Page 94 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
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The shearing strength at the bolt shank cross section is calculated by
F s
= ≤ [ ] (3.11)
1 2
d
4 0
3.5.3 Strength Analysis for Tension Bolts
Tension bolts, usually used in ordinary bolted joints, are assembled with or without
pretension. Tension bolts with pretension are capable of carrying not only static and
dynamic axial loads but also transverse loads; while tension bolts without pretension
carry axial loads only.

3.5.3.1 Tension Bolts Subjected to Axial Loads Only
A tension bolt without tightening is capable of carrying static axial loads only. One of
its limited applications is in a hoisting hook. The strength of bolt is calculated by
F
= ≤ [ ] (3.12)
1 d 2
4 1
3.5.3.2 Preloaded Tension Bolts Subjected to Transverse Loads
The purpose of using bolts is to clamp two or more elements together. The clamping
load stretches the bolt by twisting the nut until the bolt elongates approaching the proof
strength. If the nut does not loosen, this bolt tension remains as the preload. The tensile
stress caused by the initial preload Q on the bolt is
p
Q p
= (3.13)
1 2
d 1
4
The torsional shear stress due to frictional torque in the thread T generated by tight-
1
ening can be obtained from [8]
T 1 Q tan( + ) d 2 2
v
p
= =
1 3 1 3
d 1 d 1
16 16
Selecting the average value of , and d for the commonly used bolts within the
v 2
range of M10–M64, we have [8]
d 2
Q tan( + ) Q
p
v
= 2 = 0.5 p = 0.5
1 3 1 2
d d
16 1 4 1
Since the bolt is subjected to both tensile and shear stresses, the equivalent stress is
calculated by the maximum distortion energy theory as
√
2
2
= + 3 ≈ 1.3
ca
Therefore, the calculated tensile stress due to preloading is
1.3Q p
= (3.14)
ca
1 2
d
4 1