ORIGINAL ARTICLE Analysis of factors influencing deflection in sandwich panels subjected to low-velocity impact N. Rajesh Mathivanan & J. Jerald & Puspita Behera Received: 1 September 2009 / Accepted: 25 May 2010 / Published online: 10 June 2010 # Springer-Verlag London Limited 2010 Abstract Fiber reinforced sandwich structures typically respond very poorly to transverse impact events. This paper is an attempt to investigate the impact response of sandwich panels subjected to low-velocity impact. Experimental investigations were carried out on the influence of three design factors: height of fall, core thickness, and impactor mass, which are the most relevant parameters to be considered for deflection. The study of behavior of the mentioned response was done by using Design of Experi- ments tool. Response surface methodology (RSM), a sequential experimentation strategy for model building, is used to model the response in order to determine the most significant factor among the influential factors. In this case, full factorial face-centered central composite design was chosen due to the number of factors and their levels in the study. The specimen consisted of face sheets made up of bi-woven glass fiber cloth with polyurethane foam as core material. The parametric analysis reveals that deflection increases steadily with an increase in the height of fall when compared with the impactor mass and the core thickness. The reason for this study is imperative for the next generation aircraft, marine, road, and rail vehicles with improved lightweight stiff materials that can absorb higher impact energy with higher resistance to deflection. Keywords Sandwich structures . Low-velocity impact . Response surface methodology 1 Introduction Composite structures have a high stiffness-to-weight ratio, good fatigue, and corrosive properties [1]. Sandwich composites are very suitable for lightweight structures requiring high in-plane and flexural stiffness [2]. However, composite structures do have their drawbacks which include poorer performance at high temperatures, reduced failure strain at low temperatures, and poor performance to transverse impact loadings [ 3]. During low-velocity impacts, the contact duration is sufficiently long enough for the entire structure to respond to the impact. The impact energy is absorbed elastically and/or eventually in damage creation. While for high velocity the impact event is so short that the structure may have no time to respond in flexural or shear modes, and the main issue will be whether complete penetration occurs. The resulting damage mech- anisms due to impact loading can be divided into four distinct damage categories: delamination, matrix cracking, fiber breakage, and total perforation. Low-velocity impact by a foreign object (e.g., tool drops, runway debris, bird strikes, etc.) is one of the common types of localized loads which may induce impact damage and result in reduction of static and/or fatigue strength of sandwich structures. Central deflection or central deformation is a change in the shape or size of an object due to an applied force at the center of an object. This can be a result of compressive (pushing) forces at the center. As deformation occurs, internal intermolecular forces arise which oppose the applied force. If the applied force is not too large, these forces may be sufficient to completely resist the applied force, allowing the object to assume a new equilibrium state and to return to its original state when the load is removed. A larger applied force may lead to a permanent deformation N. R. Mathivanan (*) : J. Jerald : P. Behera Department of Production Engineering, National Institute of Technology, Tiruchirappalli 620015, India e-mail: rajesh_mathi@yahoo.com Int J Adv Manuf Technol (2011) 52:433–441 DOI 10.1007/s00170-010-2750-z