Structural Requirements Flashcards
Limit Load
Fl, max load structure will experience over its anticipated service life
Proof Load
Fp=Fl*Up where Up=[1.0, 1.25] is the proof factor
Ultimate Load
Fu=Fl*Uu where Uu=1.5 is the ultimate factor
Reserve Factor
Rf, (max load component can sustain)/Fu >1.0
Margin of Safety
Rf-1>0
Strength
Structure must be able to withstand:
Proof load without permanent deformation
Ultimate Load without failure
Durability
Structure must withstand repeated action of loads without failing due to fatigue
Stiffness
Must be stiff enough to maintain controllability over required operational envelope
Spars
Run span-wise throughout wing
Similar to I or C beams
Carry vertical shear forces and direct bending stresses due to bending moments
Ribs
Hold skins apart in correct aerodynamic shape
Transfer aerodynamic forces from skins to spars
Carry shear forces, bending moments, in-plane tension and compression
Skin
Smooth surface for aerodynamic flow
Resistance to bending and avoid buckling
Stiffeners/stringers
Span-wise members attached to skin
Resist buckling when in compression
Composite material advantages (x10)
Lighter & simpler structures
Increase airplane efficiency
Decrease fuel consumption
Decrease weight-based maintenance & fees
No fatigue or corrosion
Resist impacts better
Designed for easy visual inspection
Minor damage repaired in the same way as older aircraft
Crack propagation hindered by fibres
Mechanical properties can be tailored
Carbon Fibre Reinforced Polymer: Thermoset VS Thermoplastic
Thermoset: More widespread
Thermoplastic: Gaining popularity due to recyclability, can be re-melted and still maintain its composition
Composite material disadvantages (x5)
Delamination: Out of plane loads, compression loads, generally internal so not visible
Need detailed insights on load path
Joint failure due to imbalance of deformation with metals
Drilling holes breaks fibres
