236 research outputs found
Tensile and impact properties of melt-blended nylon 6/ethylene-octene copolymer/graphene oxide nanocomposites.
No full textThe addition of stiff nanoparticles to a polymer matrix usually proves beneficial for the enhancement in stiffness and strength, however, the impact strength is usually lowered. Conversely, the use of elastomeric additives can enhance the toughness and impact strength but causes a reduction in overall stiffness and strength. To take advantage of the desirable effects of both additives, they may be simultaneously added to the host matrix. Graphene oxide (GO), along with a thermoplastic elastomer ethylene-octene copolymer (EOC), was chosen to be added to nylon 6 for the current investigation. Maleated EOC (EOC-g-MA) was used as a compatibilizer for this study. 3 wt% GO nanoparticles, 20 wt% ethylene-octene copolymer (EOC) and 3 wt% EOC-g-MA were added to nylon 6 to prepare the nylon 6/EOC/GO blend-based nanocomposites. A high shear rate screw running at 300 rpm was used for melt-blending with a twin-screw extruder. Increased stiffness and tensile strength were observed by the addition of GO nanoparticles while elongation at break, toughness and impact strength were lowered by the addition of GO. The addition of EOC and EOC-g-MA enhanced the elongation at break, toughness and impact strength. However, the stiffness and strength of nylon 6/EOC blend was lower than that of the neat nylon 6. The addition of GO nanoparticles and EOC to neat nylon 6 caused a reduction in its impact strength. However, simultaneous addition of EOC and EOC-g-MA to nylon 6 caused a significant increase in the impact strength compared to neat nylon 6 and yielded a nylon 6/EOC/EOC-g-MA bend with the highest impact strength. The addition of GO nanoparticles to this blend, however, again caused a significant reduction in the impact strength. Nylon 6/EOC/EOC-g-MA blend showed the highest toughness and impact strength. Simultaneous addition of EOC and GO helped achieve a balanced stiffness and toughness
Optimization of Postbuckling-Stiffened Composite Aerostructures
No full textExperimental and numerical evidence has shown that the occurrence of secondary instabilities, or mode-jumping, can have a detrimental effect on the structural integrity of thin-skinned stiffened composite panels. The sudden release of energy has been shown to initiate skin-stiffener debonding, leading to catastrophic fracture. As a consequence, it is common practice to increase the skin thickness in vulnerable areas, leading to non-optimal, i.e., heavier, structures. In this chapter, an optimization framework is presented which couples nonlinear high-fidelity finite element modelling, which is capable of capturing mode-jumping and the evolution and propagation of damage, with a genetic algorithm for use in the design of efficient and robust postbuckling composite structures.</p
Comparison of damage characteristics of adhesively bonded and rivet-connected evtol wing under bird-strike
No full textThe advent of electric aircraft, including urban mobility vehicles, has brought renewed attention to the structural integrity of associated lightweight composite airframes. The evolution of composite passenger aircraft demonstrates the advantages of the use of these lightweight materials yet there are still certain structural components which are more susceptible to off-design loading than their metallic counterparts. For example, wing and empennage leading edges, are particularly susceptible to bird strike and are usually still made out of aluminium. Nonetheless, there are certain advantages in pursuing a composite leading edge, such as further weight reduction and enhanced laminar flow. In doing so, it becomes imperative to ensure that its energy absorption characteristics are well understood and can be predicted using computational modelling to reduce the extent of physical testing. For the case of fixed leading edges, energy absorption is likely to be dependent on the way that this leading edge is assembled and attached to the front spar, since the joint itself is a potential energy-absorbing mechanism. In this computational study two approaches are investigated; (i) the leading edge is adhesively-bonded, and (ii) riveted (Fig 1). Soft body impact, to simulate a bird strike, is achieved using Smooth Particle Hydrodynamics (SPH) which is preferred over the Arbitrary Lagrangian Eulerean (ALE) method. The analyses in this study are performed using an explicit finite element solver LS-DYNA. In this article, a composite sandwich wing model, made of unidirectional carbon-fibre polymer composite and a phenolic-based honeycomb core material, is impacted with a soft body mass in accordance with international standards and special conditions given by EASA. These standards are CS-25.631 and the special conditions for eVTOLs. The lay-up of the wing model includes unidirectional prepreg materials pertain to the face and back skin as well as the aforementioned attachment region which connects the spar and the leading edge. The substitute bird model (soft body mass) is configured using a well-defined equation of state model and the properties of homogenous gelatin.<br/
Thermoresponsive nanocomposites incorporating microplasma synthesized magnetic nanoparticles - synthesis and potential applications
No full textThe requirement for novel therapeutic and diagnostic techniques for biomedical applications has driven the development of multifunctional composite materials. This, in turn, has necessitated the use of novel synthesis and processing techniques for scalable nanocomposite production with tuneable material properties. Atmospheric Pressure Microplasma (APM) is a synthesis technique which has received considerable interest in recent years as a viable route for fabrication of nanoparticles (NPs) and NP/polymer composites. Here, we employ APM synthesis of NPs in solutions demonstrating, for the first time, the in situ synthesis of magnetic NPs (Fe3O4) in a hydrogel; fabricating a magnetic thermo‐responsive hydrogel (poly (N‐isopropylacrylamde)) composite. This demonstrates the applicability of our APM process for producing materials which are potentially relevant to the health sector
Comparison of damage characteristics of adhesively bonded and rivet-connected evtol wing under bird-strike
No full textThe advent of electric aircraft, including urban mobility vehicles, has brought renewed attention to the structural integrity of associated lightweight composite airframes. The evolution of composite passenger aircraft demonstrates the advantages of the use of these lightweight materials yet there are still certain structural components which are more susceptible to off-design loading than their metallic counterparts. For example, wing and empennage leading edges, are particularly susceptible to bird strike and are usually still made out of aluminium. Nonetheless, there are certain advantages in pursuing a composite leading edge, such as further weight reduction and enhanced laminar flow. In doing so, it becomes imperative to ensure that its energy absorption characteristics are well understood and can be predicted using computational modelling to reduce the extent of physical testing. For the case of fixed leading edges, energy absorption is likely to be dependent on the way that this leading edge is assembled and attached to the front spar, since the joint itself is a potential energy-absorbing mechanism. In this computational study two approaches are investigated; (i) the leading edge is adhesively-bonded, and (ii) riveted (Fig 1). Soft body impact, to simulate a bird strike, is achieved using Smooth Particle Hydrodynamics (SPH) which is preferred over the Arbitrary Lagrangian Eulerean (ALE) method. The analyses in this study are performed using an explicit finite element solver LS-DYNA. In this article, a composite sandwich wing model, made of unidirectional carbon-fibre polymer composite and a phenolic-based honeycomb core material, is impacted with a soft body mass in accordance with international standards and special conditions given by EASA. These standards are CS-25.631 and the special conditions for eVTOLs. The lay-up of the wing model includes unidirectional prepreg materials pertain to the face and back skin as well as the aforementioned attachment region which connects the spar and the leading edge. The substitute bird model (soft body mass) is configured using a well-defined equation of state model and the properties of homogenous gelatin.<br/
Modelling and assessing impact damage for a new generation of zero-emissions maritime vessels
No full textThis paper presents a study of the impact resistance of different composite structures which have been proposed for a new generation of zero-emissions composite maritime vessels. A mixture of flat plate specimens, eFoil leading edge models and full-scale vessel hull models were simulated in this work. These representative models are further divided into high-fidelity models (i.e. mesoscale level of analysis) and global-local finite element (FE) models of the entire structure. Impact conditions were defined based on typical loading expected during the vessels operating life. For example, the leading edge was impacted by sea ice while the hull was impacted by rigid debris. A robust intralaminar damage model was used to capture damage modes such as matrix cracking while cohesive surfaces were used to model ply-to-ply contact and capture delamination.Results have shown that the leading edge can successfully resist an ice impact with negligible predicted interlaminar delamination when compared with a rigid body impact. The use of a global-local modelling approach (a mixture of shell and solid elements and shell-solid coupling) can produce similar damage in local and global representations of the eFoil structure. Results have also shown that, when a projectile strikes the hull, interlaminar delamination was negligible.<br/
High velocity impact behaviour of additively manufactured cellular core backed Kevlar
No full textThis work investigates the effect of several parameters of a cellular core, protected by a Kevlar plate, under ballistic impact. Three core geometries, two sizes, and four relative densities are explored and their effects quantified. Overall, auxetic geometries (re-entrant and double arrowhead) result in a significant reduction in transmitted force at the cost of increasing the maximum displacement compared to a non-auxetic hexagonal structure. The cell size has no effect on the maximum displacement for any of the geometries or the transmitted force for the auxetics. A smaller cell size does, nonetheless, increase the peak transmitted force for the hexagonal structure. Increasing the relative density of the structures increases the transmitted force whilst decreasing the maximum displacement across all unit cells considered. This work provides a basis for the parameter selection when using cellular structures in an impact mitigation setting.<br/
Modelling and assessing impact damage for a new generation of zero-emissions maritime vessels
No full textThis paper presents a study of the impact resistance of different composite structures which have been proposed for a new generation of zero-emissions composite maritime vessels. A mixture of flat plate specimens, eFoil leading edge models and full-scale vessel hull models were simulated in this work. These representative models are further divided into high-fidelity models (i.e. mesoscale level of analysis) and global-local finite element (FE) models of the entire structure. Impact conditions were defined based on typical loading expected during the vessels operating life. For example, the leading edge was impacted by sea ice while the hull was impacted by rigid debris. A robust intralaminar damage model was used to capture damage modes such as matrix cracking while cohesive surfaces were used to model ply-to-ply contact and capture delamination.Results have shown that the leading edge can successfully resist an ice impact with negligible predicted interlaminar delamination when compared with a rigid body impact. The use of a global-local modelling approach (a mixture of shell and solid elements and shell-solid coupling) can produce similar damage in local and global representations of the eFoil structure. Results have also shown that, when a projectile strikes the hull, interlaminar delamination was negligible.<br/
High velocity impact behaviour of additively manufactured cellular core backed Kevlar
No full textThis work investigates the effect of several parameters of a cellular core, protected by a Kevlar plate, under ballistic impact. Three core geometries, two sizes, and four relative densities are explored and their effects quantified. Overall, auxetic geometries (re-entrant and double arrowhead) result in a significant reduction in transmitted force at the cost of increasing the maximum displacement compared to a non-auxetic hexagonal structure. The cell size has no effect on the maximum displacement for any of the geometries or the transmitted force for the auxetics. A smaller cell size does, nonetheless, increase the peak transmitted force for the hexagonal structure. Increasing the relative density of the structures increases the transmitted force whilst decreasing the maximum displacement across all unit cells considered. This work provides a basis for the parameter selection when using cellular structures in an impact mitigation setting.<br/
Comment on “A tensorial based progressive damage model for fibre reinforced polymers”
No full textThis communication is in response to unsubstantiated claims, arising from misinterpretations and misrepresentations, made by Bogenfield and Kreikemeier in their recent paper, “A tensorial based progressive damage model for fibre reinforced polymers” Bogenfeld and Kreikemeier (2017), on a damage model developed by Falzon et al. (2015). While details of this model have been extensively reported in a number of publications (e.g. Tan et al., 2015; Falzon and Tan, 2016; Chiu et al., 2016), and validated through comprehensive experimental programmes, this brief paper provides additional information on the damage model's formulation for the purpose of clarification and rebutting the conclusions in Bogenfeld and Kreikemeier (2017). The test cases reported in Bogenfeld and Kreikemeier (2017), to demonstrate the apparent shortcomings of the damage model in Tan et al. (2015), are repeated here to show that the alleged shortcomings are non-existent and consequently provide further support for the robustness and predictive capability of Falzon's progressive damage model.</p
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