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Cryogenic engine of satellite launch vehicle employs separation pyrovalves which are pyrotechnically actuated devices used for opening/closing of the flow of fluids. In the qualification test, pyrovalve withstood the functional test. However, during the post-fire acceptance test, one unit of the separation pyrovalve indicated leakage at 38 bar against specified 170 bar pressure. The leaked actuator diaphragm was investigated for identifying the reason for leakage. Leakage during post-fire acceptance test is attributed to the through-thickness hole formation on the AISI 321 stainless-steel diaphragm. Hole formation in diaphragm is caused by the impingement of molten zirconia from the combustion products of zirconium/potassium perchlorate (ZPP) charge to the diaphragm during firing operation. It was responsible for localized melting of stainless steel. After the formation of through-thickness hole on the diaphragm, the molten mixture got solidified and filled the through hole completely. During the post-fire acceptance test, the molten and solidified mixture got dislodged at 38 bar pneumatic pressure and resulted in leakage. Analysis is validated through thermal modelling and simulation, where observations are found to be matching. Estimation of combustion product required for the formation of through thickness hole of the observed dimension has also been estimated. [ABSTRACT FROM AUTHOR]

Titanium alloy (Ti6Al4V) is extensively used in the fabrication of upper stage propellant tanks for satellite launch vehicles. These tanks are of welded construction and are made from three types of domes and 5 types of rings. This paper investigates the occurrence of X-ray radiography and fluorescent penetrant indications in a specific ring component of the tank assembly after machining to thickness of 1.7 mm. The affected ring, with dimensions OD-φ1400 mm, ID-φ1300 mm, and height 410 mm, exhibited a multitude of surface and embedded indications across eight sectors, spanning approximately 140 mm in height at the mid-section of the ring. To ascertain the root cause of these indications, a comprehensive metallurgical analysis was conducted, involving X-ray radiography, optical/electron microscopy, and mechanical testing. By correlating non-destructive observations with microscopic findings, this study establishes that the occurrence of defects can be attributed to a combination of raw material and deformation processing issues. The results contribute to a better understanding of the factors influencing the quality of Ti6Al4V propellant tank rings and aid in the development of improved manufacturing processes. [ABSTRACT FROM AUTHOR]

Integrated Nano-Satellite Launcher System (INLS-2U) is a non-pyrotechnic satellite dispenser that provides safe and reliable separation of nanosatellites into orbits. After the acceptance testing of this satellite separation system, all fasteners were verified for 80% torque retention. During this verification, one of the 70 Nos. of hexagonal socket head cap fasteners (M4 × 0.7 × 10L) has failed. These fasteners are used for the assembly of side plates to the bottom and top plates of the non-pyrotechnic dispenser. The material for construction of the bottom/top/side plate is AA2014 in T651 condition, and the fasteners are made of 35NCD16 steel material with cadmium plating. Detailed metallurgical analysis was carried out to find the reason for the fastener failure. Based on the detailed fractographic and metallographic analysis, it is concluded that the root cause of fastener failure is attributed to 'hydrogen embrittlement.' [ABSTRACT FROM AUTHOR]

Hydraulic amplifier valve (HAV) spools are made up of AISI 440C stainless steel and are used as flow control devices of actuators. Failure of three numbers of HAV spools observed near the undercut region is investigated in this paper. Microstructural analysis of the failed spools revealed the presence of large amount of primary and secondary carbides in the matrix of tempered martensite. Fractographic analysis of failed HAV spools revealed features typical of overload fracture. Corrosion pits of 300–350 µm depth are observed around the periphery of the fracture surface at a few locations of the failed HAV spools. Failure of the spools is found under the application of mechanical loads, where load-bearing capability of the spools is reduced due to stress concentration near the undercut region owing to the presence of corrosion pits. This was further assisted by large primary carbides present abundantly in this alloy. [ABSTRACT FROM AUTHOR]

Austenitic stainless steels are extensively used for various aerospace applications because of their favorable high-temperature mechanical properties, excellent corrosion resistance, and good fabricability. During helium leak check of purge check valve made up of austenitic stainless steel ICSS 202 (near to AISI 202), leakage was observed. A thorough metallurgical analysis was performed through progressive polishing to reach the leak location. The leakage was primarily attributed to the accumulation of large chunks of oxide inclusions of aluminum, manganese, magnesium, and silicon aligned across the thickness of the component. [ABSTRACT FROM AUTHOR]

The propellant flow control valves, also referred to as latchable series redundant valves (LSRV's) are essentially used in satellite control systems. Main component of these valves are solenoid bobbins, which composed of four parts, three of which are made of AISI 446 ferritic stainless steel and one part is made of AISI 304L austenitic stainless steel. These parts are joined by electron beam (EB) welding after shrink fitting to form an important component for propellant flow control systems. During dye penetrant (DP) testing of these components after annealing heat treatment, discontinuous cracks were noticed in AISI 446 steel at the inner side of the bobbin. Detailed metallographic and fractographic analysis on the failed component showed a discontinuous crack path circumferentially near the HAZ region of AISI 446 steel. The fracture morphology revealed a complete transgranular cleavage fracture which indicated a brittle mode of failure. Further, AISI 446 raw material was also analyzed along with heat treatment cycle followed in the valve component. [ABSTRACT FROM AUTHOR]

EN24 steel in hardened and tempered condition is used as fasteners in aerospace applications. The aerospace component fastened by EN24 M5 shear bolts was subjected to structural qualification tests. During the physical inspection of hardware after re-torqueing, one of the shear bolts was found broken. The failed shear bolt was subjected to detailed failure analysis to know the cause of failure. Another shear bolt of the same batch was tensile tested and analyzed for comparison. This paper presents the failure analysis carried out on failed shear bolt using optical microscopy, scanning electron microscopy and Vickers microhardness test. Fractographic observations of the fracture surface indicate equiaxed dimple features at the center while elongated shear dimple at the edges. The microstructure confirmed the presence of tempered martensitic structure typical of hardened and tempered EN24 material. The failure of the shear bolt is attributed to mainly torsional overload. The presence of corrosion has additionally contributed to reducing the load bearing capacity of fastener. [ABSTRACT FROM AUTHOR]

High strength steel 35NCD16 is used as fasteners in aerospace applications. During ALMA (American Lock nut Manufacturer's Association) test, some of the fasteners failed at the corner of Head-Shank junction. A thorough metallurgical analysis was conducted to analyze the cause of failure. Tensile test and torque test of unfailed fasteners were also carried out. The fracture surface of the failed fasteners revealed fatigue beach marks with brittle features and microcracks. Microcracks were observed at the corner of head-shank junction of the torque tested, tensile tested and unused fasteners. Microstructure consisted of tempered martensite and hardness of the fasteners indicated hardened and tempered condition. Fracture analysis indicated failure is due to 'fatigue', which was initiated through the microcracks present at the head shank region acting as notch/stress raiser. [ABSTRACT FROM AUTHOR]

Ti alloy Ti6Al4V is used as fastener in solution-treated and aged (STA) condition. During the assembly of payload adaptor, one of the M4 nuts failed. Sustained load test was carried out for the assessment of nuts. A thorough analysis of failed nut, sustained load-tested nut and unused nut was carried out. Fracture analysis revealed quasi-brittle features, indicative of embrittlement of material. Hydrogen analysis showed higher hydrogen content (> 450 ppm) in the material than the specification (125 ppm max.). Failure of the M4 nut is attributed to the hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

During vacuum annealing of C-103 (Nb-10Hf-1Ti) sheets, local melting was noticed at the locations they were in contact with commercially pure titanium (CP-Ti) base sheet. On metallurgical analysis, it was noted that initially CP-Ti sheet reacted with the Inconel 600 tray, forming a series of low melting eutectics, below the annealing temperature of 1175 °C. The weight of C-103 charge experienced at the contact region between the bottom-most C-103 sheet with Inconel 600 gridded tray, where the eutectic reaction between CP-Ti and Inconel 600 occurred initially along with long annealing time, enabled interdiffusion of Ni, Cr, Ti, Nb and Hf, forming a eutectic mixture. Based on detailed metallurgical analysis, the reactions were established and the cause of melting was attributed to improper selection of base tray/sheet combination. Finally, it was recommended to use a Mo tray between Inconel 600 tray and CP-Ti sheet to overcome the problem. [ABSTRACT FROM AUTHOR]

In view of its excellent wear and corrosion resistance, AISI 440C steel is the material of choice for the fabrication of ball screws used in actuator systems of satellite launch vehicles. During the routine acceptance test of a ball screw, longitudinal cracks were observed at the shaft location of the ball screw. The optical microstructure of the ball screw material (AISI 440C) revealed the presence of aligned carbides (carbide banding). Fractographic observations revealed the cracking to be along the carbide bands. Based on detailed optical and scanning electron microscopic observations, the cracking of the ball screws was attributed to the carbide bands. [ABSTRACT FROM AUTHOR]

Hydraulic control actuation systems in launch vehicles use flexible hoses for transmission of forces to actuators at different locations. The hose ends are connected to the interface adapters by AISI 304 stainless steel sleeves. These sleeves are assembled to nipple end fittings of the high-pressure hose by a swaging operation to obtain leak-proof hose assemblies. The swaging operation is carried out at room temperature by a hydraulically operated swaging machine. Performance of the system as a whole requires strict adherence to the quality standards maintaining the critical interface dimensions within specified tolerances and ensuring the compression given to the swaged joint through the sleeve. If the joining forces are less, this can result in loose joints and gross leakage, whereas excessive compression can cause damage to the parts of the system namely the sleeve, stainless steel braid, PTFE or the adapter. The swaged joint is a single-point failure mode, indicating that a failure in the joint can lead to mission failure. It has to withstand harsh environments such as high pressure, low and high temperature extremes, fatigue loading due to pressure cycling as well as vibration. Therefore, as part of design verification, a detailed qualification plan has been prepared and the hoses were tested as per the plan. As per the test plan, these hoses undergo acceptance tests which include pneumatic and hydraulic pressure testing. During acceptance testing of hoses, one of the hose sleeves was found to be cracked. The cracking was observed after carrying out the pneumatic test when the assembly was being prepared for hydraulic pressure set-up. This paper describes the detailed metallurgical investigation carried out to understand the cause of failure and actions taken to avoid similar failures. [ABSTRACT FROM AUTHOR]

High-strength aluminum alloy AA7075 forgings are widely used in various control system components of liquid engines of satellite launch vehicles. In one such application, a forged component was found to crack under storage. Multiple cracks were noticed on the surface of the component. Fractographic features indicated intergranular mode of failure. Optical microscopic examination revealed dendritic coring in the material and crack propagation to be along the grain boundaries. Anodic dissolution of grain boundaries was also noticed. Based on detailed metallurgical investigations, it was concluded that the failure was due to 'stress corrosion cracking.' [ABSTRACT FROM AUTHOR]