Sandwich construction
Download
1 / 17

Sandwich Construction Thin composite skins bonded to thicker ... - PowerPoint PPT Presentation


  • 957 Views
  • Uploaded on

Sandwich Construction 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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Sandwich Construction Thin composite skins bonded to thicker ...' - libitha


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Sandwich construction l.jpg
Sandwich Construction

  • 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.


Slide2 l.jpg

Sandwich panels are a very efficient way of providing high bending stiffness at low weight. The stiff, strong facing skins carry the bending loads, while the core resists shear loads. The principle is the same as a traditional ‘I’ beam:


Slide3 l.jpg

Bending stiffness is increased by making beams or panel thicker - with sandwich construction this can be achieved with very little increase in weight:


Slide4 l.jpg

The stiff, strong facing skins carry the bending loads, while the core resists shear loads.

Total deflection = bending + shear

Bending depends on the skin properties; shear depends on the core


Foam core comparison l.jpg
Foam core comparison while the core resists shear loads.

PVC (closed cell)- ‘linear’ – high ductility, low properties- ‘cross-linked’ – high strength and stiffness, but brittle- ~ 50% reduction of properties at 40-60oC- chemical breakdown (HCl vapour) at 200oC


Foam core comparison6 l.jpg
Foam core comparison while the core resists shear loads.

PU- inferior to PVC at ambient temperatures- better property retention (max. 100oC)

Phenolic- poor mechanical properties- good fire resistance- strength retention to 150oC


Foam core comparison7 l.jpg
Foam core comparison while the core resists shear loads.

Syntactic foam- glass or polymer microspheres- used as sandwich core or buoyant filler- high compressive strength

Balsa- efficient and low cost- absorbs water (swelling and rot)- not advisable for primary hull and deck structures; OK for internal bulkheads, etc?


Slide8 l.jpg

Why honeycomb? while the core resists shear loads. List compiled by company (Hexcel) which sells honeycomb!


Slide9 l.jpg

Sandwich constructions made with other core materials (balsa, foam, etc) have a large surface are available for bonding the skins.

In honeycomb core, we rely on 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).


Slide10 l.jpg

Honeycomb is available in polymer, carbon, aramid and GRP. The two commonest types in aerospace applications are based on aluminium and Nomex (aramid fibre-paper impregnated with phenolic resin).

Cells are usually hexagonal:

but ‘overexpanded’ core is also used to give extra formability:


Slide11 l.jpg

Core properties depend on density and cell size. They also depend on direction - the core is much stronger and stiffer in the ‘ribbon’ or ‘L’ direction:



Slide13 l.jpg

Aluminum Honeycomb honeycomb, e.g:• relatively low cost• best for energy absorption• greatest strength/weight• thinnest cell walls• smooth cell walls• conductive heat transfer• electrical shielding• machinability

Aramid Fiber (Nomex) Honeycomb• flammability/fire retardance• large selection of cell sizes, densities, and strengths• formability and parts-making experience• insulative• low dielectric properties


Sandwich construction14 l.jpg
Sandwich Construction honeycomb, e.g:

  • Many different possible failure modes exist, each of which has an approximate design formula.


ad