Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session U4: Inelastic Deformation V |
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Chair: Peter Taylor, AWE, UK Room: Fairmont Orchid Hotel Plaza II |
Friday, June 29, 2007 8:00AM - 8:15AM |
U4.00001: Transformation of voids observed on a surface to a volumetric size distribution Lynn Seaman A new procedure, based on the Scheil$^{1}$ method, for transforming surface counts of voids or grains to volumetric size distributions has been developed. The method simultaneously smooths the surface count data and produces the volumetric distribution. A constraint has been added to require that the relative volume of the voids or grains matches the relative area of these artifacts. Here the method is applied to void count data from spall experiments in 99.999{\%} pure aluminum performed by Qi MeiLan$^{2}$ and similar experiments in several other materials. \newline \newline $^{1.}$ E. Scheil, Die Berechnung der Anzahl und Grossenverteilung kugelformiger Kristalle in undurchsichtigen K\"{o}rpern mit Hilfe durch einen ebenen Schnitt erh\"{a}ltenen Schnittkreise, Z. Anorg. Allgem. Chem., Vol 201, p259, 1931. \newline $^{2.}$ Qi MeiLan, PhD thesis, to be published. [Preview Abstract] |
Friday, June 29, 2007 8:15AM - 8:30AM |
U4.00002: Experimental Series on Behavior of Post-Damage Recollected Material Ann Kaul, George Rodriquez Spallation damage, a typical method of failure for ductile materials, results from the nucleation, growth and coalescence of voids caused by high tensile stress. Specific areas of research on spallation damage include the damage initiation regime in convergent geometry, behavior of material recollected after damage, and effects of convergent geometry (shear stresses, etc.) on the material response. Currently, models of spallation phenomena are typically based on experiments using a planar configuration, where a significant body of data exists from gas gun, laser and high-explosive experiments. Planar experiments allow for one-dimensional analysis of the evolution of failure characteristics. Using a cylindrical configuration to study spallation damage, however, requires the consideration of physical effects not present in the planar configuration. Cylindrical experiments allow for a careful analysis of the effect of convergence and two-dimensional strains and shear stresses on the spallation profile of a material. These experiments challenge existing computational material models and databases and provide motivation to improve these models and increase the predictive capabilities of codes. A series of experiments (R-Damage-0, -1 and -2) previously provided data about failure initiation of a well-characterized material (aluminum) in a cylindrical geometry. This presentation will cover the theory, design and results for the next series of experiments (R-Damage-3, -4 and -5), which studied the behavior of material recollected after damage from pressures in the damage initiation regime. [Preview Abstract] |
Friday, June 29, 2007 8:30AM - 8:45AM |
U4.00003: Aluminum Shield under Hypervelocity Impact of Mylar Flyer up to 10 km/s. Jianheng Zhao, Fuli Tan, C. Sun, C. Liu, G. Ravichandran The near-earth space environment is cluttered with man-made debris and naturally occurring meteoroids, which is a big menace to the safety of satellites and spacecrafts. This paper is addressed on the failure response of aluminum shield under milligrame level debris or meteorids with around 10 km/s velocity. A compacted electric gun is employed to accelerate mylar flyer with 8-10 mm diameter up to 10 km/s. The spallation is observed in the rear free surface of 4 mm thick monolithic aluminum shield, and its fracture mechanism changes from plastic to brittle when flyer velocity is above 6 km/s. Once the boundary of aluminum plate is fixed except the loaded area, a through hole with 8mm diameter in the impacted area of the shield is observed after which was impacted by 0.1 mm thick mylar flyer with 6km/s. Three layers of shield is impacted by a myler flyer with velocity up to 10 km/s, debris clouds are observed in the first and the second gaps during the impact process by high speed camera, and its leftover can also be observed on the surface of the third plate. [Preview Abstract] |
Friday, June 29, 2007 8:45AM - 9:00AM |
U4.00004: Numerical Simulations of Fragmentation Onset Velocity of Projectile Impact on Thin Bumper Wei Zhang, Caixia Jiang, Wenlai Ma, Baojun Pang The conventional spacecraft meteoroids and orbital debris shielding system is the Whipple shield. In general there is a threshold velocity that is just sufficient to shatter the projectile for each system consisting of a projectile and bumper. This velocity is known as the fragmentation onset velocity. To determine the fragmentation onset velocity experimentally, a number of experiments have been conducted with different projectile/bumper configuration. The numerical simulation of fragmentation onset velocity of different material projectile hypervelocity impacts on bumpers with different combination of impact velocities and bumper-thicker-to-projectile-diameter ratios (t/D) has been performed using the SPH technique of AUTODYN. The spherical projectile materials are aluminum, steel and copper. All bumper materials are aluminum alloy 6061-T6. The simulation velocities were in the range of 1km/s-7km/s. The ratios of t/D were varied from 0.01 to 0.80. The material models were consisted of Mie-Gruneisen (shock) equation of state, Steinberg-Guinan strength model and Grady fragmentation failure model. The simulation results are given and compared with the experimental results. The simulation results are consistent very well with the experimental results. [Preview Abstract] |
Friday, June 29, 2007 9:00AM - 9:15AM |
U4.00005: Studies on the Fracture of HR-2 Steel Cylinder under Imploding Haibo Hu, Tiegang Tang, Qingzhong Li, Xueling Sun The fracture phenomena of HR-2 steel cylinder under implosion loading are studied by the dynamic technologies of X-flash photography and high-speed photography. The results of X-flash photography show that the thermo-plastic instability and fracture have occurred in the HR-2 steel cylinder wall during the implosion loading process. The initiation and propagation processes of cracks on the inner wall of the hemi-cylinder have been directly observed by the high-speed photography. The comparison between the two kinds of experimental results shows that the cracks initiate firstly in the inner wall of the steel cylinder. There are clear shear characteristics on the collected fragments. The metallography examinations show that the adiabatic shear bands and microcracks initiate first near the inner wall of the steel cylinder, and propagate along the maximum shear stress paths, which agrees with the previous deduction of experiments. With loading pressure increasing, the dimension of fragments and the width of ABS both become smaller. [Preview Abstract] |
Friday, June 29, 2007 9:15AM - 9:30AM |
U4.00006: Longitudinal Fracture Propagation of Explosive Loaded Metal Shells Haibo Hu, Tiegang Tang, Bayi Hu Longitudinal fracture propagation behavior in self-organized shear bands is discussed. Shear fracture can propagate longitudinally tens of mm, while recovery observations show that fracture surface is consisted of shear fracture cells in mm length. They locate approximately along a given generatrix and coalesce longitudinally at some stage of growth breaking through shell wall. Analysis on alignment phenomenon of shear initiations, considering up-stream shear initiations influence, is given. Early shear initiations can influence sites of shear instability on neighboring down-stream section by changing local stress field within a time gap sufficient for mechanical wave propagation. It leads to shear initiation in given orientation and location along given generatrix in competition with random shear initiations. Knowing conditions for such mechanism keep on work layer after layers, not to be broken, is of importance. Simulate multi shears coalesce using a mono fracture growth model is not advisable, while to simulate the growth of tongue like shear cells individually, calculating instantaneous stress field in 3-D space is a tremendous work. To approximate such kind of process for credible modeling is important. For fragment size distribution predication, in well known models there is not adequate consideration of longitudinal propagation factor, which depends on material parameters and loading conditions. [Preview Abstract] |
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