Week 3

Which of the following best describes a symmetric laminate?

• All plies have the same thickness

• Each ply above the midplane has an identical ply below the midplane with the same thickness, orientation, and properties

• All plies are oriented at 0° or 90°

• Each ply pair has opposite fibre orientations

In a symmetric laminate, the [B] coupling matrix is

• Zero

• Equal to [A]

• Equal to [D]

• Always negative

Classical Lamination Theory assumes transverse shear strains are zero because:

• Composites are incompressible

• Plies are too stiff to deform

• Lines normal to the mid-surface remain straight and perpendicular after deformation

• The fibres prevent shear deformation

Which laminate property is characteristic of a balanced laminate?

• In-plane shear coupling stiffnesses are zero

• Equal bending and twisting stiffness

• Maximum bending stiffness in all directions

• Zero transverse shear stresses

The [A], [B], and [D] stiffness matrices represent, respectively:

• Extensional, coupling, and bending stiffness

• Axial, torsional, and bending stiffness

• Shear, extensional, and torsional stiffness

• Coupling, shear, and extensional stiffness

Why are stresses discontinuous from ply to ply in a laminate?

• Different ply orientations change the transformed stiffness matrix between layers

• Resin-rich regions cause stress spikes

• Fibre waviness alters stress transfer

• Delamination occurs between plies

A [0/90/0][0/90/0][0/90/0] laminate is:

• Symmetric and balanced

• Balanced only

• Neither symmetric nor balanced

• Symmetric only

If [B] = 0, then:

• In-plane loads cause only bending

• In-plane loads cause no bending, and bending moments cause no in-plane strains

• Shear loads are eliminated

• The laminate is unidirectional

Which type of laminate consists of pairs of plies with +θ and -θ orientations, symmetrically placed about the midplane?

• Symmetric laminate

• Antisymmetric laminate

• Balanced laminate

• Cross-ply laminate

In a symmetric laminate under pure bending, the midplane strains are:

• Maximum

• Zero

• Equal to the curvature

• Dependent on ply orientation