A common solid propellant rocket motor typically includes a nozzle (e.g., a convergent or a convergent-divergent nozzle), a tubular pressure vessel, a solid propellant (commonly referred to as “grain”), and an ignition charge. The tubular pressure vessel defines an elongated cylindrical cavity, which is fluidly coupled to the nozzle and in which the grain is stored. When ignited by the ignition charge, the grain burns in a controlled manner to produce exhaust gases, which flow through the nozzle to produce thrust. To ensure that the pressure within the cavity of the pressure vessel accumulates to a level at which ignition of the solid propellant is optimized, a burst disc (also commonly referred to as a “rupture disc,” a “rupture panel,” or a “rupture diaphragm”) is typically positioned downstream of the nozzle outlet; e.g., within the outlet plane of the nozzle. When properly installed and intact, the burst disc blocks gas flow through the nozzle to allow the accumulation of pressure within the pressure vessel. However, when the pressure within the rocket pressure vessel approaches or surpasses a predetermined pressure threshold (referred to herein as the “burst pressure”), the burst disc ruptures or fractures and dislodges from the nozzle to allow the flow of exhaust gases therethrough.
One common type of burst disc, often referred to as a “manhole-type burst disc,” assumes the form of a metal (e.g., steel) disc having a central portion that is configured to break away as single piece when pressure applied to be burst disc surpasses the burst pressure. A second common type of burst disc is commonly referred to as a “petal-type burst disc” and assumes the form of a circular material disc having two or more intersecting scribe lines, which extend across different diameters of the disc to define four or more wedge-shaped petals. If the petal-type burst disc is formed from a relatively brittle material, the burst disc petals will tend to break apart along the scribe lines, and thus be expelled from the rocket motor, when the burst disc is exposed to the predetermined burst pressure. If the petal-type burst disc is instead formed from less brittle, more ductile material (e.g., steel), the burst disc will tend to rupture or tear along the scribe lines and the petals will remain attached to the outer annular portion of the burst disc. As a result, when the petal-type burst disc is formed from less brittle, more ductile material, the petals will tend to bend outward in the direction of the exhaust gas flow to permit gas flow through the nozzle.
Conventional burst discs of the type described above are typically limited in at least one of two manners. First, many conventional burst discs (e.g., manhole-type burst discs and relatively brittle petal-type burst discs of the type described above) tend to break apart into one or more relatively large pieces upon fragmentation, which are then expelled from the rocket nozzle within the supersonic gas stream. Larger burst debris are thus ejected from the rocket nozzle at significant velocities and, thus, have kinetic energies sufficiently high to potentially damage nearby objects. Second, conventional burst discs often exhibit burst pressures that vary significantly from the predetermined, target burst disc pressure. For example, in the case of petal-type burst discs formed from less brittle, more ductile materials, the variability in burst disc pressure may arise, in part, from an initial outward bulging of the burst disc prior to rupture. In the context of solid propellant rocket motors, this variability in burst disc pressure may result in a timing delay on the order of a few fractions of a second. While such a timing delay may be acceptable in many applications, in applications characterized by extremely rapid changes in rocket position or attitude, a timing delay of a few fractions of a second can result in significant navigational errors. For example, in the case of munition having an angle of attack rotating at 5,000 degrees per second, an ignition timing delay of one millisecond within a single solid propellant rocket motor could result in a targeting error of 5 degrees.
Considering the above, it would be desirable to provide a solid propellant rocket motor including a burst disc that minimizes burst pressure variability and that minimizes the ejection of larger debris by promoting uniform and complete fragmentation. It would also be desirable to provide embodiments of a burst disc providing the aforementioned objectives that could be utilized in place of a conventional burst disc in a variety of other applications, including within gas generators of the type commonly included within vehicular airbag inflation systems. Lastly, it would be desirable to provide embodiments of a method for manufacturing such a burst disc. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and this Background.