ARPRO®: A New Structural Core Material for the Yacht Industry

Sandwich structures are increasingly used in marine applications where high bending specific stiffness and strength are required. So far, expanded polymeric foams such as Styrene Acrilonitrile (SAN) and Polyvinyl Chloride (PVC) have been proved to be the most suitable core materials for motor and sailing yacht sandwich constructions. ISO standards have accepted these materials and suggested design rules built around their mechanical properties. One of the main drawbacks in the application of sandwich composite structures is the fact that their load carrying ability may be significantly reduced by the presence of a local damage such as core indentation or partial face sheet delamination. Local damages usually take place in dynamic scenarios and they can be caused by indentation due to floating object impacts, interaction with mooring structures and rocks or by high deformations due to slamming loads. It should be noted that such damages usually cannot be observed from outside the sandwich construction and they may cause a serious reduction in load-bearing capacity, jeopardizing the safety of the boat and its crew. ARPRO® is an expanded polypropylene (EPP) foam extensively used in the automotive industry, where it has gained full approval due to its outstanding energy absorption characteristics. Unlike standard polymeric foams, ARPRO® foams possess a hyper-elastic stress versus strain response and recover their initial shape after having undergone very high deformations. For this reason this material is expected to enable the design of sandwich panels with an enhanced damage tolerance. In the case of an impact, the core stores the energy as it is compressed and once the load is released it will return to its original geometry preventing the skin from debonding. SAN or PVC cores would absorb the energy by destroying their cell structure leading in this way to core-skin delamination. On the other hand, ARPRO® has lower shear and compressive moduli which implies lower sandwich structures performances in static scenarios. This paper presents static and dynamic testing aimed at determining the relative mechanical performances of sandwich beams cored both with ARPRO® and SAN foams. Comparison of the static and dynamic response ofthe two materials shows that ARPRO® is a potentially competitive core material for composite sandwich construction.