Effect of dynamic strain rate on micro-indentation properties of pure aluminum

Yamada, Hitoshi; Hotta, Midori; Kami, Tsuyoshi; Ogasawara, Nagahisa; Chen, Xi

doi:10.1051/epjconf/20159404034

Cited by 3 publications

(2 citation statements)

References 8 publications

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“…γ and m are strain rate parameters, which are defined as dynamic constants. Experiment results of 5N aluminum (99.999 mass% purity) at low strain rate (10 −4 ,10 −2 /s) and high strain rate (10 2 /s) [18] were used. True stress-strain relationships were shown in Fig.…”

Section: Simulation Modelmentioning

confidence: 99%

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Strain rate behavior of pure aluminum in conical indentation with different indenter control methods

Kami¹,

Yamada²,

Ogasawara³

et al. 2017

Int. J. CMEM

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Strain rate effect of strength is a crucial factor for material characterization. Attempts have been made to evaluate strain rate effect by indentation tests. An indentation causes a non-uniform stress and strain field inside a specimen. This must induce a non-uniform strain rate field. However, little has been reported about strain rate distribution beneath the indenter. So far, various indenter control methods have been used. In previous studies, no direct comparisons were available as to how strain rate distribution was affected by different control methods. In this study, we report on the strain rate effect of indentation with two indenter control methods: constant loading rate (CLR) and constant indentation strain rate (CISR). The finite element method was designed to reproduce deformation caused by a conical indenter of a half apex angle of 70.3°. Pure aluminum (99.999 mass% purity), which showed high strain rate dependence of strength, was chosen as a specimen. Material properties were obtained from low strain rate (10 −4 , 10 −2 /s) to high strain rate (10 2 /s) tests, and results were incorporated into a FEM analysis using the Cowper-Symonds equation. Four constant loading rates (from 0.7 to 350 mN/s) and constant indentation strain rates (from 0.006 to 6/s) were used, and both results were compared. Differences between both indenter control methods were displacement-dependent. Loading curvature, which has been defined as a material constant in the indentation, was calculated from load divided by square of displacement. Although loading curvatures were decreased with increasing displacement for CLR, they were constant for CISR. Results also showed that values of strain rate decreased as displacement increased for CLR, whereas they were the same for CISR. Similarities of both indenter control methods were found as follows. The highest strain rate regions were observed at the edge of the indenter. In addition, higher strain rate region was distributed hemispherically from the edge of the indenter.

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Section: Simulation Modelmentioning

confidence: 99%

“…(a) Schematic image of model; (b) True stress-strain curves for 5N aluminum at the low and high strain rate[18].…”

mentioning

confidence: 99%

Strain rate behavior of pure aluminum in conical indentation with different indenter control methods

Kami¹,

Yamada²,

Ogasawara³

et al. 2017

Int. J. CMEM

Self Cite

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Ballistic Limit of Sandwich Plates With a Metal Foam Core

Cui

Zhang

et al. 2021

Journal of Applied Mechanics

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The ballistic perforation of sandwich plates comprising two identical/unidentical aluminum alloy face sheets and an aluminum foam core is investigated to gain insights into the factors governing the penetration processes. The impact velocities of projectiles with conical, flat, and hemispherical noses range from 60 ms−1 to 220 ms−1 in the experiments. Against conical-ended projectiles, petalling failure is found to be an active failure mode at the rear face sheet. Against projectiles with flat and hemispherical noses, both petalling failure and petalling-flipped-cover failure are observed. Finite element simulations considering the effect of foam meso-structure on the ballistic limit of sandwich plates are performed and validated against the experimental results. It is shown that the local bending and fracture of the cell walls significantly dissipate the kinetic energy of the projectile and restrain the occurrence of the high stress regions. Characteristic double-peak and single-peak modes of contact force time histories are observed for projectiles with various nose shapes. It is also found that a sandwich plate with thicker front face sheet has higher ballistic resistance, which may facilitate the instructional arrangement of face sheets with regard to mass distribution to achieve higher ballistic resistance. Finally, a three-stage theoretical model based on energy balance principle is developed for each type of projectile to predict the residual velocities after perforation of sandwich plate.

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Effect of strain rate on serrated load of indentation in Al-Mg alloy

Kami

Yamada

Ogasawara

2017

Transactions of the JSME (In Japanese)

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Indentation tests are used to determine the local mechanical properties of materials. Previously, the indentation strain rate was correlated with the strain rate in uniaxial tests based on the hardness, which was the obtained load divided by the cross-sectional area. However, the hardness can be influenced by pile-up of material after indentation. The purpose of this study was to relate the indentation strain rate with the uniaxial strain rate through serration behavior. The material used in this study was 5082 aluminum alloy, whose main alloying elements are aluminum and magnesium, and which is known to exhibit serration at certain temperatures and strain rates. Quasi-static uniaxial tensile tests were performed at strain rates from 10 -4 to 10 -1 s -1 at room temperature. Micro-indentation using a Berkovich indenter was performed at constant loading rates from 0.7 to 350 mN/s. The loading curvature, which was defined as the load divided by the square of the displacement, was used instead of the hardness to avoid the pile-up effect. As a result, the serrated loading curvature in the indentation tests was obtained as the decreasing loading rate. The effective strain rate, which was defined as the derivative of the load with respect to time divided by two times the applied load, decreased with increasing displacement. The serrated loading curvature changed its behavior as the effective strain rate decreased. It behaved similarly to the serration observed in uniaxial tensile tests. It was found that the indentation strain rate is correlated with the strain rate in uniaxial tensile tests through the serration behavior.

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Effect of dynamic strain rate on micro-indentation properties of pure aluminum

Cited by 3 publications

References 8 publications

Strain rate behavior of pure aluminum in conical indentation with different indenter control methods

Strain rate behavior of pure aluminum in conical indentation with different indenter control methods

Ballistic Limit of Sandwich Plates With a Metal Foam Core

Effect of strain rate on serrated load of indentation in Al-Mg alloy

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