Strength of GFRP Sandwich Plates for Small Ships

－Part 1 Material Tests and FEM Analysis－

Abstract

In recent years, the adoption of fiber reinforced plastic (FRP) sandwich structure has increased not only for small but also for large structures, since the VaRTM (Vacuum assisted Resin Transfer Molding) has been developed to practical use ¹⁾. In the structural approval inspection of small ships ^2,3), GFRP sandwich structures are allowed the same strength evaluation as single GFRP plate structures. However, not only the inclusion ratio to the thickness of core material when using material other than the specified wood materials but also the thickness ratio of the inner and outer FRP plates are regulated for the sandwich structures ³⁾. In the present study, in order to examine those influences on the bending strength of sandwich structures, tensile tests for various materials and bending tests for single GFRP plates and sandwich plates were performed. It was revealed from the test results that the inclusion rate may be considered even when a material other than the specified wood materials is used for the sandwich core. In addition, it became clear that the influence of the thickness ratio of inner/outer plates on the bending strength is relatively small compared to the variation in the test results.

Although the strength characteristics of the tested materials could be obtained from the various test results, they had large variations, so their average values were used as the reference values of the strength. By using the reference values for the tensile and compressive strengths of the test materials, the results of finite element method (FEM) analysis which are executed by the commercial FEM program LS-DYNA for the three-point bending tests of the sandwich plates show a good correlation with the test results. In the forthcoming second report, based on the reference values, FEM analysis of sandwich panels and hull models will be executed, and detailed verification of the inclusion rate of sandwich core and the thickness ratio of inner/outer plates will be performed.