Page 541 - Shigley's Mechanical Engineering Design

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Welding, Bonding, and the Design of Permanent Joints 515
9–52 Brackets, such as the one shown, are used in mooring small watercraft. Failure of such brackets is
usually caused by bearing pressure of the mooring clip against the side of the hole. Our purpose
here is to get an idea of the static and dynamic margins of safety involved. We use a bracket 1/4 in
thick made of hot-rolled 1018 steel. We then assume wave action on the boat will create force F
no greater than 1200 lbf.
(a) Identify the moment M that produces a shear stress on the throat resisting bending action with
a “tension” at A and “compression” at C.
(b) Find the force component F y that produces a shear stress at the throat resisting a “tension”
throughout the weld.
(c) Find the force component F x that produces an in-line shear throughout the weld.
(d) Find A, I u , and I using Table 9–2, in part.
(e) Find the shear stress τ 1 at A due to F y and M, the shear stress τ 2 due to F x , and combine to
find τ.
(f) Find the factor of safety guarding against shear yielding in the weldment.
(g) Find the factor of safety guarding against a static failure in the parent metal at the weld.
(h) Find the factor of safety guarding against a fatigue failure in the weld metal using a Gerber
failure criterion.

y

1 -in R
2
1 -in dia.
2 30°
1 in x
4
1 in
3
2 in 1 in
4 2

(a)

y
Problem 9–52 F
Small watercraft mooring bracket.
x
30° 1 in
B G
A
M C
F x
F
0.366 in y
F
G
0.732 in
1 in
1 in x
4
A B G O C
1 z
1 in
4
1
d = 2 in
2
(b)