Core Materials & Sandwich Structures Flashcards
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Read the first 7 Core Materials & Sandwich Structures flashcards as text
What is the main advantage of end-grain balsa wood core compared to closed-cell foam cores in marine composite applications?
Answer: Excellent compressive strength and stiffness at relatively low cost
End-grain balsa provides high compressive strength and stiffness per unit cost, making it widely used in marine sandwich construction where load distribution is critical.
What foam core type offers the best performance in applications exposed to elevated temperatures above 250°F (121°C)?
Answer: PMI (polymethacrylimide) foam such as Rohacell
PMI foams such as Rohacell maintain mechanical properties at elevated temperatures and are compatible with high-temperature autoclave cure cycles up to 350°F.
Which process is used to form flat honeycomb core into a curved shape without cutting and re-bonding?
Answer: Flex-core expansion or OML machining
Flex-core (also called over-expanded core) or CNC OML machining allows honeycomb to conform to curved geometries without slitting or dicing the core.
What structural failure occurs when the core itself fails in shear under out-of-plane loading in a sandwich panel?
Answer: Core shear failure
Core shear failure occurs when transverse shear stresses exceed the core shear strength, causing the core to fracture, often appearing as a diagonal crack through the core.
Why must foam core materials be properly vented or perforated before autoclave processing?
Answer: To prevent trapped air or volatiles from expanding and causing face sheet disbonds or blistering
Trapped air and gas in closed-cell foam expand under autoclave heat and pressure, potentially causing face sheet disbonds or blowouts if not vented.
What is the correct terminology for the tapered transition at the edge of a sandwich panel where the core thickness is gradually reduced to zero?
Answer: Core runout or core ramp
A core runout or core ramp is the engineered taper at a panel edge that transitions load smoothly from the sandwich section to the solid laminate without stress concentration.
What is the minimum recommended film adhesive weight (per square foot) typically used to bond honeycomb core to prepreg face sheets in aerospace applications?
Answer: 0.03 to 0.06 psf (0.15 to 0.30 kg/m²)
Film adhesives in the 0.03–0.06 psf range provide sufficient fillet formation into honeycomb cell walls without adding excessive weight, which is critical for aerospace panels.