Page 367 - Marine Structural Design
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Chapter I7 Fatigue Capaciq 343
17.4 Examples
17.4.1 Example 17.1: Fatigue Damage Calculation
Problem:
Two plates A and B are doubled sided butt welded, another plate C is welded to plate A by
fillet welds, as shown in Fig. 17.6. The thickness of the plate is 20 mm. The plate is subjected
to cyclic loading with a constant stress range of S=200 MPa and a total number of
cyclesn, = lo5. It is assumed that the maximum misalignment of the weld is 4mm. What is
the fatigue damage at these welds?
Figure 17.6 Fatigue of Welded Plates
Solution:
Misalignment introduces the bending moment in the plates. The corresponding bending stress
range at the butt weld is:
e
S.t*-
s AM 2 - S.3e
b- w t2 t
-
6
The maximum stress range at butt weld is:
SI,,, = (1 + :) s = SCF,,,, . s = 120M.a
S-N curve C should be used for butt weld with m=3.5, log; = 13.63. This gives the following
damage ratio:
The local stress range at the fillet weld is:
[ ( 31
SI,,, =0.5 S+S 1+- =160MPa
