19 results found
Lee JJ, Mohammed AA, Pullen A, et al., 2023, Mechanical characterisation of 3D printed lightweight lattice structures with varying internal design alterations, Materials Today Communications, Vol: 36
The recent advances in the additive manufacturing (AM) have enhanced the development of light-weight, energy-absorbing structures in many aspects with precise, designed configurations of the internal structure. Given the range of potential materials many possible variations exist compared to the existing polymer-based foams. The advantages of rapid prototyping, enabled through AM, allows a streamlined process in obtaining a structure of desired mechanical behaviour. In this work, development, and design variation of a flexible lattice structure with core strut modification is demonstrated. The core struts are varied in terms of shape and density and are fabricated using vat photopolymerisation with Formlabs Flexible 80A resin and experimental methodology is outlined for the characterisation of the printed specimen under compressive loading. Mechanical characterisation under three different compression rates presents that the implementation of the core strut increases the elastic modulus of the lattice structure. The enhanced stiffness effects are further increased with the variations in shape, while the evaluation of the density variations shows significantly different deformation behaviour and strain rate sensitivity. The behaviour of each specimen types is discussed further in terms of their functional viability and potential applications where the design specific behaviour and small, lightweight form factor can be most effectively utilised.
Farsi A, Pullen AD, Latham JP, et al., 2017, Full deflection profile calculation and Young's modulus optimisation for engineered high performance materials, Scientific Reports, Vol: 7, Pages: 1-13, ISSN: 2045-2322
New engineered materials have critical applications in different fields in medicine, engineering and technology but their enhanced mechanical performances are significantly affected by the microstructural design and the sintering process used in their manufacture. This work introduces (i) a methodology for the calculation of the full deflection profile from video recordings of bending tests, (ii) an optimisation algorithm for the characterisation of Young’s modulus, (iii) a quantification of the effects of optical distortions and (iv) a comparison with other standard tests. The results presented in this paper show the capabilities of this procedure to evaluate the Young’s modulus of highly stiff materials with greater accuracy than previously possible with bending tests, by employing all the available information from the video recording of the tests. This methodology extends to this class of materials the possibility to evaluate both the elastic modulus and the tensile strength with a single mechanical test, without the need for other experimental tools.
White TG, Patten JRW, Wan K-H, et al., 2017, A single camera three-dimensional digital image correlation system for the study of adiabatic shear bands, STRAIN, Vol: 53, ISSN: 1475-1305
Perry JI, Braithwaite CH, Taylor NE, et al., 2016, The significance of grain morphology, moisture, and strain rate on the rapid compaction of silica sands, Applied Physics Letters, Vol: 109, ISSN: 0003-6951
There is considerable interest in the high-rate compaction of brittle granular materials such as sand. However, the vast majority of studies focus on a single granular system, limiting our ability to make comparisons between materials to discern how granular structure manifests as bulk material response. Here, three different silica sands with similar grain size and shape are studied: we compare a rough quarry sand, a smoother-grained sand, and a sandy loam. Quasi-static compaction and planar shock loading responses are compared, and recovered samples analyzed. The combination provides information regarding the interplay between granular properties, loading conditions, and material response. We show that the fundamental grain-scale behaviour depends on loading conditions: At low strain rates compaction behaviour is dominated by grain morphology, and in particular, smoothness and particle size distribution. Under shock loading, grain rearrangement and force chain effects are suppressed, and the nature of inter-granular contact points, modified by the presence of moisture or fines, is most important. Furthermore, grain fracture under shock loading is substantially reduced with increasing moisture content.
Jung A, Pullen AD, Proud WG, 2016, Strain-rate effects in Ni/Al composite metal foams from quasi-static to low-velocity impact behaviour, Composites Part A - Applied Science and Manufacturing, Vol: 85, Pages: 1-11, ISSN: 1359-835X
Metal foams are used as absorbers for kinetic energy but predominantly, they have only been investigated under quasi-static load-conditions. Coating of open-cell metal foams improves the mechanical properties by forming of Ni/Al hybrid foam composites. The properties are governed by the microstructure, the strut material and geometry. In this study, the strain-rate effects in open-cell aluminium foams and new Ni/Al composite foams are investigated by quasi-static compression tests and low-velocity impact. For the first time, drop weight tests are reported on open-cell metal foams, especially Ni/Al composite foams. Furthermore, size-effects were evaluated. The microstructural deformation mechanism was analysed using a high-speed camera and digital image correlation. Whereas pure aluminium foams are only strain-rate sensitive in the plastic collapse stress, Ni/Al foams show a general strain-rate sensitivity based on microinertia effects and the rate-sensitive nano-nickel coating. Ni/Al foams are superior to aluminium foams and to artificial aluminium foams with equal density.
Farsi A, Xiang J, Latham J, et al., 2015, An application of the finite-discrete element method in the simulation of ceramic breakage: methodology for a validation study for alumina specimens, IV International Conference on Particle-based Methods, Publisher: International Center for Numerical Methods in Engineering (CIMNE), Pages: 921-932
ABSTRACT: Alumina (aluminum oxide, Al 2 O 3) particles are pelletised and fired to produce high porosity catalyst pellets of complex shapes. These pellets fill cylindrical reactor columns with particulate packing structures that are key to the in-service performance, but will suffer breakages which impact on catalyst performance. The combined Finite-Discrete Element Method (FEMDEM) is ideally suited to the simulation of both the multi-body pellet dynamic packing and quasi-static interactions as well as the stress field of each individual pellet, its deformations and fragmentation. The application of FEMDEM fracture modelling to a fine-grained brittle and porous material is novel. This paper presents a methodology for a validation study through comparison with three point-bending and Brazilian tests and discusses FEMDEM's potential in modelling multi-body fragile systems.
Pullen AD, Louca LA, Micallef K, et al., 2015, Characterization of the Mechanical Behavior of a Polymer-Based Laminate and Constituent Fibers at Various Quasi-Static Strain Rates, JOURNAL OF AEROSPACE ENGINEERING, Vol: 28, ISSN: 0893-1321
Bonner TJ, Newell N, Karunaratne A, et al., 2015, Strain-rate sensitivity of the lateral collateral ligament of the knee, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 41, Pages: 261-270, ISSN: 1751-6161
The material properties of ligaments are not well characterized at rates of deformation that occur during high-speed injuries. The aim of this study was to measure the material properties of lateral collateral ligament of the porcine stifle joint in a uniaxial tension model through strain rates in the range from 0.01 to 100/s. Failure strain, tensile modulus and failure stress were calculated. Across the range of strain rates, tensile modulus increased from 288 to 905 MPa and failure stress increased from 39.9 to 77.3 MPa. The strain-rate sensitivity of the material properties decreased as deformation rates increased, and reached a limit at approximately 1/s, beyond which there was no further significant change. In addition, time resolved microfocus small angle X-ray scattering was used to measure the effective fibril modulus (stress/fibril strain) and fibril to tissue strain ratio. The nanoscale data suggest that the contribution of the collagen fibrils towards the observed tissue-level deformation of ligaments diminishes as the loading rate increases. These findings help to predict the patterns of limb injuries that occur at different speeds and improve computational models used to assess and develop mitigation technology.
Sheridan AJ, Pullen AD, 2014, Gauged reactive confinement cell for determination of concrete triaxial properties, MAGAZINE OF CONCRETE RESEARCH, Vol: 66, Pages: 50-59, ISSN: 0024-9831
Newell N, Masouros SD, Pullen AD, et al., 2012, The comparative behaviour of two combat boots under impact, Injury Prevention, Vol: 18, Pages: 109-112, ISSN: 1353-8047
Background Improvised explosive devices have become the characteristic weapon of conflicts in Iraq and Afghanistan. While little can be done to mitigate against the effects of blast in free-field explosions, scaled blast simulations have shown that the combat boot can attenuate the effects on the vehicle occupants of anti-vehicular mine blasts. Although the combat boot offers some protection to the lower limb, its behaviour at the energies seen in anti-vehicular mine blast has not been documented previously.Methods The sole of eight same-size combat boots from two brands currently used by UK troops deployed to Iraq and Afghanistan were impacted at energies of up to 518 J, using a spring-assisted drop rig.Results The results showed that the Meindl Desert Fox combat boot consistently experienced a lower peak force at lower impact energies and a longer time-to-peak force at higher impact energies when compared with the Lowa Desert Fox combat boot.Discussion This reduction in the peak force and extended rise time, resulting in a lower energy transfer rate, is a potentially positive mitigating effect in terms of the trauma experienced by the lower limb.Conclusion Currently, combat boots are tested under impact at the energies seen during heel strike in running. Through the identification of significantly different behaviours at high loading, this study has shown that there is rationale in adding the performance of combat boots under impact at energies above those set out in international standards to the list of criteria for the selection of a combat boot.
Abbas AA, Pullen AD, Cotsovos DM, 2010, Structural response of RC wide beams under low-rate and impact loading, MAGAZINE OF CONCRETE RESEARCH, Vol: 62, Pages: 723-740, ISSN: 0024-9831
Pullen AD, Abbas AA, 2010, Experimental investigations of partially-damaged RC beams and columns, STRUCTURAL CONCRETE, Vol: 11, Pages: 139-148, ISSN: 1464-4177
Regan PE, Kennedy-Reid IL, Pullen AD, et al., 2005, The influence of aggregate type on the shear resistance of reinforced concrete, Structural Engineer, Vol: 83, Pages: 27-32, ISSN: 1466-5123
The response of reinforced concrete to shear forces depends on the transfer of shear across cracks. If aggregates fracture when cracks are formed, shear resistance is likely to be reduced and the loss of strength is likely to be a function of crack width and thence, in some cases, member depth. The analysis of new test results reported here, and others available from the literature, shows that, with limestone aggregate, the shear strengths of members without shear reinforcement are often below characteristic resistances calculated according to EC 2 and other recent recommendations. A considerable proportion of the experimental strengths can be below design resistances. The deficits of resistance are greatest where high concrete strengths are combined with relatively large effective depths. The same phenomenon appears to occur with other aggregates, but to a lesser extent. Members with shear reinforcement are similarly likely to be affected but to an extent less than that in members without shear reinforcement.
McGuire WJ, Howarth RJ, Firth CR, et al., 1997, Correlation between rate of sea-level change and frequency of explosive volcanism in the Mediterranean, NATURE, Vol: 389, Pages: 473-476, ISSN: 0028-0836
MCGUIRE WJ, MURRAY JB, PULLEN AD, et al., 1991, GROUND DEFORMATION MONITORING AT MT ETNA - EVIDENCE FOR DYKE EMPLACEMENT AND SLOPE INSTABILITY, JOURNAL OF THE GEOLOGICAL SOCIETY, Vol: 148, Pages: 577-583, ISSN: 0016-7649
MCGUIRE WJ, PULLEN AD, SAUNDERS SJ, 1990, RECENT DYKE-INDUCED LARGE-SCALE BLOCK MOVEMENT AT MOUNT-ETNA AND POTENTIAL SLOPE FAILURE, NATURE, Vol: 343, Pages: 357-359, ISSN: 0028-0836
MCGUIRE WJ, PULLEN AD, 1989, LOCATION AND ORIENTATION OF ERUPTIVE FISSURES AND FEEDER-DIKES AT MOUNT ETNA - INFLUENCE OF GRAVITATIONAL AND REGIONAL TECTONIC STRESS REGIMES, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 38, Pages: 325-344, ISSN: 0377-0273
Murray JB, Pullen AD, 1984, Three-dimensional model of the feeder conduit of the 1983 eruption of Mt. Etna volcano, from ground deformation measurements, Bulletin Volcanologique, Vol: 47, Pages: 1145-1163, ISSN: 0258-8900
A levelling network and a horizontal distance measuring network down Mt. Etna's south flank were measured before, during and after the 1983 eruption. We analyse the large movements recorded, using theoretical models of surface displacement, to determine the shape and position of the feeder conduit that supplied magma to the eruption. The results indicate that a dyke, the top surface extending nearly horizontally, connects the eruption site to a point near the Southeast Crater. The top of the dyke lies at an altitude of 2400 m to 2500 m, and dips between 75° and 90° to the west. More tentative evidence indicates that the top of the active dyke dropped by about 150 m between the 25th and the 95th day of the eruption, and that a small branching dyke 1 km long was emplaced to the east of the main dyke, but did not attain the surface. The implications of these observation are discussed. © 1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior.
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