Unequal Faces Effect on Fracture of Composite Sandwich Beam with Flexible Core
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Unequal Faces Effect on Fracture of Composite Sandwich Beam with Flexible Core Mojtaba Sadighi & Mahdi Saadati
Received: 6 April 2009 / Accepted: 11 August 2009 / Published online: 3 September 2009 # Springer Science + Business Media B.V. 2009
Abstract Sandwich panel higher order theory (SPHOT) which estimates core compression and face stresses is used to predict damage modes of a sandwich beam with unequal faces. It is shown that sandwich panel classical theory (SPCT) which is based on investigating of behavior of the structure with considering core shear stress in simply supported boundary conditions and neglecting shear modulus of core can not predict the failure load in the case of unequal faces when core yielding is happened. Comparing the results obtained by SPHOT, SPCT and available experimental ones shows that the higher order theory is a suitable approach to predict failure loads in this case for different damage modes. Keywords Sandwich beam . Composite skins . Higher order theory . Critical load . Fracture . Unequal faces
1 Introduction Light weight sandwich beams have been used widely in aerospace and other applications because of their high bending stiffness versus low weight. A sandwich structure consists of a low weight core that is coated by two stiff and thin faces. Damage of sandwich beams is very different from thick laminates. Core fracture, core yielding and face fracture are three major damage modes of sandwich beams. Allen and Plantema presented classical sandwich theory in their books [1, 2]. They considered behavior of a sandwich beam in three point bending (3PB) by superposing method. In this method deflection of a sandwich beam is calculated without core compression in 3PB state (global deformation) first and is added to deflection of a sandwich beam on the rigid ground (sandwich beam without bending). Beam on an elastic foundation is used to measure local deformation of the sandwich beam. M. Sadighi (*) : M. Saadati Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran 15875-4413, Iran e-mail: [email protected] M. Saadati e-mail: [email protected]
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Appl Compos Mater (2010) 17:111–120
Elastic foundation is Winkler foundation (parallel elastic linear springs). They assumed core compression in fully backed state. Many researchers considered damage of sandwich beam using SPCT [3–9]. They compared faces stresses with corresponding strengths for prediction of face fracture. For example Abot et al. [4] showed that Winkler foundation model is not suitable for thick sandwich beam with a flexible core. They suggested new core stiffness for better results. Zenkert et al. [5] concluded that Winkler foundation model is suitable for an ordinary sandwich beam. They used the ratio of core modulus to core thickness as core stiffness in the Winkler model. Lim et al. [9] used classic sandwich panel theory for prediction of damages in a sandwich beam with similar face thicknesses. However, SPCT cannot consider unequal face effect because beam on
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