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This paper introduces a method to determine the material constants for Johnson-Cook model of an as-extruded Mg-Gd-Y series alloy by quasistatic tests on Instron 1251 and Hopkinson bar experiment at room and elevated temperatures. The results indicate that the thermal softening exponent of the current magnesium alloy is as high as 3.05, which is obviously higher than that of most metal materials, such as steel and tungsten. High thermal softening exponent usually means high energy absorption efficiency, and the comparison of the dynamic stress-strain curves between ZK60 and Mg-Gd-Y series alloy indeed indicates that the energy absorption efficiency of the Mg-Gd-Y series alloy is higher than that of ZK60. Additionally, high energy absorption efficiency makes the Mg-Gd-Y series alloy exhibit more excellent antipenetration performance than that of 7A52 aluminum alloy at equal areal density condition. [DOI: 10.1115/1.4001291] Keywords: Mg-Gd-Y series alloy, Hopkinson bar experiments, thermal softening exponent, energy absorption efficiency, antipenetration performance

Extensive work performed by Capstone Turbine Corporation, Oak Ridge National Laboratory, and various others has shown that the traditional primary surface recuperator alloy, type 347 stainless steel, is unsuitable for applications above 650[degrees]C (~1200[degrees]F). Numerous studies have shown that the presence of water vapor greatly accelerates the oxidation rate of type 347 stainless steel at temperatures above 650[degrees]C (~1200[degrees]F). Water vapor is present as a product of combustion in the microturbine exhaust, making it necessary to find replacement alloys for type 347 stainless steel that will meet the long life requirements of microturbine primary surface recuperators. It has been well established over the past few years that alloys with higher chromium and nickel contents than type 347 stainless steel have much greater oxidation resistance in the microturbine environment. One such alloy that has replaced type 347 stainless steel in primary surface recuperators is Haynes Alloy HR-120 (Haynes and HR-120 are trademarks of Haynes International, Inc.), a solid-solution-strengthened alloy with nominally 33 wt % Fe, 37 wt % Ni and 25 wt % Cr. Unfortunately, while HR-120 is significantly more oxidation resistant in the microturbine environment, it is also a much more expensive alloy. In the interest of cost reduction, other candidate primary surface recuperator alloys are being investigated as possible alternatives to type 347 stainless steel. An initial rainbow recuperator test has been performed at Capstone to compare the oxidation resistance of type 347 stainless steel, HR-120, and the Allegheny Ludlum austenitic alloy AL 20-25 + Nb (AL 20-25 + Nb is a trademark of ATI Properties, Inc. and is licensed to Allegheny Ludlum Corporation). Evaluation of surface oxide scale formation and associated alloy depletion and other compositional changes has been carried out at Oak Ridge National Laboratory. The results of this initial rainbow test will be presented and discussed in this paper. [DOI: 10.1115/1.3157094]

This article provides a materials selection methodology applicable to lightweight actively cooled panels, particularly suitable for the most demanding aerospace applications. The key ingredient is the development of a code that can be used to establish the capabilities and deficiencies of existing panel designs and direct the development of advanced materials. The code is illustrated for a fuel-cooled combustor liner of a hypersonic vehicle, optimized for minimum weight subject to four primary design constraints (on stress, temperatures, and pressure drop). Failure maps are presented for a number of candidate high-temperature metallic alloys and ceramic composites, allowing direct comparison of their thermostructural performance. Results for a Mach 7 vehicle under steady-state flight conditions and stoichiometric fuel combustion reveal that, while C-SiC satisfies the design requirements at minimum weight, the Nb alloy Cb752 and the Ni alloy Inconel X-750 are also viable candidates, albeit at about twice the weight. Under the most severe heat loads (arising from heat spikes in the combustor), only Cb752 remains viable. This result, combined with robustness benefits and fabrication facility, emphasizes the potential of this alloy for scramjets. [DOI: 10.1115/1.2966270] Keywords: active cooling, lightweight structures, sandwich panels, hypersonics, multifunctional optimization, thermal stresses, materials selection

Fundamental study of deformation and fatigue fracture behavior of solder alloys under complex load conditions is a key to enabling implementation of sophisticated three-dimensional (3D) time-dependent nonlinear finite-element stress and strain analyses for the life assessment for electronic packages and assemblies. In this study, the ratedependent deformation and fatigue fracture behavior of Sn3.8Ag0.7Cu Pb-free alloy and Sn--Pb eutectic alloy was investigated with thin-walled specimens using a biaxial servocontrolled tension--torsion material testing system, with solder alloys subjected to a variety of complex load conditions: pure shearing at strain rates between 6.7 x [10.sup.-7]/s and 1.3 X [10.sup.-1]/s, creep at temperatures ranging from room temperature up to 125[degrees]C, and cyclic loading with frequencies of 0.001 Hz to 3 Hz. Biaxial stress conditions were imposed to investigate the effects of multiaxial stresses on deformation behavior The effects of frequency and temperature on cyclic deformation and fatigue facture were investigated for lead-free Sn3.8Ag0.7Cu and Sn--Pb eutectic solder. Fractography of fatigue tested samples was also conducted to determine possible fatigue failure mechanisms. [DOI: 10.1115/1.2721593]

A damage coupling framework is proposed with a unified viscoplastic constitutive model for the fatigue life prediction of solder alloys, including a consistent and systematic procedure for the determination of material parameters. The model also incorporates the effects of grain size and cyclic hardening/softening. The phenomenological framework of continuum damage mechanics (CDM) is modified to embed intensive researches on the ductile damage fracture by void nucleation, growth, and coalescence, based on a lower bound for the viscoplastic potential of voided materials. The damage coupling with elasticity and viscoplasticity is formulated by irreversible thermodynamic approach. The constitutive model is also extended to large deformation kinematics. The preliminary application of the model to creep damage is presented.

The simulation process and methodology for developing two models for computing recrystallized grain size in Alloy 718 billet are shown. Controlled high temperature compression testing was employed to apply alternate deformation and dwell cycles to Alloy 718 specimens. Grain size derived by simulation was found to be very much in agreement with grain size from forged billet when cooling rate was included. Findings also indicated that strain per pass and forging temperature were the predominant factors in regulating the recrystallized grain size.

A collision-limited kinetics model shows nonequilibrium pulse laser surface melting and resolidification of the pure metals Al, Cu, Ti and Ni, and dilute Al-Cu binary alloys. The rate of resolidification depends on the laser flux, pulse duration and substrate material properties. The variations in the pattern of interface velocity indicates strong interactions between heat transfer, solute partitioning, phase change kinetics and initial solute concentration.

A study of the influence of turbulence on solidification of a binary metal alloy reveals that turbulence increases mixing and decreases the effective Lewis number from 8600 almost to one, and thus reduces the tendency for channel development and macrosegregation. A laminar flow model was compared with a low-Reynolds-number k-epsilon model to determine the turbulence. The numerical model is discussed.

Ostergren, Frequency separation and Stress-Strain-Time models aid the analysis of fatigue behavior of Haynes Alloy 556, at elevated temperatures. Fatigue data obtained at strain ranges between 0.265 and 1.5% help evaluate deformation properties of the 22Cr-20Ni-18Co-Fe alloy. A Holloman-type equation comprising the 120th or midlife cyclic deformation data describes the cyclically stabilized stress-strain response of the alloy.

The measurement of local heat and mass transport coefficients at the mush/liquid interface using a two-wavelengthholographic interferometry technique is discussed. The transient solidificationof an aqueous water and ammonium chloride mixture around a cold pipe is the paticular focus of the experiment. A complex, possibly three-dimensional flow field was created in the system.

The influence of the alloy composition of high-speed steel twist drills on the devices' performance are studied by means of tool-life tests. Experiments are conducted wherein several alloy-treated high-speed steel matrix twist drill specimens with low residual carbide content are fabricated and subjected to actual tooling processes. Results show that the drills' tool-life depends largely on the structures' matrix properties rather than their alloy composition.

The wetting characteristics of molten solder alloys on metal substrates are studied. Since the performance of solder joints is partially dependent on the effects of mechanical forces during the alloys' liquifaction, it is important to investigate the nature of such forces. Tests were conducted on different kinds of alloys to determine their wetting behaviors, particularly the generation of precursor films. It was found that precursor films with different material composition were produced when the solders failed to attain a uniform equilibrium state.

The thermomechanical behaviors of a new lead free solder and eutectic 63Sn37Pb are investigated in this paper. A series of tests including tensile, creep, and fatigue, are carried out on a computer controlled 6-axis mini-fatigue tester. The thin strip specimen is used in this research, which is specially designed and verified to be suitable for the testing of solder alloys and comparable to the data from the literature. Based on the experimental study, the new lead free solder alloy shows very attractive characteristics and may have potential applications in electronics packaging products.