Research Interests
Hypervelocity Impact Phenomena
Collaborators:M. A. Adams (Senior Researcher), J. M. Mihaly (Ph.D. Candidate), J. D. Tandy (Post-Doctoral Scholar)
Hypervelocity impact by micrometeoroids and orbital debris (MMOD) poses a serious and rising threat to spacecraft. Any spacecraft intended for long duration spaceflight must be designed with the capability to withstand extended exposure to the MMOD environment. Hypervelocity impacts induce a complex dynamic material response, which includes numerous interacting phenomena such as fragmentation, spallation, melting, mixed phase flow, ionization, and vaporization. The goal of current research is to develop and implement methods to experimentally investigate the mechanisms and phenomenology responsible for damage evolution in hypervelocity impact.
Facility
To address this challenge, the California Institute of Technology, in a joint effort with NASA Jet Propulsion Laboratory, has established the Small Particle Hypervelocity Impact Range (SPHIR). This Facility utilizes a two-stage light gas gun (see Fig. 1) with a 1.8mm bore diameter launch tube capable of producing mass-dependent velocities ranging from 2 to 10 km/s. Most commonly, the facility is used to launch 5.5 mg Nylon 6/6 right cylinders (L/D = 1) to impact speeds between 5 and 10 km/s. The facility has also been used to accelerate 3.6 mg Nylon 6/6 spheres and 22.7 mg 440C steel spheres to impact speeds ranging from 5 to 6 km/s and 2 to 3 km/s, respectively. The impactors are launched into a 1 m x 1 m x 2m target chamber which is evacuated down to pressures between 1 and 50 Torr. The facility features a high-speed camera, a gated-intensified camera, a 6W solid-state 532 nm continuous wave laser, UV-vis and IR spectrograph systems, and a conoscopic profilometer. These instruments provide a foundation to experimentally investigate hypervelocity impact phenomenology.
Figure 1. The Small Particle Hypervelocity Impact Range (SPHIR) at the Graduate Aerospace Laboratories at the California Institute of Technology (GALCIT)
Instrumentation
The SPHIR Facility is currently equipped with the following instrumentation:
Cordin 214-8 Gated, Intensified Camera
This camera provides a series of up to 8 images with framing rates as high as 108 fps. The camera contains an array of 4 independent, intensified CCDs. Each of the 4 CCD provides 2 images with 1000 x 1000 pixel resolution. The second exposure of a given CCD must be taken no less than 3.7 μs after the first, limiting the maximum frame rate of 108 fps is limited to the first or last consecutive 4 images taken.
Princeton Instruments UV-vis and IR spectrograph systems
Both systems utilize an Acton SP2560 spectrograph. The UV-vis system utilizes a high-speed PI-MAX 3 camera containing an intensified CCD detector with a minimum exposure time of 28 ns. The IR system uses a liquid nitrogen cooled high-speed OMA-V camera with a minimum exposure time of 1 μs and a 320 x 256 pixel resolution. The field of view for each spectrograph system can be modified through the selection of lenses with focal lengths ranging from 8 mm to 90 mm.
Figure 2. IR images of a 1.5 mm thick 6061-T6 aluminum target at 0 degree obliquity impacted with a 1.75 mm Nylon 6/6 cylinder (L/D = 1) at approximately 5.5 km/s and 6.1 km/s respectively. The field of view of each image is approximately 25 cm wide by 20 cm high. The IR camera was exposed from 11 µs to 13 µs after impact for the first image and from 13 µs to 15 µs after impact for the second image.
Figure 3. UV-vis emission spectrum (between 370 nm and 650 nm) of uprange ejecta from a 3.0 mm thick 6061-T6 aluminum target, at 0 degree obliquity, impacted with a 1.75 mm Nylon 6/6 cylinder (L/D = 1) at 5.2 km/s. The spectrometer slit width was set to 100 µm, giving a field of view of 0.38 cm wide by 1.27 cm high and located approximately 0.5 inches (~ 12.7 mm) in front (uprange) of the aluminum target. The UV-vis camera was exposed from 1.0 µs to 6.0 µs after impact. Preliminary assignments of these spectral bands show evidence of small molecular fragments originating from both the projectile and target material.
Photron SA-1 Fastcam high-speed camera
This camera is currently used to measure the impactor velocity operating with 192 x 112 pixel resolution at 150,000 fps. Higher framing-rates may be achieved with smaller pixel resolutions.
Optimet MiniConoscan 3000 Laser Conoscope
This instrument is used to conduct post-experiment target specimen profilometry. This instrument produces a three-dimensional {x,y,z} Cartesian coordinate map describing a surface of a target with up to 6 to 10 micron precision in all directions. This allows for quantitative measurements of deformation features, such as target perforation area or surface slope field
VALYN Velocity Interferometer System for Any Reflector (VISAR)
This instrument measures the normal component of a surface velocity and is typically used to measure the back-surface of target plates in equation-of-state measurements in shock experiments. The VISAR system uses a Coherent Verdi V6 diode-pumped solid-state continuous wave laser. This 532 nm laser is configured to also provide a light-source for high-speed photography.
Diagnostics
Laser Side-Lighting Shadowgraphy
A high-speed photography system has been implemented in the SPHIR facility to create shadowgraph images of hypervelocity impact events with very short exposure times (25 ns) and short inter-frame times (<1 μs) through use of the Cordin 214-8 camera. This short exposure time enables sharp visualization of impact features with very little motion blur at the test speeds of 5-7 km/s. This technique uses illumination orthogonal to the projectile flight direction to provide a shadow image of the impact on the target. This optical imaging system uses a coherent, collimated light source produced by a Coherent Verdi 6 Watt diode-pumped solid-state 532 nm continuous wave laser. The laser illumination is expanded and collimated to produce a 100 mm diameter beam and directed into the target chamber orthogonal to the impactor velocity vector.
UV Spectroscopy/IR Spectroscopy
The two spectrograph systems (previously described) are able to record a single image or spectrum of the impact event emission by utilizing an internal directing mirror or a 150 g/mm, 600 g/mm or 1200 g/mm diffraction grating, enabling observation of broad spectra or individual spectral bands. The first spectrograph utilizes a high speed PI-MAX 3 camera system containing an intensified CCD detector, (minimum exposure time 28 ns) to observe UV-visible emission spectra over wavelengths between 300 nm and 850 nm. The second spectrograph uses a liquid nitrogen cooled OMA-V InGaAs high speed camera system (minimum exposure time 1 μs) to monitor IR emission from 0.9 μm to 1.7 μm. The field of view of each spectrograph/camera system may also be altered by utilizing lenses with focal lengths ranging from 8 mm to 90 mm.
Above: view movie of Small-Particle Hypervelocity Impact Range
PDF slideshows
EXAMPLE 1
Laser Side-Lighting Shadowgraph sequence of a Nylon 6/6 cylinder (D = 1.8 mm, L/D = 1) impacting a 1.5 mm thick 6061-T6 Aluminum target plate at 5.70 km/s. The target chamber pressure during this experiment was 1.0 Torr. This sequence taken with the Cordin gated, intensified camera show formation of an ejecta and debris cloud in front and behind the target. click to view pdf
EXAMPLE 2
Laser Side-Lighting Shadowgraph sequence of a Nylon 6/6 cylinder (D = 1.8 mm, L/D = 1) impacting a 0.5 mm thick 6061-T6 Aluminum target plate at 4.59 km/s. The target chamber pressure during this experiment was 52.0 Torr. As a result of the (relatively) high chamber pressure, the coherent light source allows for visualization of shock waves that accompany debris and ejecta formation during the experiment. click to view pdf
EXAMPLE 3
Laser Side-Lighting Shadowgraph sequence of a Nylon 6/6 sphere (D = 1.8 mm) impacting a 1.5 mm thick 6061-T6 Aluminum target plate at 5.20 km/s. The target chamber pressure during this experiment was 1.5 Torr. The target is held such that the plate normal is at an angle of 45 degrees with respect to the impact velocity vector. The angle at which ejecta is thrown from the front of the plate is seen to evolve with time during the sequence. click to view pdf
EXAMPLE 4
Laser Side-Lighting Shadowgraph sequence of a Nylon 6/6 Cylinder (d = 1.8 mm, L/D = 1) impacting a piece of candy glass (very brittle plastic). The target plate is oriented 45 degrees with respect to the velocity vector to allow the laser illumination to transmit through the transparent target. The target chamber pressure during this experiment was 19.2 Torr. Waves can be seen emanating from the impact site followed by the propagation of radial cracks. The debris cloud moving away from the target back-surface can be seen in later frames. click to view pdf
Previous Work
Above: view movie of homalite and mylar in-situ behavior
Hypervelocity Impact: Dynamic Behaviors of Brittle Polymers
View poster (pdf)
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last
update:
05/31/2016