Dynamic Analysis Of Squib Valve For Nuclear Power Considering Strain Rate Effect

Squib valve is an important equipment in nuclear structure. It will ensure the security of the nuclear power facilities when the emergency occurs. The opening of the squib valve is a highly nonlinear dynamic impact and fracture process in a very short time. During this process, some elements in the shear-cup will be subjected to the high strain rates. And the material of shear-cap is Inconel 690, whose mechanical behavior is quite dependent on strain rate. It has not only different material constitutive relationship at different strain rate, but also appears obvious brittle failure at high strain rate. This paper considers strain rate effect and analyzes the dynamic process of opening squib valve.The process of the shear-cap cut off by the piston is the key step for the opening squib valve. It needs piston owns an enough impact velocity. In this paper, the process of the piston cutting shear-cap is analyzed by explicit dynamic function of LS-DYNA and the critical velocity of piston is obtained by comparing the damage of the shear-cap under different initial velocities of the piston.In order to simulate the failure process of shear-cap under the high strain rate, on the basis of several material constitutive models of high strain rate, the constitutive curves of Inconel 690 alloy are fitted according to Zerilli-Armstrong model and the stress-strain relationship of this material under the higher strain rate is given. The numerical simulation with fitted material curves is employed and the numerical results are compared with those with the original material curves. By studying the strain rate distribution in the cross section of the shear-cap, it can be concluded that the fitted curves can obtain a more accurate results than the original material curves under the high dynamic impact velocity.By studying of the opening process of squib valve, it's found that the squib valve can be successfully opened under the given amount of powder. The tension bolt can be broken in a very short time and the shear-cap can be smoothly cut off. By extracting stress data in high stress zone in the pipe, it is found that there is no plastic deformation in the pipe. However, due to the high strain rate at the fracture surface of the shear-cap, the phenomenon of the coexistence of the ductile fracture and brittle fracture is founded in the experiment. At the same time, it is found that the brittle fracture is more serious in the high strain rate zone by analyzing strain rate distribution in the shear-cap, which proves the high strain rate causes the phenomenon of the ductile-to-brittle transition.The buffer device is needed to absorb the residual velocity of piston after it cut off the shear-cap. Finally, the effect of wall thickness, number and height of different buffer tubes on the buffer results is discussed, which provides the guidance for the engineering design. At the same time, numerical results are compared with the experimental results, and the good agreement is found, which shows the accuracy of numerical results in this paper.