Sk. Koh et Ri. Stephens, IMPROVED FATIGUE LIFE OF AN AUTOFRETTAGED THICK-WALLED PRESSURE-VESSEL WITH AN EXTERNAL GROOVE, International journal of pressure vessels and piping, 58(2), 1994, pp. 131-145
An autofrettaged thick-walled pressure vessel with an external groove
suffers a decreased fatigue life due to cracking at the exterior. In o
rder to improve the fatigue life of an autofrettaged thick-walled pres
sure vessel containing an external groove subjected to pulsating inter
nal pressure, a shape change and a shot peening were done at the exter
nal groove, which is the most vulnerable location to fatigue cracking.
The groove shape was changed by using an optimization technique in or
der to minimize the stress concentration at the groove root. Stress co
ncentration calculation during the optimization stage was carried out
by the finite element methods. Autofrettage residual stresses were sim
ulated by the thermal stresses from the thermal loading analogy. Shot
peening was performed on the changed groove region in order to induce
the surface compressive residual stresses. Fatigue tests that simulate
an autofrettaged thick-walled pressure vessel under pulsating interna
l pressure loading conditions were performed using C-shaped specimens
taken from the autofrettaged thick-walled pressure vessel. Fatigue lif
e improvement of the pressure vessel was achieved by design change of
the groove shape to relieve the high stress concentration, and also by
surface enhancement at the groove root using shot peening. Simulation
fatigue tests resulted in improved fatigue life for the changed and s
hot peened groove by a factor of 3.5 to 13, compared to the convention
al groove.