# Composite Materials Questions and Answers – Interlaminar Stresses

This set of Composite Materials Multiple Choice Questions & Answers (MCQs) focuses on “Interlaminar Stresses”.

1. The principal reason for the existence of interlaminar stresses is the mismatch of Poisson’s ratios between adjacent laminas.
a) True
b) False

Explanation: The interlaminar stresses exist in laminated composites not only because of the mismatch of Poisson’s ratio between adjacent laminas but also because of the mismatch of coefficients of mutual influence between them. If the laminas are not bonded, because of the difference in their Poisson’s ratios an axial loading would create dissimilar transverse strains in various laminas. Likewise, the difference in the coefficients of mutual influence would create dissimilar shear strains in the laminas.

2. Delamination occurs as a result of high interlaminar stresses
a) True
b) False

Explanation: Delamination is the separation of adjacent laminas due to the weakening of the interface layer between them. The free edges of the laminate have very high shear stress and transverse normal stresses. In the regions near the laminate free edges, significantly high interlaminar stresses are induced which in turn leads to delamination.

3. For an angle ply laminate in uniaxial tension normal stress is the most significant interlaminar stress.
a) True
b) False

Explanation: For an angle-ply laminate(θ/-θ) in uniaxial tension, the shear stress is the most significant interlaminar stress at the interfaces of the θ and –θ laminas. Its direction and magnitude depend greatly on the fiber orientation angle θ.

4. Which is not a method to calculate inter-laminar shear strength?
a) Finite difference method
b) 3D Finite element method
c) Mixed element formation
d) Polynomial interpolation

Explanation: Various approaches have been used to calculate inter-laminar shear stress near free edges. Some of the methods or approaches are 3D finite element method, finite difference method, using mixed element formation and stress-based methods, closed-form analytical approach and boundary layer theories.

5. Interlaminar stresses are independent of the stacking sequence of the laminas.
a) True
b) False

Explanation: Stacking sequence has a great influence on the magnitude, location, and nature of interlaminar stresses. Stacking sequences in a composite laminate can control interlaminar stresses so that to develop a broad range of mechanical and physical properties for the composite laminate.

6. For isotropic lamina, the phenomenon of coupling takes place between shear stress and normal stress.
a) True
b) False

Explanation: For an isotropic lamina, there is no coupling between the normal stresses and shear stress. In other words, normal stresses do not influence the shear strain just as the shear stress does not influence the normal strains.

7. The effects of extension-shear coupling are seen in the orthotropic lamina.
a) True
b) False

Explanation: In an orthotropic lamina, the extensional and shear deformations are coupled, unlike the isotropic lamina. In other words, shear stress causes both shear strain and normal strains and normal stresses cause both normal strains and shear strains.

8. Which fiber orientation angle composites do not exhibit extension-shear coupling?
a) 0°
b) 30°
c) 45°
d) 60°

Explanation: For the fiber orientation angle θ = 0° and 90°, the coefficients of mutual influence are zero. Therefore, there is no extension-shear coupling for these fiber orientation angles. The coefficients of mutual influence are functions of the fiber orientation angle and it shows maximum values for intermediate fiber orientations angle between 0° and 90°.

9. Which test is used to measure interlaminar shear strength?
a) ASTM D3039
b) ASTM D790
c) ASTM D2344
d) ASTM D3518

Explanation: Interlaminar shear strength is measured in a short beam shear test in accordance with ASTM D2344. This test method can be used for process specification purposes and quality control since failures are normally dominated by interlaminar properties.

10. Which is not a cause of delamination?
a) Laminate geometry
b) Transverse stresses
c) Manufacturing defects
d) Manufacturing time

Explanation: Delamination is mainly caused by factors like manufacturing defects, transverse stresses generated by load and laminate geometries like free edge, notch, cut-out, bounded joint etc. The high concentration of interlaminar stresses in these geometries is the main reason for delamination.

Sanfoundry Global Education & Learning Series – Composite Materials.

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