CERES :: Browsing by Author "Njuguna, James A. K."

Browsing by Author "Njuguna, James A. K."

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Open Access
Analyses of Power Output of Piezoelectric Energy-Harvesting Devices Directly Connected to a Load Resistor Using a Coupled Piezoelectric-Circuit Finite Element Method
(IEEE Institute of Electrical and Electronics, 2009-07-31T00:00:00Z) Zhu, Meiling; Worthington, Emma; Njuguna, James A. K.
A coupled piezoelectric-circuit finite element model (CPC-FEM) is proposed for the first time to study the power output of a vibration-based piezoelectric vibration-based piezoelectric energy harvesting devices (EHDs) that is directly connected to a resistive load. Special focus is given to the effect of the resistive load value on the vibrational amplitude of the piezoelectric EHDs, and thus on the current, voltage, and power generated by the EHDs. In the literature, these outputs are widely assumed to be independent of the resistive load value for the reduction in complexity of modelling and simulation. The presented CPC-FEM uses a cantilever with sandwich structure and a seismic mass attached to the tip to study the following load characteristics of the EHD as a result of changing the resistive load value: (1) the electric outputs of the EHD: current through and voltage across the resistive load, (2) the power dissipated by the resistive load, (3) the vibration amplitude of tip displacement of the cantilever, and (4) the shift in resonant frequency of the cantilever. Investigation results shows significant dependences of the vibration characteristics of the piezoelectric EHDs on the externally connected resistive load are found, rather than independence as previously assumed in most literature. The CPC-FEM is capable of predicting the generated power output of the EHDs with different resistive load value while simultaneously calculating the effect of the resistive load value on the vibration amplitude. The CPC-FEM is invaluable for validating the performance of designed EHDs before fabrication and testing, thereby reducing the recurring costs associated with repeat fabrication and trials. In addition, the proposed CPC-FEM is potentially useful in device designs optimisations for maximal power generation.
Open Access
The application of energy absorbing structures on side impact protection systems
(Inderscience Enterprises Ltd, 2011-01-01T00:00:00Z) Njuguna, James A. K.
This paper presents a system to improve the protection to the occupants of a World Rally Championship Car in case of a side impact involving a tree collision using energy-absorbing structures. An outline of the immediate events after the car crash into a tree is provided followed by an analysis of a typical standard rollcage, then the design criteria and features of a carefully selected design concept. The design model is produced using solid modelling/I-DEAS 11 softwares and PAM-Crash is used for the simulations. The simulation results show that Side Impact Protection System (SIPS) is capable of absorbing and dissipating 98% of the energy of a 14 m/s impact involving a 0.2 m diameter tree
Open Access
Cellulose-Based Bio- and Nanocomposites: A Review
(2011-10-01T00:00:00Z) Kalia, Susheel; Dufresne, Alain; Cherian, Bibin Mathew; Kaith, B. S.; Avérous, Luc; Njuguna, James A. K.; Nassiopoulos, Elias
Cellulose macro- and nanofibers have gained increasing attention due to the high strength and stiffness, biodegradability and renewability, and their production and application in development of composites. Application of cellulose nanofibers for the development of composites is a relatively new research area. Cellulose macro- and nanofibers can be used as reinforcement in composite materials because of enhanced mechanical, thermal, and biodegradation properties of composites. Cellulose fibers are hydrophilic in nature, so it becomes necessary to increase their surface roughness for the development of composites with enhanced properties. In the present paper, we have reviewed the surface modification of cellulose fibers by various methods. Processing methods, properties, and various applications of nanocellulose and cellulosic composites are also discussed in this paper.
Open Access
Coupled piezoelectric-circuit FEA to study influence of a resistive load on power output of piezoelectric energy devices
(2012-08-01) Zhu, Meiling; Worthington, Emma; Njuguna, James A. K.; Schmid, Ulrich
This paper presents, for the first time, a coupled piezoelectric-circuit finite element model (CPC-FEM) to analyze the power output of vibration-based piezoelectric energy harvesting devices (EHDs) when connected to a resistive load. Special focus is given to the effect of the resistive load value on the vibrational amplitude of the piezoelectric EHDs, and thus on the current, voltage, and power generated by the EHDs, which are normally assumed to be independent of the resistive load in order to reduce the complexity of modelling and simulation. The CPC-FEM presented uses a cantilever with the sandwich structure and a seismic mass attached to the tip to study the following load characteristics of the EHD as a result of changing the load resistor value: (1) the electric outputs of the EHD: current and voltage, (2) the power dissipated by the resistive load, (3) the vibration amplitude of tip displacement, and (4) the shift in resonant frequency of the cantilever. Significant dependences of the characteristics of the piezoelectric EHDs on the externally connected resistive load are found, rather than independency, as previously assumed in most literature. The CPC-FEM is capable of predicting the generated power output with different resistive load values while simultaneously considering the effect of the resistor value on the vibration amplitude. The CPC-FEM is invaluable for validating the performance of a device before fabrication and testing, thereby reducing the recurring costs associated with repeat fabrication and trials, and also for optimizing device design for maximal power-output generation.
Open Access
Design and Simulation of a Novel Bio-Mechanic Piezoresistive Sensor with Silicon Nanowires
(2012-06-01T00:00:00Z) Messina, M.; Njuguna, James A. K.; Dariol, V.; Pace, C.; Angeletti, G.
This paper presents the design of a novel single square millimeter 3-axial accelerometer for head injury detection of racing car drivers. The main requirements of this application are miniaturization and high-G measurement range. We propose a new miniature accelerometer to be incorporated into an earpiece. Nanowires as nanoscale piezoresistive devices have been chosen as sensing element, due to their high sensitivity and miniaturization achievable. By exploiting the electro-mechanical features of nanowires as nanoscale piezoresistors, the nominal sensor sensitivity is overall boosted by more than 30 times. This approach allowssignificant higher accuracy and resolution with smaller sensing element in comparison with conventional devices without the need of signal amplification. This achievement opens up new developments in the area of implanted devices where the high-level of miniaturization and sensitivity is essential.
Open Access
The effect of nanoclay on dust generation during drilling process of polyamide 6 nanocomposites
(Hindawi Publishing Corporation, 2012-06-10T00:00:00Z) Sachse, Sophia; Silva, Francesco; Zhu, Huijun; Irfan, Adeel; Leszczynska, Agneska; Pielichowski, Krzysztof; Ermini, Valentina; Blazquez, Maria; Kuzmenko, Oleksandr; Njuguna, James A. K.
During the past decade, polymer nanocomposites have emerged as a novel and rapidly developing class of materials and attracted considerable investment in research and development worldwide. However, there is currently a lack of information available in the literature on the nano and ultrafine particle emission rates from these materials. In this study, influence of nanoclay on mechanical drilling of PA6 composites, in terms of dust generation has been reported. With the help of real-time characterization, submicrometer-sized particles (5.6-512 nm) size distribution and number concentration emitted from polyamide 6/nanoclay composites during mechanical drilling is studied. Total particle concentration for the PA6/nanoclay composites was 20,000 cm-3, while unreinforced panel measured a total concentration of approximately 400,000 cm-3. While the airborne particle concentration for the PA6/ nanoclay composites was 20 times lower than for the PA6 matrix, the concentration of deposited nanoparticles doubled for the nanocomposite. The results clearly shows that more particles in the size range between 175-350 nm are generated, during drilling of the nanocomposites and this particles deposit in a shorter time. It is likely that the presence of nanoclay in some way retains the formation of high quantity of airborne particles and promotes particle deposition.
Open Access
Emission benefits in application of alternative fuels on racing car compression ignition engines
(2011-05-25T00:00:00Z) Herreros, José M.; Lapuerta, Magín; Lowe, Derek; Njuguna, James A. K.
The depletion of fossil fuels, and the weather-related disasters associated with climate change and greenhouse gas emissions plus the other human health and environmental hazards related to exhaust pollutant emissions demands the use of innovative approaches to reduce fossil fuel consumption. Motorsport industry should become a test-bed, and because of its advertising potential should promote the use of alternative steps to minimize fossil fuel consumption and address associated emission issues. In the short term, some improvements to current powertrain technologies and the use of alternative fuels such as biodiesel or the primary alcohols can reduce fossil fuel dependency and partly decrease their harmful effects. In this study a framework has been developed based on the effect of the different fuel properties to assess their suitability, performance and emission characteristics of different ‘short-term' fuels such as biodiesel and primary alcohols to reduce the use of fossil fuels in motorsport industry. A database is generated to permit the construction and theoretical application of the framework to the specific case of a turbocharged, four-stroke, compression ignition engine with common-rail injection system operating in medium/high temperature engine mode
Open Access
Epoxy-based fibre reinforced nanocomposites
(John Wiley & Sons, Ltd, 2007-10-31T00:00:00Z) Njuguna, James A. K.; Pielichowski, Krzysztof; Alcock, Jeffrey R.
The modification of epoxy resins with nanoparticles could endow the materials with some superior properties such as broadening of the glass transition temperatures, modest increases in the glassy modulus, low dielectric constant, and significant increases in key mechanical properties. In the last 15 years, some studies have shown the potential improvement in properties and performances of fibre reinforced polymer matrix materials in which nano and micro-scale particles were incorporated. From the existing literature, considerable effort has been given to the synthesis and processing of these unique polymers, but relatively little work has focused on the fibre reinforced epoxy composites. The purpose of this work, therefore, is to review the available literature in epoxy- fibre reinforced composites manufactured using carbon nanotubes, carbon nanofibre and nanoclays for reinforcement.
Open Access
Estimation of bending resistance of ionic polymer metal composite (IPMC) actuator following variable parameters pseudo-rigid body model
(Elsevier Science B.V., Amsterdam., 2012-08-31) Bandopadhya, Dibakar; Njuguna, James A. K.
In this article bending resistance of IPMC has been estimated following a newly proposed variable parameters pseudo-rigid body model. First an experiment is conducted to study the voltage versus bending characteristics of IPMC and based on the experimental data the IPMC has been modeled through the proposed technique. Simulation has been performed and estimation of bending resistance has been made based on experimental results. It is observed that bending resistance of IPMC increases with input voltages although the changes remain insignificant after certain range. (c) 2009 Elsevier B.V. All rights reserved.
Open Access
Fabrication, Characterization and low-velocity impact testing of hybrid sandwich composites with polyurethane/layered silicate foam cores
(John Wiley & Sons, Ltd, 2011-01-31T00:00:00Z) Njuguna, James A. K.; Michalowski, Slawomir; Pielichowski, Krzysztof; Kayvantash, Kambiz; Walton, A. C.
A series of nanophased hybrid sandwich composites based on polyurethane/montmorillonite (PU/MMT) has been fabricated and characterised. Polyaddition reaction of the polyol premix with 4,4'-diphenylmethane diisocyanate was applied to obtain nanophased polyurethane foams which were then used for fabrication of sandwich panels. It has been found that the incorporation of MMT resulted in higher number of PU cells with smaller dimensions and higher anisotropy index (cross-sections RI and RII). The obtained materials exhibited improved parameters in terms of thermal insulation properties. The results also show that nanophased sandwich structures are capable of upholding withstanding higher peak loads than those made of neat polyurethane foam cores when subject to low-velocity impact despite lower density than that of neat PU foams. This is especially significant for multi-impact recurrences within the threshold loads and energies studied.
Open Access
Finite element analysis of glass fiber-reinforced polyamide engine oil pan subjected to localized low velocity impact from flying projectiles
(2012-10-31T00:00:00Z) Mouti, Zakaria; Westwood, Keith; Long, Darren; Njuguna, James A. K.
This paper investigates low velocity impact involving a glass fiber-reinforced polyamide engine oil pan as part of a complete new development of thermoplastic components. The assessment of the impact resistance has driven the need to employ LS DYNA for finite element modeling in order to benchmark and predict the strength and fracture behavior of stressed plastic parts. In order to develop a reliable predictive capability and to validate simulations, complete components were manufactured by injection molding techniques for the experimental samples. Low velocity impact investigations were carried out using a gas gun and a falling weight tester in order to simulate impact events to which the oil pan is subjected whilst in operational service. This was intended to point out damage tolerance and failure mechanisms likely to occur in the structure. The study results show the significant contribution of the design in terms of shock absorption. Specific oil pan design with protective ribbing combined with a superior material considerably improves the impact resistance. The paper provides results and discussions on experimental and finite element analysis investigations before concluding with some remarks.
Open Access
Finite element analysis of localised impact loading on short glass fibrereinforced polyamide engine oil pan subjected to low velocity impact from flying projectiles
(2011-05-24T00:00:00Z) Mouti, Zakaria; Westwood, Keith; Long, Darren; Njuguna, James A. K.
This paper investigates low velocity impact involving a glass fibre-reinforced polyamide engine oil pan as part of a complete new development of thermoplastic components. The assessment of the impact resistance has driven the need to employ LS DYNA for finite element modelling in order to virtually benchmark and predict the strength and fracture behaviour of stressed plastic parts. In order to develop a reliable predictive capability and to validate simulations, complete components were manufactured by injection moulding techniques for the experimental samples. Low velocity impact investigations were carried out using a gas gun and a falling weight tester in order to simulate impact events to which the oil pan is subjected whilst in operational service. This was intended to point out damage tolerance and failure mechanisms likely to occur in the structure. The study results show the significant contribution of the design in terms of shock absorption. Specific oil pan design with protective ribbing combined with a superior material considerably improves the impact resistance. The paper provides results and discussions on experimental and finite element analysis investigations before concluding with some remarks.
Open Access
Finite element dynamic simulation of whole rallying car structure: Towards better understanding of structural dynamics during side impact
(2012-06-21) Nassiopoulos, Elias; Njuguna, James A. K.
Side impact accidents against a tree or pole remain the most dangerous accident scenarios in rally cars. Statistical data shows that 52% of the fatalities between 2004 and 2009 concern crashes against a rigid pole by the track sides, whilst among those more than 60% were side impacts. Despite the present scientific efforts, rallying cars side impacts are still among the least understood primarily due to limited space between the occupant and door sill, evolving safety regulations and vehicle dynamics. In this study, finite element dynamic characteristics of the whole car were studied. The finite element model consisted of the whole car structure and 241 parts including the engines, tyres and the suspension members with 4 different element types and 7 material models. All structural parts were modelled as low-carbon steel with the piecewise- linear-plasticity material model (mat 24). The tyres were modelled with the Blatz-Ko rubber material (mat 07) whilst also rigid and other materials (mat 020, 01, 09, S01 and S02) were used to represent different parts of the model, as the suspension members, suspension links and the engine. A rollcage and two racing seats were modelled with four-node shell elements and the use of piecewise-linear-plasticity and composite-damage materials respectively. A semi- cylindrical pole of 200mm diameter was also designed and modelled as a rigid body. The model was used to first investigate the dynamics of the crash, and later run a wide range of simulations and parametric studies in the cage, the car's floor and the seats. The important findings from the study are presented, conclusions drawn and scope for further development outlined.
Open Access
Flutter prediction, suppression and control in aircraft composite wings as a design prerequisite: a survey
(Wiley, 2007-04-27T00:00:00Z) Njuguna, James A. K.
Emergence of flutter compromises not only the long-term durability of the wing structure, but also the operational safety, flight performance and energy efficiency of the aircraft. Effectual means of flutter prevention are, therefore, mandatory in the certification of new flight vehicles. This work intends to address the flutter phenomenon highlighting the above issues, and reviews some of the most recent theoretical and experimental developments in flutter analyses. In the following subsections, theoretical, computational and experimental flutter for composite structures is pursued. In particular, panel flutter, thrust-induced flutter, wing/store-type flutter, non-linear flutter, damaged panel flutter, flutter in compressed flow and flutter control via neural networks are covered. Effects of fibre/ply orientation on flutter are also briefly covered. The review further looks into aerothermoelastic behaviour of composite structures buckling problem and hopf bifurcation point determination. Analysed flutter of actively/passively controlled composite structures is critically reviewed due to the emphasized importance in modern structures. It is appreciable that the knowledge gained from the study of flexible structures and unsteady airflows in aircraft can be transitioned back to more traditional flutter studies. It is hoped that this review work will stimulate research and collaborations that will lead to significant progress in the understanding of this dynamically rich and potentially important area of enhancement of flutter prediction, suppression and control of active and passive composite aircraft structures. Copyright (C) 2006 John Wiley & Sons, Ltd.
Open Access
Free vibration of a three-layered sandwich beam using the dynamic stiffness method and experiment
(Elsevier Science B.V., Amsterdam., 2007-05-05T00:00:00Z) Banerjee, J. R.; Cheung, C. W.; Morishima, R.; Perera, M.; Njuguna, James A. K.
In this paper, an accurate dynamic stiffness model for a three-layered sandwich beam of unequal thicknesses is developed and subsequently used to investigate its free vibration characteristics. Each layer of the beam is idealised by the Timoshenko beam theory and the combined system is reduced to a tenth-order system using symbolic computation. An exact dynamic stiffness matrix is then developed by relating amplitudes of harmonically varying loads to those of the responses. The resulting dynamic stiffness matrix is used with particular reference to the Wittrick-Williams algorithm to carry out the free vibration analysis of a few illustrative examples. The accuracy of the theory is confirmed both by published literature and by experiment. The paper closes with some concluding remarks. (c) 2007 Elsevier Ltd. All rights reserved.
Open Access
In vitro analysis of nanoparticles released from polyamide nanomaterial composites during drilling process
(2011-05-10T00:00:00Z) Irfan, Adeel; Sachse, Sophia; Njuguna, James A. K.; Zhu, Huijun; Crump, Derrick
Nanomaterials provide a new avenue of progress into technological development. By manipulating materials on the very basic atomic and molecular levels the property of a given material can be specifically altered to suit the purpose of intended applications. However, nanomaterials (nanoparticles and nanolayers) have a more complex nature in physiochemical properties and surface reactivity than their larger counterparts. Therefore, the release of these nanomaterials as dust during crushing or drilling may lead to serious health hazards for humans and the surrounding environment. This study, supported by the NEPHH (Nanomaterial-related Environmental Pollution Health Hazards), addresses two important questions about nanomaterials: - Whether nanomaterials can be released from physical process of nanoproducts. - Toxicity potential of nanodusts generated from nanoproducts in comparison with reference products. Both questions address a massive gap in knowledge for toxicity and more specifically nanomaterial toxicity.
Open Access
The Influence of Multiscale Fillers Rein forcement into Impact Resistance and Energy Absorption Properties of Polyamide 6 and Polypropylene Nanocomposite Structures
(2013-09-01T00:00:00Z) Silva, Francesco; Njuguna, James A. K.; Sachse, Sophia; Pielichowski, Krzysztof; Leszczynska, Agneska; Giacomelli, Marco
Three-phase composites (thermoplastic polymer, glass-fibres and nano-particles) were investigated as an alternative to two-phase (polymer and glass-fibres) composites. The effect of matrix and reinforcement material on the energy absorption capabilities of composite structures was studied in details in this paper. Dynamic and quasi-static axial collapse of conical structures was conducted using a high energy drop tower, as well as Instron universal testing machine. The impact event was recorded using a high-speed camera and the fracture surface was investigated with scanning electron microscopy (SEM). Attention was directed towards the relation between micro and macro fracture process with crack propagation mechanism and energy absorbed by the structure. The obtained results indicated an important influence of filler and matrix material on the energy absorption capabilities of the polymer composites. A significant increase in specific energy absorption (SEA) was observed in polyamide 6 (PA6) reinforced with nano-silica particles and glass-spheres, whereas addition of montmorillonite (MMT) caused a decrease in that property. On the other hand, very little influence of the secondary reinforcement on the energy absorption capabilities of polypropylene (PP) composites was found.
Open Access
Integration of polymer nanocomposites technologies for automotive applications: opportunities and environmental health challenges
(2008-05-14T00:00:00Z) Njuguna, James A. K.; Peña, I.; Zhu, H.; Rocks, Sophie A.; Blazquez, Maria; Desai, S. A.; Pielichowski, Krzysztof
The concept of nanostructured materials design is gaining widespread importance among the automotive industry. Although employment of nanotechnology in current and future automotives will go long way in solving energy crises, it is necessary to understand both the hazards associated with nanomaterials and the levels of exposure that are likely to occur. The existing knowledge in these areas is quite limited and it will be necessary in the near future. This paper highlights these key issues and goes a long way in pointing recent activities on environmental risks of nanomaterials. Some research directions are given and existing automotive opportunities and applications explored.
Open Access
Low Velocity Impact Behavior of Glass Filled Fiber-Reinforced Thermoplastic Engine Components
(MDPI AG, 2010-03-31T00:00:00Z) Mouti, Zakaria; Westwood, Keith; Kayvantash, Kambiz; Njuguna, James A. K.
This paper concerns automotive parts located underneath the engine and in particular the engine oil pan. Classically made of stamped steel or cast aluminum, new developments have allowed the manufacture oil pans with polyamide 66 reinforced by 35% weight of short glass fiber. However, polyamides have some limitations and the most significant is their response to localized impact loading. The nature of the impact considered here is of a typical stone collected from the road and projected into the oil pan. Low velocity impact investigations were carried out using a gas gun and drop weight tower. The study shows that the design of the oil pan has a significant contribution in the shock absorption. In addition to the material properties, the geometry and the ribbing both cleverly combined, increase the impact resistance of the component significantly. Areas of oil pan design improvement have been identified and conclusions drawn.
Open Access
Nanocomposites for vehicle structural applications
(2011-11-14T00:00:00Z) Njuguna, James A. K.; Silva, Francesco; Sachse, Sophia; Lin, T
Advancements in the nanotechnology industry promise to offer improvements in capabilities across a spectrum of applications. This is of immense strategic importance to the high performance sector which has historically leveraged technological advances. The uses of polymer nanocomposites in structures have several predictable impacts on structural design and applications, primarily by providing a safer, faster, and eventually cheaper transportation in the future. In this chapter, special attention is focused on the reinforcement of key properties of polymer nanocomposites for potential high performance structural applications. Further insight is provided on developments in both theoretical and experimental investigations providing valuable fundamental elements in strength and stiffness, impact resistant and energy absorption performance, thermal properties, age and durability performance and structural health monitoring of polymer nanocomposites for vehicular structural needs. A brief overview of modeling and simulation of nano-reinforced materials is also given reflecting its importance in vehicular structures.