D7: Laminate - Details

Question 1

What are 4 examples of discontinuities? Why is their failure typically not predictable with ELA or CLA?

Answer 1

• Thickness changes
• Edges
• Corners & curves
• Holes & notches
• Because they are prone to inter-laminar failure due to a combination of in-plane and through thickness stresses. ELA & CLA only predict intra-laminar failure.

Question 2

How can we minimise through-thickness stresses due to changes in laminate thickness?

Answer 2

• Gradual taper
• Avoid dropping 0 deg plies adjacent to 90 deg plies
• (change thickness within laminate to protect layer edges)

Question 3

Why are through thickness stresses present at the end of laminates made of UD plies? What 2 types of delamination can occur?

Answer 3

• Mismatch of elastic constants (shear couple and poisson mismatch) between adjacent plies.
• Edge peel caused by high t-t tensile stress, shear failure caused by high shear stress.

Question 4

How can we minimise radial t-t stresses at corners?

Answer 4

• Avoid high BM at corners
• Reduce thickness at the corner
• Increase corner radius
• Support corner against bending

Question 5

What general lay-up rule can we use to minimise stress concentrations at notches?

Answer 5

• Use 50% 45 deg plies to provide pseudo-elastic relief