Imperial College London

ProfessorSilvestrePinho

Faculty of EngineeringDepartment of Aeronautics

Professor in the Mechanics of Composites
 
 
 
//

Contact

 

+44 (0)20 7594 5076silvestre.pinho Website

 
 
//

Location

 

314City and Guilds BuildingSouth Kensington Campus

//

Summary

 

Publications

Publication Type
Year
to

269 results found

Kazemi ME, Medeau V, Chen Y, Xu Z, Petrinic N, Greenhalgh E, Robinson P, Finlayson J, Pinho STet al., 2024, Ballistic performance of bio-inspired hybrid interleaved composite structures suitable for aerospace applications, Composites Part A: Applied Science and Manufacturing, Vol: 179, ISSN: 1359-835X

We investigate the ballistic performance of an aircraft engine containment casing demonstrator, made of composite materials with a novel bio-inspired hybrid interleaved design, under high-velocity impact (HVI) at a specific angle. Firstly, we apply a bio-inspired (BI) helicoidal design to develop a large-scale monolithic laminate concept made of carbon fibre-reinforced polymer (CFRP). Then, we hybridise the developed BI laminate concept with interleaved blocks of Zylon fibre (PBO)-reinforced polymer to develop a large-scale BI hybrid interleaved laminate concept. We then further hybridise the developed BI hybrid concept with titanium (Ti) foils (located at the impact face) so that in total we have three large-scale laminate concepts. We manufacture 6 large-scale laminates from each concept with dimensions of 225 × 225 mm and a target areal weight of 0.95 g/cm2. We then test them (perpendicularly) under HVI ranging from 150 to 300 m/s to obtain the ballistic limit and energy dissipation. Secondly, after selecting the best-performing developed laminate concept, we scale it up to develop industrial demonstrator panels with a target areal weight of 1.5 g/cm2 and dimensions of 550 × 360 mm. We test the panels under HVI at an angle of 55° with a larger and heavier projectile, to more closely represent a fan blade-off event onto the engine casing. The results of the large-scale laminate concept tests show that the BI hybrid interleaved CFRP/PBO concept outperformed the rest of the concepts with 54% and 34% improvement in energy dissipation compared to that of quasi-isotropic (QI) and the BI monolithic CFRP, respectively. Our results show that small-scale designs for HVI-resistant CFRP-based laminates cannot be simply assumed to exhibit an equivalent performance for industrial applications with thicker laminates, heavier projectiles and impacts at an angle.

Journal article

Ueda M, Suzuki Y, Pinho ST, 2023, Estimation of axial compressive strength of unidirectional carbon fiber-reinforced plastic considering the variability of fiber misalignment, Composites Part A: Applied Science and Manufacturing, Vol: 175, ISSN: 1359-835X

The analytical method to calculate the axial compressive stress–strain relation of a unidirectional carbon fiber-reinforced plastic (UD CFRP) was presented considering the variability of the fiber misalignment angle. Because the compressive load-bearing capability of fibers surrounded by a matrix was different depending on the fiber misalignment angle, fibers were grouped based on the misalignment angle. The contribution to the load bearing was calculated and summed based on the area ratio of the fiber groups. All fibers supported a compressive load in the initial loading. However, with increased loading, the load-bearing capabilities of the different fiber groups decreased more dramatically with greater misalignment angles. The fibers with a misalignment angle of 0.5° showed a large load drop after their maximum loading, which triggered the ultimate failure. The variability of the fiber misalignment angle was indispensable to determining the axial compressive strength under the assumption of zero mean fiber misalignment angle.

Journal article

Fossati M, Breitenstein C, Pinho S, Morlier Jet al., 2023, Session 6: Enabling technologies

<jats:p>In this cross-disciplinary session we aim to make some links that otherwise may not be obvious during the workshop.</jats:p><jats:p>**Chair: Andrea Castrichini (Airbus)**</jats:p><jats:p><jats:bold>Parametric study of the aerodynamic performance of high-aspect ratio strut-braced wings</jats:bold></jats:p><jats:p>A sensitivity study based on the High-Dimensional Model Representation (HDMR) approach is used to assess the impact of changes in the operating conditions of a strut-braced airframe on the aerodynamic performance. Changes in cruise speed, altitude and angle of attack are considered to quantify the robustness of the airframe design with respect to perturbations to its nominal cruise conditions. A comparative analysis is also presented for the same airframe without a strut, i.e. an equivalent cantilever wing airframe. The comparison indicates that the presence of a strut does not have a major influence on the sensitivity, i.e. the gradients of aerodynamic drag.</jats:p><jats:p><jats:bold>Numerical Study of Maneuver Load Alleviation on a Large Transport Aircraft</jats:bold></jats:p><jats:p>With higher wing aspect ratio of a transport aircraft, the wing loads generally also increase and thus the required structural weight. Active load alleviation can help to shift the multidisciplinary optimum towards higher aspect ratios. To study this technology, fluid-structure coupled simulations are performed for quasi-steady pitching maneuvers of a large transport aircraft with a load alleviation system consisting of trailing edge flaps and droop noses at the leading edge. For the fluid part of the simulation, a RANS approach is used, whereas the structural simulation is based on a linear modal model. The selected maneuvers are located on the lift boundary of the maneuver envelope at maximum load factor, as not only are the structural loads high here, but also redistributing l

Other

da Costa ROSS, Pinho ST, 2023, Topology optimisation for robust design of large composite structures, COMPOSITE STRUCTURES, Vol: 321, ISSN: 0263-8223

Journal article

Garulli T, Katafiasz TJ, Greenhalgh ES, Pinho STet al., 2023, A novel bio-inspired microstructure for improved compressive performance of multidirectional CFRP laminates, COMPOSITES PART B-ENGINEERING, Vol: 264, ISSN: 1359-8368

Journal article

Kazemi ME, Medeau V, Greenhalgh E, Robinson P, Finlayson J, Pinho STet al., 2023, Bio-inspired interleaved hybrids: Novel solutions for improving the high-velocity impact response of carbon fibre-reinforced polymers (CFRP), Composites Part B: Engineering, Vol: 264, Pages: 1-11, ISSN: 1359-8368

We propose a novel design methodology consisting of bio-inspired (BI) and interleaved layups to develop hybrid carbon fibre-reinforced polymer (CFRP) composite structures for improved high-velocity impact (HVI) performance. Firstly, we apply a BI helicoidal design method consisting of various pitch angles (considering both thick- and thin-ply CFRP) to develop BI monolithic CFRP laminates. Secondly, we apply the interleaving design method to develop BI hybrid CFRP-based laminates interleaved with blocks of BI Zylon fibre-reinforced polymers through the thickness. We evaluate their response and compare it with traditional quasi-isotropic (QI) hybrid bulk layups. In addition to hybridising with Zylon, we apply titanium (Ti) foils to both the monolithic and hybrid CFRP-based laminates to investigate and compare their response. For all our hybrids, we kept the ratio of the hybridising material(s) to be less than 50% to ensure suitable in-plane mechanical properties and aimed at a target areal weight of 0.95 g/cm2. We also manufactured QI thick- and thin-ply monolithic CFRP laminates as baselines. We tested all laminates at 170 and 210 m/s and studied their response and failure modes. Our results show that the average energy dissipation of the QI monolithic thin-ply baseline improved by up to 22% by changing the layup from QI to BI, and by about 118% by changing the baseline QI layup to BI hybrid interleaved. Post-mortem analysis reveals that there are additional failure mechanisms activated in the BI hybrid interleaved layup with respect to the baseline.

Journal article

Kazemi ME, Medeau V, Mencattelli L, Greenhalgh E, Robinson P, Finlayson J, Pinho STet al., 2023, Novel zone-based hybrid laminate structures for high-velocity impact (HVI) in carbon fibre-reinforced polymer (CFRP) composites, Composites Science and Technology, Vol: 241, Pages: 1-10, ISSN: 0266-3538

We propose novel zone-based hybrid laminate concepts for improving the high-velocity impact (HVI) response of baseline carbon fibre-reinforced polymer (CFRP) composites while maintaining similar areal weights and retaining substantial in-plane mechanical properties by requiring that about 80% (by mass) of the baseline CFRP is kept in the hybrid concepts. We identify three zones along the thickness of the laminate according to their role during HVI and implemented tailored materials in these zones to improve the HVI response. We studied a wide range of materials, including: fibre reinforcements of carbon (thin- and thick-plies), glass, Zylon and ultra-high molecular weight polyethylene (UHMWPE); a shape memory alloy/carbon fabric; and ceramic, alumina and titanium sheets. All laminate concepts have similar areal weights for a meaningful comparison. After defining the various concepts, we manufactured and measured their specific dissipated energy under HVI, and finally carried out post-mortem analysis (including C-scan and microscopy). The results show up to 95% improvement in energy dissipation over the baseline quasi-isotropic (QI) CFRP configuration.

Journal article

Whitehouse AD, Medeau V, Mencattelli L, Blackman B, Pinho STet al., 2023, A novel profiling concept leading to a significant increase in the mechanical performance of metal to composite joints, Composites Part B: Engineering, Vol: 261, Pages: 1-15, ISSN: 0961-9526

Traditional adhesive joints with straight edged adherends suffer from a significant stress concentration in the composite coincident with the edge of the metal adherend, which can lead to accelerated translaminar failure of the substrate. In this work, we developed a novel profiling concept which improves the mechanical performance of adhesive joints between metallic adherends and composite substrates. We conducted quasi-static four-point bending (4PB) tests which showed that profiling the edge of the metallic adherend could improve the peak load by at least 27%, and that the stability of failure was simultaneously improved. We investigated varying the profile parameters and were able to conclude that further significant mechanical performance gains could be achieved by increasing any of the profile: amplitude, frequency, or number of fractal length-scales. By analysing in-situ acoustic emission (AE) monitoring data we were able to observe that profiling of the metallic adherend results in failure initiation occurring at higher loads, which suggests that the concept is successful in providing better stress distributions and lowering peak stresses. By analysing the fracture surfaces, it is apparent that the profiling concept is successful in deflecting the translaminar fracture path; and additionally that a debonding mechanism occurs at the profile tips which is thought to be an important additional mechanism for creating damage tolerant joints.

Journal article

Pinho S, 2023, Netzero: Challenges for Aviation and for Structural Aircraft Design

<jats:p>Achieving NetZero is of utmost importance for avoiding the worst effects of climate change, including frequency and intensity of natural disasters, as well as the associated socio-economic unrest and effect on our health. Aviation accounts for just over 2% of overall CO2 emissions worldwide (8% for the UK), and for about 4% of the warming effect. On current technology, aviation would use 27% of the total Carbon budget available to limit global warming to 1.5C by 2050; it would represent roughly 40% of the UK’s emissions by 2050 if other sectors decarbonise according to the government’s targets.</jats:p><jats:p>Reducing the warming effect of aviation can be achieved via a combination of greener energy carriers (as alternatives to Jet Fuel), flight-path management, demand management, and carbon capture. Greener energy carriers, such as hydrogen, pose various challenges, including large-scale green energy production, distribution, airports and aircraft design. In fact, the timescale in which we need to explore design spaces suitable for hydrogen-powered aircraft, including high aspect ratio wings and blended-wing-body aircraft, require novel and more agile structural design methods, particularly for composite structures.</jats:p><jats:p>Traditional structural design methods in Aeronautics explore a very large number of design variables using simple models, suitably calibrated following decades of experience, as well as extensive experimental and simulation data. More detailed finite element models are finally created to verify the design, but only once the design space has been very significantly reduced, and vast aspects of the design have been fixed. This process creates an obvious problem when moving away from the design space for which the simple models used at the start of this process were calibrated.</jats:p><jats:p>A possible solution to the above consists of detailed finite element models of very l

Other

Kazemi M, Medeau V, Greenhalgh E, Robinson P, Finalyson J, Pinho Set al., 2023, On the high-velocity impact response of bio-inspired interleaved hybrid carbon-fibre reinforced polymer composites, 11th International Conference on Composite Testing and Model Identification (CompTest 2023)

Conference paper

Anthony D, Woodgate C, Shaw C, Patni M, Bikos D, Gogoi R, Garulli T, Pickard L, Quino Quispe G, Gargiuli J, Pimenta S, Allegri G, Pinho S, Hamerton I, Greenhalgh E, Eichhorn S, Robinson P, Wisnom M, Trask R, Shaffer Met al., 2023, Hierarchical solutions to compressive problems in fibre-reinforced composites, ECCM20 - The 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab), Pages: 1512-1517

Currently, the useable compressive properties of a composite are restricted by set design limits well below the expected intrinsic performance of the materials contained within. The next generation of high-performance fibre-reinforced polymer composites will need to address the challenge of improving the absolute performance of composites in compression. This task requires a rethink of the whole system; not only to address practical limitations of current materials, but their combination, interface, and their architecture. The mechanisms involved do not simply act over the nano-, macro-, or meso-level independently, but are mutually related at the system level, complicating the approach.

Conference paper

Yu B, Katafiasz TJ, Nguyen S, Allegri G, Finlayson J, Greenhalgh ES, Pinho ST, Pimenta Set al., 2023, Characterising and predicting the relationship between translaminar fracture toughness and pull-out length distributions under distinct temperatures, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 381, ISSN: 1364-503X

The translaminar fracture toughness reflects the damage tolerance of a fibre-reinforced composite under longitudinal tension, which often governs the final failure of structures. One of the main energy-dissipation mechanisms that contributes to the translaminar toughness of composites is the fibre pull-out process. The present study aims to quantify and model the statistical distribution of fibre pull-out lengths formed on the translaminar fracture surface of composites, for the first time in the literature; this is done under different temperatures, so that the relationship between pull-out length distributions, micromechanical properties and the translaminar fracture toughness can be established. The fracture surfaces of cross-ply compact tension specimens tested under three different temperatures have been scanned through X-ray computed tomography to quantify the extent of fibre pull-out on the fracture surfaces; the distribution of pull-out lengths showed alarger average and larger variability with an increase in temperature, which also lead to an increase in translaminar fracture toughness. A similar trend has been captured by the proposed analytical model, which predicts the pull-out length distribution based on the analysis of quasi-fractal idealizations of the fracture surface, yielding an overall accuracy of more than 85%.This article is part of the theme issue 'Ageing and durability of composite materials'.

Journal article

Kazemi ME, Médeau V, Greenhalgh E, Robinson P, Finlayson J, Pinho STet al., 2023, BIO-INSPIRED INTERLEAVED COMPOSITE STRUCTURES FOR HIGH-VELOCITY IMPACT APPLICATIONS

We propose a novel design for improving the high-velocity impact (HVI) performance of hybrid carbon fibre-reinforced polymer (CFRP) composite structures. Our novel design consists of a non-conventional bio-inspired hybrid interleaved layup that significantly enhances damage diffusion and energy dissipation in CFRP composite structures. In our design, we retain more than 50% mass of the structure as CFRP to keep in-plane mechanical properties substantial and also aim to maintain the areal weight (compared to the monolithic CFRP baseline). We applied this design methodology to develop laminate concepts made of thin- and thick-ply CFRPs, hybridised with aramid fibre-reinforced polymer (AFRP) for one of the concepts, and also titanium foils for another concept. We tested the laminate concepts under HVI from 150 to 300 m/s and investigated their response in terms of energy dissipation, ballistic limit and failure modes. The results demonstrate a strong increase in ballistic limit and specific energy dissipation for the developed laminate concepts. The bio-inspired monolithic thin- and thick-ply CFRP laminate concepts exhibit about 15% improvement in specific energy dissipation compared to their QI monolithic baselines. Implementing interleaved blocks of AFRP into the bio-inspired monolithic CFRP laminate concepts shows an improvement in specific energy dissipation by up to 54% for the thick-ply and by up to 135% for the thin-ply, compared to their monolithic QI baselines.

Conference paper

Garulli T, Katafiasz TJ, Greenhalgh ES, Pinho STet al., 2023, BIO-INSPIRED MULTIDIRECTIONAL LAMINATES FOR IMPROVED COMPRESSIVE PERFORMANCE

In this study, we developed a novel microstructure inspired by the deep-sea glass sponge Monoraphis chuni to enhance longitudinal compressive performance of multidirectional carbon fibre reinforced polymer laminates. The microstructure features alternating stiff and soft regions, similar to those observed in the sponge's anchoring spicula. To create this microstructure, we utilized a unique manufacturing process. We then assessed the performance of the microstructure through small-scale notched compression tests, comparing it to an industrially-relevant baseline laminate. Our findings demonstrated a statistically significant increase in failure load and average ligament specific stress at failure compared to the baseline, as well as the ability to delay damage initiation and arrest damage propagation. Our research provides valuable insights for the design of lightweight structures under compression.

Conference paper

Katafiasz TJ, Garulli T, Greenhalgh ES, Pinho STet al., 2023, COMPRESSIVE FAILURE OF BORON-CARBON FIBRE HYBRID COMPOSITES: A DETAILED EXPERIMENTAL STUDY

Hybridising carbon fibre reinforced polymers (CFRP) with boron fibres offers the potential of improving the compressive response of CFRP. In this work, a small compressive translaminar fracture specimen was designed, manufactured and tested in a scanning electron microscope environment to obtain detailed information on how the presence of the boron fibres affects the typical kinkband formation and propagation within CFRP. It is shown that the boron fibres successfully stop propagating kinkbands in CFRP, and that, as the kinkband approaches a boron fibre, a large split tends to form which protects the subsequent CFRP material.

Conference paper

da Costa ROSS, Pinho ST, 2023, STRUCTURAL OPTIMISATION FOR DAMAGE TOLERANCE

Material defects are a widespread feature in the manufacturing of composite structures, especially in very large structures. These defects can lead to premature structural collapse; thus, it is important to design and optimise these large structures considering material defects. Structural optimisation methods enable targeting arbitrary design variables, such as defect tolerance, by incorporating carefully devised objective and constraint functions. In this work, we show an implementation of a topology optimisation methodology within a modelling framework designed for very large composite structures. The methodology has explicit boundary-tracking capabilities and relies on an objective function centred on the energy release rate of a crack or debond. We demonstrate how the optimisation methodology can successfully handle debonds in a model of a skin-stringer run-out assembly. We show that the method can decrease the energy release associated with the debond by changing the stringer run-out shape.

Conference paper

Whitehouse AD, Yang Y, Médeau V, Mencattelli L, Greenhalgh E, Pinho STet al., 2023, A DAMAGE TOLERANT BIO-INSPIRED INTEGRATED COMPOSITE STIFFENER VIA AFP

Stiffened composite panels are vulnerable to rapid debonding of the stiffeners, which has resulted in the development of conservative certification requirements. In this work, inspired by the branch-trunk attachment of trees, an embedded composite stiffener is developed in the pursuit of damage tolerant panels. Improved damage tolerance can pave the way for more ambitious certification requirements, which will allow for more efficient aircraft designs to be realised. Automated Fibre Placement (AFP) is increasingly utilised by industry; in this work, stiffened panels are developed which can be preformed in a single AFP process. This paper presents the results of this manufacturing endeavour, the use of a foam core and curved hat stiffener geometry is validated as an AFP manufacturing route for composite stiffened panels. Preliminary experimental results, using a notched compression configuration, of the bio-inspired embedded concept are presented. Initial stable crack growth and prevention of debonding ahead of the notch tip are demonstrated. Finally, a numerical parametric study is presented for a modified notched compression specimen design to be used in an upcoming comprehensive experimental study of the concept.

Conference paper

Medeau V, Kazemi ME, Greenhalgh E, Pimenta S, Finlayson J, Pinho Set al., 2022, Helicoidal layups and interleaved hybrids: a novel design methodology for impact-resistant composite structures, ECCM20 - The 20th European Conference on Composite Materials

Conference paper

Whitehouse A, Medeau V, Mencattelli L, Blackman B, Greenhalgh E, Pinho Set al., 2022, A novel profiling concept leading to a significant increase in the mechanical performance of metal to composite joints, ECCM20 - The 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab)

In this work, we designed metal-CFRP joints with a profiled adherend termination to improve the mechanical performance. We have applied several profiles to the edge of titanium adherends which were adhesively bonded to CFRP substrates. We conducted finite element modelling and experimental 4PB (4-Point-Bend) testing to investigate how the geometry of the adherend edge profile effects the mechanical performance of the joint. This work shows that profiling of the metal adherend can result in increases of at least 27% in the peak load, and of at least 272% in the energy dissipated up to critical failure normalised by the mechanical energy.

Conference paper

Silva Sampaio Da Costa R, Pinho S, 2022, A novel topology optimisation methodology for robust design of structural components considering material defects, 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab)

This work outlines a new Topology Optimisation methodology whereby material defects are introduced at the earliest stage of the structural design process, leading to more robust final design solutions. We couple the Levelset Method and the Floating Node Method to capture a moving material boundary explicitly on the Finite Element mesh. A continuum designsensitivity analysis scheme based on a measure of the energy release rate is used to quantify the impact of the defect. We show how the structure is optimised to reduce this measure and mitigate the impact of the material defect on the overall response.

Conference paper

Kazemi M, Medeau V, Greenhalgh E, Pimenta S, Finlayson J, Pinho Set al., 2022, Implementing structural fuses in CFRP components via microstructurally-engineered crack paths, 20th European Conference on Composite Materials, ECCM20. 26-30 June, 2022, Lausanne, Switzerland, Publisher: Composite Construction Laboratory (CCLab)

This study aims to develop and implement actual carbon fibre-reinforced polymer (CFRP) solutions for realising structural fuses in real components. To this end, we have developed various concepts for structural fuses, applied to generic idealised components and aimed at engaging different in-plane and through-the-thickness damage propagation mechanisms. Micro-cut patterns (MCPs) / crack path combinations have been engraved on thin-ply CFRP prepregs (by using a laser cut machine) for manufacturing CFRP specimens. Afterwards, we have carried out a series of experimental studies to evaluate the fracture properties of various MCPs under three-point bending (3PB). Then, 3PB results were used to refine and down-select ourconcepts, for use in our generic idealised component design to test them under indentation test using a cantilever beam rig. The test results demonstrated that MCPs can provide significant control over the fracture locus and path, additionally allowing the failure initiation load and energy dissipation to be tailored.

Conference paper

Garulli T, Greenhalgh E, Pinho S, 2022, A novel bio-inspired microstructure for progressive compressive failure in multidirectional composite laminates, 20th European Conference on Composite Materials, ECCM 2022, Publisher: Composite Construction Laboratory (CCLab)

n this study we take inspiration from biological materials to design a modified microstructure for laminated multidirectional (MD) carbon fiber reinforced polymers (CFRP), with the objective of mitigating their compressive failure behavior. We introduce soft inclusions in the form of thin longitudinal strips of foam in 0° load bearing layers, aiming at arresting kinkband propagation. We conceived a bespoke stacking sequence and developed a tailored procedure for manufacturing the microstructure. We then performed in-situ tests on small scale notched specimens from a baseline laminate and a modified one. Results are presented and discussed.

Conference paper

Pinho ST, Costa ROSS, Matos M, Ibbotsond A, Ostergaard Met al., 2022, Multiscale analysis of an aircraft wingbox, Pages: 348-355

This paper presents results of a methodology for structural simulation of very large structures. It does not assume the use of a specific failure model, but rather focuses on establishing a framework that enables failure analyses on full-wing models with a complexity comparable to real wings in large passenger aircraft.

Conference paper

Yu B, Katafiasz TJ, Nguyen S, Allegri G, Finlayson J, Greenhalgh ES, Pinho ST, Pimenta Set al., 2021, Hygrothermal effects on the translaminar fracture toughness of a highly toughened aerospace CFRP: Experimental characterisation and model prediction, Composites Part A: Applied Science and Manufacturing, Vol: 150, Pages: 1-12, ISSN: 1359-835X

The translaminar fracture toughness and its dependence on the environmental condition are key considerations in designing aerospace-grade composites with a high damage tolerance to severe service conditions in terms of temperature and moisture. The present work characterises and models the hygrothermal effects on the translaminar fracture toughness of an interlaminar toughened aerospace carbon/epoxy composite under six environmental conditions: −55 °C, 23 °C, and 90 °C, for both ‘dry’ (i.e. moisture free) and ‘wet’ (fully moisture-saturated) specimens. Cross-ply compact-tension experiments show that the translaminar fracture toughness increases with the rise of temperature for both dry and wet conditions with the latter exhibiting a much greater increase. A model to predict the effect of moisture and temperature on the translaminar fracture toughness is here proposed and developed. This approach yields good agreement with experimental results, and it allows an improved understanding of the complex synergistic effects of interfacial properties on the overall translaminar toughening mechanisms.

Journal article

Plocher J, Mencattelli L, Narducci F, Pinho Set al., 2021, Learning from nature: Bio-Inspiration for damage-tolerant high-performance fibre-reinforced composites, Composites Science and Technology, Vol: 208, ISSN: 0266-3538

Over millions of years Nature has attained highly optimized structural designs with remarkable toughness, strength, damage resistance and damage tolerance - properties that are so far difficult to combine in artificial high-performance fibre-reinforced polymers (HPFRPs). Recent studies, which have successfully replicated the structures and especially the toughening mechanisms found in flora and fauna, are reviewed in this work. At the core of the manufacturing of damage-tolerant bio-inspired composites, an understanding of the design principles and mechanisms is key. Universal and naturally-inherent design features, such as hierarchical- and organic-inorganic-structures as well as helical or fibrous arrangements of building blocks were found to promote numerous toughening mechanisms. Common to these features, the outstanding ability of diffusing damage at a sub-critical state has been identified as a powerful and effective mechanism to achieve high damage tolerance. Novel manufacturing processes suitable for HPFRP (such as tailored high-precision tape placement, micro-moulding, laser-engraving and additive manufacturing) have recently gained immense traction in the research community. This stems from the achievable and required geometrical complexity for HPFRPs and the replication of subtly balanced interaction between the material constituents. Even though trends in the literature clearly show that a bio-inspired material design philosophy is a successful strategy to design more efficient composite structures with enhanced damage tolerance and mechanical performance, Nature continues to offer new challenging opportunities yet to be explored, which could lead to a new era of HPFRP composites.

Journal article

Katafiasz T, Greenhalgh ES, Allegri G, Pinho ST, Robinson Pet al., 2021, The influence of temperature and moisture on the mode I fracture toughness and associated fracture morphology of a highly toughened aerospace CFRP, Composites Part A: Applied Science and Manufacturing, Vol: 142, ISSN: 1359-835X

This paper addresses the characterisation of the mode I interlaminar fracture toughness of a carbon fibre/epoxy composite material, toughened with thermoplastic particles in the ply interlayers. The characterisation is undertaken at −55 °C, 19 °C, and 90 °C, on both dry and fully moisture saturated coupons. Fractographic observations of the delamination surfaces allows identification of the failure mechanisms. The mode I propagation fracture toughness tested at wet/90 °C exhibits a 176% increase compared to the dry/19 °C specimens, due to enhanced plastic deformation of the interlayers and more prominent fibre bridging. Moisture-saturated coupons tested at −55 °C suffered a 57% reduction of mode I fracture toughness compared to those under dry/19 °C conditions. This is due to the dis-bond and consequent plucking of the thermoplastic particles from the surrounding matrix. This observation points to the fact that wet/cold conditions may represent the worst-case scenario for the interlaminar fracture performance of composite systems toughened with thermoplastic interleaves.

Journal article

Kocaman ES, Chen BY, Pinho ST, 2020, A floating connector element formulation for multi-level modelling of composite structures, Composite Structures, Vol: 251, Pages: 1-13, ISSN: 0263-8223

Design and optimisation of large structures, including the positioning of lower-level components, typically require extensive user involvement and sequential mechanical analysis/optimisation iterations. This paper presents an original method that enables adaptive positioning of lower-level models (such as components) within higher level-models (such as large structures), and that achieves a combined mechanical/optimisation problem for the design of structures with various hierarchical levels (such as the positioning of stiffeners within a wingbox). As the position of the lower-level model evolves, our proposed method does not require re-generating of the geometry, remeshing or modifying the stiffness matrix of the elements corresponding to the various hierarchical levels. Instead, we achieve the adaptive positioning via an original concept that we propose here: Floating Connector (FC) elements. In this paper, we validate the FC elements against reference purely-mechanical solutions, show that they can be combined with gradient-descent method and genetic algorithms, and that they can be applied to optimise the positioning of a stiffener runout taking into account a debonding manufacturing defect.

Journal article

Häsä R, Pinho ST, 2020, Bio-inspired armour: CFRP with scales for perforation resistance, Materials Letters, Vol: 273, Pages: 1-4, ISSN: 0167-577X

This paper proposes a novel biomimetic Carbon Fibre Reinforced Polymer (CFRP) with a microstructure inspired by fish scales. The aim of the novel microstructure is to improve the perforation resistance of CFRP without compromising its flexibility. To this end, we prototype the first ever CFRP laminate with scales and test it in quasi-static indentation on a soft backing material. We compare the mechanical behaviour of the CFRP with scales to two baseline configurations with conventional lay-ups. The results presented in this paper suggest that the CFRP with scales significantly outperforms the two baseline configurations in terms of force and displacement at penetration, while being flexible. This makes CFRPs with scales an attractive alternative for applications where perforation resistance is paramount, such as body armour against low velocity strikes.

Journal article

da Costa ROSS, Pinho ST, 2020, A novel formulation for the explicit discretisation of evolving boundaries with application to topology optimisation, Computer Methods in Applied Mechanics and Engineering, Vol: 367, Pages: 1-30, ISSN: 0045-7825

Evolving boundaries are an intrinsic part of many physical processes and numerical methods. Most efforts to model evolving boundaries rely on implicit schemes, such as the level-set method (LSM). LSM provides the means to efficiently model the evolution of a boundary, but lacks the ability to transmit information or provide information directly at the boundary. Explicit alternatives based on remeshing or partial-remeshing are often computationally expensive and inherently complex to implement. This work proposes a solution to this dichotomy: a novel finite element method (FEM) based formulation capable of explicitly discretising moving boundaries in an accurate and numerically-efficient way. It couples the floating node method (FNM) with LSM for the first time, which yield a methodology suitable for implementation as user-element in a generic FEM package. The explicitly discretised boundary allows for a new velocity-extension methodology, and a new LSM-reinitialisation procedure, which show benefits in accuracy and efficiency. The potential of this formulation is showcased within topology optimisation, showing greater geometrical accuracy and improvements in the optimum solution attained when compared to implicit methods.

Journal article

Pascoe JA, Pimenta S, Pinho ST, 2020, The effect of tab orientation on the toughening mechanisms produced by interlocked interlaminar thin-ply CFRP reinforcements, Composite Structures, Vol: 238, Pages: 1-12, ISSN: 0263-8223

The use of interlaminar reinforcement units, containing an interlocked tab-and-slit geometry, is a new concept for improving interlaminar fracture toughness. It was recently shown that such reinforcement units are capable of substantially increasing mode I fracture toughness, but mode II fracture toughness was unaffected.This paper presents an investigation into the effect of tab orientation on the toughening mechanisms, comparing the experimentally determined Mode I and II interlaminar fracture toughness for different tab orientations.The results show that the previously reported lack of mode II toughness increase was due to an unsuitable tab orientation. With a better choice of tab orientation a mode II propagation toughness increase (of 23.5%) could be obtained, while simultaneously increasing the mode I propagation toughness further than previously reported (up to a 109% improvement).Fractography was used to investigate the toughening mechanisms. It was found that the two main toughening mechanisms are crack bridging (in mode I) and deflection of the delamination path (in both mode I and II). The relationship between the tab orientation and the obtained increase of fracture toughness can be explained by the effect of tab orientation on these mechanisms.

Journal article

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-html.jsp Request URI: /respub/WEB-INF/jsp/search-html.jsp Query String: respub-action=search.html&id=00358636&limit=30&person=true