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Gilchrist, M. D.
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Gilchrist, M. D.
Official Name
Gilchrist, M. D.
Research Output
Now showing 1 - 10 of 133
- PublicationRayleigh-Lamb wave detection of two-dimensional defects in metal platesNondestructive 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.
62 - PublicationThe Association among Injury Metrics for Different Events in Ice Hockey Goaltender Impact(International Research Council on Biomechanics of Injury (IRCOBI), 2016-09-16)
; ; ; Current ice hockey goaltender helmet standards use a drop test and peak linear acceleration to evaluate performance. However, ice hockey goaltenders are exposed to impacts from collisions, falls and pucks which each create unique loading conditions. As a result, the use of peak linear acceleration as a predictor for brain trauma in current ice hockey standards may not be most appropriate. The purpose of this study was to determine how kinematic response measures correlate to maximum principal strain and von Mises stress for different impact events. A NOCSAE headform was fitted with three ice hockey goaltender helmet models and impacted under conditions representing these three different impact events (fall, puck, collision). Peak resultant linear acceleration, rotational acceleration and rotational velocity of the headform were measured. Resulting accelerations were input into the University College Dublin Brain Trauma Model, which calculated maximum principal strain and von Mises stress in the cerebrum. The results demonstrated that the relationship between injury metrics in ice hockey goaltender impacts is dependent on the impact event and velocity. As a result of these changing relationships, the inclusion of finite element analysis in test protocols may provide a more practical representation of brain loading in evaluating the performance of ice hockey goaltender helmets.483 - PublicationUse of advanced composite materials in the construction of suspension push-rods for a Formula one racing carAdvanced composite materials, particularly carbon fibre-reinforced epoxies, are used extensively in the construction of contemporary Formula One racing cars because of their high specific stiffness and strength properties. The present Chapter is concerned with one significant load-bearing component, namely the suspension push-rod. These push-rods exist at the four corners of a car and link the monocoque, engine and gearbox casing to a racing track and, as such, they are subject to severe inertial forces and dynamic compressive and flexure forces. The design, manufacture and in-service behaviour of carbon/epoxy push-rods are discussed in the present Chapter. Both uniform and tapered layups of unidirectional and woven cross-ply prepreg have been used to manufacture pushrods of aerofoil cross-sections. These structural components have been loaded to catastrophic failure and the identified damage mechanisms were seen to includefibre micro buckling, fibre kinking and fibre fracture. A comparison has been made between the actual and theoretically predicted failure strains and it is seen that buckling was the ultimate cause of failure in all cases. The ultimate strength of the carbon/epoxy composite material was greater than the compressive strength of the push-rods and consequently, scope exists for improving the performance of the present design of composite push-rods.
199 - PublicationEffect of design on the replication of micro/nano scale features by micro injection mouldingThe replication of micro/nano scale features is of great interest for MEMS and Microsystems. However, the flow behaviour of melts into a micro/nano cavity is still not well understood. In this work, we used the micro injection moulding process to replicate micro/nano scale channels and ridges from a Bulk Metallic Glass (BMG) cavity insert. High density polyethylene (HDPE) was used as the moulding material. The influence of feature configuration, length, width, gap distance between features, location on substrate, and substrate thickness on the quality of replication was investigated. The experiments revealed that the replication of ridges, including feature edge, profile and filling distance, was sensitive to the flow direction; a critical feature length was found below which the filling of features was significantly reduced. Both the feature location and the substrate thickness had an influence on the filling of micro/nano features while the gap distance had a negligible effect on the replication of features.
215 - Publication
108 - PublicationAn in-depth analysis of real world fall accidents involving brain traumaThis Chapter provides clinical, physical and mechanical details of a set of ten real world accidental falls which resulted in non-fatal head impact injury in the form of various traumatic brain lesions. These are described in depth and as such constitute a database of documented head injury cases that may be of use to the wider research community. Accompanying time profiles of linear and angular velocities, which were predicted using multibody dynamics modeling simulations, are freely available to those researchers who would wish to use this set of data upon direct request to the authors.
204 - PublicationInnovations in Undergraduate Engineering Mechanics Education : Use of Team-Based Research-Led Project Methods for Large Student CohortsAs a cornerstone subject for all undergraduate engineering degree programmes, mechanics is best taught from fundamental principles and by reinforcing students’ learning through active learning strategies. This approach provides students with a solid understanding of basic concepts before they subsequently study more advanced topics such as dynamics, control, solid mechanics and fluid mechanics. MEEN10030, Mechanics for Engineers, is a compulsory module taught annually in Semester I to 260 First Year students at University College Dublin, Ireland’s largest university. The syllabus topics include forces, Newton’s laws of motion, statics in two and three dimensions, equilibrium, friction, trusses and cables, distributed forces, centres of mass and centroids, motion, and kinematics of a particle and of a rigid body. Traditional teaching of this subject relies solely on formal lectures and tutorials, without any laboratory sessions or student assignments, both of which are resource intensive. Five years ago, following a programme review in 2006, this module was completely revised and the subject material was rationalised with regard to what is taught in subsequent Second Year modules. Three entirely integrated laboratory sessions were developed so that groups of students would complete a variety of analytical and enquiry-led exercises in numerical, graphical and written form. A more recent additional major initiative, introduced three years ago in 2008, provides team-based assignments to the entire 260 students in which groups of up to five students are set a design challenge directly related to one specific topic from the course material. These changes have proven popular with students and have led to improved learning outcomes and student performance without compromising on academic standards. This paper describes these innovative developments in which Irish engineering students have opportunities for research-led active learning in this manner.
332 - PublicationLinear Viscoelastic Properties of Cerbral Cortex at Thresholds for Axonal DamageTraumatic brain injury (TBI) is caused by rapid deformation of the brain that leads to shearing of axons. While deformation below the limits of ultimate failure can activate pathophysiological cascades that cause neurodegeneration [1], bleeding does not always occur even after tearing of axons. Traditional imaging studies such as CT and MRI are designed to detect areas of bleeding but these can fail to detect the presence of multiple, widespread, microscopic axonal injuries that can result in devastating neurological deficits. A large knowledge gap still exists defining the relationship between axonal injury at a microscopic level (morphological injury) and the material properties of the corpus callosum, hippocampus and cerebral cortex on the macroscopic level, but at identical strain levels. This research investigates the linear viscoelastic properties of the cerebral cortex at known thresholds of axonal injury (0.14 - 0.34 strains [2]). During quasi static loading of tissue in creep tests, instantaneous strains were generated corresponding to axonal thresholds. A linear viscoelastic constitutive model was used to determine six Prony parameters suitable for finite element simulation in ABAQUS and ANSYS. Use of such properties at the levels of axonal damage will help to accurately predict injuries during numerical simulations, to design safety helmets and air bags, and also to refine existing injury criteria and to improve the precision in surgical procedures.
130 - PublicationIn-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.351