9 results found
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.
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.
Del Rosso S, Iannucci L, 2020, On the compressive response of polymeric cellular materials, Materials, Vol: 13, ISSN: 1996-1944
This paper presents a series of compression tests performed on a variety of high performance lightweight cellular materials conventionally used in energy absorption applications. Compressive tests were performed over a range of strain rates with a universal testing machine and a single stage gas gun. Experimental results revealed a dependency of the mechanical properties on the polymeric precursor, density, infill topology and strain rates. The dynamic strength of the investigated materials was determined through a material parameter identification study via the finite element (FE) method. Numerical results matched well with the experimental results and revealed a substantial enhancement in the compressive strength of the tested material from quasi-static to dynamic loading regimes by as much as 87%. The strength of 3D printed polymers was superior with respect to the tested polymeric foams. On the other hand, polymeric foams showed higher efficiency and energy absorption ability.
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.
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.
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.
Hammad A, Swinburne TD, Hasan H, et al., 2015, Theory of the deformation of aligned polyethylene, Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 471, ISSN: 1471-2946
Solitons are proposed as the agents of plastic and viscoelastic deformation in aligned polyethylene. Interactions between straight, parallel molecules are mapped rigorously onto the Frenkel–Kontorova model. It is shown that these molecular interactions distribute an applied load between molecules, with a characteristic transfer length equal to the soliton width. Load transfer leads to the introduction of tensile and compressive solitons at the chain ends to mark the onset of plasticity at a well-defined yield stress, which is much less than the theoretical pull-out stress. Interaction energies between solitons and an equation of motion for solitons are derived. The equation of motion is based on Langevin dynamics and the fluctuation–dissipation theorem and it leads to the rigorous definition of an effective mass for solitons. It forms the basis of a soliton dynamics in direct analogy to dislocation dynamics. Close parallels are drawn between solitons in aligned polymers and dislocations in crystals, including the configurational force on a soliton. The origins of the strain rate and temperature dependencies of the viscoelastic behaviour are discussed in terms of the formation energy of solitons. A failure mechanism is proposed involving soliton condensation under a tensile load.
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.
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