Problem 4 (20 pts):

The two plies as shown in the left figure has the same lamina elastic constants of E₁ = 160

Gpa; E2 10 Gpa; G12= 6 Gpa; V12 = 0.3. The fibers in the top ply (ply 1) is oriented at

600 and the bottom ply (ply 2) is oriented at 120° with respect to the global coordinate x.

Both plies are subjected to an in-plane tensile stress ox = 50 MPa.

(1) Please calculate the strains (¹), Ey(¹), Yxy (1); Ex (2), Ey (2), Yxy (2))

(2) Please illustrate (hand draw ok) the deformation of the two plies

(3) Imagine now the two plies are bonded by an interface and subjected to the same stress

ox as shown in the right figure, please comments what the interface needs to provide

(i.e., what stress will develop at the interface) to ensure an iso-strain condition at

cross-sections.

2

60⁰

120°

Ply 1

Ply 2

ab

in

-50 MPa

- 50 MPa

-50 MPa

y

iso-strain

Cross-section

deformation

-50 MPa