Temperature effects on Kevlar/hybrid and carbon fiber composite sandwiches under impact loading Amin Salehi-Khojin a , Mohammad Mahinfalah a, * , Reza Bashirzadeh b , Brian Freeman a a Department of Mechanical Engineering and Applied Mechanics, North Dakota State University, Fargo, ND 58105, United States b Amir-Kabir University, Tehran 4413-15875, Iran Available online 25 October 2005 Abstract This paper presents the results of a research on impacted sandwich composites with Kevlar/hybrid and carbon faceshee different temperatures. Testing was performed to determine bending and core shear stresses, maximum energy absorptio ing energy and moment parameter’’ (AEMP), ‘‘performance parameter’’ (PP), and compression strength after impact (CSA were tested at temperature range of 50 C to 120 C and were subjected to low velocity impact energies of 15 J, 25 J, and 45 J. Tested composite specimens have a urethane filled honeycomb core sandwiched between a variation of four-layered Kevla and carbon facesheets. Results showed that the impact performance of these composite sandwiches changed over the ran ature and that testing at ambient temperature is not sufficient in the development and full understanding of composite sa properties. 2005 Elsevier Ltd. All rights reserved. Keywords: Impact; Temperature effect; Crash performance; Strength after impact 1. Introduction The need for lightweightmaterials with high flexural stiffness for use in aircraft and aerospace vehicles has led to the development of sandwich composites. Sandwich construction typically consists of two facesheets (facings) and a core. The facings are made of the noble material in the sandwich and they must resistin plane and bending loads. The core is made of light, inexpensive material and it must keep the facings supported, separated, and working as a single unit. It must also resist the transverse shear and transverse normal loads [1]. A sandwich composite is often subjected to thermal loading due to the environment and significant dynamic loads due to impact by foreign objects, tool drops, mine blast and slamming waves. The stressing conditions and the environments to which a composite is subjected play a key role in determining its impact failure process especially, when using polymer foam core sandw composites [2]. Generally, when a sandwich structure is subjected to a impact,part of the energy associated with the impact is used for elastic deformation of the material and is return back to the system.The energy in excess is dissipated through several mechanisms, such as fibers breakage, sk delamination,fiber–matrixand fiber–foam debonding; while the core dissipates energy by crushing and shear deformation [3]. Many authors have studied the impact response of sandwich structures at room temperature [4 6] and they have shown that both the facesheet configur tion and the core density control their impactbehavior. However,the fracture behavior of sandwich composites at low and high temperature levels is complicated when compared with those of the composite at room temperature. 0263-8223/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2005.09.005 * Corresponding author. Tel.: +1 701 231 8839; fax: +1 701 231 8913. E-mail address: M.Mahinfalah@ndsu.edu (M. Mahinfalah). www.elsevier.com/locate/compstruct Composite Structures 78 (2007) 197–206