Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session J03: Diagnostic Development IIRecordings Available
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Chair: Erin Nissen, Sandia National Laboratories Room: Anaheim Marriott Platinum 1 |
Tuesday, July 12, 2022 11:00AM - 11:15AM |
J03.00001: Chirped pulse line velocimetry (CPLV) as a new diagnostic tool Paulius Grivickas, Christian M Childs, Jason G Mance, Brandon M La Lone, Michael R Armstrong, Kyle T Sullivan PDV is currently the most common velocimetry technique fielded in various dynamic compression experiments. However, PDV is inherently limited to a single point measurement and requires multiple probes and expensive scope channels to obtain spatially resolved information. Line VISAR has been used to detect velocimetry profiles along a continuous line on a surface, but due to complexity and sensitivity of this system it is usually paired only with large scale platforms like the Omega laser facility. Here we present a line velocimetry technique, named chirped pulse line velocimetry (CPLV), which stems from ultrafast laser applications. Taking advantage of the recent advances in fiber optics used by the telecom industry, we demonstrate a prototype system with chirped pulses extending up to 100 ns and open new diagnostic possibilities in laser compression experiments. Key factors of the system architecture are discussed, and a few implementation examples are presented. |
Tuesday, July 12, 2022 11:15AM - 11:30AM |
J03.00002: Residual Prill Structure in Pressed PBX Charges Explored by Micro Computed Tomography Michelle A Espy, Larry G Hill, Christina J Hanson PBX prills are spongy nuggets a few millimeters in diameter, comprising a nonuniform distribution of HE crystals and binder. When pressed—especially at elevated temperatures at which the binder has softened or melted—one hopes that it will flow to uniformly coat the HE crystals. In reality it does so imperfectly, such that x-ray tomographic scans often look like a collection of prills mashed together. Lore is that the larger the prill, the more nonuniform is the binder distribution. Even if that were not so, the larger the prill the farther binder must flow in order to homogenize. Thus, the degree to which it homogenizes depends in part on prill size. The degree to which binder flows during pressing in turn affects the void distribution within pressed charges, which one suspects will affect shock sensitivity and material strength. In this paper we explore, via micro computed tomography for several PBX explosives, the residual prill structure within ½-in × ½-in cylindrical pellets. |
Tuesday, July 12, 2022 11:30AM - 11:45AM |
J03.00003: Method to dynamically measure optical return loss from shocked metal surfaces Noah W Birge, Kyle Hughes, Patrick W Younk Optical return loss from a surface is the fraction of light returned along a line-of-sight from the given surface. It is a useful quantity in determining whether interrogation via Photonic Doppler Velocimetry (PDV) or other optical diagnostics is possible. In this contribution, we present a novel method to make this measurement for shock metal surfaces with a time resolution of nanoseconds and a power resolution of about one in ten million. By comparing the power of the Broadband Laser Ranging (BLR) signal before and after shock breakout on a given surface, a relative change in reflection loss is observed at 40 MHz. When combined with optical backscatter reflectometer measurements which measure static reflection losses at a surface, a measure of the total dynamic reflection loss can be constructed. We present a series of small-scale, proof-of-principle xperiments performed at Los Alamos National Laboratory. An explosive drive consisting of an RP-1 detonator initiating a PBX-9501 pellet was used. Directly in contact with the high explosive was a stainless steel disk. Three surface finishes were investigated: 32 μin (0.8 μm) regularly machined grooves, a near mirror finish, and 32 μin surface that had been Scotchbrited to irregularly scratch the surface. Results show that surface treatment had minimal impact on the change in return loss after shock break-out. Statistically, changes in total reflection loss were centered around 0 dB with decreasing standard deviation as the probe angle was increased. |
Tuesday, July 12, 2022 11:45AM - 12:00PM |
J03.00004: Optical measurements of shock propagation in PMMA around arrays of inclusions Logan Byrom, Noah Edwards, Veronica Espinoza, Jamie Kimberley, Michael J Hargather The optical refractive imaging techniques quantitative schlieren and coherent gradient sensing are applied here to study shock wave propagation in optically transparent polymethyl methacrylate (PMMA) samples. The approximately two-dimensional samples have holes and embedded metallic rods as inclusions with which the shock waves interact. The schlieren imaging yields quantitative measurement of the density gradients and thus density field as a function of time and space in the PMMA materials during the shock wave loading. Coherent gradient sensing provides quantitative stress field information behind the shock front. When combined, these techniques provide a characterization of the material state throughout the shock wave loading process. Shock loading is generated using gun-launched projectiles with impact velocities on the order of 1000 m/s. PMMA samples with varied geometrical arrays of inclusions demonstrate the ability to alter the shock propagation and locations of shock wave focusing due to complex shock wave reflections and diffractions. High-speed digital cameras are utilized to record the schlieren and coherent gradient sensing images at sub-microsecond timescales, allowing for detailed analysis of wave interactions. |
Tuesday, July 12, 2022 12:00PM - 12:15PM |
J03.00005: Chirped Fibre Bragg Grating Cutback Tests Callum Pryer UK Ministry of Defence © Crown Owned Copyright 2022/AWE |
Tuesday, July 12, 2022 12:15PM - 12:30PM |
J03.00006: Experimental investigation of the fragmentation of metallic rings under dynamical radial expansion Fanny GANT, Gabriel SEISSON, Patrice LONGERE, Skander El MAÏ, Jean-Luc ZINSZNER Under explosive loading, thin-cased structures made of ductile material, e.g. air-launched warheads, undergo radial expansion until fragmentation occurs. The knowledge of the fragment population (mass, number, velocity, angle of ejection) helps to estimate the extent of lethality area. In literature, some theoretical, experimental and numerical studies consider simplified configurations such as ring expansion in order to get a better insight in the processes governing fragmentation. In this line, a new experimental set-up, namely the plate-impact-driven fragmentation test (PIDRET), has been developed for expanding ring using a single-stage gas gun. A steel projectile launched by the gas gun impacts a thin polymer disk circled by a metallic ring. Compressed against a thick anvil, the polymer disk flows radially putting under pressure the ring inner surface. The ring expands then homogeneously, reaching a hoop strain rate value close to 104 s-1, until fragmentation. Ultra-high-speed cameras and photon Doppler velocimetry (PDV) probes are used as time and space resolved diagnostics. Tests carried out on rings made of different metals and alloys evidence the strong dependence of the expansion kinematics and fragmentation process on the nature and state of the material. |
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