cranfield university mahadi abd murad an integrated structural ...

3.7.3 Internal Pressure
For a pipe under internal pressure, the hoop stress, h , and the axial stress, a
are the two major stress components that are always considered. In this FE model, the
maximum hoop and axial stresses were taken at the notch root and nominal hoop and
axial stresses were taken at the point away from the defect (refer to Figure 3.5) which
gives the stress concentration factor, K t , by
h
Kt
h
max
h
nom
a
max
a
(Equation 3.5) and Kt
a
82
nom
(Equation 3.6)
The problem of SCF for circumferentially notched pipe has been examined by several
authors (Carpinteri et al., 2004), yet a study on an arc-shaped notch in a pipe has not
been carried out so far. The outer radius of the external notch is difficult to obtain
because of the nature of its geometry and this makes comparison against other types of
notches (e.g. those given by Pilkey (1997)) impractical. Prior to making experimental
measurements, confidence can be attributed to the current FEA by considering the
results of the parametric variations and using engineering experience and judgment.
Convergence tests were carried out on all notch geometries, as represented in
Table 3.4 and Figures 3.16 and 3.17. These show that all the convergence results of
stress concentration factors are based on both hoop and axial stresses as the number of
elements increases and the size of the elements becomes smaller.