Composite Materials 2025

(a) The primary role of the matrix in a composite material is to:

1. Provide tensile strength
2. Transfer load and protect fibers
3. Reduce stiffness
4. Increase brittleness

(b) Which fiber is known for high impact resistance and is used in bulletproof vests?

1. Carbon fiber
2. Glass fiber
3. Aramid fiber
4. Ceramic fiber

(c) Which assumption is valid for a lamina under plane stress?

1. $\sigma_x = 0$
2. $\sigma_z = 0$
3. $\tau_{xy} = 0$
4. $\epsilon_x = 0$

(d) In the isotropic limit case, which relation holds true?

1. $E_1 \neq E_2$
2. $G_{12} = E / (2(1 + \nu))$
3. $\nu_{12} = 0$
4. $\bar{Q}_{11} = \bar{Q}_{22} = 0$

(e) Rule of mixtures is used to predict:

1. Fiber orientation
2. Composite stiffness
3. Lamina thickness
4. Transformation matrix

(f) Von Mises criterion is primarily used for:

1. Brittle failure
2. Ductile isotropic materials
3. Composite laminates
4. Maximum strain analysis

(g) In a cross-ply laminate, fiber orientations are typically:

1. $\pm 45^\circ$
2. $0^\circ$ and $90^\circ$
3. $30^\circ$ and $60^\circ$
4. Random

(h) Tsai-Hill criterion is primarily used for:

1. Isotropic metals
2. Fiber-reinforced composites
3. Brittle ceramics
4. Polymer matrices

(i) Thermal stresses in laminates occur due to:

1. Fiber breakage
2. Matrix cracking
3. Difference in thermal expansion coefficients
4. Excessive load

(j) Natural frequencies of laminated plates are obtained by solving:

1. Static equilibrium equations
2. Energy minimization
3. Eigenvalue problem
4. Rule of mixtures

(a) Define composite materials and explain why they are used instead of conventional materials.

(b) Discuss the properties and applications of carbon fiber composites.

(a) Compare polymer matrix composites with metal matrix composites in terms of properties and applications.

(b) Explain the role of fibers and matrices in determining the overall performance of composite materials.

(a) Derive the generalized Hooke's law for an orthotropic lamina under plane stress.

(b) What is the rule of mixtures? Derive expressions for longitudinal and transverse modulus.

(a) Discuss the transformation matrix and its role in stress-strain transformation.

(b) Explain the concept of transformed stiffness matrix and its importance in laminate analysis.

(a) State and explain the basic assumptions of laminated anisotropic plate theory.

(b) Differentiate between symmetric laminates, angle ply laminates, and cross ply laminates with examples.

(a) Explain maximum stress and maximum strain failure criteria for composite laminates.

(b) Derive Von Mises yield criterion and discuss its application for isotropic materials.

(a) State and explain the Tsai-Hill failure criterion for composite laminates with its mathematical form.

(b) Discuss thermal analysis of composite laminates and how thermal stresses are computed.

(a) Explain the energy formulation approach for buckling analysis of laminated plates.

(b) Discuss the procedure for determining natural frequencies of laminated plates using free vibration analysis.