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Journal articleAfkhami S, Amraei M, Gardner L, et al., 2022,
Mechanical performance and design optimisation of metal honeycombs fabricated by laser powder bed fusion
, Thin Walled Structures, Vol: 180, Pages: 1-17, ISSN: 0263-8231Honeycomb structures have a wide range of applications, from medical implants to industrial components. In addition, honeycombs play a critical role when passive protection is required due to their low density and high energy absorption capabilities. With the transition of additive manufacturing from a rapid prototyping approach to a manufacturing process, this technology has recently offered designers and manufacturers the ability to fabricate and modify lattice structures such as honeycombs. The current study presents the application of laser powder bed fusion, a common additive manufacturing process for producing industrial metal components, for fabricating metal honeycombs. In addition, this study examines three modified designs that can only be practically fabricated using additive manufacturing and compares them with conventional honeycombs. For this purpose, quasi-static and dynamic compression tests are conducted to evaluate and compare the performance of the honeycomb structures. The results show that the structures produced by additive manufacturing have acceptable performance compared to conventional honeycomb structures, and laser powder bed fusion can be considered to be a reliable manufacturing method for honeycomb production. Furthermore, the honeycombs produced according to the modified designs generally outperformed their counterparts made from the typical hexagonal cells. Ultimately, the use of triangular cells as a design modification is proposed toproduce honeycombs with promising performance characteristics in all of their principal axes and under various pressure scenarios, from quasi-static to dynamic loading rates. Finally, this study also investigates the applicability of a newly developed maraging steel for additive manufacturing of honeycombs. Microstructural analysis and quasi-static tensile tests have confirmed the material properties for this purpose.
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Journal articleMedvedev GS, Mizuhara MS, Phillips A, 2022,
A global bifurcation organizing rhythmic activity in a coupled network
, CHAOS, Vol: 32, ISSN: 1054-1500- Cite
- Citations: 3
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Journal articleBehzadi-Sofiani B, Gardner L, Wadee MA, 2022,
Testing, numerical analysis and design of stainless steel equal-leg angle section beams
, Structures, Vol: 37, Pages: 977-1001, ISSN: 2352-0124The stability and design of stainless steel equal-leg angle section members subjected to uniaxial bending are studied herein. An experimental investigation, comprising material testing, initial geometric imperfection measurements and physical tests on hot-rolled austenitic stainless steel equal-leg angle section beams is first presented. The test results are then used to validate shell finite element models developed within ABAQUS, which are in turn used to undertake numerical parametric studies that consider both hot-rolled and cold-formed equal-leg angle section beams in austenitic, duplex and ferritic stainless steel with a wide range of slenderness values. Recent studies have shown that for angles under major-axis bending, both lateral-torsional and local buckling can arise, while under minor-axis bending, lateral-torsional buckling and Brazier-type flattening can occur. When designing for major-axis bending according to Eurocode 3, both local and lateral-torsional buckling are considered; it is shown herein that equal-leg angle sections under major-axis bending can be designed using a normalised slenderness based on the minimum of the local and lateral-torsional elastic buckling moments, while also considering their ratio. Under minor-axis bending, however, in comparison with the current provisions in Eurocode 3 that only require cross-section checks, it is shown that both safer and more accurate resistance predictions can be achieved when account is taken for lateral-torsional buckling and Brazier-type flattening. New design proposals for stainless steel equal-leg angle section beams, covering both major- and minor-axis bending, are therefore developed. The proposed design rules offer substantially more accurate and consistent resistance predictions compared to existing codified design rules. The reliability of the new design provisions, with a recommended partial safety factor γM1 = 1.1 , is verified following the procedure provided in EN 1990.
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Conference paperBehzadi-Sofiani B, Gardner L, Wadee MA, 2022,
Numerical simulation and design of steel equal-leg angle section beams
, 8th International Conference on Structural Engineering, Mechanics and Computation (SEMC), Publisher: CRC PRESS-TAYLOR & FRANCIS GROUP, Pages: 327-328 -
Journal articleBai L, Wadee MA, Köllner A, et al., 2021,
Variational modelling of local-global mode interaction in long rectangular hollow section struts with Ramberg-Osgood type material nonlinearity
, International Journal of Mechanical Sciences, Vol: 209, ISSN: 0020-7403A variational model describing the nonlinear mode interaction in thin-walled box-section struts under pure axial compression made from a nonlinear material obeying the Ramberg–Osgood law is presented. The formulation combines continuous displacement functions and generalized coordinates, leading to the derivation of a system of differential and integral equations that describe the static equilibrium response of the strut. Solving the system of equations using numerical continuation techniques reveals the strongly unstable post-buckling response arising from combined geometrical and material nonlinearities during the interactive buckling of the global and local buckling modes—the resulting behaviour being more unstable with decreasing material hardening. A finite element (FE) model is also devised and reveals very similar post-buckling behaviour as highlighted in the variational model. The results compare very well in terms of the mechanical destabilization and the post-buckling deformation, which verifies the analytical model.
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Journal articleKyvelou P, Slack H, Daskalaki Mountanou D, et al., 2020,
Mechanical and microstructural testing of wire and arc additively manufactured sheet material
, Materials and Design, Vol: 192, ISSN: 0264-1275Wire and arc additive manufacturing (WAAM) is a method of 3D printing that enables large elements to be built, with reasonable printing times and costs. There are, however, uncertainties relating to the structural performance of WAAM material, including the basic mechanical properties, the degree of anisotropy, the influence of the as-built geometry and the variability in response. Towards addressing this knowledge gap, a comprehensive series of tensile tests on WAAM stainless steel was conducted; the results are presented herein. As-built and machined coupons were tested to investigate the influence of the geometrical irregularity on the stress-strain characteristics, while material anisotropy was explored by testing coupons produced at different angles to the printing orientation. Non-contact measurement techniques were employed to determine the geometric properties and deformation fields of the specimens, while sophisticated analysis methods were used for post processing the test data. The material response revealed a significant degree of anisotropy, explained by the existence of a strong crystallographic texture, uncovered by means of electron backscatter diffraction. Finally, the effective mechanical properties of the as-built material were shown to be strongly dependent on the geometric variability; simple geometric measures were therefore developed to characterise the key aspects of the observed behaviour.
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Journal articleChampneys AR, Dodwell TJ, Groh RMJ, et al., 2019,
Happy catastrophe: Recent progress in analysis and exploitation of elastic instability
, Frontiers in Applied Mathematics and Statistics, Vol: 5, Pages: 1-30, ISSN: 2297-4687A synthesis of recent progress is presented on a topic that lies at the heart of both structural engineering and nonlinear science. The emphasis is on thin elastic structures that lose stability subcritically — without a nearby stable post-buckled state — a canonical example being a uniformly axially-loaded cylindrical shell. Such structures are hard to design and certify because imperfections or shocks trigger buckling at loads well below the threshold of linear stability. A resurgence of interest in structural instability phenomena suggests practical stability assessment require stochastic approaches and imperfection maps. This article surveys a different philosophy; the buckling process and ultimate post-buckled state are well described by the perfect problem. The significance of the Maxwell load is emphasised, where energy of the unbuckled and fully developed buckle patterns are equal, as is the energetic preference of localised states, stable and unstable versions of which connect in a snaking load-deflection path. The state of the art is presented on analytical, numerical and experimental methods. Pseudo15 arclength continuation (path-following) of a finite-element approximation computes families of complex localised states. Numerical implementation of a mountain-pass energy method then predicts the energy barrier through which the buckling process occurs. Recent developments also indicate how such procedures can be replicated experimentally; unstable states being accessed by careful control of constraints, and stability margins assessed by shock sensitivity experiments. Finally, the fact that subcritical instabilities can be robust, not being undone by reversal of the loading path, opens up potential for technological exploitation. Several examples at different length scales are discussed; a cable-stayed prestressed column, two examples of adaptive structures inspired by morphing aeroelastic surfaces, and a model for a functional auxetic material.
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Journal articleGibson D, Anand V, Dehlinger J, et al., 2019,
Accredited Undergraduate Cybersecurity Degrees: Four Approaches
, COMPUTER, Vol: 52, Pages: 38-47, ISSN: 0018-9162- Cite
- Citations: 2
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Conference paperSpaccasassi C, Yordanov B, Phillips A, et al., 2019,
Fast Enumeration of Non-isomorphic Chemical Reaction Networks
, 17th International Conference on Computational Methods in Systems Biology (CMSB), Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 224-247, ISSN: 0302-9743- Cite
- Citations: 1
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Conference paperRaj RK, Anand V, Gibson D, et al., 2019,
Cybersecurity Program Accreditation: Benefits and Challenges
, 50th ACM-SIGCSE Technical Symposium on Computer Science Education (SIGCSE), Publisher: ASSOC COMPUTING MACHINERY, Pages: 173-174- Cite
- Citations: 2
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