CCT Core Materials & Sandwich Structures 3

Question 1

What is the standard method for sealing exposed honeycomb core edges to prevent moisture ingress in service?

Accepted Answer

Filling edge cells with compatible potting compound or applying a fiberglass edge closure strip

Answer

Applying a bead of silicone sealant to the raw edge

Answer

Leaving edges open to allow moisture equalization

Answer

Painting the edge with standard topcoat paint only

Question 2

What is the typical cell size designation for standard aerospace-grade Nomex honeycomb, and how is it measured?

Accepted Answer

Cell size is the distance between parallel cell walls measured across the flat side

Answer

Cell size is the wall thickness measured in mils (thousandths of an inch)

Answer

Cell size is the core density measured in pounds per cubic foot

Answer

Cell size is the height of the honeycomb block before slicing

Question 3

When installing a through-bolt insert in a sandwich panel, what is the correct sequence of operations?

Accepted Answer

Drill hole → clean → apply primer → fill with potting compound → cure → drill final hole → install fastener

Answer

Drill hole → torque bolt → inject potting compound → cure → install fastener

Answer

Drill hole → install fastener → inject potting compound around shank → cure

Answer

Drill hole → heat core with heat gun → press-fit insert without potting

Question 4

What phenomenon causes the density of a honeycomb core to increase when the core is curved (bent) around a mold?

Accepted Answer

Cell wall compression on the inner radius causing cells to buckle and close slightly

Answer

Cell wall resin absorption during cure

Answer

Moisture absorption during forming increases mass per unit volume

Answer

Film adhesive flows into cell walls during autoclave processing

Question 5

Which core material property is most critical to evaluate when designing a sandwich panel for compressive out-of-plane loads such as bearing on a floor panel?

Accepted Answer

Core flatwise compressive strength and modulus

Answer

Core flatwise tensile strength

Answer

Core ribbon-direction shear strength

Answer

Core panel peel strength

Question 6

What is the purpose of an 'insert doubler' or 'insert plate' added to a sandwich panel at a fastener location?

Accepted Answer

To spread the fastener bearing load over a larger area of the face sheet and core, reducing local stress

Answer

To increase panel thermal conductivity around the fastener

Answer

To provide a visual indicator of fastener location for maintenance

Answer

To prevent galvanic corrosion between the fastener and core material

Question 7

What is the correct storage condition for unexpanded (block form) or pre-expanded Nomex honeycomb core to maintain its properties before fabrication?

Accepted Answer

Store in a dry, controlled-humidity environment per manufacturer specification, typically below 50% RH

Answer

Store frozen at -10°F (-23°C) in nitrogen atmosphere

Answer

Store submerged in deionized water to prevent outgassing

Answer

No special storage required; Nomex is immune to environmental degradation