The Effect of Specimen Geometry on Determination of Elongation in Sheet Tensile Specimens

Kula, Eric B.; Fahey, Norbert H.

doi:10.21236/ada950317

Cited by 4 publications

(2 citation statements)

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“…This means that the samples commonly had thicknesses that were orders of magnitude smaller than the in-plane dimensions. Such geometries are problematic, as they introduce a geometric sample size effect, with strain-to-failure decreasing as sample thickness decreases [25]. Brooks et al [26] explored this effect specifically in nanocrystalline Ni, showing that samples with thicknesses below ~100 µm experienced macroscopically brittle fracture that was not representative of the intrinsic material response.…”

Section: Introductionmentioning

confidence: 99%

Emergence of localized plasticity and failure through shear banding during microcompression of a nanocrystalline alloy

Khalajhedayati

Rupert

2014

Acta Materialia

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Microcompression testing is used to probe the uniaxial stress-strain response of a nanocrystalline alloy, with an emphasis on exploring how grain size and grain boundary relaxation state impact the complete flow curve and failure behavior. The yield strength, strain hardening, strain-to-failure, and failure mode of nanocrystalline Ni-W films with mean grain sizes of 5, 15, and 90 nm are studied using taper-free micropillars that are large enough to avoid extrinsic size effects. Strengthening is observed with grain refinement, but catastrophic failure through strain localization is found as well. Shear banding is found to cause failure, resembling the deformation of metallic glasses. Finally, we study the influence of grain boundary state by employing heat treatments that relax nonequilibrium boundary structure but leave grain size unchanged. A pronounced strengthening effect and increased strain localization is observed after relaxation in the finer grained samples.

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Section: Introductionmentioning

confidence: 99%

Emergence of localized plasticity and failure through shear banding during microcompression of a nanocrystalline alloy

Khalajhedayati

Rupert

2014

Acta Materialia

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“…In brief, under some conditions, it is a good approximation for rectangular bars, which follow this comparison [72]:…”

Section: Effects Of Tensile Pre-strain On the Bake Hardening Responsementioning

confidence: 88%

Conservation Research and Development/ New Ultra-Low Carbon High Strength Steels with Improved Bake Hardenability for Enhanced Stretch Formability and Dent Resistance

DeArdo¹,

García²

2003

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Project Objective: The major objectives of this program were to investigate the bake hardening (BH) mechanism in ultra-low carbon (ULC) steels and use the better understanding of this mechanism to design and process a new generation of bake hardening steels for automotive applications. These new steels will be thoroughly characterized in terms of their microstructure, formability, BH response, and tensile properties. Background:Current bake hardening ULC steels offer bake hardening increments (BHI) in the range of 35 MPa (5 ksi). These current BH ULC steels are limited by the level of understanding of the strengthening mechanisms operative in these steels. It has been proposed that higher levels of BHI await a better understanding and application of these mechanisms. The purpose of this program is to develop an ULC steel that can provide a consistent BH increment of 100 MPa, while retaining good formability. This is important for improving product quality and consistency as well as saving resources and energy, since a higher degree of consistency means fewer rejects, less scrap and less remelting, and fewer failures during the fabrication process. Since only one year of research was funded by the sponsor, this Final Technical Report represents the progress made during the first year of the project. METHOD OF APPROACH:The experimental work can be divided into four phases, as summarized in Table 1. In each phase, the materials were received or designed, processed and tested, to evaluate the BH increment or response, as a function of compositions and processing conditions. Microstructural characterization by various techniques was performed in order to gain insights into the mechanisms of flow stress increment by bake hardening. Efforts are made to clarify the following features:1) the overall nature of the matrix, such as polygonal or acicular ferrite, and grain size, 2) the density, distribution, configuration and overall mobility of dislocations, 3) the amount of C and other alloying elements in solid solution, 4) grain boundary characteristics, such as grain boundary misorientations and distribution, 5) hardness across grain boundaries (nano-scale), and 6) distribution of C around dislocations and grain boundaries (atomic scale). Modeling of the dent resistance using current steel properties would be performed and reported by ORNL. The purpose here was to study the BHI of the commercial BH steel in the batch annealed condition. Very small amounts of carbon were expected to be in solid solution in this condition. There were two goals of this phase. First, to measure the magnitude of BHI in this commercial steel, and, second to begin to examine the role of solute carbon in contributing to the BHI. The steel used in this phase is shown in Table 2. The as-received commercial bake hardenable low carbon steel (with Temper Rolling of ~ 1%) were pre-strained to 2% and 5% and then subjected to the BH treatments as follows:0% strain -180°C/ 20 minutes -ACRT. 0% strain -180°C/ 30 minutes -ACRT. 0% strain -180°C/ 60 minute...

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The development of miniature tensile specimens with non-standard aspect and slimness ratios for rapid alloy prototyping processes

Zhang

Harrison

Yar

et al. 2021

Journal of Materials Research and Technology

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The Effect of Specimen Geometry on Determination of Elongation in Sheet Tensile Specimens

Cited by 4 publications

References 0 publications

Emergence of localized plasticity and failure through shear banding during microcompression of a nanocrystalline alloy

Emergence of localized plasticity and failure through shear banding during microcompression of a nanocrystalline alloy

Conservation Research and Development/ New Ultra-Low Carbon High Strength Steels with Improved Bake Hardenability for Enhanced Stretch Formability and Dent Resistance

The development of miniature tensile specimens with non-standard aspect and slimness ratios for rapid alloy prototyping processes

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