With attention concentrated on the pole of bulge profile, tensile instability which results in the fracture of forward acting rupture discs has been studied. A formula was developed to calculate the theoretical limit pressure of rupture discs, and the theoretical predictions were compared with the measured data. It is found that the strain-hardening exponent of sheet metals has no influence on the limit pressure, whereas the limit pressure is in direct proportion to the strength coefficient of sheet metals. It is important to realize that the strength coefficient of sheet metals can be acquired easily from the limit pressure. This has potential value for the tests of mechanical properties of sheet metals.
