Effects of Seawater and Low Temperatures on Polymeric Foam Core Material A. Siriruk & D. Penumadu & A. Sharma Received: 28 February 2011 /Accepted: 10 October 2011 /Published online: 5 November 2011 # Society for Experimental Mechanics 2011 Abstract Polymeric composite sandwich structures, often manufactured using a thick foam core material and thin composite facings, are of significant interest in naval applications. This paper summarizes the coupled effect of sea water and low temperature on the mechanical properties of closed cell polymeric H100 foam core material. The study considers the effects of harsh sea environmental conditions on the fracture and deformation behavior of such a foam material under complex loading conditions that include tension, torsion, compression, and true-triaxial stress paths. Mechan- ical testing techniques are developed using coupon samples of suitable geometry that minimize grip effects on these low density complex foam materials, along with information associated with the observed cross-anisotropic behavior. Interfacial delamination fracture response for the sandwich structures due to the combined effects of sea water and low temperature are evaluated and the associated degradation in critical energy release rate for delamination is found to be substantial. Experimental data for H100 foam cores associated with moisture induced expansional strains are also included. Keywords Sea water . Low temperature . Polymeric foam . Sandwich structures . Mechanical properties Introduction The utilization of polymeric composite-based sandwich structures in naval crafts is of current interest to the U.S. and several European navies. Typically, these sandwich lay- ups are made from closed-cell and low-density polymeric foam core material placed between fiber-reinforced poly- meric composite facings. The resulting sandwich compo- nents possess an exceedingly light weight, thereby increasing the buoyancy of submersible vessels and, when employed in ship-structure design, may enhance a ship’ s stability by lowering its center of gravity. In marine applications, such materials and their associated structural components are exposed to the sea environment over extended periods of time, experiencing degradation in mechanical properties as a result of moisture absorption and temperature variations; this is a major concern with regard to naval structural materials and is the focus of this paper. Past studies have focused on understanding the mechanical behavior of naval foam core material (e.g. Divinycell) and have been limited to studying virgin materials, not those exposed to environmental degradation conditions. These past studies evaluated the stress–strain behavior of polymeric foam under compressive and tensile conditions [1, 2]. Gibson and Ashby [2] have comprehen- sively described the tensile and compressive behavior of cellular materials. The tensile and fracture behaviors of various densities of closed cell foam materials have been previously described [3]. It was noted that polymeric PVC foams of 100 kg/m 3 density (H100) demonstrated orientation-dependence material properties [4]. However, multi-axial experimental data on polymeric closed-cell foam material are, to date, very limited, especially under a state of pure shear stress (torsional testing). The moisture uptake of H100 foam core has been examined under conditions of 95% relative humidity (RH) and sea water immersion [5]. The results indicated that sea-water ingress into the foam core by immersion was much greater when compared to exposure of 95% RH. Sea water-induced A. Siriruk : D. Penumadu (*) : A. Sharma Civil and Environmental Engineering, University of Tennessee, 223 Perkins Hall, Knoxville, TN 37996-2010, USA e-mail: dpenumad@utk.edu Experimental Mechanics (2012) 52:25–36 DOI 10.1007/s11340-011-9564-2