Foam Testing and Material Data

The mechanical testing of foams requires several adaptations due to their low strengths and stiffnesses. These are mostly concerned with the method of load introduction and the selection of appropriately sensitive load cells. 

Typical dumbbeU-shaped test specimens, such as that shown in Fig. 8.10 (Siriruk et al. 2009a), were chosen for the performance of tensile and torsional tests with loads introduced through friction over the top and bottom circular portions. 

Two techniques, direct shear and torsion, were used to test foam samples in shear as shown in Figs. 8.11 and 8.12. Tensile and shear stress strain data for HlOO foam are shown in Figs. 8.13 and 8.14, respectively. The initial slopes in those figures correspond to = 60 MPa and G = 21 MPa. Note that those values are averaged over a scatter of about 6%. It was also noted that stiffnesses increase monotoiucally toward the center of a 25 mm thick foam slab. 

An estimate for the stiffnesses within the saturated outer region can be obtained from torsional data on coupons that were preimmersed to saturation. A sketch of a cross section of a test sample with dry inner core and a saturated boundary zone is shown in Fig. 8.15 and a sample torsional data for a coupon that was tested in the dry state and subsequently at equilibrium saturation weight is shown in Fig. 8.15. It follows from the torque/rotation plots in Fig. 8.16 that for that particular sample Gw 0.84 G, where G denotes the shear modulus of the immersed sample, averaged over its cross section. 

8 Sea Water Effects on Foam-Cored Sandwich Structures 

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