High strain-rate material model validation for laser peening simulation

Finite element modeling can be a powerful tool for predicting residual stresses induced by laser peening; however the sign and magnitude of the stress predictions depend strongly on how the material model captures the high strain rate response. Although a Johnson-Cook formulation is often employed, its suitability for modeling phenomena at very high strain rates has not been rigorously evaluated. In this paper, we address the effectiveness of the Johnson-Cook model, with parameters developed from lower strain rate material data (∼10^3 s^–1), to capture the higher strain rate response (∼10^5–10^6 s^–1) encountered during the laser peening process. Published Johnson-Cook parameters extracted from split Hopkinson bar testing were used to predict the shock response of aluminum samples during high-impact flyer plate tests. Additional quasi-static and split Hopkinson bar tests were also conducted to study the model response in the lower strain rate regime. The overall objective of the research was to ascertain whether a material model based on conventional test data (quasi-static compression testing and split Hopkinson bar measurements) can credibly be used in FE simulations to predict laser peen-induced stresses

Mechanical Behavior and Microstructural Development of Low-Carbon Steel and Microcomposite Steel Reinforcement Bars Deformed under Quasi-Static and Dynamic Shear Loading

Reinforcement bars of microcomposite (MC) steel, composed of lath martensite and minor amounts of retained austenite, possess improved strength and corrosion characteristics over low-carbon (LC) steel rebar; however, their performance under shear loading has not previously been investigated at the microstructural level. In this study, LC and MC steel cylinders were compression tested, and specimens machined into a forced-shear geometry were subjected to quasi-static and dynamic shear loading to determine their shear behavior as a function of the strain and strain rate. The as-received and sheared microstructures were examined using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Higher-resolution microstructural examinations were performed using transmission electron microscopy (TEM). The influence of the starting microstructure on the shear behavior was found to depend strongly on the strain rate; the MC steel exhibited not only greater strain-rate sensitivity than the LC steel but also a greater resistance to shear localization with load. In both steels, despite differences in the starting microstructure, post-mortem observations were consistent with a continuous mechanism operating within adiabatic shear bands (ASBs), in which subgrains rotated into highly misoriented grains containing a high density of dislocations

Effect of liquid phase on superplastic behavior of a modified 6061 aluminum alloy

It is shown that a 0.15%Zr + 0:7%Cu-modified 6061 aluminum alloy with an initial grain size of about 11 μm exhibits a maximum elongation-to-failure of 1300% at 590º C and an initial strain rate of 2.8 × 10⁻⁴ s⁻¹ in a partially melted stateyesBelgorod State Universit

Effect of Cu and Zr additions on the superplastic behavior of 6061 aluminum alloy

Experiments were conducted to evaluate the influence of zirconium and copper additions on superplastic behavior of a 6061 aluminum alloy. The results suggest the addition of Zr provides high stability of the fine-grained structure under superplastic deformation at high temperatures by precipitation of Al₃Zr dispersoids. Apparently, the increased amount of liquid phase caused by the copper addition can enhance the superplastic properties of the 6061 alloyyesBelgorod State Universit

Effect of liquid phase on superplastic behavior of a modified 6061 aluminum alloy

yesIt is shown that a 0.15%Zr + 0:7%Cu-modified 6061 aluminum alloy with an initial grain size of about 11 μm exhibits a maximum elongation-to-failure of 1300% at 590º C and an initial strain rate of 2.8 × 10⁻⁴ s⁻¹ in a partially melted stateBelgorod State Universit

Effect of Cu and Zr additions on the superplastic behavior of 6061 aluminum alloy

yesExperiments were conducted to evaluate the influence of zirconium and copper additions on superplastic behavior of a 6061 aluminum alloy. The results suggest the addition of Zr provides high stability of the fine-grained structure under superplastic deformation at high temperatures by precipitation of Al₃Zr dispersoids. Apparently, the increased amount of liquid phase caused by the copper addition can enhance the superplastic properties of the 6061 alloyBelgorod State Universit

Liquid-metal embrittlement of refractory metals by molten plutonium

Embrittlement by molten plutonium of the refractory metals and alloys W-25 wt % Re, tantalum, molybdenum, and Ta-10 wt % W was studied. At 900/sup 0/C and a strain rate of 10/sup -4/ s/sup -1/, the materials tested may be ranked in order of decreasing susceptibility to liquid-plutonium embrittlement as follows: molybdenum, W-25 wt % Re, Ta-10 wt % W, and tantalum. These materials exhibited a wide range in susceptibility. Embrittlement was found to exhibit a high degree of temperature and strain-rate dependence, and we present arguments that strongly support a stress-assisted, intergranular, liquid-metal corrosion mechanism. We also believe microstructure plays a key role in the extent of embrittlement. In the case of W-25 wt % Re, we have determined that a dealloying corrosion takes place in which rhenium is selectively withdrawn from the alloy