Page 89 - Analysis and Design of Machine Elements

Figure 3.6 Locking devices. Detachable Joints and Fastening Methods 67

(a) (b)
convenient and effective method to re-establish a proper preload to prevent excessive
loosening.
Several methods are available to restrain a nut from becoming loose on a bolt. The
first is by increasing supplementary friction, such as using jam nuts or double nuts in
Figure 3.6a, or using a split helical lock washer in Figure 3.3a. The second is by using
special devices, as illustrated in Figure 3.6b, by inserting a split cotter pin through the
cross-hole drilled in bolt passing through the slotted nut and in Figure 10.8b by locknut
and lock washer. The third is to permanently damage screw threads by brazing, solder-
ing, punching or gluing.

3.4 Force Analysis of Multiply Bolted Joints
In common practice, a group of bolts are placed in a specified pattern to form a multiply
bolted joint to carry various external loads, as illustrated in Figure 3.7. The external
loads are shared among these bolts. Since the materials, dimensions, preloads and so
on are usually identical for each bolt in a multiply bolted joint, it is therefore important
to identify the bolt that carries the largest load and ensure its safety. This section will
analyse force distribution among bolts within a group under typical loading conditions.

3.4.1 Multiply Bolted Joints Subjected to Symmetric Transverse Loads

If a transverse load is applied symmetrically to a multiply bolted joint, as illustrated in
Figure 3.8a, it is usually acceptable to assume that the loads are uniformly distributed

Figure 3.7 Loads carried by multiply bolted Z
joints.

Fz
T
O Fx Mx
X

Fy
My
Y