Sandwich Structures PDF

SANDWICH STRUCTURES A sandwich structure is a composite structural panel concept commonly used in aerospace applications, consisting of two relatively thin, parallel face sheets bonded to and separated by a relatively thick, lightweight core. This type of construction provides a high strength-to-we...

SANDWICH STRUCTURES A sandwich structure is a composite structural panel concept commonly used in aerospace applications, consisting of two relatively thin, parallel face sheets bonded to and separated by a relatively thick, lightweight core. This type of construction provides a high strength-to-weight ratio, which is crucial for aircraft performance. Face Sheets Face sheets are the outer layers of sandwich structures, providing the main structural support. Common materials used include: Aluminum, Fiberglass, Kevlar®, Carbon Fiber - Used in honeycomb structures, these materials each have specific benefits, such as lightweight properties, strength, and resilience. Carbon Fiber cannot be used with aluminum honeycomb due to corrosion concerns. Titanium and Steel are utilized in high-temperature, specialized applications. Many face sheets in components like spoilers and flight controls are very thin, often only 3 or 4 plies thick. Core Materials The core is essential for providing structural stability and separating the face sheets. Various core materials are used depending on the specific requirements: Honeycomb Core Materials: Kraft Paper - Low strength, good insulating properties, economical. Thermoplastics - Good insulation, moisture resistance, smooth cell walls, low cost. Aluminum - High strength-to-weight ratio, good heat transfer, and electromagnetic shielding. Steel - Good heat transfer and electromagnetic shielding, heat-resistant. Specialty Metals (Titanium) - High strength, good heat resistance, and chemical resistance. Aramid Paper (Nomex®, Korex®) - Flame resistant, good formability, low dielectric properties. Fiberglass - Customizable shear properties, good formability, low dielectric properties. Carbon - Excellent stability, high stiffness, heat-resistant, but expensive. Ceramics - Heat-resistant to very high temperatures, available in small cell sizes, and very expensive. CORE STRUCTURE: Honeycomb core cells are typically hexagonal, created by expanding stacked sheets bonded at specific locations. Cell Size and Density - Smaller cells provide better support for face sheets. Higher-density cores are stronger and stiffer. FOAM Foam cores are less commonly used in commercial aircraft due to their weight but are popular in lighter and home-built aircraft. Polystyrene (Styrofoam) - High compressive strength, water-resistant, and easily shaped using hot wire cutting. Phenolic - Excellent fire resistance but low mechanical properties. Polyurethane- Inexpensive, fuel resistant, used for fuselage and wing tips, easily contoured with a knife.  Polypropylene- Compatible with most adhesives, suitable for airfoil shapes. Polyvinyl Chloride (PVC)- High compression strength, fire-resistant, suitable for vacuum forming and heat bending. Polymethacrylimide (Rohacell) - Superior mechanical properties, high stability under heat, but expensive. BALSA WOOD Balsa - A natural wood product with elongated, closed cells. It has a lower density compared to conventional woods but is denser than most structural foams. Balsa provides high stiffness and is commonly used for certain structural elements requiring moderate strength. Sandwich structures provide an efficient way to achieve lightweight and strong components critical for aerospace applications. By combining different face sheets and core materials, aircraft designers can tailor these panels to specific performance requirements, whether for low weight, high strength, thermal resistance, or electromagnetic shielding.