Lecture 8 Flashcards
(11 cards)
What do A13 and A23 relate to?
They relate the in-plane direct forces to in-plane shear, or in-plane shear force t in- plane direct strains.
What do B11, B12 and B22 relate?
They relate in-plane direct forces to plate curvatures, or bending moments to in-plane direct strains.
What do B13 and B23 relate?
They relate the in-plane direct forces to plate twisting, or torque to in-plane direct strains.
What does B33 relate?
It relates the in-plane shear force to plate twisting, or torque to in-plane shear strain.
What does D13 and D23 relate?
They relate the bending moments to plate twisting, or torque to plate curvatures.
How would you ensure no coupling would result between direct stresses and shear strains?
If A13 = A23 = 0
This can be achieved if the lay-up is balanced (i.e. for every layer with a +θ orientation there is an identical -θ orientation ply). Unless the angle is 0 or 90.
Balanced laminates does not necessarily mean they are symmetric. [Examples are (+30/-30); (0/+45/-45); (90/+25/-25)s]
For cross-ply (0,90) laminates what is true of the ABD matrix?
A13 = A23 = D13 = D23 = 0
How can the bending membrane coupling be avoided?
If the B matrix is zero.
This is achieved by making the laminate symmetric about its mid-plane.
Explain what quasi-isotropic laminates are and how
The in-plane effective stiffness is the same in all directions so they appear to be isotropic.
For such laminates A11 = A22 and A13 = A23 =0. Also A11 - A12 = 2*A33.
All quasi-isotropic laminates of one material have similar in-plane properties.
What is a balanced anti-symmetric laminate?
For every +θ layer at a given distance from the mid-plane there is an identical thickness and properties oriented at -θ at the same distance below the mid-plane.
Bending-twisting coupling is eliminated if D13 = D23 = 0.
This is achieved by unidirectional and cross-ply laminates, or with balanced anti-symmetric lay-ups.
How can coupling phenomena be eliminated?
By correct choice of lay-up and/or stacking sequence.
