Finite element method-based failure prediction and redesign ofa launch vehicle valve

The fluid feed circuit of liquid propellant-based rocket engine employs several valves for directing and controlling the flow of fuel and oxidiser. The valves undergo several types of tests as part of their qualification process. One such test is the cyclic actuation test wherein it will be subjected to multiple numbers of actuations with or without the presence of actual pressurisation medium. During the course of such a test, cracks were observed in a newly designed valve of ISRO. The cracks were visually seen at an area that had only minor functional implication on the overall structural integrity of the valve. Nevertheless, numerical simulation of the valve using finite element method was performed to learn about the likely cause of these cracks. The analysis indicated that the observed cracks could be due to a combination of high cycle fatigue and low cycle fatigue. Furthermore, analysis predicted that the loading could cause even more severe damage to some of the internal components which if unmitigated, would impair the functionality of the valve and compromise its structural integrity. The results from finite element simulations were confirmed by NDT of the valve which revealed permanent deformations of some of the internal components. In the light of these observations, the valve internals were redesigned so that the stresses and strains are well within their permissible limits. The structural adequacy of the re-designed configuration was established through finite element analysis. A qualification hardware was also fabricated and successfully subjected to the required number of cyclic actuations. This paper presents the studies undertaken to establish the likely cause of the observed cracks in the original configuration of the valve. The failure mitigation by means and redesign, its finite element simulation and subsequent experimental validation are also presented.