6. ELONGATION OF UNIFORMLY TAPERING CIRCULAR ROD
❖ Let us consider the uniformly tapering circular rod
❖ length of the uniformly tapering circular rod is 𝐿
❖ larger diameter of the rod is 𝐷1 at one end
❖ circular rod will be uniformly tapered and hence other end diameter of the circular
rod will be smaller
L
0
𝑥 𝑑𝑥
P
P
𝐷1 𝐷2
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
7. ❖ let us assume that diameter of other end is 𝐷2.
❖ Uniformly tapering circular rod is subjected with an axial tensile load 𝑃
❖ Let us consider one infinitesimal smaller element of length 𝑑𝑥 and its diameter will
be at a distance 𝑥 from its larger diameter end.
L
0
𝑥 𝑑𝑥
P
P
𝐷1 𝐷2
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
8. Let us consider that diameter of infinitesimal smaller element is 𝐷𝑥
Diameter
൯
𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑟𝑜𝑑 𝑎𝑡 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑥 (𝐷𝑥
= 𝐷1 −
𝐷1 − 𝐷2
𝐿
𝑥
𝐷𝑥 = 𝐷1 − 𝑘𝑥 𝑊ℎ𝑒𝑟𝑒, 𝑘 =
𝐷1 − 𝐷2
𝐿
Area of cross section
Area of cross section of circular bar at a distance x from its larger diameter end is 𝐴𝑥
൯
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 (𝐴𝑥
=
𝜋
4
× 𝐷𝑥
2
𝐴𝑥 =
𝜋
4
× 𝐷1 − 𝑘𝑥 2
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
9. Stress
Let us consider that stress induced in circular bar at a distance x from its larger
diameter end is 𝜎𝑥
൯
𝑆𝑡𝑟𝑒𝑠𝑠 (𝜎𝑥 =
𝐿𝑜𝑎𝑑
𝐴𝑟𝑒𝑎
𝜎𝑥 =
𝑃
𝐴𝑥
𝜎𝑥 =
𝑃
𝜋
4
× 𝐷1 − 𝑘𝑥 2
𝜎𝑥 =
4𝑃
𝜋 𝐷1 − 𝑘𝑥 2
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
10. Strain
Let us consider that strain induced in circular bar at a distance 𝑥 from its larger
diameter end is 𝑒𝑥
൯
𝑆𝑡𝑟𝑎𝑖𝑛 (𝑒𝑥 =
𝑠𝑡𝑟𝑒𝑠𝑠
𝑌𝑜𝑢𝑛𝑔′𝑠 𝑀𝑜𝑑𝑢𝑙𝑢𝑠
𝑒𝑥 =
𝜎𝑥
𝐸
𝑒𝑥 =
4𝑃
𝜋 𝐷1 − 𝑘𝑥 2
𝐸
𝑒𝑥 =
4𝑃
𝜋𝐸 𝐷1 − 𝑘𝑥 2
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
11. Change in length of infinitesimal smaller element
Change in length of infinitesimal smaller element will be determined by recalling
the concept of strain.
𝛿𝑙𝑥 = 𝑒𝑥 𝑑𝑥
𝛿𝑙𝑥 =
4𝑃
𝜋𝐸 𝐷1 − 𝑘𝑥 2
𝑑𝑥
Total change in length
The total change in length of the uniformly tapering circular rod is obtained by
integrating the above equation from 0 to L.
𝛿𝑙 = න
0
𝐿
4𝑃
𝜋𝐸 𝐷1 − 𝑘𝑥 2
𝑑𝑥
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
14. 𝛿𝑙 =
4𝑃𝐿
π E 𝐷1 − 𝐷2
1
𝐷2
−
1
𝐷1
𝛿𝑙 =
4𝑃𝐿
π E 𝐷1 − 𝐷2
𝐷1 − 𝐷2
𝐷1 𝐷2
𝜹𝒍 =
𝟒𝑷𝑳
𝛑 𝐄 𝑫𝟏 𝑫𝟐
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
15. Problem 01
Find the modulus of elasticity of the rod, which tapers uniformly from 30mm to 15mm
diameter in a length of 350mm. The rod is subjected to an axial load of 5.5KN and
extension of the rod is 0.025mm.
𝑮𝒊𝒗𝒆𝒏 𝒅𝒂𝒕𝒂:
𝑻𝒐 𝒇𝒊𝒏𝒅:
𝐷1 𝐷2
L
𝑀𝑜𝑑𝑢𝑙𝑢𝑠 𝑜𝑓 𝑒𝑙𝑎𝑠𝑡𝑖𝑐𝑖𝑡𝑦 𝐸 =?
𝐷1 = 30 𝑚𝑚 𝐷2 = 15 𝑚𝑚 𝐿 = 350 𝑚𝑚
𝑃 = 5.5 𝑘𝑁 = 5.5 × 103 𝑁 𝛿𝑙 = 0.025 𝑚𝑚
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
18. ELONGATION OF UNIFORMLY TAPERING RECTANGULAR BAR
❖ A rectangular bar is basically taper uniformly from one end to another end
throughout the length and therefore its one end will be of larger width and other
end will be of smaller width.
❖ However, thickness of the rectangular rod will be constant throughout the length of
bar.
𝑎
𝑏
L
𝑥
𝑑𝑥
0
P
P
𝑡
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
19. ❖ Let us consider the uniformly tapering
rectangular bar.
❖ length of the uniformly tapering
rectangular bar is 𝐿.
❖ Width of larger end of the bar is ‘𝑎’
❖ Rectangular bar will be uniformly tapered
and hence width of the rectangular bar at
the other end will be smaller.
𝑎
𝑏
L
𝑥
𝑑𝑥
0
P
P
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
20. ❖ let us assume that width of another
end is ‘ 𝑏 ’. Let us assume that
thickness of the rectangular bar is ′𝑡′.
❖ Let us consider that uniformly
tapering rectangular bar is subjected
with an axial tensile load 𝑃.
❖ Let us consider one infinitesimal
smaller element of length 𝑑𝑥 and its
width will be at a distance 𝑥 from its
larger end.
𝑎
𝑏
L
𝑥
𝑑𝑥
0
P
P
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
21. Width
Let us consider that width of infinitesimal smaller element is 𝐵𝑥
൯
𝑊𝑖𝑑𝑡ℎ 𝑜𝑓 𝑏𝑎𝑟 𝑎𝑡 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑥 (𝐵𝑥
= 𝑎 −
𝑎 − 𝑏
𝐿
𝑥
𝐵𝑥 = 𝑎 − 𝑘𝑥 𝑊ℎ𝑒𝑟𝑒, 𝑘 =
𝑎 − 𝑏
𝐿
Area of cross section
Area of cross section of bar at a distance 𝑥 from its larger end is 𝐴𝑥
൯
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 (𝐴𝑥
= 𝑊𝑖𝑑𝑡ℎ × 𝑇ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠
𝐴𝑥 = 𝐵𝑥 × 𝑡
𝐴𝑥 = 𝑎 − 𝑘𝑥 × 𝑡
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
22. Stress
Let us consider that stress induced in bar at a distance 𝑥 from its larger end is 𝜎𝑥
൯
𝑆𝑡𝑟𝑒𝑠𝑠 (𝜎𝑥 =
𝐿𝑜𝑎𝑑
𝐴𝑟𝑒𝑎
=
𝑃
𝐴𝑥
𝜎𝑥 =
𝑃
𝑎 − 𝑘𝑥 × 𝑡
Strain
Let us consider that strain induced in bar at a distance x from its larger diameter
end is 𝑒𝑥
൯
𝑆𝑡𝑟𝑎𝑖𝑛 (𝑒𝑥 =
𝑠𝑡𝑟𝑒𝑠𝑠
𝑌𝑜𝑢𝑛𝑔′𝑠 𝑀𝑜𝑑𝑢𝑙𝑢𝑠
=
𝜎𝑥
𝐸
𝑒𝑥 =
𝑃
𝑎 − 𝑘𝑥 × 𝑡
𝐸
𝑒𝑥 =
𝑃
𝐸𝑡 𝑎 − 𝑘𝑥
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
23. Change in length of infinitesimal smaller element
Change in length of infinitesimal smaller element will be determined by recalling
the concept of strain.
𝛿𝑙𝑥 = 𝑒𝑥 𝑑𝑥
𝛿𝑙𝑥 =
𝑃
𝐸𝑡 𝑎 − 𝑘𝑥
𝑑𝑥
Total change in length
The total change in length of the uniformly tapering rectangular bar is obtained by
integrating the above equation from 0 to L.
𝛿𝑙 = න
0
𝐿
𝑃
𝐸𝑡 𝑎 − 𝑘𝑥
𝑑𝑥
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
24. 𝛿𝑙 =
𝑃
Et
න
0
𝐿
1
𝑎 − 𝑘𝑥
𝑑𝑥
𝛿𝑙 =
𝑃
Et
𝑙𝑛 𝑎 − 𝑘𝑥 0
𝐿
× −
1
𝑘
𝛿𝑙 =
−𝑃
kEt
𝑙𝑛 𝑎 − 𝑘𝐿 − 𝑙 𝑛 𝑎
𝛿𝑙 =
−𝑃
kEt
𝑙𝑛 𝑎 − 𝑘𝐿 − 𝑙 𝑛(𝑎 − 0)
𝛿𝑙 =
𝑃
kEt
𝑙𝑛 𝑎 − 𝑙𝑛 𝑎 − 𝑘𝐿
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
25. Substituting 𝑘 =
𝑎−𝑏
𝐿
in the above equation
𝑇𝑜𝑡𝑎𝑙 𝑒𝑥𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝛿𝑙 =
𝑃
𝑎 − 𝑏
𝐿
Et
𝑙𝑛 𝑎 − 𝑙𝑛 𝑎 −
𝑎 − 𝑏
𝐿
𝐿
𝛿𝑙 =
𝑃𝐿
𝑎 − 𝑏 Et
൯
𝑙𝑛 𝑎 − 𝑙𝑛 𝑎 − (𝑎 − 𝑏
𝛿𝑙 =
𝑃𝐿
𝑎 − 𝑏 Et
𝑙𝑛 𝑎 − 𝑙𝑛 𝑎 − 𝑎 + 𝑏
𝛿𝑙 =
𝑃𝐿
𝑎 − 𝑏 Et
𝑙𝑛 𝑎 − 𝑙𝑛 𝑏
𝜹𝒍 =
𝑷𝑳
𝒂 − 𝒃 𝐄𝐭
𝒍𝒏 (𝒂/𝒃)
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
26. Problem 01
A rectangular steel bar of length 400mm and thickness 10mm having 𝐸 = 2 × 105 𝑁/
𝑚𝑚2. The extension due to load is 0. 21mm. The bar tapers uniformly in width from
100mm to 50mm. Determine the axial load on the bar.
𝑮𝒊𝒗𝒆𝒏 𝒅𝒂𝒕𝒂:
𝑻𝒐 𝒇𝒊𝒏𝒅:
𝑎
𝑏
L
𝐿 = 400 𝑚𝑚 𝑡 = 10 𝑚𝑚
𝐸 = 2 × 105 Τ
𝑁 𝑚 𝑚2
𝛿𝑙 = 0.21 𝑚𝑚
𝑎 = 100 𝑚𝑚
𝑏 = 50 𝑚𝑚
𝐴𝑥𝑖𝑎𝑙 𝑙𝑜𝑎𝑑 𝑜𝑛 𝑡ℎ𝑒 𝑏𝑎𝑟 𝑃 =?
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY