Now showing 1 - 10 of 101
  • Publication
    Manufacturing & design with engineering polymers: Educational aspects of a specialist dissertation in a part-time elective postgraduate mechanical engineering degree course for industry-based students
    (Tempus Publications, 1999)
    The elective course on Manufacturing & Design with Engineering Polymers that is available to postgraduate students on the Master of Engineering Design degree programme at The National University of Ireland, Dublin uses active learning to teach students about processing and performance related issues pertinent to polymer engineering for Irish industry. A significant element of this course is undertaken by students preparing a Specialist Dissertation that is pertinent to their particular industry and employer and which simultaneously implements and illustrates many specific topics on the course syllabus (e.g., viscoelasticity, deformation & fracture, processing, design for manufacture, design for strength, etc.). The case of a recent student, employed as a full-time R&D engineer by a company manufacturing viscoelastic pressure relieving pressure pads, is used to illustrate the practical educational issues that arise when implementing such a teaching method. This method of education, i.e., by means of a Specialist Dissertation, proved to be an effective and popular teaching method in that specific concepts that were integral to the aims and objectives of the Manufacturing & Design with Engineering Polymers course were learned actively by the student. This method of teaching works well with relatively small class sizes but does require a tutorial style of involvement between course teacher and students. It is recommended that further uses of this method of teaching within the present context of the Master of Engineering Design degree programme be explored further.
      282
  • Publication
    Rayleigh-Lamb wave detection of two-dimensional defects in metal plates
    Nondestructive testing of engineering structures is essential to ensure safety. Ultrasonic C-scanning uses waves ropagating normal to a plane surface. This is accurate, but slow for planar structures. Longitudinal waves would allow quicker testing of such structtwes. This paper considers the reflection of low to moderate frequency Rayleigh­ Lamb waves by a through width lozenge-shaped defect in an isotropic plate. A numerical method is used. It is shown that such longitudinal ultrasonic waves can be used with success to detect and locate structural defects if care is exercies in frequency selection.
      96
  • Publication
    In-situ Accelerated Testing of Bituminous Mixtures
    (Informa UK (Taylor & Francis), 2001-12-15) ; ; ;
    The in-service behaviour of a standard Irish Dense Base Coarse Macadam mixture (DBC) was evaluated by using the material to overlay a road section, which was based upon a weak pavement structure. The response of the layer under a fully laden dual axle truck was examined using a series of pressure cells and asphalt strain gauges that were embedded in the test section. The section was traversed repeatedly until a network of fatigue cracks was observed on the road surface. The transverse horizontal tensile strain was found to be the most critical parameter with respect to crack initiation. When based on in-situ measured strain data, the analytical model that was developed to predict pavement performance on the basis of fundamental laboratory test data, was found to underestimate the in-service fatigue life of the DBC mixture by a factor of 13.5. The underestimation may be attributed to factors that are not accounted for in the analytical models such as material healing, traffic wander and in-situ environmental , which possibly lead to lower fatigue estimates.
      493
  • Publication
    Comparative multibody dynamics analysis of falls from playground climbing frames
    This paper shows the utility of multibody dynamics in evaluating changes in injury related parameters of the head and lower limbs of children following falls from playground climbing frames. A particular fall case was used as a starting point to analyze the influence of surface properties, posture of the body at impact, and intermediate collisions against the climbing frame before impacting the ground. Simulations were made using the 6-year-old pedestrian MADYMO rigid body model and scaled head contact characteristics. Energy absorbing surfaces were shown to reduce injury severity parameters by up to 30-80% of those of rigid surfaces, depending on impact posture and surface. Collisions against components of a climbing frame during a fall can increase injury severity of the final impact of the head with the ground by more than 90%. Negligible changes are associated with lower limb injury risks when different surfacing materials are used. Computer reconstructions of actual falls that are intended to quantify the severity of physical injuries rely on accurate knowledge of initial conditions prior to falling, intermediate kinematics of the fall and the orientation of the body when it impacts against the ground. Multibody modelling proved to be a valuable tool to analyze the quality of eye-witness information and analyze the relative injury risk associated with changes in components influencing fall injuries from playground climbing frames. Such simulations can also support forensic investigations by evaluating alternative hypotheses for the sequence of kinematic motion of falls which result in known injuries.
    Scopus© Citations 43  694
  • Publication
    Performance of nickel and bulk metallic glass as tool inserts for the microinjection molding of polymeric microfluidic devices
    Electroformed nickel and bulk metallic glasses (BMGs) can be designed to incorporate features withlength scales ranging from millimeters to nanometers. This, combined with their good mechanical prop-erties relative to other materials, makes them competitive candidates for manufacturing multi-scalemolds to produce high volumes of polymeric microfluidics components and other micro/nano devices.Despite this attractiveness, BMGs are newly developed engineering materials and their capabilities asa mold material have not been evaluated. This paper compares the performance of nickel tools madeby an electroforming process and BMG tools made by a thermoplastic forming process, specifically withregard to typical microfluidics patterns and features. Ni shows excellent capabilities for good featurereplication. BMG thermoplastic forming is highly dependent on the choice of alloy composition, whichrestricts the achievable feature size and aspect ratio. Compared to Ni, BMG has hardness values that areclose to those of stainless steel and shows the superior mechanical strength that is required for massproduction applications. However, oxidation in BMG tool manufacturing process affects the tool surfacefinish significantly and reduces the tool¿s corrosion resistance. Future development of BMG tools includepreventing the formation of oxidation layers or developing BMGs with an anti-oxidation composition,and further reducing their overall cost and widening its processing window parameters. Despite thesechallenges, however, BMGs are shown to combine excellent mechanical properties and capabilities formulti-scale forming; this makes them significantly more attractive than relatively soft Ni tools.
    Scopus© Citations 24  669
  • Publication
    Comparison of MADYMO and physical models for brain injury reconstruction
    (Informa UK (Taylor & Francis), 2014-05-04) ; ;
    Brain injury is researched using physical, mathematical, anatomical, and computational models. However, there has been little research to quantify the expected differences between these methods of brain injury research. The purpose of this research was to compare the brain deformation responses of identical traumatic brain injury (TBI) reconstructions, which were conducted first with Mathematical Dynamic Models (MADYMO) and then again with a Hybrid III headform. The ensuing finite element modelling was done using the University College Dublin Brain Trauma Model. The brain deformation parameters were analysed in discrete regions of interest which matched the TBI lesion as identified on computed tomography scans of the subject. The results indicated that overall the Hybrid III provided responses which were of considerably larger magnitude than the MADYMO simulation for all metrics analysed. The larger magnitude responses are likely a product of the more rigid nature of the Hybrid III in comparison to the MADYMO simulations. Interestingly, when the results are compared to the literature, the Hybrid III results match well with mild traumatic brain injury (mTBI) and TBI research, while the MADYMO simulations produce what would be considered very low local brain deformation responses for TBI lesions.
    Scopus© Citations 8  509
  • Publication
    Mechanical characterization of the P56 mouse brain under large-deformation dynamic indentation
    The brain is a complex organ made up of many different functional and structural regions consisting of different types of cells such as neurons and glia, as well as complex anatomical geometries. It is hypothesized that the different regions of the brain exhibit significantly different mechanical properties, which may be attributed to the diversity of cells and anisotropy of neuronal fibers within individual brain regions. The regional dynamic mechanical properties of P56 mouse brain tissue in vitro and in situ at velocities of 0.71-4.28 mm/s, up to a deformation of 70 μm are presented and discussed in the context of traumatic brain injury. The experimental data obtained from micro-indentation measurements were fit to three hyperelastic material models using the inverse Finite Element method. The cerebral cortex elicited a stiffer response than the cerebellum, thalamus, and medulla oblongata regions for all velocities. The thalamus was found to be the least sensitive to changes in velocity, and the medulla oblongata was most compliant. The results show that different regions of the mouse brain possess significantly different mechanical properties, and a significant difference also exists between the in vitro and in situ brain.
      276Scopus© Citations 37
  • Publication
    Towards nano-injection molding
    Bulk metallic glasses (BMGs), having no limiting microstructure, can be machined or thermoplastically-formed with sub-micron precision while still retaining often-desirable metallic properties such as high compressive strength. These novel materials thus have enormous potential for use as multi-scale tools for high-volume manufacturing of polymeric MEMS and information storage devices. Here we show the manufacture of a prototype BMG injection molding tool capable of producing cm-long polymeric components, with sub-micron surface features.
      619Scopus© Citations 55
  • Publication
    Mechanical performance of carbon-fibre and glass-fibre-reinforced epoxy I-beams: II. Fractographic failure observations
    This present paper is the second in a series which together detail the static behaviour, fractographic observations, fatigue behaviour and finite element predictions of composite I-beams subjected to mechanical loads. Fractographic observations associated with the mechanical behaviour under static load of both unnotched and web- and flange-notched continuously reinforced carbon-fibre/epoxy and E-glass-fibre/epoxy I-beams are discussed. Ultrasonic scanning, X-radiography and both optical and scanning electron microscopy have been used to elucidate the presence of different damage mechanisms and the directions of delamination growth in different regions of the beams. The principal damage mechanisms which have been identified as causing failure are delamination, matrix cracking, splitting and fibre fracture. As discussed in detail in the previous paper, a four-point flexural configuration was used. A mode of buckling that was antisymmetric across the width of the compressive flange was observed prior to failure in all cases. Failure of the unnotched I-beams initiated from a buckle on the compressive flange and the subsequent damage was predominantly in the form of delamination. The main delaminations were along the interfaces between the separate sub-components which comprise the I-beams: namely, the flange caps and C-sections and the backs of the two C-sections. These are all interfaces i.e. the relative fibre angle between the adjacent plies is 90 °. Failure of the notched I-beams initiated from a shear-loaded circular cutout within the web. The critical damage mechanism was matrix cracking in local plies which were subject to local tensile stresses. Fibre fracture and component failure resulted from this matrix cracking.
    Scopus© Citations 24  421
  • Publication
    Temperature effects on brain tissue in compression
    Extensive research has been carried out for at least 50 years to understand the mechanical properties of brain tissue in order to understand the mechanisms of traumatic brain injury (TBI). The observed large variability in experimental results may be due to the inhomogeneous nature of brain tissue and to the broad range of test conditions. However, test temperature is also considered as one of the factors influencing the properties of brain tissue. In this research, the mechanical properties of porcine brain have been investigated at 22 °C (room temperature), and at 37 °C (body temperature) while maintaining a constant preservation temperature of approximately 4–5 °C. Unconfined compression tests were performed at dynamic strain rates of 30 and 50 s−1 using a custom made test apparatus. There was no significant difference (p=0.8559–0.9290) between the average engineering stresses of the brain tissue at the two different temperature conditions. The results of this study should help to understand the behavior of brain tissue at different temperature conditions, particularly in unconfined compression tests.
      566Scopus© Citations 28