Shear strength is one of the most critical mechanical properties of a foam core because the core primarily transfers shear loads between the two face sheets of a sandwich structure. When a sandwich panel bends under load, the top skin experiences compression while the bottom skin experiences tension. The foam core resists the sliding force generated between these skins.
If the core has insufficient shear strength, the panel may fail even if the face sheets remain intact. Common failure modes include:
- Core cracking
- Shear buckling
- Delamination
- Sudden stiffness collapse
PVC foam cores are widely used because they offer high shear strength combined with good fatigue resistance. PET foam also provides stable shear performance, especially in thermoplastic composite systems. XPS, while lightweight and economical, generally has lower shear properties and is better suited for insulation applications.
Engineering designers calculate allowable shear stress based on:
- Span length
- Load distribution
- Dynamic loading
- Environmental exposure
Higher shear modulus improves panel rigidity and reduces deflection under long-term service conditions.
