Degradation mechanisms of balsa wood and PVC foam sandwich core composites due to freeze/thaw exposure in saline solution

Structural engineers commonly use balsa wood and PVC foam as core materials for sandwich composite structures. These structures are frequently exposed to thermal cycling in sea water. The long-term performance and damage mechanism of these composite sandwich structures under such environmental conditions are still unclear. To simulate these effects, sandwich panels using balsa wood (SB100) and foam core (Airex C70.55) with fiber glass/vinyl ester face sheets were exposed to 100 days of freeze/thaw exposure (−20℃ to 20℃). The freezing and thawing occurred in presence of a saline solution. A total of 150 samples were tested for core shear, core compression, and peel tests. Results confirmed that exposure reduced the balsa wood core shear strength by 14%, compression strength by 36%, and compression modulus by 33%. Interestingly, the PVC foam core shear modulus increased by 25% after exposure, whereas the compression modulus reduced by 12%. Simulated lifetime core shear fatigue curves were developed and evaluated. Additional testing techniques such as scanning electron microscopy, optical microscopy, dynamical mechanical analysis, and X-ray computed tomography were used to rationalize the static and fatigue behavior of the core materials.