Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session E4: MS: Strength & Spall I |
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Chair: Naresh Thandhani, Georgia Tech Room: Pavilion West |
Monday, June 17, 2019 3:30PM - 3:45PM |
E4.00001: The Response of High-Purity Titanium to Sweeping Detonation Waves Lawrence Hull, George Gray, Phillip Miller, Thomas Nizolek Loading from sweeping detonation waves possess enhanced shear relative to loading from ordinary one-dimensional plane detonation waves. Our experiments use cylindrical detonation waves that are driven into flat samples of high-purity titanium. The waves driven into the sample by the explosive interact obliquely from the free surface as the wave sweeps along the sample, develop toward quasi-steady motion from effectively zero obliquity, and therefore induce a variation of shear along the sample. The type and thickness of the explosive is also varied, from experiment to experiment, in order to access conditions that bridge the alpha to omega phase transition in pure titanium. The primary dynamic diagnostic is Photon-Doppler-Velocimetry (PDV) using a crossed pair of probes directed at each spot with sufficient view direction (vectorial) independence such that the normal and in-surface tangential velocity may be inferred. Various quantities that characterize the dynamic response of the material are derived from the PDV data and reported (e. g. spall strength, etc.). The samples are recovered and metallurgical analysis performed to characterize the deformation mechanics (e. g. twinning) and likelihood of the presence of the alpha to omega phase transition (e.g. retained omega phase) associated with various loading conditions. [Preview Abstract] |
Monday, June 17, 2019 3:45PM - 4:00PM |
E4.00002: The role of microstructure on elastic precursor decay John Jonsson, David Chapman, Daniel Eakins The elastic precursor wave has long been a focus for the study of yielding during intense dynamic loading, as its evolution is directly linked to the time-dependent movement and generation of dislocations at the onset of plastic flow. Previous studies of precursor decay have mostly concentrated on strain-rate and temperature dependence of various metals such as aluminium, iron and copper, typically in the idealised annealed or single-crystal conditions. There has been comparatively limited exploration of the role of the initial microstructural state, specifically the initial defect density and material processing history. Here we present results from a series of PDV instrumented plate-impact experiments on aluminium and magnesium using a single-stage gas gun, in which a range of initial microstructural states have been examined. In aluminium, both pure and alloyed samples with varying degrees of heavy prior cold working (swaging) of up to three passes are studied. In magnesium, we examine both conventionally cast and high shear melt conditioned samples. We discuss the observed decay rates in light of dislocation measurements and the variations in material processing histories. [Preview Abstract] |
Monday, June 17, 2019 4:00PM - 4:30PM |
E4.00003: Towards Predicting a Microstructure's Susceptibility to Spall Invited Speaker: Saryu Fensin Understanding and predicting the response of materials under dynamic loading is a challenging problem due to complexities involved with the loading state and its interaction with various features in the microstructure. Previous experiments to study dynamic fracture in Tantalum (Ta) manufactured via Additive manufacturing (AM) has shown differences not only in the elastic plastic transition but also its spall properties. The goal of this work is to understand this difference in the dynamic response of AM vs. wrought Ta through the use of non-equilibrium molecular dynamics (MD) simulation. Both experiments and simulation data showed that altering the processing conditions also changed the number fraction of specific grain boundary types in the wrought and AM materials. To investigate if this change in boundary type distribution is the main cause of differences in the dynamic response of these materials, bi-crystal simulations were performed to quantify the effect of boundary type and structure on spall strength. \\ \\In collaboration with: Jie Chen, University of Connecticut; Eric Hahn, George Gray III, Los Alamos National Laboratory [Preview Abstract] |
Monday, June 17, 2019 4:30PM - 4:45PM |
E4.00004: The effect of peak stress (3.0 GPa to 20.0 GPa) on the spallation of lean duplex stainless steel Juan Pablo Escobedo, Ali Ameri, Manny Gonzales, Hongxu Wang, Raymond Miller, Paul Hazell, Zakaria Quadir This study examines the dynamic fracture behaviour and spall strength of a high hardness armour (HHA) steel and an improved rolled homogenous armour (IRHA) steel. Flyer plate impact tests were conducted at about 240 and 500 m/s, which provided peak stresses of 4.5 GPa, which caused incipient damage, and 10 GPa which resulted in full spall. Free surface velocities were measured by Photon Doppler Velocimetry (PDV) and the damage examination was conducted by conventional light optical microscopy (LOM) and scanning electron microscopy (SEM). Results show that HHA specimens exhibited about 10{\%} higher spall strength and Hugoniot elastic limit (HEL) than IRHA specimens at the same peak compressive stresses. Post-mortem examinations revealed that the HHA steel exhibits brittle fracture indicated by shear banding seen on the fracture surface and crack propagation through the thickness. In contrast, a more ductile fracture indicative of void growth and coalescence fracture mechanisms, was observed throughout the fracture surface of IRHA. [Preview Abstract] |
Monday, June 17, 2019 4:45PM - 5:00PM |
E4.00005: Shock recompression of spall damage David Jones, Saryu Fensin, Robert Hixson Dynamic loading of a material often results in spall fracture. When a material subjected to shock compression is allowed to release, rarefaction waves propagate into the material. If two rarefactions intersect, they can create a region of high-rate tension, generating damage through a series of void nucleation, growth, and coalescence (in ductile materials). As shock loading is closely linked to the aerospace and defense fields, it is important to understand how a damaged material will respond to a second dynamic loading event. Here, we investigate the effect of a second shock applied to pre-damaged copper that contains incipient spall damage (i.e. voids that have not yet coalesced). Flyer-plate impact experiments are used to first generate samples containing spall damage, which are then thoroughly characterized. These samples are then subjected to a second flyer-plate impact to examine how the shock interacts with the spall region. The double-shocked samples were sectioned to reveal that at relatively modest shock stresses of 2GPa the pre-existing spall damage is completely recompacted. Electron microscopy shows that the voids are compacted with enough energy to drive localized recrystallization, effectively welding the material back together to a fully dense state. [Preview Abstract] |
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