Ans:
CE 0.00250 mm mm, BD 0.00107 mm mm
105
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2–2. A thin strip of rubber has an unstretched length of
15 in. If it is stretched around a pipe having an outer diameter
of 5 in., determine the average normal strain in the strip.
L0 = 15 in.
L = p(5 in.)
L - L0 5p - 15 =
L =
15 = 0.0472 in.>in.
0
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2–2. A thin strip of rubber has an unstretched length of
375 mm. If it is stretched around a pipe having an outer
diameter of 125 mm, determine the average normal strain
in the strip.
L0 = 375 mm
L = p(125 mm)
ee 5 L – L0 5
125p – 375 = 0.0472
mm/mm
Ans.
L0 375
Ans:
P = 0.0472 mm>mm
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2–3. The rigid beam is supported by a pin at A and wires
BD and CE. If the load P on the beam causes the end C to D E
be displaced 10 mm downward, determine the normal strain developed in wires CE and BD.
4 m
P
A B C
3 m 2 m 2 m
¢LBD
3 =
¢ LCE
7
¢LBD = 3 (10)
7 = 4.286 mm
¢ LCE 10
PCE = L
= 4000
= 0.00250 mm>mm
Ans.
PBD =
¢ LBD
L =
4.286
4000 = 0.00107 mm>mm
Ans.
Ans:
PCE = 0.00250 mm>mm, PBD = 0.00107 mm>mm
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*2–4. The force applied at the handle of the rigid lever
causes the lever to rotate clockwise about the pin B through
an angle of 2°. Determine the average normal strain
developed in each wire. The wires are unstretched when the
lever is in the horizontal position.
200 mm
300 mm
A B
G F
200 mm
300 mm
E
C D 200 mm
H
2°
Geometry: The lever arm rotates through an angle of u = a 180
b p rad = 0.03491 rad.
Since u is small, the displacements of points A, C, and D can be approximated by
dA = 200(0.03491) = 6.9813 mm
dC = 300(0.03491) = 10.4720 mm
dD = 500(0.03491) = 17.4533 mm
Average Normal Strain: The unstretched length of wires AH, CG, and DF are
LAH = 200 mm, LCG = 300 mm, and LDF = 300 mm. We obtain
(Pavg)AH =
(Pavg)CG =
(Pavg)DF =
dA =
LAH
dC =
LCG
dD =
LDF
6.9813
200 = 0.0349 mm>mm
10.4720
300 = 0.0349 mm>mm
17.4533
300 = 0.0582 mm>mm
Ans.
Ans.
Ans.
108
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2–5. The two wires are connected together at A. If the force P
causes point A to be displaced horizontally 2 mm, determine
the normal strain developed in each wire. C
30 P
30 A
B
Lœ 2 2AC = 2300 + 2
Lœ
- 2(300)(2) cos 150° = 301.734 mm
PAC = PAB = AC - LAC
LAC
301.734 - 300 =
300 = 0.00578 mm>mm
Ans.
Ans:
PAC = PAB = 0.00578 mm>mm
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r
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2–6. The rubber band of unstretched length 2r
0 is forced
down the frustum of the cone. Determine the average r0
normal strain in the band as a function of z.
z
2r0 h
Geometry: Using similar triangles shown in Fig. a,
h¿ h¿ +h = ;
0 2r0
h¿ = h
Subsequently, using the result of h¿
r r0
z + h =
h ;
r0 r = (z + h)
h
Average Normal Strain: The length of the rubber band as a function of z is 2pr0
L = 2pr = (z + h). With L0 = 2r0, we have h
2pr0
Pavg =
L - L0
L0
h (z + h) -
2r0
= = 2r0
p (z + h) - 1
h
Ans.
Ans:
Pavg =
p
(z + h) - 1 h
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2–7. The pin-connected rigid rods AB and BC are inclined P
at u = 30° when they are unloaded. When the force P is
applied u becomes 30.2°. Determine the average normal B
strain developed in wire AC.
u u
600 mm
A C
Geometry: Referring to Fig. a, the unstretched and stretched lengths of wire AD are
LAC = 2(600 sin 30°) = 600 mm
LAC ¿ = 2(600 sin 30.2°) = 603.6239 mm
Average Normal Strain:
LAC ¿ - LAC
603.6239 - 600 - 3
(Pavg)AC = = LAC 600
= 6.04(10
) mm>mm Ans.
Ans:
(Pavg)AC = 6.04(10 - 3) mm>mm
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P
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*2–8. Part of a control linkage for an airplane consists of a u
rigid member CBD and a flexible cable AB. If a force is D
applied to the end D of the member and causes it to rotate
by u = 0.3°, determine the normal strain in the cable.
Originally the cable is unstretched. 300 mm
B
300 mm
A C
400 mm
AB = 24002 + 3002 = 500 mm
AB¿ = 24002 + 3002 - 2(400)(300) cos 90.3°
= 501.255 mm
AB¿ -AB
501.255 - 500
PAB = AB
= 500
= 0.00251 mm>mm Ans.
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2–9. Part of a control linkage for an airplane consists of a
rigid member CBD and a flexible cable AB. If a force is
applied to the end D of the member and causes a normal
strain in the cable of 0.0035 mm>mm, determine the
displacement of point D. Originally the cable is unstretched.
u
D P
300 mm
B
300 mm
A C
400 mm
AB = 23002 + 4002 = 500 mm
AB¿ = AB + eABAB
= 500 + 0.0035(500) = 501.75 mm
501.752 = 3002 + 4002 - 2(300)(400) cos a
a = 90.4185°
pu = 90.4185° - 90° = 0.4185° =
180° (0.4185) rad
p ¢D = 600(u) = 600(
180°)(0.4185) = 4.38 mm
Ans.
Ans:
¢D = 4.38 mm
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y
2–10. The corners of the square plate are given the
displacements indicated. Determine the shear strain along A the edges of the plate at A and B.
16 mm
D
3 mm
B x
3 mm 16 mm
C
16 mm
16 mm
At A: u¿ - 1
2 = tan
9.7 a
10.2 b = 43.561°
u¿ = 1.52056 rad
p(gA)nt =
2 - 1.52056
= 0.0502 rad
Ans.
At B:
f¿
- 1
2 = tan
10.2 a
9.7 b = 46.439°
f¿ = 1.62104 rad
p(gB)nt =
2 - 1.62104
= - 0.0502 rad
Ans.
Ans:
(gA)nt = 0.0502 rad, (gB)nt = - 0.0502 rad
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2–11. The corners B and D of the square plate are given y
the displacements indicated. Determine the average normal
strains along side AB and diagonal DB. A
16 mm
D
3 mm
B x
3 mm 16 mm
C
16 mm
16 mm
Referring to Fig. a,
LAB = 2162 + 162 = 2512 mm
LAB¿ = 2162 + 132 = 2425 mm
LBD = 16 + 16 = 32 mm
LB¿D¿ = 13 + 13 = 26 mm
Thus,
A eavg B AB = LAB¿ - LAB
LAB
LB¿D¿ - LBD
2425 - 2512 =
2512
26 - 32
= - 0.0889 mm>mm
Ans.
A eavg B BD = LBD
= 32
= - 0.1875 mm>mm
Ans.
115
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2–12
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2–13 .
Ans:
PDB = PAB cos2 u + PCB sin2 u
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2–14. The force P applied at joint D of the square frame
causes the frame to sway and form the dashed rhombus.
Determine the average normal strain developed in wire AC.
Assume the three rods are rigid.
200 mm 200 mm P D E C
3
400 mm
A B
Geometry: Referring to Fig. a, the stretched length of LAC ¿ of wire AC¿ can be
determined using the cosine law.
LAC ¿ = 24002 + 4002 - 2(400)(400) cos 93° = 580.30 mm
The unstretched length of wire AC is
LAC = 24002 + 4002 = 565.69 mm
Average Normal Strain:
LAC ¿ - LAC
580.30 - 565.69
(Pavg)AC = = LAC 565.69
= 0.0258 mm>mm
Ans.
Ans:
(Pavg)AC = 0.0258 mm>mm
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2–15. The force P applied at joint D of the square frame
causes the frame to sway and form the dashed rhombus.
Determine the average normal strain developed in wire
AE. Assume the three rods are rigid.
200 mm 200 mm P D E C
3
400 mm
A B
Geometry: Referring to Fig. a, the stretched length of LAE¿ of wire AE can be
determined using the cosine law.
LAE¿ = 24002 + 2002 - 2(400)(200) cos 93° = 456.48 mm
The unstretched length of wire AE is
LAE = 24002 + 2002 = 447.21 mm
Average Normal Strain:
(Pavg)AE =
LAE ¿ - LAE
LAE
456.48 - 447.21
= 447.21
= 0.0207 mm>mm
Ans.
Ans:
(Pavg)AE = 0.0207 mm>mm
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*2–16. The triangular plate ABC is deformed into the y
shape shown by the dashed lines. If at A, eAB = 0.0075, PAC = 0.01 and gxy = 0.005 rad, determine the average
normal strain along edge BC. C
300 mm gxy
A B x
400 mm
Average Normal Strain: The stretched length of sides AB and AC are
LAC¿ = (1 + ey)LAC = (1 + 0.01)(300) = 303 mm
LAB¿ = (1 + ex)LAB = (1 + 0.0075)(400) = 403 mm
Also,
p
180°
u = 2
- 0.005 = 1.5658 rad a p rad
b = 89.7135°
The unstretched length of edge BC is
LBC = 23002 + 4002 = 500 mm
and the stretched length of this edge is
LB¿C¿ = 23032 + 4032 - 2(303)(403) cos 89.7135°
= 502.9880 mm
We obtain,
PBC =
LB¿C¿ - LBC
LBC
502.9880 - 500
= 500
= 5.98(10
- 3) mm>mm
Ans.
120
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2–17. The plate is deformed uniformly into the shape y
shown by the dashed lines. If at A, gxy = 0.0075 rad., while y¿
PAB = PAF = 0, determine the average shear strain at point G with respect to the x¿ and y¿ axes.
F E
x¿
C600 mm D
gxy
300 mm
180°
Geometry: Here, gxy = 0.0075 rad a p rad
b = 0.4297°. Thus,
A G B x
600 mm 300 mm
c = 90° - 0.4297° = 89.5703° b = 90° + 0.4297° = 90.4297°
Subsequently, applying the cosine law to triangles AGF¿ and GBC¿, Fig. a,
LGF¿ = 26002 + 3002 - 2(600)(300) cos 89.5703° = 668.8049 mm
LGC¿ = 26002 + 3002 - 2(600)(300) cos 90.4297° = 672.8298 mm
Then, applying the sine law to the same triangles,
sin f
600 =
sin 89.5703° ;
668.8049
f = 63.7791°
sin a
300 =
sin 90.4297° ;
672.8298
a = 26.4787°
Thus,
u = 180° - f - a = 180° - 63.7791° - 26.4787°
p rad = 89.7422° a
180° b = 1.5663 rad
Shear Strain:
(gG)x¿y¿ =
p
2 - u =
p
2 - 1.5663 = 4.50(10
- 3) rad
Ans.
Ans:
(gG)x¿y¿ = 4.50(10 - 3) rad
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2–18. The piece of plastic is originally rectangular.
Determine the shear strain gxy at corners A and B if the
plastic distorts as shown by the dashed lines.
2 mm
y
2 mm
C
5 mm
B
4 mm
300 mm
D A
400 mm
2 mm x
3 mm
Geometry: For small angles,
2 a = c =
302 = 0.00662252 rad
2 b = u =
403 = 0.00496278 rad
Shear Strain:
(gB)xy = a + b
= 0.0116 rad = 11.6 A 10 - 3 B rad
(gA)xy = u + c
= 0.0116 rad = 11.6 A 10 - 3 B rad
Ans. Ans.
Ans:
(gB)xy = 11.6(10 - 3) rad,
(gA)xy = 11.6(10 - 3) rad
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2–19. The piece of plastic is originally rectangular.
Determine the shear strain gxy at corners D and C if the
plastic distorts as shown by the dashed lines.
2 mm
y
2 mm
C
5 mm
B
4 mm
300 mm
D A
400 mm
2 mm x
3 mm
Geometry: For small angles,
2 a = c =
403 = 0.00496278 rad
2 b = u =
302 = 0.00662252 rad
Shear Strain:
(gC)xy = a + b
= 0.0116 rad = 11.6 A 10 - 3 B rad
(gD)xy = u + c
= 0.0116 rad = 11.6 A 10 - 3 B rad
Ans. Ans.
Ans:
(gC)xy = 11.6(10 - 3) rad,
(gD)xy = 11.6(10 - 3) rad
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*2–20. The piece of plastic is originally rectangular.
Determine the average normal strain that occurs along the
diagonals AC and DB.
2 mm
y
2 mm
C
5 mm
B
4 mm
300 mm
D A
400 mm
2 mm x
3 mm
Geometry:
AC = DB = 24002 + 3002 = 500 mm
DB¿ = 24052 + 3042 = 506.4 mm
A¿C¿ = 24012 + 3002 = 500.8 mm
Average Normal Strain:
PAC =
A¿C¿ -AC AC
=
500.8 - 500
500
= 0.00160 mm>mm = 1.60 A 10 - 3 B mm>mm Ans.
PDB =
DB ¿ -DB DB
=
506.4 - 500
500
= 0.0128 mm>mm = 12.8 A 10 - 3 B mm>mm Ans.
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2–21. The rectangular plate is deformed into the shape of a
parallelogram shown by the dashed lines. Determine the
average shear strain gxy at corners A and B.
y
5 mm
D C
300 mm
A B 400 mm
5 mm x
Geometry: Referring to Fig. a and using small angle analysis,
5 u =
300 = 0.01667 rad
5 f =
400 = 0.0125 rad
Shear Strain: Referring to Fig. a,
(gA)xy = u + f = 0.01667 + 0.0125 = 0.0292 rad
(gB)xy = u + f = 0.01667 + 0.0125 = 0.0292 rad
Ans.
Ans.
Ans:
(gA)xy = 0.0292 rad, (gB)xy = 0.0292 rad
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2–22. The triangular plate is fixed at its base, and its apex A is
given a horizontal displacement of 5 mm. Determine the shear
strain, gxy, at A.
y
45
800 mm
45
x¿ A 45
A¿ 5 mm
800 mm
x
L = 28002 + 52 - 2(800)(5) cos 135° = 803.54 mm
sin 135°
803.54 =
p
sin u ;
800
p
u = 44.75° = 0.7810 rad
gxy = 2
- 2u = 2
- 2(0.7810)
= 0.00880 rad
Ans.
Ans:
gxy = 0.00880 rad
126
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2–23. The triangular plate is fixed at its base, and its apex A
is given a horizontal displacement of 5 mm. Determine the
average normal strain Px along the x axis.
y
45
800 mm
45
x¿ A 45
A¿ 5 mm
800 mm
x
L = 28002 + 52 - 2(800)(5) cos 135° = 803.54 mm
Px = 803.54 - 800
800 = 0.00443 mm>mm
Ans.
Ans:
Px = 0.00443 mm>mm
127
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*2–24. The triangular plate is fixed at its base, and its apex A
is given a horizontal displacement of 5 mm. Determine the
average normal strain Px¿ along the x¿ axis.
y
45
800 mm
45
x¿ A 45
A¿ 5 mm
800 mm
x
L = 800 cos 45° = 565.69 mm
5 Px¿ =
565.69 = 0.00884 mm>mm
Ans.
128
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dy
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y
2–25. The square rubber block is subjected to a shear strain of gxy = 40(10 - 6)x + 20(10 - 6)y, where x and y are in mm. This deformation is in the shape shown by the dashed D C lines, where all the lines parallel to the y axis remain vertical after the deformation. Determine the normal strain along
edge BC.
Shear Strain: Along edge DC, y = 400 mm. Thus, (gxy)DC = 40(10 - 6)x + 0.008.
dy
400 mm
Here, dx
= tan (gxy)DC = tan 340(10 - 6)x + 0.0084. Then,
dy =
L0 L0
tan [40(10 - 6)x + 0.008]dx A B
x
1 dc = -
40(10 - 6)
= 4.2003 mm
e ln cos c 40(10 - 6)x + 0.008 d f `
300 mm
0
300 mm
- 6 Along edge AB, y = 0. Thus, (gxy)AB = 40(10
tan [40(10 - 6)x]. Then,
)x. Here, dx
= tan (gxy)AB =
dB
dy = L0
300 mm
tan [40(10 - 6)x]dx L0
1
300 mm
dB = - 40(10 - 6)
= 1.8000 mm
e ln cos c 40(10 - 6)x d f ` 0
Average Normal Strain: The stretched length of edge BC is
LB¿C¿ = 400 + 4.2003 - 1.8000 = 402.4003 mm
We obtain,
(Pavg)BC =
LB¿C¿ - LBC
LBC
402.4003 - 400
= 400
= 6.00(10
- 3) mm>mm
Ans.
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Ans:
(Pavg)BC = 6.00(10 - 3) mm>mm
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2– 26.
Ans:
1Pavg 2CA =
- 5.59110-32 mm > mm
130
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2–27. The square plate ABCD is deformed into the shape
shown by the dashed lines. If DC has a normal strain
Px = 0.004, DA has a normal strain Py = 0.005 and at D,
y
y¿ x¿
600 mm
gxy = 0.02 rad, determine the shear strain at point E with respect to the x¿ and y¿ axes.
A¿ B¿ A B
600 mm E
x
D C C ¿
Average Normal Strain: The stretched length of sides DC and BC are
LDC¿ = (1 + Px)LDC = (1 + 0.004)(600) = 602.4 mm
LB¿C¿ = (1 + Py)LBC = (1 + 0.005)(600) = 603 mm
Also,
p
180°
a = 2
- 0.02 = 1.5508 rad a p rad
b = 88.854°
p 180° f =
2 + 0.02 = 1.5908 rad a
p rad b = 91.146°
Thus, the length of C¿A¿ and DB¿ can be determined using the cosine law with
reference to Fig. a.
LC¿A¿ = 2602.42 + 6032 - 2(602.4)(603) cos 88.854° = 843.7807 mm
LDB¿ = 2602.42 + 6032 - 2(602.4)(603) cos 91.146° = 860.8273 mm
Thus,
LE¿A¿ =
LC¿A¿
2 = 421.8903 mm
LE¿B¿ =
LDB¿
2 = 430.4137 mm
Using this result and applying the cosine law to the triangle A¿E¿B¿, Fig. a,
602.42 = 421.89032 + 430.41372 - 2(421.8903)(430.4137) cos u
p rad u = 89.9429° a
180° b = 1.5698 rad
Shear Strain:
(gE)x¿y¿ =
p
2 - u =
p
2 - 1.5698 = 0.996(10
- 3) rad
Ans.
Ans:
(gE)x¿y¿ = 0.996(10 - 3) rad
131
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0
2
L
=
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*2–28. The wire is subjected to a normal strain that is 2
P (x/L)e–(x/L)2
defined by P = (x>L)e - (x>L) . If the wire has an initial x
length L, determine the increase in its length. x
L
1 ¢L =
L L xe
- (x>L)2
dx
= - L c
e - (x>L) L
2 d
0
L
2 31 - (1>e)4
L =
2e 3e - 14
Ans.
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132
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2–29.
Ans:
1Pavg 2AC = 0.0168 mm >mm,
1gA 2xy = 0.0116 rad
133
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2–30. The rectangular plate is deformed into the shape
shown by the dashed lines. Determine the average normal
strain along diagonal BD, and the average shear strain at
corner B.
y
2 mm 2 mm
400 mm
6 mm
6 mm
D C
300 mm
Geometry: The unstretched length of diagonal BD is
LBD = 23002 + 4002 = 500 mm
A B
400 mm
2 mm
x
3 mm
Referring to Fig. a, the stretched length of diagonal BD is
LB¿D¿ = 2(300 + 2 - 2)2 + (400 + 3 - 2)2 = 500.8004 mm
Referring to Fig. a and using small angle analysis,
2 f =
403 = 0.004963 rad
3 a =
300 + 6 - 2 = 0.009868 rad
Average Normal Strain: Applying Eq. 2,
(Pavg)BD =
LB¿D¿ - LBD
LBD
500.8004 - 500
= 500
= 1.60(10
- 3) mm>mm
Ans.
Shear Strain: Referring to Fig. a,
(gB)xy = f + a = 0.004963 + 0.009868 = 0.0148 rad
Ans.
Ans:
(Pavg)BD = 1.60(10 - 3) mm>mm,
(gB)xy = 0.0148 rad
134
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L
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2–31. The nonuniform loading causes a normal strain in
the shaft that can be expressed as Px = kx2, where k is a
constant. Determine the displacement of the end B. Also, A B
what is the average normal strain in the rod?
x
d(¢x) 2
dx = Px = kx
(¢x)B =
L
kx2
L0
kL3
= 3
kL3
Ans.
(Px)avg = (¢x)B
L =
3 kL2
L =
3
Ans.
Ans:
(¢x)B =
kL3
, (Px)avg = 3
kL2
3
135
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b 3
3
b
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*2–32 The rubber block is fixed along edge AB, and edge
CD is moved so that the vertical displacement of any point
in the block is given by v(x) = (v0>b3)x3. Determine the
shear strain gxy at points (b>2, a>2) and (b, a).
y
v (x)
v0 A D
a
x
B C
Shear Strain: From Fig. a, b
dv
dx = tan gxy
3v0 2
b3 x
= tan gxy
3v0
gxy = tan - 1 a x2
b
Thus, at point (b>2, a>2),
3v0 b 2
gxy = tan - 1 c b
a 2
b d
= tan - 1 c 3
a v0
b d Ans.
4 b
and at point (b, a),
gxy = tan - 1 c
3v0
b3
(b2) d
v0
= tan - 1 c 3 a b d
Ans.
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LA B A 2
1
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2–33. The fiber AB has a length L and orientation u. If its
ends A and B undergo very small displacements uA and vB,
respectively, determine the normal strain in the fiber when
it is in position A¿B¿.
y
B¿
vB
B
L u
x A uA A¿
Geometry:
¿ ¿ = 2(L cos u - u ) + (L sin u + vB)2
2 2
= 2L2 + uA + vB + 2L(vB sin u - uA cos u)
Average Normal Strain:
LA¿B¿ - L PAB =
L
2 2
= A
1 + uA + v B
L2 +
2(vB sin u - uA cos u) - 1
L
Neglecting higher terms u2 and v2 A B
PAB = B 1 +
2(vB sin u - uA cos u) 2
L R - 1
Using the binomial theorem:
1 PAB = 1 +
2 ¢
2vB sin u
L -
2uA cos u
L ≤ + . . . - 1
vB sin u =
L -
uA cos u
L
Ans.
Ans.
PAB =
vB sin u
L -
uA cos u
L
137
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