Fatigue tests on a Cu safety rupture disc were carried out under constant and two-step variable pressure amplitudes. Fatigue strength and change of burst pressure caused by repeated pressure were studied. In addition, deformation behaviour, tensile properties and crack growth in fatigue process were observed.
Under the application of constant pressure amplitude
PC, burst pressure
PCS decreased with increasing cycle ratio
R. Variation of
PCS is expressed by a following empirical equation
(P
CS-P
C)/(P
S-P
C)=(1-R)
mwhere
PS is rated burst pressure and
m is a material constant which is dependent on
PC. The decrease of
PCS could be attributed to reduction of tensile strength and growth of fatigue cracks. Allowable number of cycles
NL (critical number of cycles in which
PCS falls below 95% of the rated burst pressure
PS) may be estimated by use of above equation.
Experimental cycle ratio sums with respect to
NL as well as fatigue life
Nf were greater than unity for variable amplitude tests in which the lower cyclic pressure was followed by higher pressure. These values tend to become larger with increasing the difference between primary and secondary pressure level. Estimation of
Nf and
NL based on above equation results in conservative prediction.
View full abstract