-healing concepts, from solid-state diffusion to liquid-phase healing in a broad range... more
The concept of self-healing materials has gained widespread acceptance in the research community. Over recent years a diverse array of bio-inspired self-healing concepts, from solid-state diffusion to liquid-phase healing in a broad range of engineering materials, embracing ceramics, polymers and fibre reinforced polymer composite materials have been proposed in the open literature. In this research study the liquid-phase healing of operational damage, namely impact damage, is being addressed. The challenge of self-healing advanced fibre reinforced polymer composites is ensuring healing success without degrading the host composite’s performance, a problem not encountered in the self-healing of generic polymeric systems. In the genre of self-healing fibre reinforced composite materials, autonomous healing has been undertaken by a healing medium already located within the damage zone and released through the damage site either passively or actively through human invention. This approa...
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ABSTRACT
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A study of the influence of embedded circular hollow vascules on structural performance of a fibre-reinforced polymer (FRP) composite laminate is presented. Incorporating such vascules will lead to multi-functional composites by bestowing... more
A study of the influence of embedded circular hollow vascules on structural performance of a fibre-reinforced polymer (FRP) composite laminate is presented. Incorporating such vascules will lead to multi-functional composites by bestowing functions such as self-healing and active thermal management. However, the presence of off-axis vascules leads to localized disruption to the fibre architecture, i.e. resin-rich pockets, which are regarded as internal defects and may cause stress concentrations within the structure. Engineering approaches for creating these simple vascule geometries in conventional FRP laminates are proposed and demonstrated. This study includes development of a manufacturing method for forming vascules, microscopic characterization of their effect on the laminate, finite element (FE) analysis of crack initiation and failure under load, and validation of the FE results via mechanical testing observed using high-speed photography. The failure behaviour predicted by ...
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Self-healing is receiving an increasing amount of worldwide interest as a method to autonomously address damage in materials. The incorporation of a self-healing capability within fibre-reinforced polymers has been investigated by a... more
Self-healing is receiving an increasing amount of worldwide interest as a method to autonomously address damage in materials. The incorporation of a self-healing capability within fibre-reinforced polymers has been investigated by a number of workers previously. The use of functional repair components stored inside hollow glass fibres (HGF) is one such bioinspired approach being considered. This paper considers the placement of self-healing HGF plies within both glass fibre/epoxy and carbon fibre/epoxy laminates to mitigate damage occurrence and restore mechanical strength. The study investigates the effect of embedded HGF on the host laminates mechanical properties and also the healing efficiency of the laminates after they were subjected to quasi-static impact damage. The results of flexural testing have shown that a significant fraction of flexural strength can be restored by the self-repairing effect of a healing resin stored within hollow fibres.
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This paper presents the design considerations for successful incorporation of bioinspired vascules into a carbon fibre-reinforced epoxy composite laminate. A vasculature capable of delivering functional agents from an external reservoir... more
This paper presents the design considerations for successful incorporation of bioinspired vascules into a carbon fibre-reinforced epoxy composite laminate. A vasculature capable of delivering functional agents from an external reservoir to regions of internal damage potentially offers the host structure an autonomous self-healing function without incurring a mass penalty. Minimising disruption to the host laminate, in terms of fibre architecture,
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ABSTRACT This paper presents a rigorous numerical investigation into the structural response of a composite laminate T-piece specimen subjected to a mechanical “pull-off” load case. Initially, a linear elastic stress analysis is... more
ABSTRACT This paper presents a rigorous numerical investigation into the structural response of a composite laminate T-piece specimen subjected to a mechanical “pull-off” load case. Initially, a linear elastic stress analysis is conducted, showing very high stresses at the free-edge. In a further analysis, special-purpose interface elements are then inserted where appropriate and used to predict both the crack pattern and the load to failure. It is demonstrated that that using realistic cohesive maximum strength values requires a very fine mesh. Reducing the values to ensure initiation occurs leads to conservative and mesh independent predictions and that a suitable choice leads to good correlation with the experimental results. This study also shows that the T-piece failure is controlled by crack propagation.
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ABSTRACT A technique for controlling delamination growth in a GFRP panel subjected to a low velocity impact is presented. Deploying discrete thermoplastic film rings at selective interfaces centred around the impact site has been shown to... more
ABSTRACT A technique for controlling delamination growth in a GFRP panel subjected to a low velocity impact is presented. Deploying discrete thermoplastic film rings at selective interfaces centred around the impact site has been shown to arrest delamination thus allowing damage control. Using six different layup configurations the thermoplastic film rings have been shown to suppress delamination crack growth at the desired interfaces. This resulted in manipulation of the damage footprint areas. Configurations that reduced delamination area by up to 38% demonstrated an improved CAI strength of up to 18% relative to a baseline panel. However, two configurations which saw an increase in delamination area by up to 30% showed similar CAI strengths to the baseline panel. This finding would confirm that it is the delamination interface location that influences the CAI strength not the damage footprint area.
Research Interests: Materials Engineering, Mechanical Engineering, Aerospace Engineering, Materials Science, Composite Materials, and 14 moreDamage Mechanics, Resistance, Reinforcement, Delamination, Composite Material, Laminated Composites, Low Velocity Impact, Footprint, Fracture Toughness, Impact Behaviour, Damage Tolerance, Epoxy Composite, Crack Arrest, and Stacking Sequence
An investigation is described concerning the interaction of propagating interlaminar cracks with embedded strips of interleaved materials in E-glass fibre reinforced epoxy composites. The approach deploys interlayer strips of a... more
An investigation is described concerning the interaction of propagating interlaminar cracks with embedded strips of interleaved materials in E-glass fibre reinforced epoxy composites. The approach deploys interlayer strips of a thermoplastic film, thermoplastic particles, chopped fibres, glass/epoxy prepreg, thermoset adhesive film and thermoset adhesive particles ahead of the crack path on mid-plane of Double Cantilever Beam (DCB) specimens. During these mode I tests, the interlayers were observed to confer an apparent increase in the toughness of the host material. The crack arrest performance of individual inclusion types are discussed and the underlying mechanisms for energy absorption and the behaviour of the crack at the interaction point of the interleave edge were analysed using scanning electron microscopy.
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Autonomic self-healing materials, where initiation of repair is integral to the material, are being developed for engineering applications. This bio-inspired concept offers the designer an ability to incorporate secondary functional... more
Autonomic self-healing materials, where initiation of repair is integral to the material, are being developed for engineering applications. This bio-inspired concept offers the designer an ability to incorporate secondary functional materials capable of counteracting service degradation whilst still achieving the primary, usually structural, requirement. Most materials in nature are themselves self-healing composite materials. This paper reviews the various self-healing technologies currently being developed for fibre reinforced polymeric composite materials, most of which are bioinspired, inspired by observation of nature. The most recent self-healing work has attempted to mimic natural healing through the study of mammalian blood clotting and the design of vascular networks found in biological systems. A perspective on current and future self-healing approaches using this biomimetic technique is offered. The intention is to stimulate debate outside the engineering community and reinforce the importance of a multidisciplinary approach in this exciting field.
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The use of functional repair components stored inside hollow reinforcing fibres is being considered as a self- repair system for future composite structures. This paper considers the problem of introducing a liquid healing resin,... more
The use of functional repair components stored inside hollow reinforcing fibres is being considered as a self- repair system for future composite structures. This paper considers the problem of introducing a liquid healing resin, contained within hollow glass storage vessels, within a space environment. The problem of resin outgassing of a commercially available 2-part epoxy resin system and the thermal cycling of the glass storage vessels, and their sealing caps, are discussed. The mechanical property assessment of the baseline hollow fibre laminate, the damaged hollow fibre laminate and the healed hollow fibre laminate is discussed revealed that a self-healed laminate had a residual strength of 87% compared to an undamaged baseline laminate and 100% compared to an undamaged self-healing laminate. This study provides clear evidence that a FRP laminate containing hollow fibre layers can successfully self-heal.