Mechanical & Materials Engineering Research Collection
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- Publication3D Printing of Fibre-Reinforced Thermoplastic Composites Using Fused Filament Fabrication—A ReviewThree-dimensional (3D) printing has been successfully applied for the fabrication of polymer components ranging from prototypes to final products. An issue, however, is that the resulting 3D printed parts exhibit inferior mechanical performance to parts fabricated using conventional polymer processing technologies, such as compression moulding. The addition of fibres and other materials into the polymer matrix to form a composite can yield a significant enhancement in the structural strength of printed polymer parts. This review focuses on the enhanced mechanical performance obtained through the printing of fibre-reinforced polymer composites, using the fused filament fabrication (FFF) 3D printing technique. The uses of both short and continuous fibre-reinforced polymer composites are reviewed. Finally, examples of some applications of FFF printed polymer composites using robotic processes are highlighted.
59Scopus© Citations 59 - PublicationAccurate measurement of nanofluid thermal conductivity by use of a polysaccharide stabilising agentMeasuring the thermal conductivity of low viscosity fluids such as aqueous nanofluids is challenging due to the formation of convection currents. In the current work, a modification of the transient hot-wire thermal conductivity measurement technique was investigated to address this problem. The polysaccharide agar was used as a gelling agent to prevent the formation of convection currents, thereby enabling measurement of thermal conductivity. The experimental method was validated by comparison of experimentally measured thermal conductivity values with published reference values over a range of temperatures for two reference fluids stabilised by agar: water and an ethylene glycol/water solution. The precision of thermal conductivity measurements was found to be significantly improved by use of this gelling agent. These findings indicate that agar, or a similar gelling agent, can be used to enable accurate measurement of the thermal conductivity of aqueous fluids. This measurement technique was utilised to accurately measure the thermal conductivity enhancements of copper and alumina aqueous nanofluids with low nanoparticle concentrations, over a range of temperatures. The thermal conductivities of these nanofluids were found to be within ± 2 % of those predicted by the Maxwell model.
360Scopus© Citations 4 - PublicationAccurate prediction of blood flow transients : a fluid-structure interaction approach(Computational & Mathematical Biomedical Engineering (CMBE), 2009-07-01)
; ; Numerical studies are widely employed in establishing blood flow transients in arteries. Unfortunately, many of these are based on rigid arterial geometries where the physiological interaction between the flowing blood and the dynamics of a deforming arterial wall is ignored. Although many recent studies have adopted a fluid-structure interaction (FSI) approach, they lack the necessary validation and, thus, cannot guarantee the accuracy of their predictions. This work employs a well-validated FSI model to establish the dependency of WSS transients on arterial flexibility and predict flow transients in arterial geometries. Results show a high dependency of WSS transients on arterial wall flexibility, with hoop strains of as low as 0.15% showing significant differences in these transients compared to that seen in a rigid geometry. It is also shown that flow in the atherosclerosis susceptible regions of the vascular tree is characterised by a highly disturbed flow. In these regions, WSS magnitudes are at their lowest, while the WSS spatial gradients, rate of change and oscillatory shear index are at their highest.349 - PublicationAcoustic Metrology : From Atmospheric Plasma to Solo Percussive Irish DanceLabVIEW software is used to decode step sequences generated by Irish light and hard shoes and bare feet. To remove the low frequency reverberation of the floor a Savitzky-Golay digital filter is used to de-convolute the percussion sound of the step sequences. Floor types and foot apparel are compared.
227 - PublicationAdditive Manufacture of Composite Soft Pneumatic Actuators(Mary Ann Liebert, 2018-12-07)
; ; ; ; ; ; This article presents a direct additive manufacturing method for composite material soft pneumatic actuators that are capable of performing a range of programmable motions. Commonly, molding is the method used to manufacture soft fluidic actuators. This is material, labor, and time intensive and lacks the design freedom to produce custom actuators efficiently. This article proposes an alternative semiautomated method of designing and manufacturing composite soft actuators. An affordable, open-source, desktop three-dimensional (3D) printer was modified into a four-axis, combined, fused deposition modeling, and paste extrusion printer. A Grasshopper 3D algorithm was devised to implement custom actuator designs according to user inputs, resulting in a G-code print file. Bending, contracting, and twisting motion actuators were parametrically designed and subsequently additively manufactured from silicone and thermoplastic elastomer (TPE) materials. Experimental testing was completed on these actuators along with their constitutive materials. Finite element models were created to simulate the actuator's kinematic performance. Having a platform method to digitally configure and directly additively manufacture custom-motion, composite soft actuators has the potential to accelerate the development of more intricate designs and lead to potential impacts in a range of areas, including in-clinic personalization of soft assistive devices and patient-specific biomedical devices.1285Scopus© Citations 35 - PublicationAerosols, airflow, and airspace contamination during laparoscopy(Oxford University Press, 2021-09-27)
; ; ; ; Laparoscopic surgery has been undermined throughout the COVID-19 pandemic by concerns that it may generate an infectious risk to the operating team through aerosolization of peritoneal particles. There is anyway a need for increased awareness and understanding of the occupational hazard for surgical teams regarding unfiltered escape of pollutants generated by surgical smoke and other microbials. Here, the aerosol-generating nature of this access modality was confirmed through repeatable real-time methodology both qualitatively and quantitively to inform best practice and additional engineering solutions to optimize the operating room environment.22Scopus© Citations 5 - PublicationAir and Water Flow Rate Optimisation For a Fan Coil Unit in Heat Pump ApplicationsThe degradation in efficiency of auxiliary components in heating/cooling systems when operating at part load is frequently reported. Through the use of variable speed components, the supplied capacity can be reduced to match the required load and hence reduce unnecessary energy consumption. However, for fan coil units, difficulties can arisewhen optimizing fan and pump speeds at part load. Practicallylocating optimal water and air flowrates from readily available information and for varying supplied capacities is necessary,in order to reduce the fan coil power consumption. This research attempts to identify whether optimal fan and pump speeds exist for a fan coil unit and how they can be implemented, in a practical manner, in a system control applications. Using an empirical fan coil and pump model, the total power consumption (fan and pump) for different combinations of fan and pump speeds over a range of capacities was calculated. It was observed that, for a given capacity, an optimal combination of fan and pump speeds exists and there was a significant change in power consumption for different combinations of fan and pump speeds supplying the same capacity. A control strategy is described that utilizes a simple fan coil capacity estimation model, coupled with air and water flowrates, along with nominal design data. The pump speed is optimized using PID control to maintain the space temperature at the chosen set-point, which matches the supplied capacity to the required capacity. At set-time intervals, the capacity estimation model is utilized to optimize the water and air flowrates for the required capacity. The control strategy is evaluated, using a full building simulation model for a daily load profile and is compared to two baseline conditions: for no control of the fancoils/pump combination and for PID circulation control of the pump only. The optimal fan and pump speed control resulted in a 43% and 24% decrease in power consumption with compared to the no control baseline and the PID controlled circulation pump strategy, respectively.
254 - PublicationAn alternative TLM method for steady-state convection-diffusionRecent papers have introduced a novel and efficient scheme, based on the transmission line modelling (TLM) method, for solving one-dimensional steady-state convection–diffusion problems. This paper introduces an alternative method. It presents results obtained using both techniques, which suggest that the new scheme outlined in this paper is the more accurate and efficient of the two. Copyright © 2009 John Wiley & Sons, Ltd.
287 - PublicationAnalysis and optimization of sandwich tubes energy absorbers under lateral loadingIn this paper, the sandwich tubes, which consist of thin-walled circular tubes with aluminium foam core, were proposed as energy absorption devices. The sandwich tubes were laterally crushed under quasi-static loading conditions. Detailed finite element model, validated against existing experimental results, was developed using the explicit code (ANSYS-LSDYNA) to assess the energy absorption responses and deformation modes. Response surface methodology (RSM) was employed in parallel with the finite element models to perform both parametric studies and multi-objective optimization in order to establish the optimal configuration of the sandwich tube. Sampling designs of the sandwich tubes were constructed based on a D - optimal design of experiment (DOE) method. Factorial analysis was performed using the DOE results to investigate the influences of the geometric parameters on the responses of sandwich tubes. In addition, multi-objective optimization design (MOD) of the sandwich tubes is carried out by adopting a desirability approach. It was found that the tube with a minimum diameter of the inner layer and a maximum foam thickness are more suitable for use as energy absorbing components.
249Scopus© Citations 82 - PublicationAnalysis of a Microgravity Solidification Experiment for Columnar to Equiaxed Transitions with Modeling ResultsThis paper studies the Columnar to Equiaxed Transition (CET) in an Al-7wt%Si binary alloy with and without Al-Ti-B grain refiner. A microgravity experiment was designed to produce a CET in this alloy system. The experiment was flown onboard the MAXUS-7 sounding rocket platform, which achieved twelve minutes of microgravity. Examples of CET were successfully produced during the unmanned flight. Temperature data were recorded from thermocouples in the crucible walls of the furnace. Post-mortem material characterization of the grain structure was also performed. Subsequently a model of the furnace, which used a front-tracking model of solidification and an inverse heat calculation method, was developed. In this paper, results from the model are compared to the experimental findings; agreement is found with the CET predictions. The results from the model are then used to compare findings with the CET criterion of Hunt from the literature. Agreement is found between the model predictions and the Hunt criterion.
399Scopus© Citations 7 - PublicationAnalysis of an Equiaxed Dendrite Growth Model with Comparisons to In-Situ Results of Equiaxed Dendritic Growth in an Al-Ge Alloy(Trans Tech Publications, 2010-06)
; ; ; The Lipton Glicksman Kurz (LGK) growth model is commonly used to predict growth rates for equiaxed dendrites in solidifying mushy zones. However, the original LGK method treats an isolated dendrite growing in an infinite volume of liquid. In an equiaxed mushy zone, with multiple nucleation events, thermal and solutal interactions take place between the equiaxed dendrites. A modified version of the LGK model was developed that allows for measurement of the solute build-up ahead of the dendrites. To investigate the validity of the model, comparisons are made with results obtained from in-situ synchrotron X-ray videomicroscopy of solidification in a Bridgman furnace of an Al-12wt.%Ge alloy inoculated with Al-Ti-B grain refiner. Comparisons between the original LGK and modified LGK models are presented for discussion. The modified LGK model shows realistic tip temperature trends.549Scopus© Citations 18 - PublicationAnalysis of End-Stop Parameters on the Performance of Heaving Point Absorber Wave Energy Convertors(2016-09-14)
; ; Wave energy converters (WEC) have the potential to generate a sizeable proportion of Ireland’s energy needs. Although there has been a great deal of research into WEC technology, no commercial devices exist at this time. One reason for this, has been underestimating the forces involved in the marine environment, and thus under designing components, especially power take off (PTO) systems. End stops are a crucial component of all moving body converters, which have rigid connections to PTOs. They are designed to protect the PTO mechanism by restricting the allowable travel distance. End stops, although vital components of WEC technology limit energy generation and thus must be taken into account in initial design. In this paper, a torus shaped point absorber moving against a monopile is numerically modelled in operational conditions using combined potential flow boundary element method and modified Morison's equation viscous drag. Two torus geometries are modelled, varying the radius and draft. The effect of various end-stop parameters on PTO forces and average annual energy generation are analysed. These parameters being; WEC travel distance, end stop distance and stiffness. Two separate Irish sites are analysed, a high energy site off the west coast and a medium energy site off the south coast. This paper aids WEC development by describing the performance effects of end stop design.79 - PublicationAnalysis of fibre orientation effects on injection moulded componentsFibre orientation, and thus the mechanical behaviour of short-fibre-reinforced thermoplastics (SFRTPs), depends greatly on the flow conditions in the mould. In order to design with SFRTPs, a thorough understanding of the processing conditions is required, together with the influence that the fibre orientation distribution (FOD) has upon the resulting mechanical properties. This work investigates the influence of primary injection moulding process parameters on the final properties of a simple planar injection-moulded component through design of experiments (DOE) and analysis of variance (ANOVA) techniques. Four factors are seen to have greatest effect on the mechanical properties: cavity thickness, packing pressure, packing time, and melt temperature. A systematic procedure is then employed to vary the levels of each factor, and the FOD and mechanical properties are studied. The final orientation is complex and is shown to vary throughout the part and depend heavily on the values selected for each parameter. Experimentally measured orientation results are then compared against those predicted by commercially available software for this planar geometry component. It is found that the predicted orientations were significantly over-predicted (34 per cent on average), from a minimum of 15 per cent for a 2 mm mould cavity up to 40 per cent for the larger 5 mm cavity thickness. This discrepancy in turn leads to an over-prediction, of approximately 50–60 per cent, between predicted and measured stiffness.
380Scopus© Citations 8 - PublicationAnalysis of heart rate variability amongst cyclists under perceived variations of risk exposureCycling as a mode of travel provides an opportunity for many people to increase their levels of regular physical activity and contribute to their mental and physical health. Heart rate is often used as a means of measuring the intensity and energy expenditure of physical activity. However, heart rate is also linked to emotional factors such as anxiety and fear. Perceptions of risk due to external factors such as other road users and infrastructure may arouse such emotions in urban cyclists. The present study set out to investigate whether or not perceptions of risk among urban cyclists may lead to increased heart rates. Cyclists completed a test route in normal traffic conditions in Cork, Ireland and heart rates and self-reported risk ratings were recorded in real time. Evidence was found of a link between perceptions of risk and heart rates. This raises questions regarding the use of heart rate to estimate exercise intensity and energy expenditure during urban cycling. The perceptions of cyclists of their safety in relation to various road elements on familiar routes were also assessed, as well as specific events which they perceive to be high in risk. The results indicate that incidents involving car traffic and busy roads which offer no protection from interaction with car traffic are associated with greatest perceptions of risk.
301Scopus© Citations 19 - PublicationAnalysis of loading curve characteristics on the production of brain deformation metricsTraumatic and mild traumatic brain injuries are incurred as a result of the complex motions of the head after an impact. These motions can be quantified in terms of linear and rotational accelerations which cause the injurious levels of brain deformation. Currently, it is unclear what aspects of the linear and rotational acceleration loading curves influence injurious brain deformation. This research uses the University College Dublin Brain Trauma Model to analyse the loading curve shapes from a series of centric and non-centric impacts to a Hybrid III headform fitted with different hockey helmets. The results found that peak resultant linear acceleration did not always correlate with brain deformation measures. The results also indicated that, due to the complex nature of the interaction between loading curve characteristic and tissue parameters, there was no commonality in curve shape which produced large magnitudes of brain deformation. However, the discriminant function did show that angular acceleration loading curve characteristics would predict brain deformation more reliably than linear acceleration loading curves.
342Scopus© Citations 13 - PublicationAnalysis of Rayleigh-Lamb wave scattering by a crack in an elastic plateThis paper considers the scattering of low-frequency elastic waves by a crack in a plate. A simple formula is derived for the reflection coefficient which serves as a lower bound to the reflection coefficient at higher frequencies.
300Scopus© Citations 19 - PublicationAnalysis of the influence of independent variables used for reconstruction of a traumatic brain injury incidentTraumatic brain injuries contribute to a high degree of morbidity and mortality in society. To study traumatic brain injuries researchers reconstruct the event using both physical and FE models. The purpose of these reconstructions is to correlate the brain deformation metric to the type of injury as a measure for prediction. These reconstructions are guided by a series of independent variables which all have influence upon the outcome variables. This research uses a combination of physical and FE modelling to quantify how independent variables such as velocity and impact vector (angle) contribute to the resulting variance in brain deformation metrics. The results indicated that using a Hybrid III neck controls the rotational acceleration response from an impact. Also, it was found that strain rate and product of strain and strain rate were more sensitive to changes in impact angle. Linear acceleration decreased with increasing impact angle, while brain deformations did not follow this trend, which suggests that peak linear acceleration may not be the only factor in the production of larger brain deformations.
360Scopus© Citations 23 - PublicationAnalysis of two-phase ceramic composites using micromechanical modelsMicromechanical models of two-phase ceramic composites are created using a modified Voronoi tessellation approach. These representative Finite Volume (FV) microstructures are used to investigate the role of microstructure on fracture of advanced ceramics. An arbitrary crack propagation model using a cell-centred finite volume based method is implemented. In particular the effect of matrix content is examined. It is shown that the underlying microstructure significantly affects the local stress and strain distributions for a two-phase ceramic containing hard particles in a softer matrix. Simulation results indicate that an increase in the volume fraction of these hard grains leads to an increase in strength of the composite material. Furthermore, it is found that the homogeneity of the microstructure affects the overall strength.
377Scopus© Citations 10 - PublicationAnimal models of traumatic brain injury : a critical evaluationAnimal models are necessary to elucidate changes occurring after brain injury and to establish new therapeutic strategies towards a stage where drug efficacy in brain injured patients (against all classes of symptoms) can be predicted. In this review, six established animal models of head trauma, namely fluid percussion, rigid indentation, inertial acceleration, impact acceleration, weight-drop and dynamic cortical deformation are evaluated. While no single animal model is entirely successful in reproducing the complete spectrum of pathological changes observed after injury, the validity of these animal models including face, construct, etiological and construct validity and how the models constitute theories about brain injury is addressed. The various types of injury including contact (direct impact) and non-contact (acceleration/deceleration) and their associated pathologies are described. The neuropathologic classifications of brain injury including primary and secondary, focal and diffuse are discussed. Animal models and their compatibility with microdialysis studies are summarised particularly regarding the role of excitatory and inhibitory amino acid neurotransmitters. This review concludes that the study of neurotransmitter interactions within and between brain regions can facilitate the development of novel compounds targeted to treat those cognitive deficits not limited to a single pharmacological class and may be useful in the investigation of new therapeutic strategies and pharmacological testing for improved treatment for traumatic head injury.
1028Scopus© Citations 143 - PublicationAntifouling coatings made with Cold Spray onto polymers: Process characterizationCold Spray (CS) of copper particles onto polymers has been validated as an effective tool for maintaining surface integrity in bioenvironments. CS requires limited heat input, can be applied locally or in large areas. The key parameters are particle penetration depth and copper surface coverage. However, the process parameters that can optimize the coating performance with deposition have not been comprehensively explored. In this paper, copper particles were deposited onto two polymers used in marine applications. A detailed analysis was carried out to correlate the key surface properties to the process so as to determine the optimum conditions.
607Scopus© Citations 17