22 results on '"Gray III, G. T."'
Search Results
2. The Shock Induced Mechanical Response of the Fluorinated Tri-polymer, Viton B
- Author
-
Millett, J. C. F., Brown, E. N., Bourne, N. K., Whiteman, G., and Gray, III, G. T.
- Published
- 2021
- Full Text
- View/download PDF
3. Contributions to Dynamic Behaviour of Materials Professor John Edwin Field, FRS 1936–2020
- Author
-
Andrews, D. R., Bourne, N. K., Brown, E. N., Dear, J. P., Dickson, P., Freeman, C. J., Goveas, S. G., Gray, III, G. T., Hauser, H., Huntley, J. M., Hutchings, I. M., Leighton, T. G., Matthewson, M. J., Meyers, M., Rae, P. J., Siviour, C. R., Swain, M., Townsend, D., van der Zwaag, S., Walley, S. M., and Williamson, D. M.
- Published
- 2021
- Full Text
- View/download PDF
4. The High-Strain-Rate Constitutive Behavior and Shear Response of Pure Magnesium and AZ31B Magnesium Alloy
- Author
-
Cerreta, E. K., Fensin, S. J., Perez-Bergquist, S. J., Trujillo, C. P., Morrow, B. M., Lopez, M. F., Roach, C. J., Mathaudhu, S. N., Anghel, V., and Gray, III, G. T.
- Published
- 2021
- Full Text
- View/download PDF
5. The Effects of Changing Chemistry on the Shock Response of Basic Polymers
- Author
-
Millett, J. C. F., Brown, E. N., Gray, III, G. T., Bourne, N. K., Wood, D. C., and Appleby-Thomas, G.
- Published
- 2016
- Full Text
- View/download PDF
6. Spall fracture in additive manufactured tantalum.
- Author
-
Jones, D. R., Fensin, S. J., Ndefru, B. G., Martinez, D. T., Trujillo, C. P., and Gray III, G. T.
- Subjects
THREE-dimensional printing ,TANTALUM ,LASER velocimeters ,ANISOTROPY ,MICROSTRUCTURE - Abstract
We present a series of experiments on the response of additive manufactured (AM) tantalum to dynamic loading, specifically the spall strength. Rectangular plates of AM tantalum were produced, with subsequent characterization revealing a highly anisotropic microstructure. Samples were taken from these plates to investigate the effect of anisotropy on the spall strength: the resistance to high strain-rate tensile damage. A conventional, wrought tantalum sample, possessing an equiaxed microstructure, was also tested to serve as a control. Shock loading was performed via light gas-gun flyer-plate impact experiments, with laser velocimetry on the rear of the samples to record the shock wave profiles and soft-recovery techniques to allow post-mortem analysis. In general, the AM samples were found to have a higher Hugoniot elastic limit, the dynamic yield strength under shock loading, while having a reduced spall strength, when compared to the wrought tantalum samples. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
7. Effect of peak stress and tensile strain-rate on spall in tantalum.
- Author
-
Jones, D. R., Fensin, S. J., Martinez, D. T., Trujillo, C. P., and Gray III, G. T.
- Subjects
TANTALUM ,TRANSITION metals ,STRAINS & stresses (Mechanics) ,STRENGTH of materials ,TANTALUM capacitors - Abstract
Materials subjected to dynamic environments experience a complex and wide range of stress, strain, and strain-rate conditions. To have confidence in material models, an accurate, predictive capability is required. In this study, we present a series of flyer-plate impact tests on well characterized, high purity tantalum. The shock-waves generated at impact release from the free-surfaces, reflect, and interact to produce incipient spall fracture. By varying the flyer-plate material and impact velocity, both the peak stress and the strain-rate in the samples were controlled independently. Velocimetry was used on the rear free-surface of the samples to measure the shock-response and the spall strength. While this measurement provided the same spall strength for all cases, at approximately 5.1 GPa, when the samples were sectioned during post-mortem, the quantity and distribution of internal damage was markedly different. For the high-strain rate cases, voids remained small and isolated, whereas in the lower strain-rate experiments, the spall damage was far more localized, with a well-defined continuous spall plane. With the use of hydrocode simulations, this was discovered to result from how the different release rates affect the interaction volume inside the sample. These results highlight the importance of careful sample recovery, and the risks of relying solely on free-surface velocity measurements. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
8. Multi-phase equation of state of ultrapure hafnium to 120 GPa.
- Author
-
Huston, L Q, Velisavljevic, N, Smith, J S, Gray III, G T, and Sturtevant, B T
- Published
- 2022
- Full Text
- View/download PDF
9. Spall fracture in additive manufactured Ti-6Al-4V.
- Author
-
Jones, D. R., Fensin, S. J., Dippo, O., Beal, R. A., Livescu, V., Martinez, D. T., Trujillo, C. P., Florando, J. N., Kumar, M., and Gray III, G. T.
- Subjects
ADDITIVES ,VELOCIMETRY ,FLUID dynamic measurements ,QUASISTATIC processes ,ANISOTROPY - Abstract
We present a study on the spall strength of additive manufactured (AM) Ti-6Al-4V. Samples were obtained from two pieces of selective laser melted (SLM, a powder bed fusion technique) Ti-6Al-4V such that the response to dynamic tensile loading could be investigated as a function of the orientation between the build layers and the loading direction. A sample of wrought bar-stock Ti-6Al-4V was also tested to act as a baseline representing the traditionally manufactured material response. A single-stage light gas-gun was used to launch a thin flyer plate into the samples, generating a region of intense tensile stress on a plane normal to the impact direction. The rear free surface velocity time history of each sample was recorded with laser-based velocimetry to allow the spall strength to be calculated. The samples were also soft recovered to enable post-mortem characterization of the spall damage evolution. Results showed that when the tensile load was applied normal to the interfaces between the build layers caused by the SLM fabrication process the spall strength was drastically reduced, dropping to 60% of that of the wrought material. However, when loaded parallel to the AM build layer interfaces the spall strength was found to remain at 95% of the wrought control, suggesting that when loading normal to the AM layer interfaces, void nucleation is facilitated more readily due to weaknesses along these boundaries. Quasi-static testing of the same sample orientations revealed a much lower degree of anisotropy, demonstrating the importance of rate-dependent studies for damage evolution in AM materials. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
10. The effect of distribution of second phase on dynamic damage.
- Author
-
Fensin, S. J., Jones, D. R., Walker, E. K., Farrow, A., Imhoff, S. D., Clarke, K., Trujillo, C. P., Martinez, D. T., Gray III, G. T., and Cerreta, E. K.
- Subjects
DYNAMICS ,NUCLEATION ,ANALYTICAL mechanics ,DISCONTINUOUS precipitation ,MICROSTRUCTURE - Abstract
For ductile metals, dynamic fracture occurs principally through void nucleation, growth, and coalescence at heterogeneities in the microstructure. Previous experimental research on high purity metals has shown that microstructural features, such as grain boundaries, inclusions, vacancies, and heterogeneities, can act as initial void nucleation sites. In addition, other research on two-phase materials has also highlighted the importance of the properties of a second phase itself in determining the dynamic response of the overall material. However, previous research has not investigated the effects of the distribution of a second phase on damage nucleation and evolution. To approach this problem in a systematic manner, two copper alloys with 1% lead materials, with the same Pb concentration but different Pb distributions, have been investigated. A new CuPb alloy was cast with a more homogeneous distribution of Pb as compared to a CuPb where the Pb congregated in large "stringer" type configurations. These materials were shock loaded at ~1.2 GPa and soft recovered. In-situ free surface velocity information, and post mortem metallography, reveals that even though the spall strength of both the materials were similar, the total extent and details of damage in the materials varied by 15%. This suggests that altering the distribution of Pb in the Cu matrix leads to the creation of more void nucleation sites and also changed the rate of void growth. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
11. Response and representation of ductile damage under varying shock loading conditions in tantalum.
- Author
-
Bronkhorst, C. A., Gray III, G. T., Addessio, F. L., Livescu, V., Bourne, N. K., MacDonald, S. A., and Withers, P. J.
- Subjects
- *
TANTALUM capacitors , *POLYCRYSTALLINE semiconductors , *POLYCRYSTALLINE silicon , *TANTALUM , *VELOCIMETRY - Abstract
The response of polycrystalline metals, which possess adequate mechanisms for plastic deformation under extreme loading conditions, is often accompanied by the formation of pores within the structure of the material. This large deformation process is broadly identified as progressive with nucleation, growth, coalescence, and failure the physical path taken over very short periods of time. These are well known to be complex processes strongly influenced by microstructure, loading path, and the loading profile, which remains a significant challenge to represent and predict numerically. In the current study, the influence of loading path on the damage evolution in high-purity tantalum is presented. Tantalum samples were shock loaded to three different peak shock stresses using both symmetric impact, and two different composite flyer plate configurations such that upon unloading the three samples displayed nearly identical "pull-back" signals as measured via rear-surface velocimetry. While the "pull-back" signals observed were found to be similar in magnitude, the sample loaded to the highest peak stress nucleated a connected field of ductile fracture which resulted in complete separation, while the two lower peak stresses resulted in incipient damage. The damage evolution in the "soft" recovered tantalum samples was quantified using optical metallography, electron-back-scatter diffraction, and tomography. These experiments are examined numerically through the use of a model for shock-induced porosity evolution during damage. The model is shown to describe the response of the tantalum reasonably well under strongly loaded conditions but less well in the nucleation dominated regime. Numerical results are also presented as a function of computational mesh density and discussed in the context ofimproved representation of the influence of material structure upon macro-scale models of ductile damage. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
12. Dynamic failure in two-phase materials.
- Author
-
Fensin, S. J., Walker, E. K., Cerreta, E. K., Trujillo, C. P., Martinez, D. T., and Gray III, G. T.
- Subjects
NUCLEATION ,MICROSTRUCTURE ,POLYCRYSTALLINE semiconductors ,PHASE transitions ,CONDENSED matter - Abstract
Previous experimental research has shown that microstructural features such as interfaces, inclusions, vacancies, and heterogeneities can all act as void nucleation sites. However, it is not well understood how important these interfaces are to damage evolution and failure as a function of the surrounding parent materials. In this work, we present results on three different polycrystalline materials: (1) Cu, (2) Cu-24 wt. %Ag, and (3) Cu-15 wt.%Nb which were studied to probe the influence of bi-metal interfaces on void nucleation and growth. These materials were chosen due to the range of difference in structure and bulk properties between the two phases. The initial results suggest that when there are significant differences between the bulk properties (for example: stacking fault energy, melting temperature, etc.) the type of interface between the two parent materials does not principally control the damage nucleation and growth process. Rather, it is the "weaker" material that dictates the dynamic spall strength of the overall two-phase material. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
13. High-resolution measurements of shock behavior across frictional Be/Cu interfaces.
- Author
-
Loomis, E., Hammerberg, J., Cooley, J. C., Shimada, T., Johnson, R. P., Peralta, P., Olson, R., and Gray III, G. T.
- Subjects
MECHANICAL shock measurement ,FRICTION ,BERYLLIUM compounds ,COPPER compounds ,SIMULATION methods & models ,DIFFUSION bonding (Metals) - Abstract
A longstanding question in the field of multi-material behavior pertains to the treatment of interfaces possessing finite frictional strength under high dynamic pressures and shear. Here, we examine the effects of constrained interface sliding on local deformation near the boundary using new, highresolution measurements combined with simulations to infer friction strength. The experiments use laser driven plate impacts at the Los Alamos National Laboratory TRIDENT Laser Facility to launch a shock wave into a target consisting of a central cylindrical plate of Be and an outer ring of Cu oriented, such that the shock propagates at nearly a 90° angle to the interface normal producing a large velocity gradient across the material boundary. Impact experiments were performed on targets that underwent diffusion bonding of the two materials and on targets that were only press fit together. Friction-induced surface deformation was diagnosed using line-imaging velocity interferometry and surface Transient Imaging Displacement Interferometry in the immediate region of the interface. In these studies, we observed a significant behavioral change in both simulations and experiments between targets with diffusion bonded interfaces and those that were press fit. Bonded targets exhibited a mutual dragging between the Be and Cu parts throughout the entire experiment, whereas unbonded targets displayed a surface slope reversal on the Cu side of the interface, which simulations suggest arise due to altered wave interactions from a 3× lower frictional force compared to the bonded interface. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
14. The response of high-purity titanium to sweeping detonation waves.
- Author
-
Hull, L. M., Gray III, G. T., Miller, P. I., Nizolek, T. J., Lane, J. Matthew D., Germann, Timothy C., Armstrong, Michael R., Wixom, Ryan, Damm, David, and Zaug, Joseph
- Subjects
- *
DETONATION waves , *PHASE transitions , *TITANIUM , *DEFORMATIONS (Mechanics) , *FREE surfaces , *NANODIAMONDS , *METALLURGICAL analysis - Abstract
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 α → ω 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 are found. Various quantities that characterize the dynamic response of the material are derived from the PDV data and reported, such as spall strength. The samples are recovered and metallurgical analysis performed to characterize the deformation mechanics, such as twinning, and likelihood of the presence of the α → ω phase transition via retained ω −phase associated with various loading conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
15. Structure / Property Characterization of Spallation in Wrought and Additively Manufactured Tantalum.
- Author
-
Gray III, G. T., Knapp, C. M., Jones, D. R., Livescu, V., Fensin, S., Morrow, B. M., Trujillo, C. P., Martinez, D. T., and Valdez, J. A.
- Subjects
- *
MICROSTRUCTURE , *TANTALUM , *METALLOGRAPHY , *SPALLATION (Nuclear physics) , *NUCLEAR reactions - Abstract
Certification and product qualification of an engineering component generally involves meeting engineering and physics requirements tied to its functional requirements. . In this paper, the results of a study quantifying the microstructure and the dynamic damage evolution of Tantalum (Ta) fabricated using an EOS laser-powder-bed machine are presented. The microstructure of the AM-Ta is detailed and compared / contrast to wrought Ta. The dynamic damage evolution and failure response of the AM-Ta material, as well as wrought Ta, was probed using flyer-plate impact driven spallation experiments. The differences in the spallation response between the AM and wrought Ta were measured using in-situ velocimetry as well as postmortem quantification of damage in "soft-recovered" samples. The damage evolution of the AM and wrought Ta were characterized using optical metallography. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
16. The Response of a Commercial Fluorinated Tri-Polymer to 1-D Shock Loading.
- Author
-
Whiteman, G., Millett, J. C. F., Brown, E. N., Gray III, G. T., and Bourne, N. K.
- Subjects
POLYETHYLENE ,POLYPROPYLENE ,POLYTEF ,SHEAR strength ,POLYMERS - Abstract
The response of simple polymers to shock loading is governed by a number of factors such as the complexity of the polymer chains and nature of the atoms attached to the main carbon-carbon backbone. In the case of polyethylene based materials such as polyethylene, polypropylene and polytetrafluoroethylene the competing effects of inter chain tangling (tacticity) and electrostatic repulsion between adjacent polymer chains have been shown to have a profound effect on shock velocity, release velocity and shear strength development. In this work, we apply these considerations to a commercially available fluoro-tripolymer, Viton-B, where all these molecular features are present. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
17. On the Dynamic Tensile Strength of an FCC Metal.
- Author
-
Bourne, N. K., Jones, D., Fensin, S., Trujillo, C., Martinez, D., and Gray III, G. T.
- Subjects
TENSILE tests ,POLYCRYSTALS ,DEFORMATIONS (Mechanics) ,NUCLEATION ,FRACTURE mechanics ,DYNAMIC testing of materials ,ELECTRON backscattering - Abstract
The tensile response of ductile, polycrystalline metals is often accompanied by the formation of pores within the material, which coalesce and fail a plane within a metal. This large deformation process is broadly progressive, with a physical path consisting of nucleation, growth, coalescence, and failure, which occur individually over short periods of time. Thus distinct micro-mechanisms operate, each influenced by microstructure, loading path, and loading profile, which remains a significant challenge to represent and predict numerically at the macroscale. In a previous study, the influence of loading path on damage evolution in high-purity tantalum has been presented; in this paper, complimentary measurements are made on a pure, FCC copper. Samples were shock loaded to three different peak stresses using both symmetric impact, and two different composite flyer plate configurations, such that upon unloading, the three samples were subject to nearly identical tensile loading. The damage evolution in the soft-recovered copper samples was then quantified using optical metallography and electron-back-scatter diffraction. We shall compare metallurgical observations, velocimetry histories and simulations to discuss the dynamic failure mechanics observed. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
18. Yield Strength of Cu and a CuPb alloy (1% Pb).
- Author
-
Buttler, W. T., Gray III, G. T., Fensin, S. J., Grover, M., Prime, M. B., Stevens, G. D., Stone, J. B., and Turley, W. D.
- Subjects
- *
ALLOY testing , *CRYSTAL grain boundaries , *YIELD stress , *STRESS-strain curves , *WAVELENGTHS - Abstract
With PBX9501 we explosively loaded fully annealed OFHC-Cu and an OFHC-CuPb (extruded with 1% Pb that aggregates at the Cu grain boundaries) to study the effects of the 1% Pb on the elastic-plastic yield Y of Cu. The yield-stress Y was studied through observation of surface velocimetry and total ejected mass ρA from periodic surface perturbations machined onto the sample surfaces. The perturbation's wavelengths were λ ≈ 65 μm, and their amplitudes h were varied to determine the wavenumber (2π=λ) amplitude product kh at which ejecta production for the Cu and CuPb begins, which relates to Y. The Y of the two materials is apparently different. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
19. Influence of Sample Geometry on Sweeping-Detonation-Wave Spallation in Tantalum.
- Author
-
Gray III, G. T., Hull, L. M., Livescu, V., Briggs, M. E., and Meyer, R. K.
- Subjects
- *
DETONATION waves , *SHOCK waves , *BLAST effect , *ACOUSTIC vibrations , *SURFACE hardening - Abstract
Widespread research since 1950 has provided a wealth of experimental data concerning shock hardening and the spallation response of materials subjected to square-topped shock-wave loading profiles. Sweeping-wave loading is a significantly different loading history than that achieved by a square-topped impulse or 1-D HE-driven plane-wave shock in terms of the evolving spherical and shear stresses applied. Sweeping-wave loading in a flat-plate geometry was previously observed to: a) yield a lower spall strength than previously documented for 1-D supported-shock-wave loading, b) exhibit increased shock hardening as a function of increasing obliquity, and c) lead to an increased incidence of deformation twin formation with increasing shock obliquity (1). The current sweeping-wave loading of a 10 cm radius curved Ta plate is observed to: a) lead to an increase in the shear stress as a function of increasing obliquity, and b) display a more developed level of damage evolution, extensive voids and coalescence, and lower spall strength with obliquity in the curved plate than in the flat-plate sweeping-detonation wave loading for an equivalent HE loading. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
20. Critical Conditions for Failure; Stress Levels, Length Scales, Time Scales.
- Author
-
Bourne, N. K., Gray III, G. T., and Bronkhorst, C. A.
- Subjects
- *
MECHANICAL stress analysis , *STRAINS & stresses (Mechanics) , *CONDENSED matter physics , *COMPRESSION loads , *DYNAMIC testing of materials - Abstract
There is a range of thresholds for the response of condensed matter under loading in compression, from the yield point to that at which the bond strength is overcome and warm dense matter is formed. Yield stress shows a correlation between the length scale swept by the rise of the pulse and the defect distribution within the target for a range of materials. Strain rate is also a useful term that reflects the evolution of the stress state within a target but must also be defined for a volume element containing a particular defect distribution to reflect continuum conditions acting within; it thus applies to a defined length scale within a target. Examples are shown using shock pulses that spall metal targets. Different stacking shows differing behaviour yet in each case momentum is conserved. This overview suggests simple observations must take account of mechanisms operating at different timescales and lengthscales in the development of damage in materials and structures. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
21. Nucleation and Evolution of Dynamic Damage at Cu/Pb Interfaces Using Molecular Dynamics.
- Author
-
Fensin, S. J., Valone, S. M., Cerreta, E. K., Gray III, G. T., and Shao, S.
- Subjects
NUCLEATION ,DUCTILITY ,MOLECULAR dynamics ,METALS ,COPPER - Abstract
For ductile metals, the process of dynamic fracture occurs through nucleation, growth and coalescence of voids. For high purity single-phase metals, it has been observed by numerous investigators that voids tend to heterogeneously nucleate at grain boundaries and all grain boundaries are not equally susceptible to void nucleation. However, for materials of engineering significance, especially those with second phase particles, it is less clear if the type of bi-metal interface between the two phases will affect void nucleation and growth. To approach this problem in a systematic manner two bi-metal interfaces between Cu and Pb have been investigated: {111} and {100}. Qualitative and quantitative analysis of the collected data from molecular dynamics shock and spall simulations suggests that Pb becomes disordered during shock compression and is the preferred location for void nucleation under tension. Despite the interfaces being aligned with the spall plane (by design), they are not the preferred location for void nucleation irrespective of interface type. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
22. In Situ and Postmortem Measures of Damage in Polymers at High Strain-Rates.
- Author
-
Brown, E. N., Ramos, K. J., Dattelbaum, D. M., Jensen, B. J., Iverson, A. J., Carlson, C. A., Fezzaa, K., Gray III, G. T., Patterson, B. M., Trujillo, C. P., Martinez, D. T., Pierce, T. H., and Furmanski, J.
- Published
- 2015
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.