Localized buckling in sandwich struts with inhomogeneous deformation in both face plates

A nonlinear analytical model for investigating localized interactive buckling in simply supported thin-face plate sandwich struts with weak cores is extended to account for local deformations in both face plates, which have been observed in experiments and finite element simulations. The original model is based on potential energy principles with large displacement assumptions. It assumes Timoshenko shear deformable theory for the core and approximates the overall mode as a half-sine wave along the length of the strut while the local face plate displacements are initially unknown and are found as solutions of the governing equations. The extended model is able to capture measurable local face plate displacements in the less compressed face plate, beyond the secondary bifurcation which leads to localized interactive buckling, for the case where overall buckling is critical. Moreover, the allowance of local displacements in both face plates allows the extended model to predict the post-buckling behavior better in cases where local buckling is critical. The results from this model compare very well with nonlinear finite element simulations with respect to both the equilibrium paths and panel deformations

Geometric modelling of kink banding in laminated structures

An analytical model founded on geometric and potential energy principles for kink band deformation in laminated composite struts is presented. It is adapted from an earlier successful study for confined layered structures which was formulated to model kink band formation in the folding of geological layers. The principal aim is to explore the underlying mechanisms governing the kinking response of flat, laminated components comprising unidirectional composite laminae. A pilot parametric study suggests that the key features of the mechanical response are captured well and that quantitative comparisons with experiments presented in the literature are highly encouraging

Mode interaction and localization in sandwich struts and beam-columns

Ph.D--Department of Civil and Environmental Engineering, Imperial College Londo

Wrinkling patterns of electrospun nanofabrics in uniaxial tension

Electrospun nanofabrics are gaining popularity in a variety of applications [1,2]. One such application is the use of nanofabrics, as enhancers of the mechanical performance of fiber-reinforced polymers (FRPs). The enhancement is realized through a multi-scale structure comprising the polymer matrix, the fibers which form the layered macro scale reinforcement and the nano-scale reinforcement introduced as interlayers [3]. Candidate nanofabric systems, were investigated in uniaxial tension in order to evaluate their potential as interlayer reinforcements. This contribution, aims to bring forth wrinkling pattens that were observed in the transverse direction, during the performed tensile strength tests. The tests were performed with a custom-made tensile apparatus which provided force and displacement resolutions of 0.25N of 200 microns. The specimens used for tensile testing were two strips of nanofabric placed back to back, with gauge length between 122-125 mm, width 32 mm and thickness ranging between 9-16 microns per strip, depending on the nanofabric system. The testing was captured on video and the evolution of wrinkling patterns were inferred by video analysis. We find that out of plane wrinkling initiates at small linear strains at the direction normal to the loading axis. In the post-wrinkling stage, mode-jumping is observed with higher frequency wrinkles at lower amplitudes, which manifest beyond the nanofabrics’ yielding stress. Furthermore, wrinkling appears to be heterogeneous, in the sense that there are regions within the specimen that exhibit higher frequency wrinkles than others for the same loading increment, while there exist bands in between them that show none to minimal wrinkling. These phenomena will be juxtaposed to the measured stress-strain curves for a selection of the nanofabrics tested and will be discussed in relationship to existing analytical models [4] and the potential development of further analytical models to describe this response. [1] Z.-M. Huang, Y.-Z. Zhang, M. Kotaki, and S. Ramakrishna, “A review on polymer nanofibers by electrospinning and their applications in nanocomposites,” Compos. Sci. Technol., vol. 63, no. 15, pp. 2223–2253, 2003, doi: https://doi.org/10.1016/S0266-3538(03)00178-7. [2] N. E. Zander, “Hierarchically Structured Electrospun Fibers,” Polymers (Basel)., vol. 5, no. 1, pp. 19–44, 2013, doi: 10.3390/polym5010019. [3] V. Kostopoulos, A. Masouras, A. Baltopoulos, A. Vavouliotis, G. Sotiriadis, and L. Pambaguian, “A critical review of nanotechnologies for composite aerospace structures,” CEAS Sp. J., vol. 9, no. 1, pp. 35–57, 2017, doi: 10.1007/s12567-016-0123-7. [4] E. Cerda and L. Mahadevan, “Geometry and Physics of Wrinkling,” Phys. Rev. Lett., vol. 90, no. 7, p. 74302, Feb. 2003, doi: 10.1103/PhysRevLett.90.07430

Discussion: “On interactive buckling in a sandwich structure” by C. D. Coman

A recent article by Coman (Z Angew Math Phys 2009) on the response of compression sandwich struts made some claims on the quality of the simplified version of the interactive buckling model presented in Hunt and Wadee (Proc R Soc A 454(1972):1197–1216, 1998). Some of these claims are examined in detail herein; it is concluded that great care must be exercised when performing parametric studies with equations that have been derived from simplifying a mechanical model. This is because the resulting system of equations does not necessarily describe the original mechanical system in full, since the key assumptions necessarily change

Redeveloping Nicosia International Airport: an extroverting Y2 group design project

This article follows the timeline of the ‘Nicosia International Airport: The Return’ Integrated Design Project which was undertaken by Year 2 students of Civil Engineering and Geomatics at the Cyprus University of Technology in Cyprus. The Nicosia International Airport was the first and main airport of the Republic of Cyprus since its independence from the British Empire in 1960. The airport remains closed since the Turkish invasion of 1974 and is located in the buffer zone administered by the United Nations Peace-keeping Force in Cyprus. In this work, the innovative aspects of a project to inspire and train engineering students are highlighted, while special attention is given to the dissemination and outreach of the project through the social media. The attracted attention of national media and the project's impact on the local society had a cyclical effect, further inspiring students to work hard and act as responsible professional engineers. ‘Nicosia International Airport: The Return’ is a case study of how an academic engineering project can have societal impact, by inspiring students, engaging practitioners from a wide spectrum of disciplines, captivating the general public and raising the profile of Civil Engineering in the society

Metal foams: A review for mechanical properties under tensile and shear stress

ue to their mechanical properties, metal foams are used in various fields. The aim of the present research is to collect different studies about the important mechanical properties of metal foams, such as Young’s modulus, tensile and shear strength, relative density, etc. under tensile and shear loading. Gaps were identified in the methodological embodiments of the experiments due to the use of different standards, as well as in the calculation of mechanical properties through mathematical relations in tensile and shear, which led to deviations between the experimental results and these. Furthermore, this work records sequences and connections between experimental results of different tasks as well as solutions to the aforementioned issues