78 results found
Kempesis D, Iannucci L, Ramesh KT, et al., 2022, Micromechanical analysis of high fibre volume fraction polymeric laminates using micrograph-based representative volume element models, Composites Science and Technology, Vol: 229, Pages: 109680-109680, ISSN: 0266-3538
This work develops RVE-based finite element (FE) models to understand how the microstructure of Ultra-High-Molecular-Weight Polyethylene (UHMWPE) composites affects the overall mechanical behaviour of the laminate. The models represent a [0/90] configuration with a random fibre packing sequence through the thickness of each ply, as well as a variation in the cross-sectional shape of the fibres, both obtained from laminate cross section micrograph images. The uncertainty of interface properties and its effects on the overall mechanical response is also investigated. The response of the fibre is assumed to be viscoelastic-plastic and transversely isotropic and the three-dimensional constitutive behaviour is implemented through a user-defined subroutine in the LS-DYNA explicit FE code. Constituent properties are calibrated using experimental results on UHMWPE single fibres and a generic thermoplastic polyurethane resin material. The numerical results generated by the RVE models are validated against experimental results found in the open literature. Special focus was given to the in-plane shear and out-of-plane compression response of UHMWPE laminates. Our results can be used as inputs in a homogenised continuum level model, to express the effect of uncertainties which propagate from the microstructure to the macro-scale response.
Del Rosso S, Iannucci L, Kempesis D, et al., 2022, Self-heating effect on ultra-high molecular weight polyethylene fibres and composites, Materials and Design, Vol: 220, Pages: 1-12, ISSN: 0264-1275
This paper investigates the self-heating effect observed during testing ultra-high molecular weight polyethylene (UHMWPE) fibres and their composites, in particular Dyneema® SK76 fibres and Dyneema® HB26 laminates. Monotonic and cyclic tests were carried out at strain rates between 0.00833 s−1 and 250 s−1, frequencies up to 20 Hz, and different mean stress, amplitude stress and stress ratios to evaluate the self-heating effect developing in the materials. Measurements of the specimen’s temperature were carried out using a thermochromic liquid crystal paint and an infrared sensor. Experimental results showed that the temperature increased during fibre testing by as much as 13.2 ± 0.2 °C and, even though the maximum temperature was below the melting temperature of the material, melting was observed. Tension-tension cyclic tests showed that the fatigue life of the coupon specimens significantly depended on the testing conditions. In some cases, the measured temperature was as high as 102 ± 1 °C. Depending on the fatigue parameters, the laminates showed two different types of failure modes: mechanical or thermal. Hence, it is important to take into account self-heating effects when designing engineering parts reinforced with UHMWPE fibres.
Tagarielli V, 2021, The sensitivity of the tensile properties of PMMA, Kevlar® and Dyneema® to temperature and strain rate, Polymer, Vol: 225, Pages: 1-11, ISSN: 0032-3861
We employed a new test technique to measure the tensile response of PMMA, Kevlar® and Dyneema® products at strain rates ranging from 10−4 to 323 s−1. We then extended this technique to allow quasi-static measurements at temperatures in the range −40 to 70 °C. We characterised a monolithic polymer blend, a Kevlar® 49 fibre yarn, a Dyneema SK75 yarn and a Dyneema® tape, exploring the effects of temperature and strain rate on their tensile responses. The sensitivities of the tensile properties to temperature and strain rate were correlated using the time-temperature equivalence, allowing estimates of the mechanical properties of Kevlar and Dyneema at strain rates in excess of 103 s−1.
Kempesis D, Iannucci L, Del Rosso S, et al., 2021, A representative volume element model for ultra-high-molecular-weight-polyethylene composites, Composite Structures, Vol: 262, Pages: 1-11, ISSN: 0263-8223
This paper presents the development of a Representative Volume Element (RVE) for Ultra-high-Molecular-Weight-Polyethylene (UHMWPE) composites. The numerical models were based on the fibrillar nature of UHMWPE fibres, which consist of smaller scale, continuous through-the-length macro-fibrils. A three-dimensional constitutive model for UHMWPE macro-fibrils was developed and implemented in the LS-DYNA explicit finite element (FE) code, through a user-defined subroutine. The proposed transversely isotropic model accounts for viscoelastic effects in the principal direction of the fibre coupled with the continuum damage mechanics approach. Energy dissipation associated with failure was controlled through an objectivity algorithm to provide mesh insensitive solutions. Hill’s yield criterion was used to capture the non-linear response of the fibre in the transverse direction. The RVE was built from macro-fibrils and a Thermoplastic Polyurethane (TPU) resin in order to study the micromechanical response of the polymeric composite laminate. Periodic boundary conditions (PBC) were imposed in the model and a penalty-based cohesive contact algorithm was used to simulate interfibrillar interactions and the interface between the macro-fibrils and the resin. The proposed RVE model provides insight on microscale deformation mechanisms in UHMWPE composites under different loading conditions.
Zhou J, Pellegrino A, Heisserer U, et al., 2019, A new technique for tensile testing of engineering materials and composites at high strain rates, PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 475, ISSN: 1364-5021
Del Rosso S, Iannucci L, Curtis P, 2019, Finite element simulation of the braiding process, Mechanics of Advanced Materials and Modern Processes, Vol: 5
Braiding is one of the most common technique employed for the manufacture of fabrics and ropes. It is also commonly used to produce near-net shaped preforms for advanced fibre reinforced composites. This paper presents an explicit finite element approach to create and simulate the braiding process for the virtual manufacture of 2D braids. The process starts from the definition of an analytical function which describes the movement of the carriers on a braiding track plate. Models of idealised Maypole-type braiding machines are built and used to shape virtual yarns into braids. This procedure can be used in a parameter control fashion, to optimise or to create virtual braided structures, which can serve as input for other structural analyses. It is emphasised that multiple cylinders are required for the modelling of a multifilament yarn to achieve better correlation with the experimental results. A parametric study is presented to investigate the effect of the number of virtual cylinders to represent a real yarn and the shape of the final braid. Excellent correlation was found between the virtual models and the experimental results when comparing the braid angle and yarn width.
Iannucci L, Del Rosso S, Curtis P, et al., 2018, Understanding the thickness effect on the tensile strength property of Dyneema®HB26 laminates, Materials, Vol: 11, Pages: 1-18, ISSN: 1996-1944
In this study, an experimental and numerical investigation is presented on the effect of thickness and test rate within the pseudo static regime on the tensile properties of Dyneema®HB26 laminates. A detailed experimental presentation on the tensile testing of different thickness is presented and highlights the commonly seen observation that the tensile strength of a laminate reduces as a function of the specimen thickness. To understand these experimental observations, a constitutive material model of the individual macro fibril is developed and applied to modelling the fibre and upscaling to the laminate. The modelling strategy is implemented into ls-dyna and used to perform a parameter study on the specimen geometries used in the experimental study. The model assumes that the fibril strength is a function of the amorphous volume within the fibre and hence fibril. It can be observed that the experimental behaviour can be simulated by modelling the interface between laminate plies and the fibril, and hence fibre failure. The weak interfaces from the fibril to the laminate scale make the testing of fibres and laminates very difficult. Hence, it is proposed that the intrinsic fibril strength should be used as a measure of strength, and the fundamental strength is determined through numerical studies.
Zhou J, Tagarielli V, Heisserer U, et al., 2018, An apparatus for tensile testing of engineering materials, Experimental Mechanics, Vol: 58, Pages: 941-950, ISSN: 0014-4851
We develop a novel apparatus and an associatedtest protocol to measure the tensile response of materials. The apparatus allows testing of ring-shaped specimens,fibre yarns and tapes of arbitrary length; it can be employed to conduct experiments at different strain rates and in different environmental conditions.The technique is tested at low rates of strain on several materials, including carbon fibres, metals, polymers and ceramics; the tensile responses measured with the new apparatus are compared to those obtained from conventional measurements and found to be in good agreement with these.
Cwik T, Iannucci L, Curtis P, et al., 2017, Design and ballistic performance of hybrid composite laminates, Applied Composite Materials, Vol: 24, Pages: 717-733, ISSN: 0929-189X
This paper presents an initial design assessment of a series of novel, cost-effective, and hybrid composite materials for applications involving high velocity impacts. The proposed hybrid panels were designed in order to investigate various physical phenomenon occurring during high velocity impact on compliant laminates from a previous study on Dyneema® and Spectra®. In the first, screening phase of the study twenty different hybrid composite laminates were impacted with 20 mm Fragment Simulating Projectiles at 1 km/s striking velocity. The best performing concepts were put forward to phase II with other hybrid concepts involving shear thickening fluids, commonly used in low velocity impacts. The results indicated that it is possible to design hybrid laminates of similar ballistic performance as the reference Dyneema® laminate, but with lower material costs. The optimal hybrid concept involves a fibre reinforced Polypropylene front and a Dyneema® backing.
Raza I, Iannucci L, Curtis PT, 2017, Introducing a Multimaterial Printer for the Deposition of Low MeltingPoint Alloys, Elastomer, and Ultraviolet Curable Resin, 3D PRINTING AND ADDITIVE MANUFACTURING, Vol: 4, Pages: 83-89, ISSN: 2329-7662
Hazzard MK, Hallett SR, Curtis PT, et al., 2017, Effect of fibre orientation on the low velocity impact response of thin Dyneema (R) composite laminates, International Journal of Impact Engineering, Vol: 100, Pages: 35-45, ISSN: 0734-743X
Ultra-high molecular weight polyethylene (UHMWPE) fibre reinforced composite materials are widely used in ballistic impact and collision scenarios due to their extremely high specific strength and stiffness. Exceptional levels of protection are provided by controlling the damage and deformation mechanisms over several length scales. In this study, the role of UHMWPE fibre architecture (cross-ply, quasi-isotropic and rotational “helicoidal” layups) is considered on the damage and deformation mechanisms arising from low velocity impacts with 150 J impact energy and clamped boundary conditions. Dyneema® panels approximately 2.2 mm thick were impacted with a fully instrumented hemi-spherical impactor at velocities of 3.38 m/s. Full field deformation of the panels was captured through digital image correlation (DIC). The results indicate that the cross-ply laminate [0°/90°] had the largest back face deflection, whilst quasi-isotropic architectures restricted and reduced the central deflection by an average of 43%. In the case of the [0°/90°] panel, the deformation mechanisms were dominated by large amounts of in-plane shear with limited load transfer from primary fibres. Conversely, the failure of the quasi-isotropic panels were dominated by large amounts of panel buckling over various length scales. The observed mechanisms of deformation with increasing length scale were; through thickness fibre compression, fibre micro-buckling, fibre re-orientation with large matrix deformation, lamina kink band formation, and laminate buckling. The helicoidal panels showed that bend-twist and extension-twist coupling were important factors in controlling clamped boundary conditions and the laminate buckling/wrinkling shape. Further examination of the impact zone indicated that the damage mechanisms appear to be fibre orientation dependent, with quasi-isotropic laminates having up to 37.5% smaller impact damage zones compared with [0°/90°]. The
Ćwik TK, Iannucci L, Curtis P, et al., 2016, Investigation of the ballistic performance of ultra high molecular weight polyethylene composite panels, Composite Structures, Vol: 149, Pages: 197-212, ISSN: 0263-8223
The ballistic performance of Dyneema® HB26 and Spectra® 3124 subjected to high velocity impact of steel and copper Fragment Simulating Projectiles was evaluated. A 3D High Speed Digital Image Correlation was used for measurement of the panels front face deformation and the back face deformation. The information obtained from the measurements, along with the post-mortem observation of the panels, allowed to draw conclusions with respect to the importance of various energy dissipation mechanisms that occurred in the tested materials. It was observed that, although Dyneema® HB26 and Spectra® 3124 deform very differently during the impact event, they had a similar ballistic performance.
Wang L, Tomlin A, Pandita SD, et al., 2016, In-situ monitoring of cross-linking reactions using E-glass fibres and evanescent wave spectroscopy, SENSORS AND ACTUATORS B-CHEMICAL, Vol: 236, Pages: 358-366, ISSN: 0925-4005
Malik SA, Wang L, Curtis PT, et al., 2016, Self-sensing composites: in-situ detection of fibre fracture, Sensors, Vol: 16, ISSN: 1424-8239
The primary load-bearing component in a composite material is the reinforcing fibres. This paper reports on a technique to study the fracture of individual reinforcing fibres or filaments in real-time. Custom-made small-diameter optical fibres with a diameter of 12 (±2) micrometres were used to detect the fracture of individual filaments during tensile loading of unreinforced bundles and composites. The unimpregnated bundles were end-tabbed and tensile tested to failure. A simple technique based on resin-infusion was developed to manufacture composites with a negligible void content. In both cases, optical fibre connectors were attached to the ends of the small-diameter optical fibre bundles to enable light to be coupled into the bundle via one end whilst the opposite end was photographed using a high-speed camera. The feasibility of detecting the fracture of each of the filaments in the bundle and composite was demonstrated. The in-situ damage detection technique was also applied to E-glass bundles and composites; this will be reported in a subsequent publication.
Del Rosso S, Iannucci L, Curtis P, 2016, On the ballistic impact response of microbraid reinforced polymer composites, Composite Structures, Vol: 137, Pages: 70-84, ISSN: 0263-8223
This paper presents the behaviour of microbraid reinforced polymer composites (mBRPC) subjected to impact loading conditions. Ballistic impact tests were performed by firing 7.94 mm steel balls onto composites reinforced with microbraids having different architectures, braid angles and of different materials (Kevlar® and Dyneema®). Two high speed cameras were employed to record the impact events. Experimental results revealed an improvement in the ballistic limit, of up to 19.5% for certain types of mBPRC, with respect to composites made with unidirectional fibres. Visual inspection of the impacted laminates revealed similar deformation mechanisms for composites reinforced with microbraids having different architectures and of different material. The slippage of the impactor through the layers of the laminates could have had detrimentally affected the ballistic properties of the manufactured composites. Modifications in the arrangement of the reinforcing phase are needed to fully exploit the potential of the microbraids in polymeric structures.
Raza IM, Iannucci L, Curtis PT, 2016, Additive manufacturing of locally resonant composite metamaterials
This article introduces a custom built multi-material 3D printer that is capable of depositing three different materials during one print. The printer utilises both continuous and droplet direct-write methods to deposit a UV cure plastic adhesive, latex rubber, and SAC solder metal in one single object. The printer is fully controlled via LabVIEW, allowing all aspects of the printing process to be adjusted. The purpose for this printer is to facilitate the manufacture of composite acoustic and elastic metamaterials.
Del Rosso S, Iannucci L, Curtis PT, et al., 2016, Hybrid UHMwPE/carbon microbraids for ductile composites
This paper presents a comprehensive series of mechanical tests performed on core-filled hybrid microbraids and composites manufactured using those microbraids as the reinforcing phase. Tensile tests performed on dry microbraids revealed the dependence of the mechanical properties on the bias angle of the fibres. During tensile loading conditions, the unidirectional core failed first, the bias yarns contained the failed core and shared the load until final failure occurred. The observed saw-tooth stress vs. strain curved can be attributed to multiple fractures of the inner core. The trends witnessed during testing the dry microbraids were very similar to those seen during tensile testing the composites.
Micallef K, Fallah AS, Curtis PT, et al., 2015, On the dynamic plastic response of steel membranes subjected to localised blast loading, International Journal of Impact Engineering, Vol: 89, Pages: 25-37, ISSN: 1879-3509
Permanent plastic deformation is expected when close-in blasts due to e.g. detonation of Improvised Explosive Devices (IED's) hit thin metallic targets. A circular thin steel plate i.e. a membrane is studied in the present work subject to a general form of a localised blast loading. The spatial shape of the pulse is fixed and different temporal shapes are investigated. Dynamic analyses are conducted and the permanent transverse displacements are found for each case.For high amplitude pulse loads of short duration, it was found that the permanent transverse displacement can be found by replacing the load by an impulse without the loss of accuracy. Excellent correlation with numerical simulations obtained from ABAQUS/Explicit is achieved. The predicted final displacements for different pulse shapes are also found to be similar, thus where membrane action is dominant, the response is insensitive to pulse shape.
Iannucci L, cwik T, curtis P, et al., 2015, Investigation of the ballistic performance of ultra high molecular weight polyethylene composite panels, Composite Structures, ISSN: 1879-1085
Pullen AD, Louca LA, Micallef K, et al., 2015, Characterization of the Mechanical Behavior of a Polymer-Based Laminate and Constituent Fibers at Various Quasi-Static Strain Rates, JOURNAL OF AEROSPACE ENGINEERING, Vol: 28, ISSN: 0893-1321
Del Rosso S, Iannucci L, Curtis PT, 2015, Experimental investigation of the mechanical properties of dry microbraids and microbraid reinforced polymer composites, Composite Structures, Vol: 125, Pages: 509-519, ISSN: 1879-1085
This paper presents a comprehensive series of mechanical tests performed on two high performance polymeric fibres, microbraids and microbraid reinforced polymer composites (mBRPC). Quasi-static tests were performed on the raw materials and the effect of different gauge lengths and strain rates investigated. Then, microbraids having sub-millimetre diameters were manufactured from the raw yarns using a Maypole-type braiding machine. The effects of different braid architectures, number of braided yarns and bias angles were assessed through a series of tensile tests on dry microbraids. A novel and unique manufacturing method of aligning microbraids in a unidirectional fashion via robotised filament winding was developed to manufacture microbraid reinforced polymer composites (mBRPC). Quasi-static tensile tests performed on mBRPC showed improved mechanical properties, for certain architectures, with respect to those noted for unidirectional composites manufactured using same technique.
Tsampas SA, Greenhalgh ES, Ankersen J, et al., 2015, Compressive failure of hybrid multidirectional fibre-reinforced composites, Composites Part A - Applied Science and Manufacturing, Vol: 71, Pages: 40-58, ISSN: 1359-835X
In this paper, the hybridisation of multidirectional carbon fibre-reinforced composites as a means of improving the compressive performance is studied. The aim is to thoroughly investigate how hybridisation influences the laminate behaviour under different compression conditions and thus provide an explanation of the “hybrid effect”. The chosen approach was to compare the compressive performance of two monolithic carbon fibre/epoxy systems, CYTEC HTS/MTM44-1 and IMS/MTM44-1, with that of their respective hybrids. This was done by keeping the same layup throughout ((0/90/45/−45)2S) while replacing the angle plies in one case or the orthogonal plies in the other case with the second material, thus producing two hybrid systems. To investigate the compressive performance of these configurations, compact and plain compression test methods were employed which also allowed studying the sensitivity of compressive failure to specimen geometry and loading conditions. The experimental results and the subsequent fractographic analysis revealed that the hybridisation of selective ply interfaces influenced the location and severity of the failure mechanisms. Finally, in light of this knowledge, an update of the generic sequence of events, previously suggested by the authors, which lead to global fracture in multidirectional fibre-reinforced composites under compression is presented.
Fallah AS, Micallef K, Langdon GS, et al., 2014, Dynamic response of Dyneema® HB26 plates to localised blast loading, International Journal of Impact Engineering, Vol: 73, Pages: 91-100, ISSN: 0734-743X
This paper reports on the dynamic response of a potential blast-resistant lightweight alternative to steel for military applications, namely ultra-high molecular weight polyethylene (UHMwPE) fibre composites known as Dyneema®. The results of localised air-blast loading tests on Dyneema HB26 panels are reported and analysed. Various failure modes were observed, including permanent deformation, delamination, in-plane shear, buckling around the boundary, localised melting and matrix damage. Total penetration (rupture) at the highest charge masses was also exhibited by the Dyneema panels. The experimental results are compared to the numerically simulated responses of mild steel and armour steel plates of equal areal density and reasonable correlation was observed in most cases. Dimensional analysis was used to compare the responses and showed that there is a possibility of unifying all the results i.e. the responses for all materials once a newly proposed slenderness ratio was incorporated into the formulation. Simple dimensionless expressions are proposed to predict permanent midpoint transverse displacements, irrespective of the particular material type. It was also observed that armour steel and Dyneema HB26 offer potential displacement reductions of almost 50% and 30%, respectively for the range of impulses tested.
Ghajari M, Iannucci L, Curtis P, 2014, A peridynamic material model for the analysis of dynamic crack propagation in orthotropic media, Computer Methods in Applied Mechanics and Engineering, Vol: 276, Pages: 431-452, ISSN: 0045-7825
A new material model for the dynamic fracture analysis of anisotropic materials has been proposed within the framework of the bond-based peridynamic theory. This model enables predicting complex fracture phenomena such as spontaneous crack nucleation and crack branching, curving and arrest, a capability inherited from the bond-based peridynamic theory. An important feature of the model is that the bond properties, i.e. the stiffness constant and critical stretch, are continuous functions of bond orientation in the principal material axes. This facilitates fracture analysis of anisotropic materials with random orientations, such as polycrystalline microstructures. Elastic and fracture behaviour of the model has been verified through simulating uniaxial tension of a composite plate and fracture of a cortical bone compact tension specimen, and making quantitative comparisons to analytical and experimental data. To further demonstrate the capabilities of the proposed model, dynamic fracture of a polycrystalline microstructure (alumina ceramic) has been simulated. The influence of the grain boundary and grain interior fracture energies on the interacting and competing fracture modes of polycrystalline materials, i.e. intergranular and transgranular fracture, has been studied.
Micallef K, Fallah AS, Curtis PT, et al., 2013, A homogenised continuum constitutive model for visco-plastic deformation of uni-directional composites, Composite Structures, ISSN: 0263-8223
This paper presents the development of multifunctional materials that perform a structural role whilst simultaneously storing electrical energy as a supercapacitor. Two structural carbon fibre woven electrodeswere separated by a woven glass fibre layer, and infused with a multifunctional polymer electrolyte. Following characterisation of electrochemical and compressive performance, working structural supercapacitor prototypes were demonstrated. Since the relative mechanical and electrical demands are application specific, an optimisation methodology is proposed. Multifunctional composites were achieved, which had compressive moduli of up to 39 GPa and capacitances of up to 52 mF g 1.
Ćwik TK, Iannucci L, Robinson P, et al., 2012, Investigation of factors influencing dynamic response of a tensile split hopkinson pressure bar, ISSN: 0273-4508
The paper presents results of a parametric study made on a tensile split Hopkinson pressure bar. The aim of the study was to identify factors influencing generation of the incident signal in the input bar, by employing advanced finite element techniques. The study showed that geometry of each Hopkinson bar component considered in this paper influences the shape of the incident signal to a certain extent. Predictions obtained from the finite element simulations were validated with experiments, and presented a very good agreement with the experimental data. © 2012 AIAA.
Ćwik TK, Iannucci L, Robinson P, et al., 2012, Investigation of factors influencing dynamic response of a tensile split Hopkinson pressure bar
The paper presents results of a parametric study made on a tensile split Hopkinson pressure bar. The aim of the study was to identify factors influencing generation of the incident signal in the input bar, by employing advanced finite element techniques. The study showed that geometry of each Hopkinson bar component considered in this paper influences the shape of the incident signal to a certain extent. Predictions obtained from the finite element simulations were validated with experiments, and presented a very good agreement with the experimental data. © 2012 by Tomasz Cwik. Published by the American Institute of Aeronautics and Astronautics, Inc.
Raimondo L, Iannucci L, Robinson P, et al., 2012, Modelling of strain rate effects on matrix dominated elastic and failure properties of unidirectional fibre-reinforced polymer-matrix composites, COMPOSITES SCIENCE AND TECHNOLOGY, Vol: 72, Pages: 819-827, ISSN: 0266-3538
Raimondo L, Iannucci L, Robinson P, et al., 2012, A progressive failure model for mesh-size-independent FE analysis of composite laminates subject to low-velocity impact damage, COMPOSITES SCIENCE AND TECHNOLOGY, Vol: 72, Pages: 624-632, ISSN: 0266-3538
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