CCT Core Materials & Sandwich Structures 2

Question 1

What is the main advantage of end-grain balsa wood core compared to closed-cell foam cores in marine composite applications?

Accepted Answer

Excellent compressive strength and stiffness at relatively low cost

Answer

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.

Question 2

What foam core type offers the best performance in applications exposed to elevated temperatures above 250°F (121°C)?

Accepted Answer

PMI (polymethacrylimide) foam such as Rohacell

Answer

PMI foams such as Rohacell maintain mechanical properties at elevated temperatures and are compatible with high-temperature autoclave cure cycles up to 350°F.

Question 3

Which process is used to form flat honeycomb core into a curved shape without cutting and re-bonding?

Accepted Answer

Flex-core expansion or OML machining

Answer

Flex-core (also called over-expanded core) or CNC OML machining allows honeycomb to conform to curved geometries without slitting or dicing the core.

Question 4

What structural failure occurs when the core itself fails in shear under out-of-plane loading in a sandwich panel?

Accepted Answer

Core shear failure

Answer

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.

Question 5

Why must foam core materials be properly vented or perforated before autoclave processing?

Accepted Answer

To prevent trapped air or volatiles from expanding and causing face sheet disbonds or blistering

Answer

Trapped air and gas in closed-cell foam expand under autoclave heat and pressure, potentially causing face sheet disbonds or blowouts if not vented.

CCT - Certified Composite Technician Practice Test

CCT - Certified Composite Technician Practice Test

CCT Core Materials & Sandwich Structures 2