Fatigue loading refers to repeated cyclic stress over time. Even when individual loads are below ultimate strength limits, continuous cycling can gradually damage the sandwich structure.
This is especially important in:
- Wind turbine blades
- Marine hulls
- Vehicle floors
- Aircraft interiors
Under cyclic loading, the foam core experiences repeated shear stress. Weak cores may develop:
- Microcracks
- Cell collapse
- Delamination
- Progressive stiffness reduction
PVC foam is highly valued in structural composites because of its strong fatigue resistance. It maintains mechanical integrity under millions of load cycles.
PET foam also performs well, particularly in thermoplastic composite systems.
XPS and low-density PU foams are generally less suitable for high-fatigue structural environments.
Engineering fatigue analysis often involves:
- S-N curve testing
- Cyclic shear evaluation
- Environmental fatigue simulation
Long-term fatigue behavior is one of the main reasons structural composite applications prioritize engineered cores over simple insulation foams.
