Anna University, Chennai

**SRINIVASAN ENGINEERING COLLEGE PERAMBALUR**

**DEPARTMENT OF AERONAUTICAL ENGINEERING**

__COMPOSITE MATERIALS AND STRUCTURES__

__16 MARKS QUESTION BANK__

__Unit 1__

**1. Obtain an expression for E****1 ****, E****2****, and G****12 ****in terms of material properties with respect to principal material directions using mechanics of material approach**.

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 159-173.*

**2. (a) What are the advantages of composite material? And explain its area of application?**

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 28-45.*

(b) Show the reduction of anisotropic material stress-strain equations to those of a monoclinic material stress-strain equations.

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 75-77.*

**3. For a graphite/epoxy unidirectional lamina, find the following. (a) Compliance matrix.**

**(b) Minor poisons ratio.**

**(c) Reduced stiffness matrix.**

**(d) Strains in the 1-2 co-ordinate system if the applied stresses are _****1****=2MPa, E****1****=181GPa, E****2****=10.3 GPa, _****12****=0.28,G****12****=7.17 GPa.**

**4. Explain the Hooke.s law for different materials?**

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 67-69.*

**5. Explain monoclinic material with compliance and stiffness matrices.**

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 70-72 .*

**1. (a)For glass epoxy laminate E****f ****= 85 Gpa, E****m ****= 3.4 GPa, _****m ****= 0.3 and _****f ****= 0.25, find the minor Poisson’s ratio _****21 ****and G****12 ****for a fiber volume fraction of 70%. Ans; _****21 ****=0.23; G****12 ****=0.03939.**

**(b) What weight of glass fibers must be added to 1kg of epoxy to produce a composite with a density of 1700 kg/m****3****, _****f ****= 2500kg/m****3 ****and _****m ****=1200 kg/m****3****. ***Ans: Weight of glass fibers = 1.3007kg*

**2. (a) Describe stress strain relations for a lamina of arbitrary orientation.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 115-116.*

**(b) A graphite/ epoxy cuboid specimen with voids has dimensions a x b x c an its mass is Mc. After putting it in a mixture of sulphuric acid and hydrogen peroxide, the remaining graphite fibers have a mass Mf. From independent tests, the densities of graphite and epoxy are _****f ****and _****m, ****respectively. Find the volume fraction of the voids in terms of a, b, c, Mf,Mc, _****f and ****_****m.**

**3. Explain the elasticity approach to find four elastic moduli.**

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw p180-183.*

**4. Explain Hooke.s law for a twodimensional unidirectional lamina?**

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 80-82.*

**5. Find the following for a 60º angle lamina of graphite /epoxy. E****1****=181GPa, E****2****=10.3GPa, _****12****=0.28,G****12****=7.17 GPa.**

**(a) Transformed compliance matrix**

**(b) Transformed reduced stiffness matrix**

**If the applied stress is _****x ****=2 MPa, _****y ****=-3MPa, _****xy ****= 4MPa, also find**

**(c) Global strains (d) Local strains (e) Local stresses**

**1. Explain Tsai-Hill failure theory used for anisotropic materials.**

**Show that for unidirectional lamina the failure theory can be written as**

**S****2 ****= 1 where _****1, ****_****2, ****_****12 ****are the stress**

**components with respect to principal material direction and X, Y and Z are failure strengths of the lamina.**

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 119-122.*

**2. (a) What are the types of laminates given below? Mention which elements of**

**21[A],[B] and [D] are zero for each of them. (1) [ ± 45 / ± 45]**

**(2) [ 30 / -45 / -30 / 45] (3) [0 / 90 / 0 / 90]**

*Ans: (1) Angle ply laminate*

*(2) Balanced laminate*

*(3) Cross ply laminate and also*

*Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 269-271. (b) Compute [A] matrix for a [0/±45] laminate with the following laminate properties. E1 =145 GPa, E2 =10.5 GPa, _12 = 0.28 and G12 =7.5 GPa. Thickness of each lamina is 0.25 mm.*

**3. Find the stiffness matrices [A], [B] for a three ply [0/30/-45] graphite epoxy laminate. Assume each lamina has a thickness of 5mm. The properties of graphite/epoxy E***l ***=181 GPa, E***t ***=10.3 GPa, _***lt ***= 0.28 and G***lt ***=7.17 GPa.**

**4. A symmetric angle ply laminate hae the following data: 4 Layers of each**

**0.5mm thick +45º/-45º/-45º/+45º . E****l ****=210 GPa, E****t ****=21 GPa, _****it ****= 0.3 and**

**G****it ****=7 GPa. Compute the in-plane stiffness matrix of the laminate.**

*Ans: Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 237-23.*

**5. Derive the governing differential equation for a laminated unidirectional anisotropic plate.**

*Ans: Refer ‘Mechanics of composite materials’ by Robert M. Jones pp 290-299.*

__Unit 4__

**1 (a) What are the materials used for sandwich construction.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 68-76. (b) Write short notes on the failure modes of sandwich panels.*

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 83.*

**2. (a) Explain basic design concept of sandwich construction.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 81-82.*

*22*

**(b) Explain the two methods of honey comb core manufacturing.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 77-78*.

**3. Explain the cell configuration in honeycomb cores?**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 78-79.*

**4. Obtain an expression for the flexural modulus of a**

**Sandwich plate with different face thickness.**

**Sandwich plate with different face thickness and material.**

*Ans:Refer ‘Mechanics of materials approach’ by Autar K.Kaw pp 84-88.*

**5. Explain the honeycomb processes.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 81-82.*

__Unit 5__

**1. (a)What are the functions and desirable properties of resins?`**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 33-34.*

*(b) Write short notes on vacuum bag moulding and continuous pultrusion. Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 201-203;215-*

*217.*

**2. (a) Explain with neat sketches the production of carbon fibers.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 15-18.*

**(b) What are the commercial forms of fibers?**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 9-32.*

**3. Explain open and closed mould processes.**

**Explain with neat sketches one fabrication process under each method.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 189-215.*

**4. Explain any two methods of glass fiber manufacturing with neat sketch.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 11-14.*

**5. (a) Explain the applications of resins.**

*Ans: Refer ‘Advanced composite materials’ by Lalit Gupta pp 43-44.*

**(b) Write short notes on Netting analysis.**

*Ans: Refer ‘Mechanics of composite materials’ by Robert M. Jones pp 253-*

*254.*