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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
- 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.
286 - PublicationWheeltracking Fatigue Simulation of Bituminous MixturesIn order to better simulate the dynamic effects of a rolling wheel travelling over an asphalt pavement, and to better understand the initiation and growth of cracks in bituminous pavement layers, a wheeltracking fatigue simulation facility was developed. This experimental facility permitted the testing of large slab specimens (305x305x50mm) using dynamic wheel loadings. The slab specimens were supported on a soft elastomeric foundation that simulated overlay behaviour on top of a weak pavement structure. Digital photography and image analysis techniques were utilised to monitor the initiation and propagation of fatigue cracks on the bottom of these slabs. Two standard Irish mixtures, a Dense Base Course Macadam (DBC) and Hot Rolled Asphalt (HRA), were evaluated with the fatigue simulation facility. Crack damage was seen to initiate on the bottom face of the slab specimen in a direction parallel to the direction of wheel travel. These cracks would interconnect to form a full width crack that propagated through the depth of the slab. Under similar loading conditions the DBC mix had significant lower fatigue strength (two orders of magnitude).
543 - PublicationFull scale accelerated testing of bituminous road pavement mixturesThe 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 in initiating pavement damage
450 - PublicationAn Investigation into Scalpel Blade Sharpness Using Cutting Experiments and Finite Element AnalysisThis paper presents an investigation into the sharpness of a surgical scalpel blade. An experiment was carried out in which a surgical scalpel blade was pushed through an elastomeric substrate at a constant velocity. The force-displacement characteristics were examined by plotting the stiffness as a function of blade displacement and it was found that this curve could clearly identify the point where the material separates to form a cut. A blade sharpness measurement was defined as the energy required to initiate an opening or cut in the substrate. A finite element model was developed to examine the stress state in the substrate at the point where the opening initiates. The development of this model is described. The model was validated against the experiment and close agreement was obtained. The von-Mises stress distribution under the blade tip was plotted and it was shown that the peak stress actually occurs away from the blade tip, suggesting that material separation would initiate away from the substrate surface.
483 - PublicationExperimental Characterisation of Neural Tissue at Collision Speeds(International Research Council on the Biomechanics of Injury, 2012)
; ; Mechanical characterization of brain tissue at high loading velocities is particularly important for modelling Traumatic Brain Injury (TBI). During severe impact conditions, brain tissue experiences a mixture of compression, tension and shear. Diffuse axonal injury (DAI) occurs in animals and humans when both the strains and strain rates exceed 10% and 10/s, respectively. Knowing the mechanical properties of brain tissue at these strains and strain rates is of particular importance, as they can be used in finite element simulations to predict the occurrence of brain injuries under different impact conditions. In this research, we describe the design and operation of a High Rate Tension Device (HRTD) that has been used for tensile tests on freshly harvested specimens of porcine neural tissue at speeds corresponding to a maximum strain rate of 90/s. We investigate the effects of inhomogeneous deformation of the tissue during tension by quasi‐static tests (strain rate 0.01/s) and dynamic tests (strain rate 90/s) using different thickness specimens (4.0, 7.0, 10.0 and 13.0 mm) of the same diameter (15.0 mm). Based on a combined experimental and computational analysis, brain specimens of aspect ratio (diameter/thickness) S = 10/10 or lower (10/12, 10/13) are considered suitable for minimizing the effects of inhomogeneous deformation during tension tests. The Ogden material parameters were derived from the experimental data both at quasi‐static conditions (µ = 440 Pa and α = ‐4.8 at 0.01/s strain rate) and dynamic conditions (µ = 4238 Pa and α = 2.8 at 90/s strain rate) by performing an inverse finite element analysis to model all experimental data. These material parameters will prove useful for the nonlinear hyperelastic analysis of brain tissue.209 - PublicationEffect of impact surface in equestrian falls(International Society of Biomechanics in Sports (ISBS), 2016-07-22)
; ; ; ; This study examines the effect of impact surface on head kinematic response and maximum principal strain (MPS) for equestrian falls. A helmeted Hybrid III headform was dropped unrestrained onto three impact surfaces of different stiffness (steel, turf and sand) and three locations. Peak resultant linear acceleration, rotational acceleration and duration of the impact events were measured. A finite element brain model was used to calculate MPS. The results revealed that drops onto steel produced higher peak linear acceleration, rotational acceleration and MPS but lower impact durations than drops to turf and sand. However, despite lower MPS values, turf and sand impacts compared to steel impacts still represented a risk of concussion. This suggests that certification standards for equestrian helmets do not properly account for the loading conditions experienced in equestrian accidents.216 - PublicationMiniaturization/process dependent mechanical properties of microinjection moldings(2015-04)
; Product miniaturization and high shear/cooling rates in microinjection molding increase the volume of highly oriented skin layer, which modifies a product’s mechanical properties and needs careful consideration for product design.162 - PublicationThe effects of miniaturization and processing on microinjection moldingsProduct miniaturization and high shear/cooling rates during microinjection molding increase the volume of the highly oriented skin layer, thereby modifying the mechanical properties of the fabricated product.
165 - PublicationModelling of failure of structural textile compositesThis paper summarizes extensive experimental work regarding the manufacture, mechanical characterization and modelling of textile thermoplastic composites produced by means of commingled yarns. These composites are believed to have a high potential for applications in structural automotive components. However, methods need to be developed for faster manufacturing and reliable prediction of the component mechanical performance and failure. A practical approach of finite element modelling of the stiffness and strength behaviour of these composites is briefly discussed.
421Scopus© Citations 3 - PublicationPerformance of nickel and bulk metallic glass as tool inserts for the microinjection molding of polymeric microfluidic devicesElectroformed 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.
678Scopus© Citations 24