Background: Squib valve is a key valve in the new generation nuclear power plant

which has not been localized and the research on the failure process of shear-cap is necessary.Purpose: This research aims to study the influence of material on the failure process of shear-cap in squib valve.Methods: The finite element method is used to simulate the shear-caps’ sheared process of different materials—Inconel 690

304 stainless steel and 321 stainless steel.Results: As a result

the failure time and the final speed of piston are shown at each impact speed.Conclusions: The shear-cap of Inconel 690 is hardest to shear.A method to get the critical impact speed in the open process of valve is proposed.It can be found that the residual kinetic energy of the piston has the common feature and is 25% of the initial kinetic energy.Piston’s final speed has a linear relationship to its initial speed for all three materials.