Fragments Produced When Tungsten Penetrates Aluminum

Tungsten rods were shot through blocks of 6061T6 aluminum. The rods were partially eroded, and the remaining length emerged from behind the aluminum accompanied by a large number of small tungsten particles. These constitute behind-armor debris, which is of great practical importance. Analysis of data shows that most debris is generated near the exit face of the aluminum, the particle number increases with velocity, and the particle size increases with rod diameter. The latter two observations are consistent with the Grady–Kipp theory for rate effects on fracture. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Thermal Stability, Glass-Formation Ability, and Mechanical Properties of (Zr41.2Ti13.8Cu12.5Ni10Be22.5)100?xNbx Amorphous Alloys

Bulk amorphous alloys of (Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5)_100−x Nb _x with x = 0, 5, 11, and 13 were prepared by water quenching. Differential scanning calorimeter (DSC) analysis revealed that the addition of Nb enhances the thermal stability but appreciably decreases the glass-forming ability (GFA) of the alloys. Scanning electron microscope (SEM) and compression tests indicated that the Nb addition effectively improves the strength and plasticity of a Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 amorphous alloy, which benefits from multiple shear bands induced by ductile crystalline phase dispersing in the amorphous matrix. The bulk amorphous alloy with x = 5 exhibits a fracture stress of 2070 MPa and total strain to fracture of 25.8 pct, respectively. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007, during the TMS Annual Meeting in Orlando, FL, under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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Fracture of Nitinol under Quasistatic and Dynamic Loading

Owing to the potential application of Nitinol as an advanced structural material, it is essential to thoroughly understand the deformation and fracture behavior of Nitinol under various loading conditions. The present study explores the fracture behavior of Nitinol under quasistatic and dynamic loading, with emphasis on the fracture toughness and fracture mechanism of Nitinol. To this end, the precracked bend sample was employed to perform dynamic fracture testing using a modified (pulse-shaped) Hopkinson-pressure-bar-loaded fracture-testing system. The dynamic fracture initiation toughness was measured under stress-state equilibrium conditions at a loading rate of . To further investigate the fracture mechanism, additional dynamic fracture tests were performed using double-crack, four-point bend samples. The experimental results indicate that the dynamic fracture toughness of Nitinol is higher than it is under quasistatic loading, and that the loading rate influences the fracture mechanisms of Nitinol. The interplay between the dynamic strength of Nitinol and the activation stress for stress-induced martensite (SIM) transformation plays an important role in the fracture behavior of Nitinol. This article is based on a presentation given in the symposium “Dynamic Behavior of Materials,” which occurred February 26–March 1, 2007, during the TMS Annual Meeting in Orlando, FL, under the auspices of the TMS Structural Materials Division and the TMS/ASM Mechanical Behavior of Materials Committee.

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Comparison of the Influence of Temperature on the High-Strain-Rate Mechanical Responses of PBX 9501 and EDC37

Many high-strain-rate compression measurements (2000 per second) using a specially designed split Hopkinson pressure bar (SHPB) for the plastic-bonded explosive PBX9501 have been reported in the literature, but there is a sparsity of data for a United Kingdom polymer-bonded explosives (PBX) known as EDC37. Both EDC37 and PBX9501 are cyclotetramethylenetetranitramine-based (HMX-based) PBXs with high filler contents. The binder systems for the PBXs are very different: EDC37 consists of a nitroplasticized nitrocellulose and PBX9501 a nitroplasticized ESTANE. PBX9501 exhibits nearly invariant fracture strains of ∼1.5 pct as a function of temperature at high strain rates, whereas EDC37 fails at ∼2 to 2.5 pct. The maximum compressive strengths for both PBXs were measured at 150 Mpa at −55 °C, but at +55 °C, the PBX was found to have a maximum strength of ∼55 MPa compared with ∼20 MPa for EDC37. Both PBXs exhibit an increasing loading moduli, E, with increasing strain rate or decreasing temperature. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Effects of Deformation Twinning on Energy Dissipation in High Rate Deformed Zirconium

The posit that deformation twinning can result in energy storage is examined by measuring the temperature increase of zirconium during adiabatic compression at high strain rates and correlating the response with the resulting microstructure. After examining the underlying assumptions of homogeneous deformation via microscopy and numerical modeling, it is determined that the occurrence of twinning does not correlate with significant energy storage relative to dissipation, and the appearance of storage may be caused by inhomogeneity in the deformation. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Microstructural Effects in Face-Centered-Cubic Alloys after Small Charge Explosions

Effects on metal targets after an explosion include the following: fracture, plastic deformation, surface modifications, and microstructural crystallographic alterations with ensuing mechanical properties changes. In the case of small charge explosions, macroscopic effects are restricted to small charge-to-target distances, whereas crystal alterations can still be observed at moderate distances. Microstructural variations, induced on gold-alloy disk samples, as compared to previous results on AISI 304Cu steel samples, are illustrated. The samples were subjected to blast-wave overpressures in the range of 0.5 to 195 MPa. Minimum distances and peak pressures, which could still yield observable alterations, were especially investigated. Blast-related microstructural features were observed on the explosion-exposed surface and on perpendicular cross sections. Analyses using X-ray diffraction (XRD) were performed to identify modifications of phase, texture, dislocation density, and frequency of mechanical twins, before and after the explosions. Optical metallography (OM) and scanning electron microscopy (SEM) observations evidenced partial surface melting, zones with recrystallization phenomena, and crystal plastic deformation marks. The latter marks are attributed to mechanical twinning in the stainless steel and to cross-slip (prevalent) and mechanical twinning (possibly) in the gold alloy. This article is based on a presentation given in the symposium “Dynamic Behavior of Materials,” which occurred February 26–March 1, 2007, during the TMS Annual Meeting in Orlando, FL, under the auspices of the TMS Structural Materials Division and the TMS/ASM Mechanical Behavior of Materials Committee.

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Mechanical Properties,Dislocation Density and Grain Structure of Ultrafine-Grained Aluminum and Aluminum-Magnesium Alloys

The kind and amount of alloying elements strongly affects the formation of ultrafine-grained microstructures. Aluminum alloys with different amounts of the alloying element magnesium, and a commercially pure aluminum alloy, have been investigated in order to evaluate how the obtained microstructures will affect the mechanical properties. X-ray profile analysis has been used to determine grain size and dislocation density. With increasing amounts of alloying elements, a smaller grain size and a higher dislocation density after severe plastic deformation (SPD) are obtained, which lead to higher hardness and improved fatigue properties. This article is based on a presentation made in the symposium entitled “Ultrafine-Grained Materials: from Basics to Application”, which occurred September 25-27, 2006 in Kloster Irsee, Germany.

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Multistage Fatigue Modeling of Cast A356-T6 and A380-F Aluminum Alloys

This article presents a microstructure-based multistage fatigue (MSF) model extended from the model developed by McDowell et al.[1,2] to an A380-F aluminum alloy to consider microstructure-property relations of descending order, signifying deleterious effects of defects/discontinuities: (1) pores or oxides greater than 100 μm, (2) pores or oxides greater than 50 μm near the free surface, (3) a high porosity region with an area greater than 200 μm, and (4) oxide film of an area greater than 10,000 μm². These microconstituents, inclusions, or discontinuities represent different casting features that may dominate fatigue life at stages of fatigue damage evolutions. The incubation life is estimated using a modified Coffin–Mansion law at the microscale based on the microplasticity at the discontinuity. The microstructurally small crack (MSC) and physically small crack (PSC) growth was modeled using the crack tip displacement as the driving force, which is affected by the porosity and dendrite cell size (DCS). When the fatigue damage evolves to several DCSs, cracks behave as long cracks with growth subject to the effective stress intensity factor in linear elastic fracture mechanics. Based on an understanding of the microstructures of A380-F and A356-T6 aluminum alloys, an engineering treatment of the MSF model was introduced for A380-F aluminum alloys by tailoring a few model parameters based on the mechanical properties of the alloy. The MSF model is used to predict the upper and lower bounds of the experimental fatigue strain life and stress life of the two cast aluminum alloys. This article is based on a presentation made in the symposium entitled “Simulation of Aluminum Shape Casting Processing: From Design to Mechanical Properties,” which occurred March 12–16, 2006 during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum Committee.

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Comparison of Crevice Corrosion of Fe-Based Amorphous Metal and Crystalline Ni-Cr-Mo Alloy

The crevice corrosion behaviors of an Fe-based bulk metallic glass alloy (SAM1651) and a Ni-Cr-Mo crystalline alloy (C-22) were studied in 4M NaCl solution at 100 °C with cyclic potentiodynamic polarization and constant-potential tests. The corrosion damage morphologies, corrosion products, and the compositions of corroded surfaces of these two alloys were studied with optical three-dimensional reconstruction, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Auger electron spectroscopy (AES). It was found that the Fe-based bulk metallic glass (amorphous alloy) SAM1651 had a more positive breakdown potential and repassivation potential than crystalline alloy C-22 in cyclic potentiodynamic polarization tests and required a more positive oxidizing potential to initiate crevice corrosion in constant-potential tests. Once crevice corrosion initiated, the corrosion propagation of C-22 was more localized near the crevice border compared to SAM1651, and SAM1651 repassivated more readily than C-22. The EDS results indicated that the corrosion products of both alloys contained a high amount of O and were enriched in Mo and Cr. The AES results indicated that a Cr-rich oxide passive film was formed on the surfaces of both alloys, and both alloys corroded congruently in the crevice corrosion damage areas. This article is based on a presentation given in the symposium entitled “Iron-Based Amorphous Metals: An Important Family of High-Performance Corrosion-Resistant Materials,” which occurred during the MSandT meeting, September 16–20, 2007, in Detroit, Michigan, under the auspices of The American Ceramics Society (ACerS), The Association for Iron and Steel Technology (AIST), ASM International, and TMS.

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Effects of Test Temperature and Loading Conditions on the Tensile Properties of a Zr-Based Bulk Metallic Glass

The effects of changes in test temperature (20 °C, 260 °C, 330 °C, and 380 °C), strain rate (10⁻⁵ to 10⁻¹ s⁻¹), and loading conditions (displacement control vs loading-rate control) on the tensile behavior of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 (LiquidMetal 1 (LM1)), a bulk metallic glass (BMG), have been determined. Significant effects of the test temperature, strain rate, and loading condition were observed on the strength, ductility/elongation, and mechanisms of failure (shear, ductile rupture, etc.). This material exhibited extensive elongation (i.e., >100 pct) prior to failure when tested near the glass transition temperature (T _g  ≈ 375 °C) at sufficiently low strain rates, while higher strain rates or lower test temperatures produced shear fracture at low elongation. The flow and fracture behavior was also significantly affected by the loading condition (i.e., displacement vs loading-rate control). The effective strain rate necessary to cause failure in shear without significant global flow was several orders of magnitude lower in loading-rate control than in displacement control. Samples exhibiting high elongation tested in displacement control gently and convexly drew to a near point (i.e., ductile rupture). Samples tested at the same temperature exhibiting high elongation in loading-rate control rapidly and concavely necked, followed by drawing to a constant diameter “wire” (i.e., ductile drawing), eventually failing by nearly pure ductile rupture. All samples that displayed significant elongation did so inhomogeneously, and were characterized by non-Newtonian global flow. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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Slip-System-Related Dislocation Study from <Emphasis Type="Italic">In-Situ</Emphasis> Neutron Measurements

A combined experimental/computational approach is employed to study slip-system-related dislocation-substructure formation during uniaxial tension of a single-phase, face-centered-cubic (fcc), nickel-based alloy. In-situ neutron-diffraction measurements were conducted to monitor the peak-intensity, peak-position, and peak-broadening evolution during a displacement-controlled, monotonic-tension experiment at room temperature. The measured lattice-strain evolution and the macrostress/macrostrain curves were used to obtain the material parameters required for simulating the texture development by a visco-plastic self-consistent (VPSC) model. The simulated texture compared favorably with experimentally-determined texture results over a range of 0 to 30 pct engineering strain. The grain-orientation-dependent input into the Debye-intensity ring was considered. Grains favorably oriented relative to the two detector banks in the geometry of the neutron experiment were indicated. For the favorably oriented grains, the simulated slip-system activity was used to calculate the slip-system-dependent, dislocation-contrast factor. The combination of the calculated contrast factor with the experimentally-measured peak broadening allows the assessment of the parameters of the dislocation arrangement within the specifically oriented grains, which has a quantitative agreement with the transmission-electron-microscopy results. This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,” which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee.

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Fatigue and Tensile Behavior of Cast,Hot-Rolled,and Severely Plastically Deformed AZ31 Magnesium Alloy

The work focuses on experimental examination of the fatigue behavior of magnesium alloy AZ31 produced by three different procedures: squeeze casting (SC), hot rolling (HR), and equal-channel angular pressing (ECAP). The microstructures produced were studied by light and transmission electron microscopy (TEM). Squeeze-cast AZ31 had low porosity and coarse grains, while hot-rolled material showed microstructure with grain size of 3 to 20 μm. The finest grain structure with the average grain size of about 1 to 2 μm was found in the material pressed 4 times at 200 °C using the ECAP technique, route B _c . It was shown that low- and high-cycle fatigue behavior under symmetric loading at room temperature and with loading frequency of 20 Hz is strongly dependent on the technique employed in producing the alloy. The ECAP was shown to improve the fatigue life of the material in the low-cycle region over that of the squeeze-cast material. However, the fatigue life of AZ31 after ECAP was slightly lower than that of the hot-rolled material. In the high-cycle region, the hot-rolled material and the material that underwent ECAP exhibit the same fatigue strength, which is superior to that of the squeeze-cast alloy. Fatigue crack initiation and the character of fracture were examined by means of scanning electron microscopy. This article is based on a presentation made in the symposium entitled “Ultrafine-Grained Materials: from Basics to Application,” which occurred September 25–27, 2006 in Kloster Irsee, Germany.

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Improved Pulse Shaping to Achieve Constant Strain Rate and Stress Equilibrium in Split-Hopkinson Pressure Bar Testing

Assuring a constant strain rate during dynamic testing is highly desirable to support the development of physically based predictive, constitutive material models. Many dynamic tests conducted on high-work-hardening materials, or materials that do not display a classic power-law-type hardening behavior, such as materials exhibiting complex sigmoidal concave-upward hardening (shape-memory alloys or a number of textured hexagonal metals due to deformation twinning), often result in continuously decreasing strain rates as a function of strain throughout the test. Incident pulse shaping has not been fully developed or successfully demonstrated over a large range of strain in high work hardening or complex-hardening materials. To shape an incident pulse for a constant strain rate in a split-Hopkinson pressure bar (SHPB) test, a high-strength, high-work-hardening rate (HSHWHR) material was selected to fabricate the pulse shaper. Several test sample materials, namely, 50-50 NiTi superelastic alloy, higher strength 60NiTi alloy, tungsten single crystals, interstitial-free (IF) steel, and MACOR (a glassy ceramic), which display a range of strength levels, work-hardening rates, and superelastic hardening behavior in the case of 50-50 NiTi, were tested in the SHPB with and without a pulse shaper at different temperatures and strain rates. The current experiments demonstrate that HSHWHR pulse-shaper materials are ideally suited to shape the incident pulse to achieve constant strain rates and achieve stress state equilibrium, while inherently dampening high frequency oscillations in the incident pulse. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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