230606 - Composite Materials

Question 1

Difference between symmetric laminate and asymmetric laminate.

Answer 1

You input a tension (force) and the output (stress) will not be a constant as you could expect in an isometric material.
Laminate asymmetrical: mixture of bending (linear stress distribution) and tension (constant stress distribution).

Question 2

Failure in tensile tests for composite

Answer 2

The failure in tensile tests for composite is not uniform, it occurs in several instances, step by step. If one layer fails, then the other ones may still be able to carry the load, and not all fail at the same time.

Question 3

Specific modulus

Answer 3

Typical metals around 20, how do you get it?
* Dupont E130 carbon fiber: 417
* Glass fiber: 40

Question 4

Typical specific modulus for matrix materials?

Answer 4

Epoxy, Polyester around 2 or 3

Question 5

Micromechanics and macromechanics of laminae?

Question 6

manufacturing methods for glass and for carbon fiber?

Answer 6

• Hand lamination, also known as wet layup or wet lay carbon fiber, is a common method of fabricating carbon fiber composites.
• Advanced techniques are often employed in industrial settings where higher production volumes or specific performance requirements are needed.

Question 7

Prediction of elastic properties of Laminae

Answer 7

• Mechanics of materials approach (stress-strain, hookes law):
  ** Young’s Modulus:
• Parallel direction: linear relation between the Fiber volume and the lamina modulus.
• Perpendicular direction: non-linear growing shape.
  ** Poisons ratio:
• Parallel direction: linear relation between the Fiber volume and the lamina modulus.
  ***Shears modulus (micromechanics):
• In-plane direction: non-linear growing shape.

Question 8

difference

Answer 8

Tsai:
* Parameter k is introduced to represent the misalignment of the fibers.
Fitting parameters, between mechanics of materials approach and tsai solutions.

Answer 9

constitutive: stress and strain
equilibrium: internal reactions to external load
kinematics: strain and

Question 10

Orthotropic material (slides 3a)

Answer 10

• 5 constants in Hooke’s law: E1, E2, v12 (major Poisson ratio, fiber direction) and v21 (minor Poisson ratio).
• 4 independent (instead of 2 as with isotropic materials)

Question 11

What is an orthotropic material?

Answer 11

• Type of anisotropic material that exhibits different mechanical properties in three perpendicular directions. It means that the material has unique and independent material properties along each of the three principal axes.
• Each layer or constituent can have its own orientation, fiber arrangement, or material composition

Question 12

Typical elongation at failure for steels? For aluminum?

Answer 12

• Carbon steels: Elongation at failure can range from around 10% to 40%
• Wrought aluminum alloys: Elongation at failure can vary from approximately 10% to 30%
• Carbon fiber: exhibit brittle failure with very little elongation. Elongation at failure of carbon fiber composites is generally low, typically less than 2%.

Question 13

Failure criteria

Answer 13

• Maximum stress and maximum strain, smaller than the tensile, greater than the compressive.
• Sigma12, smaller than the shear limit.
  Do not consider interaction of sigma1 and sigma2.
  —
• tsai-hill considers the interaction between sigma 1 and sigma2
  *

Question 14

Generalized strain matrix

Answer 14

• symmetric laminates: no coupling (3c.13), nothing superimposed, tension twist bending shear coupling and bending tension coupling

Question 15

What is a cross-ply laminate?

Answer 15

• Orthotropic laminae (plies) at right angles to one another.
• Provide enhanced stiffness and strength in two orthogonal directions.
• Predictable mechanical properties, and improved resistance to delamination
• WHICH COMPLETE QUADRANTS ARE ZERO?

Question 16

Angle ply laminate?

Answer 16

±45°, ±30°, ±60°,

Question 17

Symmetric balanced laminate

Answer 17

• all identical laminae at angles other than 0◦ and 90◦ occur only in ± pairs
• WHICH COMPLETE QUADRANTS ARE ZERO?

Question 18

quasi-isotropic laminate

Answer 18

• Individual layers or plies are arranged in a specific stacking sequence to achieve near isotropic behavior.
• WHICH COMPLETE QUADRANTS ARE ZERO?

Question 19

3d symmetric laminate

Answer 19

** tension load case: **
* STRESS:
Constant stress layerwise (3d.19) magnitude stiffness of each (90deg: minimum, 0deg: maximum). Sketch the stress distribution from the laminate distribution.
* STRAIN:
Constant.
** bending :**
* STRESS:
Minimum on 90deg
Max on 0deg:
* STRAIN:
Z distribution. Same as in isotropic materials, no change

Question 20

asymmetric laminates

Answer 20

3d.47? How does the stress behave?
* How does the strain behave?
Superimposed the elongation + bending
it does not matter if we have the right angle for the inclination as long as we know when is it inclined or not
* WHICH COMPLETE QUADRANTS ARE ZERO? WHY?