Mechanical & Materials Engineering Research Collection
Permanent URI for this collection
For more information, please visit the official web page.
Browse
Browsing Mechanical & Materials Engineering Research Collection by Type "Book Chapter"
Now showing 1 - 17 of 17
Results Per Page
Sort Options
- PublicationCeremonial or deadly serious? New insight into the function of irish early bronze age halberdsThis paper describes a series of highly focused experiments, carried out under laboratory conditions, as part of a wider Irish-Scottish project which is investigating the function of the Early Bronze Age halberd. Earlier trials showed that these artefacts, when hafted properly, were capable of piercing sheep-skulls without suffering significant damage and that by extension they were therefore capable of being used as weapons. Having observed that up to 50% of museum specimens bore evidence of edge damage, a new set of laboratory trials were undertaken to replicate this damage and to determine how it occurred and under what circumstances. Thse trials indicate that most of the edge damage on Irish halberds results from impact with other halberds, in a yielding environment (suggesting that both halberds could move) and at tightly-controlled engergy-levels which remained capable of lethal efrect. It is argued that this is consistent with skilled combat-use and that many of the Irish halberds must have been employed to such end.
491 - PublicationDrivers of Globalisation of Higher Education over the Last 70 YearsThe 70th anniversary of the International Association of Universities provides an opportunity to look back over the post-World War II era, and to reflect on the drivers that have led to the international higher education environment we experience today. The anniversary also provides an opportunity to look forward and to consider how such a globalised system of universities might contribute to future society.
158 - PublicationEvaluation of Dynamic Response and Brain Deformation Metrics for a Helmeted and Non-Helmeted Hybrid III Headform Using a Monorail Centric/Non-Centric Protocol(ASTM International, 2014-03-17)
; ; ; Head injuries, and concussion in particular, have become a source of interest in the sport of ice hockey. This study proposes a monorail test methodology combined with a finite element method to evaluate ice hockey helmets in a centric/non-centric protocol with performance metrics more closely associated with risk of concussion. Two conditions were tested using the protocol: (a) helmeted versus no helmet, and (b) vinyl nitrile lined hockey helmet versus expanded polypropylene lined hockey helmet. The results indicate that the impact velocities and locations produced distinct responses. Also, the protocol distinguished important design characteristics of the two helmet liner types, with the vinyl nitrile lined helmet producing lower strain responses in the cerebrum. Furthermore, it was discovered that low risk of injury peak linear and rotational acceleration values can combine to produce much higher risks of injury when using brain deformation metrics. In conclusion, the use of finite element modeling of the human brain along with a centric/non-centric protocol provides an opportunity for researchers and helmet developers to observe how the dynamic response produced by these impacts influences brain tissue deformation and injury risk. This type of centric/non-centric physical to finite element modeling methodology could be used to guide innovation for new methods to prevent concussion.542 - PublicationEvolution of dynamic fractures in PMMA : experimental and numerical investigations(WIT Press / Computational Mechanics, 2004-10-20)
; ; ; ; A combined experimental/numerical study has been conducted to investigate dynamic fractures in poly(methyl methacrylate) (PPMA). The results obtained from single-edge-notched-tensile (SENT) fracture tests support the idea that the evolution of fracture in PMMA is governed by nucleation, growth and coalescence of penny-shaped micro-cracks. The density of the microcracks and therefore the roughness of the fracture surface increase with the crack velocity. Both the surface roughness and the size of the process region increase with the crack length for a given specimen. Microscopy of the virgin material and fractured surfaces showed no consistent evidence of pre-existing flaws, dust particles or other impurities that would provide nucleation sites for the micro-cracks. Instead, it was observed that molecular weight significantly affects the fracture, and therefore must play an important role in the nucleation of micro-cracks. The crack velocity measurements show rapid initial crack acceleration followed by a nearly constant mean velocity, which was in some cases well above previously reported terminal crack speed. The mean velocity is found to increase with decreasing initial notch depth. Oscillations in the crack velocities were also observed and they were more pronounced at higher crack velocities. To a large extent, the degree of crack velocities oscillations is dependent on the filtering technique applied to process the raw experimental data. Therefore, no conclusive correlation between the fracture histories and fracture surfaces was obtained. Finite Volume (FV) method was developed for the numerical simulations of the experiments. Global material behaviour was approximated as linear elastic, while a Cohesive Zone Model (CZM) was used for defining the local separation process of the material. Numerical predictions show good agreement with experimentally observed variations of the process region and the crack velocity with initial crack length. Oscillations in the crack speed are also predicted.458 - PublicationFor ASTM F-08: Protective Capacity of Ice Hockey Player Helmets against Puck ImpactsMany studies have assessed the ability of hockey helmets to protect against falls and collisions, yet none have addressed the injury risk associated with puck impacts. Thus, the purpose of this study was to document the capacity of a typical vinyl nitrile ice hockey helmet to reduce head accelerations and brain deformation caused by a puck impact. A bare and a helmeted Hybrid III male 50th percentile headform was struck with a puck three times to the forehead at 17, 23, 29, 35, and 41 m/s using a pneumatic puck launcher. Linear and rotational accelerations were captured using accelerometers fitted in the headform and used as input in the University College Dublin Brain Trauma Model to obtain brain deformation. The helmet reduced peak resultant linear acceleration, peak resultant rotational acceleration, and maximum principal strain, but a comparison with published brain injury risk curves shows that it did not reduce the concussion risk below 50 % for impacts at or above 23 m/s. Thus, a vinyl nitrile ice hockey helmet can protect players from direct puck impacts in amateur and youth leagues but may not be adequate in competitive elite leagues, where the puck can be shot at velocities well above 23 m/s. Furthermore, competitive adult male ice hockey players struck to the helmet by a puck may need to consider changing their helmet, as it was shown that direct impacts at or above 35 m/s decreased the helmet’s ability to reduce head peak linear acceleration in subsequent impacts.
460Scopus© Citations 8 - 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.
274 - PublicationThe Influence of Impact Angle on the Dynamic Response of a Hybrid III Headform and Brain Tissue DeformationThe objective of this study was to investigate the influence of impact angle on the dynamic response of a Hybrid III headform and brain tissue deformation by impacting the front and side of the headform with four angle conditions (0° at the impact site and 5°, 10° and 15° counter-clockwise rotations from 0°) as well as three additional angles of -5°, -10° and -15° (clockwise rotations from 0°) at the side location to examine the effect of direction. The acceleration-time curves were used as input into a finite element model of the brain where maximum principal strain was calculated. The results from this study show that impact angle has an asymmetrical influence on headform dynamic responses and strain. An increase in impact angle tends to result in a growth of headform linear and rotational acceleration and maximum principal strain for the front location as well as the negative angles (0 to -15°) at the side, however varying trends were observed for the positive angles (from 0° to 15°) at the side. When developing sophisticated impact protocols and undertaking head injury reconstruction research, it is important to be aware of impact angle.
360Scopus© Citations 2 - PublicationThe Influence of Impactor Mass on the Dynamic Response of the Hybrid III Headform and Brain Tissue DeformationWhen determining head injury risks through event reconstruction, it is important to understand how individual impact characteristics influence the dynamic response of the head and its internal structures. The effect of impactor mass has not yet been analyzed in the literature. The purpose of this study was to determine the effects of impactor mass on the dynamic impact response and brain tissue deformation. A 50th-percentile Hybrid III adult male head form was impacted using a simple pendulum system. Impacts to a centric and a non-centric impact location were performed with six varied impactor masses at a velocity of 4.0 m/s. The peak linear and peak angular accelerations were measured. A finite element model (University College Dublin Brain Trauma Model) was used to determine brain deformation, namely, peak maximum principal strain and peak von Mises stress. Impactor mass produced significant differences for peak linear acceleration for centric (F5,24 = 217.55, p = 0.0005) and non-centric (F5,24 = 161.98, p = 0.0005) impact locations, and for peak angular acceleration for centric (F5,24 = 52.51, p = 0.0005) and non-centric (F5,24 = 4.18, p = 0.007) impact locations. A change in impactor mass also had a significant effect on the peak maximum principal strain for centric (F5,24 = 11.04, p = 0.0005) and non-centric (F5,24 = 5.87, p = 0.001) impact locations, and for peak von Mises stress for centric (F5,24 = 24.01, p = 0.0005) and non-centric (F5,24 = 4.62, p = 0.004) impact locations. These results confirm that the impactor mass of an impact should be considered when determining risks and prevention of head and brain injury.
1034Scopus© Citations 15 - PublicationIntellectual Property Protection and Security in Additive ManufacturingProduct data management along a product lifecycle is complicated due to a wide range of resources, stakeholders and technologies being involved. During the product development phase, complex information is exchanged among several engineering teams and legal entities. Product lifecycle management (PLM) systems streamline and control the product data shared with other engineering and manufacturing parties. In additive manufacturing (AM), however, as opposed to the conventional manufacturing (CM) data supply chain, the ease with which intellectual property (IP) can be compromised by theft or malicious attacks, creates a significant challenge. These attacks can lead to loss of revenue due to illegal counterfeiting, or even failure of mission-critical parts where design could be modified to a functionally impaired configuration. This paper outlines and reviews the current strategies and new approaches possible to secure IP in AM systems, comparing the advantages and disadvantages of these technologies.
141Scopus© Citations 1 - PublicationA Numerical Investigation of the Dynamic Behaviour of Functionally Graded FoamsTwo Finite Element models approximating the dynamic behaviour of functionally graded foam materials (FGFMs) have been developed under free weight drop impact and Kolsky wave propagation conditions. The FGFM is modeled by discretising the material into a large number of layers through the foam thickness. Each layer is described by a unique constitutive cellular response, which is derived from the initial relative density, ρ∗, unique to that layer. Large strain uniaxial compressive tests at strain rates of 0.001, 0.01 and 0.1/s were performed on expanded polystyrene (EPS) and ALPORASⓇ Aluminium (Al) foam and their σ − ε response was used as input to a modified constitutive model from the literature. Simulations were then performed on both uniform and graded specimens. For both impact and wave propagation conditions it is found that under certain conditions an FGFM can outperform a uniform foam of equivalent density in terms of reducing peak accelerations imparted from an impact, or mitigating stress wave magnis through increased plastic deformation. These properties provide significant insight into the hypothesised behaviour of FGFMs and elucidate the potential for the future use in the design of next generation cushioning structures.
303Scopus© Citations 4 - PublicationProduct Lifecycle Management Strategies Focusing on Additive Manufacturing WorkflowProduct lifecycle management (PLM) is a strategy enabling the efficient exchange of information between relevant stakeholders in a manufacturing network. Various approaches utilising PLM platforms have been developed and used by a range of companies and organisations in a number of manufacturing domains. Additive manufacturing (AM) will force companies to rethink their strategies to account for its implications across the entire product lifecycle. Current PLM approaches were designed for conventional manufacturing (CM) methods, such as machining and forming and are therefore not adapted to cope with AM. Despite its advantages regarding increased design freedom, customisability, lightweighting, consolidation of parts and faster deployment, AM also introduces challenges due to issues regarding repeatability and quality, build rate, cost of materials, process monitoring and control, as well as standardisation. This paper will review the implications of AM on current PLM approaches across the entire product lifecycle, as well as problems and opportunities for further progress.
198 - PublicationReconstructing Real Life Accidents Towards Establishing Criteria for Traumatic Head Impact InjuriesBrain injury is the leading cause of death in those aged under 45 years in both Europe and the United States. The objective of this research is to reconstruct and analyse real world cases of accidental head injury, thereby providing accurate data which can be used subsequently to develop clinical tolerance levels associated with particular traumatic injuries and brain lesions. In this study, MADYMO pedestrian models are used to analyse a well-defined set of non-fatal accidents involving simple falls. The effect of varying the initial conditions is systematically examined and the predicted MADYMO results are compared against literature data.
371Scopus© Citations 8 - PublicationReconstruction of Head Injury Cases Arising from Falls Using the UCD Brain Trauma ModelWhile Road Traffic Accidents continue to be the largest contributor to head injury, falls are usually second in prevalence. This paper looks at numerical modelling techniques, namely multibody body dynamics and finite element methods, in order to reconstruct two real-life accident cases arising from falls. Various modelling strategies are explored, and the results are compared with existing published brain injury tolerance levels.
399Scopus© Citations 4 - PublicationA Selective Depolarisation-Induced Increase in Excitatory Amino Acid Neurotransmitter Release in Rat Medial Prefrontal Cortex Using a Microdialysis Model of Traumatic Brain InjuryThis study describes a microdialysis model that investigates the biochemical response of the brain to non-fatal impact trauma. A controlled cortical impact (mild and severe) was performed to the left medial prefrontal cortex (mPfc) in the isoflurane-anaesthesised rat. This was followed by intracerebral microdialysis whereby a microdialysis probe was implanted into the site of the injury. Changes in dialysate glutamate, aspartate and GABA levels were investigated immediately (i.e. 25 min) and 265 min following a local mild and severe impact to the brain. In addition, the effect of local perfusion with a depolarizing concentration of KCl (100 mM, 20 min) was also investigated 165 min after impact. Dialysate levels measured 25 min after impact (n=14) showed an impactdependent increase in glutamate (6 and 8-fold), aspartate (4 and 5-fold) and GABA (3 and 6-fold) following mild and severe impact respectively compared to non-impact controls. Dialysate levels measured 265 min after mild (n=12) and severe (n=13) impt had stabilized and continued to show a local 5-fold (mild) and 4-fold (severe) increase in local glutamate, a 6-fold (mild) and 3-fold (severe) increase in aspartate and a (3-fold (mild) and 5-fold (severe)) increase in GABA levels compared to control. Intra-mPfc KCl (n=14) increased local dialysate glutamate levels (4-fold following mild impact and 3-fold following severe impact) and aspartate levels (2-fold after both mild and severe impact) while GABA levels did not differ from non-impacted controls following either a mild or severe impact. The present findings show that microdialysis in intact brain can be combined with the controlled cortical impact model to reveal selective impact-dependent and prolonged increases in local dialysate amino acid neurotransmitter levels. Furthermore, we reveal that 165 min following either a mild or severe impact to the left mPfc KCl-stimulated glutamate and aspartate release is abnormally increased while GABA release is not different compared to non-impacted controls. Ths finding may in part explain the excitotoxicity that contributes to diffuse posttraumatic lesions associated with secondary injury.
302Scopus© Citations 2 - PublicationThe Study on Microstructural Evolution During Post-processing of Additively Manufactured Ti64The effect of furnace heat treatments to 850 °C, on the evolution of microstructure in Ti–6Al–4V alloy produced via selective laser melting (SLM), was studied using optical microscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Columnar prior-β grains in the build direction with lamellar α-martensite laths contained within the prior-β grains were determined. α-martensite laths present in the as-built microstructure had thicknesses around 236 nm while the heat-treated microstructure showed an α-lath thickness values of around 1.8 μm. Based on XRD analysis, upon heat treatment the formation of β-phase was determined with associated peaks around 41° and 58°, corresponding to (110) and (200) planes, respectively.
139Scopus© Citations 1 - PublicationA Theoretical Study Of The Tensile Test For Highly Anisotropic Composite MaterialsThe stress field in a tabbed straight-sided tensile test specimen has been studied theoretically and experimentally. It is shown that the stress field has to be studied at every point in the specimen. It is also shown that the tab should be made as thick as possible and the clamping force set as large as possible in order to minimize the intensity of the stress field in the specimen. The tab's Young's modulus in the test direction is the elastic constant having the largest influence on the stress field in the specimen. However, it is shown that it is not possible to set general guidelines regarding the choice of the tab material. Failure modes of specimens where the tabs are bonded and where the tabs are molded directly on the test material were compared. Molded specimens produce better quality results.
387Scopus© Citations 3 - 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