A Novel Method for Determining the Temperature Dependence of Shear Properties of Structural Foams

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Abstract
A glass reinforced plastic( GRP) /foam sandwich has been chosen for the construction of the new Royal Australian Navy minehunter. Previous work has determined that elevated temperatures possible in Australian tropical conditions can have a deleterious effect on the foam core of such composites with subsequent reductions in composite structural strength. Full scale tests and underwater shock trials have shown that shear stress in the core is a prime cause of composite failure and hence reductions in core shear properties under the influence of temperature may affect the service performance of the vessel. Core shear properties in the temperature range 20–90°C have been monitored using a new torsional shear instrument which for thick foam materials offers substantial advantages in comparison with standard plate shear methods. Results for a number of commercial closed cell modified PVC foams are presented and indicate that at 90° C the decline in shear strength and shear modulus is 30–50%. Comparisons between torsional and plate shear procedures were also undertaken and a rationalisation for observed differences is proposed