### COMPOSITE MATERIALS AND STRUCTURES Questions Bank 2014

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 E1 , E2, and G12 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, E1=181GPa, E2=10.3 GPa, _12=0.28,G12=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 Ef = 85 Gpa, Em = 3.4 GPa, _m = 0.3 and _f = 0.25, find the minor Poisson’s ratio _21 and G12 for a fiber volume fraction of 70%. Ans; _21 =0.23; G12 =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/m3, _f = 2500kg/m3 and _m =1200 kg/m3. 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. E1=181GPa, E2=10.3GPa, _12=0.28,G12=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

S2 = 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 El =181 GPa, Et =10.3 GPa, _lt = 0.28 and Glt =7.17 GPa.

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

0.5mm thick +45º/-45º/-45º/+45º . El =210 GPa, Et =21 GPa, _it = 0.3 and

Git =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.

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(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.