Samiches

Question 1

What can sandwich composites provides in means of properties improvement

Answer 1

improve in-plane laminate stiffness and rigidity by incorporating a design where uniaxial forces can be
supported most effectively with very low weight.

Question 2

What are the various components of a sandwich composite?

Answer 2

a. Face sheets, facings, skins, traditional laminates – fiberglass, carbon
b. core material, metal, fiber, foam, wood, lightweight rigid materials
c. adhesives - epoxies, resins, tapes,

Question 3

Describe different types of core materials used in sandwich composites?

Answer 3

a. Honeycomb expansion process or corrugation process, determines difference in L/W
performance. Materials include: aluminum, aramid fiber reinforced phenolic; glass reinforced
phenolic; glass reinforced polyimide; thermoplastic
b. Closed cell rigid foam
c. Cast (expanding) foam
d. Balsa or cork wood

Question 4

Why would you want to use honeycomb vs another material?

Answer 4

Foam includes
– polyvinyl chloride
(PVC)
– polymethacrylimide
– polyurethane
– polystyrene
– phenolic
– polyethersulfone
(PES)

And has properties:
Relatively low crush
strength and stiffness
Increasing stress with
increasing strain
Friable
Limited strength
Fatigue
Cannot be formed around
curvatures

Wood-based includes
– plywood
– balsa
– particleboard

And has properties:
Very heavy density
Subject to moisture
degradation
Flammable

Over this, Honeycomb has
Excellent crush strength and
stiffness
Constant crush strength
Structural integrity
Exceptionally high strengths
available
High fatigue resistance
OX-Core and Flex-Core cell
configurations
for curvatures
Excellent strength-to-weight ratio
Excellent moisture resistance
Self-extinguishing, low smoke
versions available

Question 5

What is crucial for honeycomb composites performance?

Answer 5

A small fillet of adhesive at the edge of the cell walls. The fillet is crucial to the performance of the
sandwich, yet it is very dependent on manufacturing factors (resin viscosity, temperature, vacuum, etc).

Question 6

What are the general mechanical properties of a sandwich construction? Benefits?

Answer 6

• Thin composite skins bonded to thicker, lightweight core.
• Large increase in second moment of area without weight penalty.
• Core needs good shear stiffness and strength.
• Skins carry tension and compression loads.

Question 7

What are the types of failures seen in sandwich composites?

Answer 7

Skin tension fail, Excessive deflection, panel buckling, shear crimping, skin wrinkling, intracellular
buckling, local compression.

Question 8

Why is it recommend to use hard points when fastening to a sandwich panel?

Answer 8

Often required to mechanically attach another piece to a composite structure, A hole in any composite is
a form of defect, and will create high local stress when loaded. The hole must be reinforced to accept
the loads imposed by the attachment otherwise premature failure will occur.

Question 9

Describe briefly the steps required to make a Plug Molded Part.

Answer 9

Preparation:
Surface must be at least as good as the part you wish to make, so it must be polished and have as few surface (or otherwise) defects as possible. This is called a "class A" finish.

Mold Construction:
First apply mold release to the plug, so as to remove it from the mold, usually PVA, then lay up multiple layers of epoxy-impregnated fiberglass in the plug to create a mold. After the laid-up fiberglass has finished curing, paint on the bright orange gel-coat.

Material Lay-up:
Apply release agent to the inside of the mold then lay up multiple layers of fiberglass or carbon fiber and apply uncured epoxy to each layer.
Finishing:
Wet sand surface with high-grit sandpaper to achieve class-A finish.
Mold Maintenance:
Remove residue with high-grit sandpaper, then apply polishing compound.