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NASA NTRS2014

Induction Heating of Hypervelocity Impact Samples to 2500 Degrees Centigrade

The Remote Hypervelocity Test Laboratory (RHTL) at White Sands Test Facility (WSTF) was asked to heat samples up to 2500 degrees Centigrade (4532 degrees Fahrenheit) to simulate reentry scenarios of crafts where heated shields are impacted with single small particles ranging from 0.2 to 1.0 millimeters (.008 to.039 inches) of various materials. The team decided an electromagnetic induction (induction heater) was the best method to achieve and control the temperatures in a rapid manner. The samples consisted of three-dimensional carbon-carbon and two-dimensional carbon-phenolic, which are both electrically conductive. After several attempts the team was able to achieve over 2500 degrees Centigrade (4532 degrees Fahrenheit) in ambient atmosphere. When the system was moved to the target chamber and the vacuum system evacuated down to 250 millitorr, arcing occurred between the bus bars and tank, the feedthrough fittings that carried the coolant and current, and between the target sample and coil. To overcome this arcing, conformal coatings, room temperature vulcanization (RTV) silicone, and other non-conductive materials were used to isolate the electromagnetic fields.

Simmons, Joshua↗

NASA NTRS2012

Design and Characterization of Thin Stainless Steel Burst Disks for Increasing Two-Stage Light Gas Launcher Efficiency

Laser etched 300 series Stainless Steel Burst Disks (SSBD) ranging between 0.178 mm (0.007-in.) and 0.508mm (0.020-in.) thick were designed for use in a 17-caliber two-stage light gas launcher. First, a disk manufacturing method was selected using a combination of wire electrical discharge machining (EDM) to form the blank disks and laser etching to define the pedaling fracture pattern. Second, a replaceable insert was designed to go between the SSDB and the barrel. This insert reduced the stress concentration between the SSBD and the barrel, providing a place for the petals of the SSDB to open, and protecting the rifling on the inside of the barrel. Thereafter, a design of experiments was implemented to test and characterize the burst characteristics of SSBDs. Extensive hydrostatic burst testing of the SSBDs was performed to complete the design of experiments study with one-hundred and seven burst tests. The experiment simultaneously tested the effects of the following: two SSBD material states (full hard, annealed); five SSBD thicknesses 0.178, 0.254, 0.305, 0.381 mm (0.007, 0.010, 0.012, 0.015, 0.020-in.); two grain directions relative); number of times the laser etch pattern was repeated (varies between 5-200 times); two heat sink configurations (with and without heat sink); and, two barrel configurations (with and without insert). These tests resulted in the quantification of the relationship between SSBD thickness, laser etch parameters, and desired burst pressure. Of the factors investigated only thickness and number of laser etches were needed to develop a mathematical relationship predicting hydrostatic burst pressure of disks using the same barrel configuration. The fracture surfaces of two representative SSBD bursts were then investigated with a scanning electron microscope, one burst hydrostatically in a fixture and another dynamically in the launcher. The fracture analysis verified that both burst conditions resulted in a ductile overload failure indicated by transgranular microvoid coalescence, non-fragmenting rupture and mixed tensile and shear failure modes, regardless of the material states tested. More testing is underway to determine the relationship between SSBD burst pressure and projectile velocity.

Tylka, Jonathan M.↗