D9: Section - Monolithic

Question 1

What’s an area of weakness in stiffeners? Why?

Answer 1

• Regions between flange caps and web layers
• Because they’re resin-rich

Question 2

What are the limitations of normal blade stiffeners? How can we reduce them?

Answer 2

• End of blade susceptible to impact damage & shear transfer
• Sophisticated pultrusion methods for continuous web layers, rolled over at the end
• Creates a bulb that increases axial stiffness

Question 3

How can we optimise the design of elements made up of multiple sections?

Answer 3

• By using different layups for each section, depending on its function structurally

Question 4

What are the 4 assumptions used for composite laminate section analysis?

Answer 4

• Thickness, layup, and strength constant within a section element, but can differ from element-to-element.
• Symmetric, specially orthotropic layups
• Single or double anti-symmetric sections (geometry and stiffness)
• Thin wall assumption (t/b<10)

Question 5

Given that buckling is stacking-sequence-dependent, how can we design for it?

Answer 5

• Include 45 deg as outer plies, to increase torsional stiffness (D66)
• Lay-up outer ply in the direction of the buckling load
• Restrict post-buckled design to panels with b/t > 30, because buckling can lead to inter-laminar shear and tensile failure

Question 6

How can we assess buckling strength for specially orthotropic laminates? What about generally orthotropic?

Answer 6

• Closed-form analytical solutions (ESDU)
• Can estimate with ESDU, but be aware of the errors

Question 7

When is simple buckling analysis acceptable?

Answer 7

• When bend-twist coupling stiffnesses are small compared to other bending stiffnesses (D16 & D26 < D11, D22, & D66)
• When laminate thickness >2-3mm
• When laminate aspect ratio is > 4