Browsing by Author "Flores-Johnson, EA"

Now showing 1 - 9 of 9
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    Ballistic performance of multi-layered metallic plates impacted by a 7.62-mm APM2 projectile
    (Elsevier, 2011-12-01) Flores-Johnson, EA; Saleh, M; Edwards, L
    This paper presents a numerical investigation of the ballistic performance of monolithic, double- and triple-layered metallic plates made of either steel or aluminium or a combination of these materials, impacted by a 7.62-mm APM2 projectile in the velocity range of 775-950 m/s. Numerical models were developed using the explicit finite element code LS-DYNA. It was found that monolithic plates have a better ballistic performance than that of multi-layered plates made of the same material. This effect diminishes with impact velocity. It was also found that double-layered plates with a thin front plate of aluminium and thick back steel plate exhibit greater resistance than multi-layered steel plates with similar areal density. These predictions indicate that multi-layered targets using different metallic materials should be investigated for improved ballistic performance and weight-savings. Crown Copyright (C) 2011 Published by Elsevier Ltd.
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    Ballistic performance of thermoplastic composite laminates made from aramid woven fabric and polypropylene matrix
    (Elsevier, 2012-06-01) Carrillo, JG; Gamboa, RA; Flores-Johnson, EA; González-Chi, PI
    The ballistic behavior of multi-layer Kevlar (R) aramid fabric/polypropylene (PP) composite laminate (CL) and plain layered aramid fabric (AF) impact specimens was investigated. It was found that the thermoplastic PP matrix increases the ballistic performance of CL targets when compared to AF targets with similar areal density, resulting in less aramid fabric needed to obtain the same level of protection when the PP matrix is incorporated. It was found that the improved ballistic performance of CL targets is due to the fact that the thermoplastic matrix enables energy absorbing mechanisms such as fabric/matrix debonding and delamination. The ballistic limit and penetration threshold energy of the CL configurations, which were predicted using an empirical model, were found to be higher than those of the AF targets. These results show that aramid fabric/PP laminates should be further studied for improved ballistic performance at lower costs. (C) 2012 Elsevier Ltd. All rights reserved.
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    The effect of microstructure and welding-induced plasticity on the strength of Ni–Mo–Cr alloy welds
    (Elsevier, 2021-06) Danon, AE; Muránsky, O; Zhu, HL; Wei, T; Flores-Johnson, EA; Li, ZJ; Kruzic, JJ
    The mechanical performance of a Ni–Mo–Cr (GH3535) alloy weldment, produced using a matching filler metal, was assessed and compared to the surrounding parent metal. Ambient-temperature mechanical characterisation included hardness testing, small punch testing and uniaxial tensile testing, while a crystal plasticity finite element model was used to assess the impact of crystallographic texture on the mechanical properties. Despite the similar chemical composition, the weld metal exhibited superior strength and ductility to that of the parent metal. The higher strength was primarily attributed to the high dislocation density in the weld metal imbued by the welding-induced thermo-mechanical loading. In contrast, the ductility difference was attributed to M6C carbide stringers in the parent metal that initiated fracture at lower strains when compared to the weld metal, with the latter containing finer, well-dispersed M6C carbides. © 2021 Acta Materialia Inc. Published by Elsevier B.V.
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    Hard projectile penetration and trajectory stability
    (Elsevier, 2011-10-21) Li, QM; Flores-Johnson, EA
    We present a general framework to describe the dynamics of a hard projectile penetrating into a solid target. Rigid body dynamics, differential area force law and semi-empirical resistance function are used to formulate the motion of the hard projectile. The proposed model is capable of predicting the projectile trajectory under various oblique and yaw angles. Critical conditions for the occurrences of the instability and the reverse of the projectile trajectory are discussed. It was found that the relative location of mass centre of the projectile has strong influence on the control of the rotation of the projectile, and thus, the projectile stability and the change of trajectory direction. The validity of the proposed model is limited to deep penetration and when the wake separation and reattachment between projectile body and target have negligible influence on the target resistance to the projectile. (C) 2011 Elsevier Ltd.
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    Keynote: Modelling the quasi-static and high-strain rate deformation behaviour of magnesium alloy AZ31
    (Scientech, 2015-07-14) Proust, G; Li, L; Flores-Johnson, EA; Shen, LM; Muránsky, O
    In hexagonal close-packed (hcp) metals, plastic deformation is accommodated by different slip and twinning systems. Various factors affect the activation of the deformation mechanisms: alloy composition, grain size, temperature of deformation, strain rate and loading direction. The multiplicity of deformation mechanisms that can be activated and the dependence on loading conditions explain the observed asymmetry and anisotropy on the hardening behaviour and texture evolution. It is therefore important to be able to characterise these deformation mechanisms for specific loading conditions to gain a thorough understanding of the mechanical behaviour of hcp materials. Modern microscopy techniques, such as electron backscatter diffraction (EBSD), enable the quantitative analysis of twinning which is an important deformation mechanics for magnesium alloys. These characterisation techniques allow a better understanding of the way materials deform and provide valuable information for predicting their behaviour. For example using such techniques one can determine the different twinning modes that have contributed to deformation but also the volume fraction of material that has twinned. These microscopy techniques have enabled modellers to better understand the contribution of twinning in the hardening behaviour of the materials and to devise schemes to incorporate the effects of twinning on the hardening response or/and texture evolution of hcp materials. In this work we are investigating the deformation behaviour of magnesium alloys AZ31 under quasi-static and high-strain rate loading. The high-strain rate experiments were carried out using a Hopkinson bar and the microstructure of the deformed samples was measured using EBSD. The experimental results were used to calibrate and test the robustness of a strain-dependent visco-plastic self-consistent crystal plasticity model. © 2015 Scientech
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    Numerical analysis of the effect of weld-induced residual stress and plastic damage on the ballistic performance of welded steel plate
    (Elsevier, 2012-06-01) Flores-Johnson, EA; Muránsky, O; Hamelin, CJ; Bendeich, PJ; Edwards, L
    The current paper presents numerical analyses that elucidate the effects of post-weld residual stress and associated plastic damage on the ballistic performance of 316L austenitic steel plate. Impact simulations of an 18 mm thick plate with a centreline three-pass slot weld by hemispherical-nosed and flat-nosed projectiles are performed, with initial velocities in the range of 300-800 m/s. The numerical framework consists of three interdependent stages: (i) a weld model was developed in Abaqus/Standard and validated using two independent experimental data sets; (ii) a Johnson-Cook material model is calibrated and validated along with the shear failure fracture criterion available in Abaqus/Explicit for impact models; and (iii) the weld modelling results were transferred to an impact model built in Abaqus/Explicit, which employs the validated material and fracture models to predict the ballistic performance of welded plate. It is shown that the associated plastic strain damage accumulated during the welding process - and its distribution - has an adverse effect on the ballistic performance. It has also been determined that a fracture criterion that accounts for pre-existing damage in the weldment must be used for accurate impact analyses of welded structures. Crown Copyright (C) 2012 Published by Elsevier B.V.
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    Photoelastic evaluation of fiber surface-treatments on the interfacial performance of a polyester fiber/epoxy model composite
    (Elsevier, 2011-08-01) Flores-Johnson, EA; Vázquez-Rodríguez, JM; Herrera-Franco, PJ; González-Chi, PI
    The interfacial adhesion between a polyester fiber and an epoxy matrix was improved by chemical and topological modifications of the fiber surface. The maximum interfacial shear strength was measured using photoelasticity to assess the interfacial performance in pull-out single-fiber composite specimens. An increase of the interfacial shear strength was observed when plasma-treated or surface-modified fibers were used: also, as the applied load to the free fiber was increased, the fiber treatment caused a reduction of the debonded area at the fiber-matrix interface. (C) 2011 Elsevier Ltd.
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    Progressive fracture testing of carbon–carbon composites
    (Elsevier, 2022-10-22) Reiner, J; Narain, D; Zhang, P; Flores-Johnson, EA; Muránsky, O
    Carbon–Carbon (C/C) composites can retain their mechanical properties at extreme temperatures of up to 3000 °C. This study quantifies damage resistance in cross-ply C/C composites by means of compact tension tests at room temperature adapted from typical tests on carbon fibre reinforced polymers. The analysis of different specimen sizes reveals that baseline (dimensions: 70 mm × 90 mm) and large scaled-up samples yield consistent fracture energy values of 15–30 kJ/m2 while the scaled-down version shows unwanted failure around the loading pins. A microscopic cross-sectional analysis explains the relatively low fracture energy values of carbon/carbon composites compared to carbon fibre reinforced polymers. It is found that only 20%–40% of the carbon fibres in loading direction fail in C/C composites which leads to reduced energy absorption during the progressive fracture test.
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    Structural behaviour of composite sandwich panels with plain and fibre-reinforced foamed concrete cores and corrugated steel faces
    (Elsevier, 2012-04-01) Flores-Johnson, EA; Li, QM
    This paper studies the four-point bending response and failure mechanisms of sandwich panels with corrugated steel faces and either plain or fibre-reinforced foamed concrete core. Mechanical properties of both plain and polyvinyl alcohol fibre-reinforced foamed concrete were obtained, which are needed for the design of sandwich panel and numerical modelling. It is found that the fibre-reinforcement largely enhances the mechanical behaviour of foamed concrete and composite sandwich panels. Finite element code Abaqus/Standard was employed to investigate the influence of face/core bonding and fastening on the four-point bending response of the sandwich panels. It was found that face/core bonding plays a crucial role in the structural performance while the influence of fastening is negligible. (C) 2011 Elsevier Ltd. All rights reserved.