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 Issue Date
Now showing 1 - 20 of 572
Results Per Page
Sort Options
- PublicationA finite element technique for the investigation of the shape development of planar cracks with initially irregular profilesThe introduction to this paper describes a general finite element model used to calculate opening mode stress intensity factors (KI) along the front of an irregular planar crack. Crack advance is calculated as a function of KI and a new profile is thus defined. Automatic reconfiguration of the finite element mesh enables the crack development to be followed. The use of this technique to investigate various problems of practical interest is then described. These examples include the effect of constrained and unconstrained corners on developing cracks, the interaction of two adjacent thumbnail cracks, the breakout of an internally initiated crack and the effect of a surface crack in a leak before break situation.
399Scopus© Citations 16 - PublicationA fractographic analysis of delamination within multidirectional carbon/epoxy laminatesMultidirectional laminates of the continuously reinforced carbon/epoxy composite T300H/914C have been tested under static and fatigue conditions by the use of fracture mechanics coupons. Loadings of pure mode I, pure mode II and different ratios of mixed mode I/II, i.e. opening tension and sliding shear, have been applied to double cantilever beam (DCB), end-loaded split (ELS), fixed-ratio mixed-mode (FRMM), and mixed-mode bending (MMB) specimens. Optical and scanning electron microscopy techniques were used to identify distinguishing fractographic features and to establish the differences between static and fatigue fracture, as well as the differences between the various modes of fracture. The cusp angle and the amount of fibre pull-out on the fracture surface can be used to characterise the different loading modes. A large amount of fibre pull-out is the dominant feature of a mode I fracture whereas cusps are characteristic features of a mode II fracture. Fatigue fracture surfaces exhibited slightly more debris than static fracture surfaces: this is thought to be due to the fretting nature of fatigue. For the same reason, shear cusps (hackles) were more rounded and less distinct in fatigue than on static fracture surfaces. In certain fatigue cases, it was observed that polyethersulphone (PES), a toughening agent used in the formulation of the epoxy resin, came out of the matrix; the reason for this is not fully understood.
516Scopus© Citations 76 - PublicationMechanical performance of carbon-fibre and glass-fibre-reinforced epoxy I-beams: II. Fractographic failure observationsThis 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.
371Scopus© Citations 24 - PublicationMechanical performance of carbon-fibre- and glass-fibre-reinforced epoxy I-beams: I. Mechanical behaviourThis paper is the first in a series which detail the mechanical behaviour, finite element predictions and fractographic observations of the failure of composite I-beams. Experimental investigations into the behaviour under static load of both unnotched and web- and flange-notched continuously reinforced carbon-fibre/epoxy and glass-fibre/epoxy I-beams are discussed. A four-point flexural configuration is used. The global static response and ultimate failure are described in terms of strains, compliance, buckling and final fracture. A mode of buckling that is antisymmetric across the width of the compressive flange is observed prior to failure in all cases. Failure of the unnotched I-beams is concentrated around a buckle on the compressive flange whilst failure of the notched I-beams initiates from a shear-loaded circular cutout within the web. Buckling of the unnotched beams occurs at loads that are approximately 50% of the failure loads. Failure of the notched beams occurs at loads that are approximately 75% of the failure loads of the unnotched beams. Buckling and failure of the glass/epoxy beams occur at loads that are approximately 75% of the corresponding loads in the carbon/epoxy beams.
388Scopus© Citations 38 - PublicationCompression strength of composite suspension push-rods for Formula 1 racing carsAdvanced composite materials are extensively used in the construction of a contemporary Formula 1 racing car. This paper describes the manufacture and ultimate mechanical performance under compression of composite suspension push-rods that could typically be used in a Grand Prix racing car. An aerofoil-type cross-section was used with different lay-ups of unidirectional and woven cross-ply carbon/epoxy composite. Failure mechanisms including compression and buckling were observed and the ultimate strength of the component under compression was significantly less than that of the material
880 - PublicationStress intensity factors of embedded elliptical cracks and an assessment of the ASME XI defect recharacterisation criteriaThis paper considers aspects related to the calculation of the stress intensity factors of planar embedded defects in a solid under tension. The determination of stress intensity factor solutions using a modified body force method is described, this technique having certain advantages over existing finite element, boundary element and ordinary body force methods. Furthermore, comprehensive modified body force solutions are presented and discussed for a range of elliptical defect geometries. These solutions have then been used to asses the conservation of the recharacterisation procedure for defects of complex geometry described in Section XI of the ASME Boiler and Pressure Vessel Code. Maximum stress intensity factor values calculated using both the modified body force method and the ASME XI rules in conjunction with standard solutions are compared and contrasted. The results of this analysis show that, by and large, ASME XI is conservative and hence safe. However, geometries for which ASME XI provides non-cservative estimates have been encountered and, in certain circumstances, this may be a cause for concern.
312Scopus© Citations 5 - PublicationAnalysis of Rayleigh-Lamb wave scattering by a crack in an elastic plateThis paper considers the scattering of low-frequency elastic waves by a crack in a plate. A simple formula is derived for the reflection coefficient which serves as a lower bound to the reflection coefficient at higher frequencies.
300Scopus© Citations 19 - PublicationMixed Mode delamination of multidirectional carbon fibre/epoxy laminatesScanning electron microscopy was used to identify fractographic features that are characteristic of different modes of interlaminar fracture. The cusp angle and the amount of fiber pull-out on the fracture surface can be used to characterize the different loading modes. A large amount of fiber pull-out is the dominant feature of a mode I fracture, while in mode II large cusp angles and many cusps are the main characteristics. The amount of fiber pull-out, and subsequently brokenfibers, per unit area was investigated and found to vary in proportion to the degree of mode I loading. Such methods can be used to analyze failure and the propagation ofdelamination in structural components. The energy associated with cusp formation constitutes a large proportion of the mode IIfracture toughness component, while the amount of fiber pull-out and fracture has a considerable influence on the mode I fracture component. The cusp angle was seen to provide a quantitative measure of the fracture surface roughness. A failure criterion that takes the fracture surface appearance into account was evaluated. The cusp angle was subsequently used to modify this failure criterion. As a consequence, this provided improved agreement with the experimental data.
547Scopus© Citations 30 - PublicationFracture and fatigue performance of textile commingled yarn compositesThe response to mechanical loads of unidirectional commingled warp knitted and woven glass fibre reinforced polyethylene terephthalate laminates has been characterized. The mechanical properties of the two materials were determined under tension, in-plane shear and flexure. The flexural fatigue properties were determined for the woven laminates by means of three-point bending tests with a loading ratio of R"0.1 at stress levels of 50Ð90% of the ultimate static strength. The Mode I, Mode II and mixed mode (Mode I : II ratios 4 : 1, 1 : 1 and 1 : 4) interlaminar fracture toughnesses of the laminates were determined by means of the double cantilever beam and mixed mode bending tests, respectively. The main fractographic features, as determined by a scanning electron microscopy examination, of the Mode I dominated failures were a brittle matrix failure and larger amounts of fibre pull-out. As the Mode II loading component increased, the amount of fibre pull-out was reduced and the features of the matrix appeared to be more sheared. Cusps were found on the fracture surfaces of specimens tested in pure Mode II and mixed mode I : II"1 : 4. Cusps are normally not found in thermoplastic matrix composites.
849Scopus© Citations 24 - PublicationInterlaminar Fracture of Commingled GF/PET Composite LaminatesThe Mode I, Mode II and mixed mode (Mode I:II ratios of 4:1, 1:1 and 1:4) fracture behavior of novel textile glass fiber reinforced polyethylene terephthalate (GF/PET) laminates has been investigated. The laminates were manufactured by compression molding two different fabrics produced by weaving and warp knitting commingled GF/PET yarns. The initiation fracture toughness of the woven laminates in pure Mode I and Mode II were slightly higher than those of the warp knitted laminates. For the mixed modes, the difference between the fracture toughness of the two materials was smaller. An extensive scanning electron microscopy (SEM) investigation of the fracture was conducted to identify any characteristic failure mechanisms. The main fractographic features of the Mode I dominated failures were a brittle matrix failure and large amounts of fiber pull-out. As the Mode II loading component increased, the amount of fiber pull-out was reduced and the matrix had a more sheared appearance. A relatively large amount of cusps were found in pure Mode II and mixed mode I:II = 1:4; such features are seldom seen in thermoplastic matrix composites. A general mixed mode failure criterion, which accounts for the appearance of the fracture surface, was evaluated and was seen to give a good fit to the experimental fracture toughness values.
380Scopus© Citations 17 - PublicationAttenuation Of Ultrasonic Rayleigh-Lamb Waves By A Symmetrical Embedded Crack In An Elastic PlateThe present paper illustrates how embedded vertical defects can be detected rapidly in sheet metal by using longitudinal ultrasonic waves. Computational methods are used to validate analytical predictions of the reflection coefficients due to the attenuation of such ultrasonic waves by physically small defects. It is shown that detectable attenuation of the lowest order symmetric Rayleigh–Lamb wave (S0) occurs for a range of small defects (sub-millimeter in length) when using high-frequency waves (MHz range).
170 - PublicationManufacturing & design with engineering polymers: Educational aspects of a specialist dissertation in a part-time elective postgraduate mechanical engineering degree course for industry-based studentsThe 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.
166 - PublicationExperimental Facility for Simulating the Initiation and Propagation of Fatigue Damage in Bituminous Road Paving MaterialsAn exoerimental simulation facility was designed and constructed for the purpose of investigating the initiation and development of fatigue damage in bituminour road paving material. The design of the test facility was based upon a cicular wheel track which incorporated four pavement monitoring stations. Hot Rollede Asphalt specimens were manufactured and prepared for testing in order to verify the operation of this experimental facility. The variation of strains, deformations, and the distribution of pavement damage, in the form of cracking, were monitored digitally with increasing cycles of fatigue loading. Failure of pavement specimen due to local tensile strains, propogated through the complete thickness of the specimen and became apparent on the top surface.
248 - PublicationMechanical Test Procedures for Bituminous MixturesIn recent years the increasing traffic volumes on the world’s highways have indicated shortcomings in the existing empirical procedures that are used to assess road building materials. As a result, new fundamental performance based test procedures have been developed that are currently being considered for acceptance in defining material specification codes of practise. In Ireland, to date, it has only been possible to observe and monitor these developments. The procedures will shortly be introduced by the Central European Standards Organisation (CEN) and will affect Irish material suppliers, design engineers in local authorities and consulting engineers.
107 - PublicationManufacturing and ultimate mechanical performance of carbon fibre-reinforced epoxy composite suspension push-rods for a Formula 1 racing carThe contemporary Formula 1 racing car makes extensive use of advanced composite materials in its construction. The design, manufacture, and ultimate performance under compression of composite suspension push-rods that typically could be used in a Grand Prix racing car are described in this present paper. An aerofoil cross section has been used based on different lay-ups of carbon/epoxy composite. One push-rod was manufactured using a uniform layup of unidirectional and woven cross-ply prepreg whilst a further three push-rods were manufactured with a tapered layup of unidirectional and woven cross-ply prepreg. Failure mechanisms including fibre microbuckling, fibre kinking and fibre fracture were observed whilst comparisons have been made between the experimentally observed failure strains and those that were predicted using simple buckling theory. The ultimate compressive strength of the structural component was significantly less than that of the carbon/epoxy composite.
642Scopus© Citations 3 - PublicationAttenuation of ultrasonic Rayleigh–Lamb waves by small horizontal defects in thin aluminium platesThe present paper illustrates how horizontal symmetric crack-like defects can be detected rapidly in thin isotropic plates by using longitudinal ultrasonic waves. The use of such longitudinal waves offers the potential of being significantly faster for non-destructively detecting defects than conventional ultrasonic techniques, which rely on transverse waves propagating through the thickness of a plate. Computational and analytical methods are used to predict reflection coefficients due to the attenuation of a longitudinal ultrasonic wave by physically small defects. It is shown that detectable attenuation (>10%), i.e. reflection coefficients, of the lowest order symmetric Rayleigh–Lamb wave (S0) occurs for a range of small defects (sub-millimeter in length) when using high-frequency waves (MHz range).
412Scopus© Citations 12 - 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.
374Scopus© Citations 3 - PublicationSimulation of the development of frontal head impact injuryThis paper describes the results of computational simulations of a frontal impact to the head and the predicted development of coup and contrecoup contusion (i.e., at and opposite the site of impact, respectively) within brain tissue. Three separate two-dimensional plane strain finite element models of the head, each of which incorporated the skull, the cerebrospinal fluid and the brain, were constructed. Two of these models represented the coronal plane of the head as being elliptic whilst the third model was geometrically representative of an actual human head. This third model was taken in an off-centre mid-sagittal plane in an anterior–posterior direction and all three models were used to investigate the dynamic response of the human head when subject to direct translational impact events. The physiological consequences of modelling the human brain as being elastic were established. Compressive and tensile strains were predicted at the coup and contrecoup sites for a simulated frontal impact event by means of a simple elastic analysis. These distributions of most severe strain correspond directly to the occurrence of coup and contrecoup contusion such as are witnessed in clinical studies which arise under the action of translational acceleration.
393Scopus© Citations 42 - 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
352 - 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.
61