Nanocrystalline metals go ductile under shear deformation

Ames, Markus; Grewer, Manuel; Braun, Christian; Birringer, R.

doi:10.1016/j.msea.2012.03.061

Cited by 16 publications

(16 citation statements)

References 57 publications

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“…Applying load to the top and bottom faces forces the SCS to shear along the gauge section, which has been oriented 45 • relative to the load direction. Such miniaturized SCS have been successfully applied to large strain testing of NC PdAu alloys by Ames et al [14]. Since plastic deformation is confined to the gauge section [30], the SCS is ideally suited for synchrotron based transmission experiments with the scattering vector probing the in-plane evolution of XRD peak parameters during deformation.…”

Section: Methodsmentioning

confidence: 99%

“…Since plastic deformation is confined to the gauge section [30], the SCS is ideally suited for synchrotron based transmission experiments with the scattering vector probing the in-plane evolution of XRD peak parameters during deformation. To avoid shadowing of the scattering cones by the edges of the gauge slits, we deviate from the SCS design in [14] by using a trapezoid slit profile (see Fig. 1) to adapt the geometry of the SCS to the diffraction measurement.…”

Section: Methodsmentioning

confidence: 99%

“…In a recent work Ames et al [14] demonstrated that NC Pd 90 Au 10 (D ≤ 10 nm) exhibits a pronounced strain-rate dependence prevailing up to large strains. Utilizing activation parameters to identify active deformation mechanisms, they found the measured activation volume and strain-rate sensitivity of NC Pd 90 Au 10 to be compatible within the error margins with partial dislocation activity (PDA), STs (the generic flow event in metallic glasses) and SDGBM.…”

Section: Introductionmentioning

confidence: 99%

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Anatomizing deformation mechanisms in nanocrystalline Pd 90 Au 10

Grewer

Braun

Deckarm

et al. 2017

Mechanics of Materials

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We utilized synchrotron-based in-situ diffraction and dominant shear deformation to identify, dissect, and quantify the relevant deformation mechanisms in nanocrystalline Pd 90 Au 10 in the limiting case of grain sizes at or below 10 nm. We could identify lattice and grain boundary elasticity, shear shuffling operating in the core region of grain boundaries, stress driven grain boundary migration, and dislocation shear along lattice planes to contribute, however, with significantly different and nontrivial stress-dependent shares to overall deformation. Regarding lattice elasticity, we find that Hookean linear elasticity prevailed up to the maximal stress value of ≈ 1.6 GPa. Shear shuffling that propagates strain at/along grain boundaries increases progressively with increasing load to carry about two thirds of the overall strain in the regime of macroplasticity. Stress driven grain boundary migration requires overcoming a threshold stress slightly below the yield stress of ≈ 1.4 GPa and contributes a share of ≈ 10 % to overall strain. Appreciable dislocation activity begins at a stress value of ≈ 0.9 GPa to then increase and eventually propagate a maximal share of ≈ 15 % to overall strain. In the stress regime below 0.9 GPa, which is characterized by a markedly decreasing tangent modulus, shear shuffling and lattice-and grain boundary elasticity operate exclusively. The material response in this regime seems indicative of nonlinear viscous behavior rather than being correlated with work-or strain hardening as observed in conventional fcc metals.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Anatomizing deformation mechanisms in nanocrystalline Pd 90 Au 10

Grewer

Braun

Deckarm

et al. 2017

Mechanics of Materials

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“…A miniature version of the SCS was used for the characterization of nanomaterials [12], and a modified SCS geometry was developed to investigate the mechanical response of polymers [13,14]. An analytical data reduction scheme was proposed by [15].…”

Section: Introductionmentioning

confidence: 99%

Modification of the Shear-Compression Specimen for Large Strain Testing

2015

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A modified shear-compression specimen (SCS), for large strain testing over a wide range of strain rates is presented. The original SCS design includes two rectangular slots that are machined at 45°with respect to the longitudinal axis. The modification consists of creating two diametrically opposed semi-circular slots. The new "circular" specimen is first thoroughly investigated numerically under quasi-static and dynamic loading using an elastoplastic material model. The results of the comparison between the two-slot designs confirm the feasibility of the new specimen for larger strain testing and indicates its advantages over the rectangular slot design: larger strain range characterization, failure and fracture within the gauge, and constant Lode parameter during plastic deformation. Both types of SCS as well as cylindrical specimens are used to characterize the flow behavior of steel 1020, in the quasi-static and dynamic regimes using a split Hopkinson pressure bar. Dog-bone specimens are also tested quasi-statically in tension. A very good agreement is achieved for the results of all specimens in both the quasi-static and dynamic regimes. The numerical validation procedure shows that the flow stress of 1020 steel obtained with the new SCS is~3 % lower in the quasistatic regime, and 8 % lower in the dynamic regime with respect to the flow stress of the rectangular SCS. This difference is attributed to effect of the third invariant of the stress deviator (i.e., Lode parameter), which is considerably lower in the new SCS design.

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“…The specimen is similar to the known shear compression specimen (SCS) which was introduced in [16] and was validated numerically for static and dynamic loading and parabolic hardening materials in [17][18][19]. The SCS was used in several investigations [20][21][22][23][24][25][26][27] and was recently modified to have a circular gauge [28]. The STS consists of a long cylinder having an inclined gage section created by two diametrically opposed semi-circular slots which are machined at 45°with respect to the longitudinal axis.…”

Section: Introductionmentioning

confidence: 99%

A Shear-Tension Specimen for Large Strain Testing

2015

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A new shear-tension specimen (STS) is designed, evaluated and tested quasi-statically and dynamically. The specimen consists of a long cylinder having an inclined gauge section created by two diametrically opposed semi-circular slots which are machined at 45°with respect to the longitudinal axis. The geometry imposes stress condition within the gauge section which correspond to a Lode parameter of− 0.5, between pure shear (0) and uniaxial tension (−1). It thus provides a wider span of loading conditions for a material. A thorough numerical study reveals that the stresses and strains within the gauge are rather uniform, and the average Mises stress and plastic strain on the mid-section of the gauge represent the material true stress-strain characteristics. The data reduction technique to determine the stresses and strains is presented. Quasi-static and dynamic tests at strain rate of 10 4 1/s were carried out on specimens made of 1020 cold-rolled steel. No necking or softening was observed with this specimen, and the fracture location was always well within the gauge. The obtained stress-strain curves and ductility were validated numerically. The STS is a new specimen to study the combined influence of tension and shear on the mechanical characteristics of a material.

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Nanocrystalline metals go ductile under shear deformation

Cited by 16 publications

References 57 publications

Anatomizing deformation mechanisms in nanocrystalline Pd 90 Au 10

Anatomizing deformation mechanisms in nanocrystalline Pd 90 Au 10

Modification of the Shear-Compression Specimen for Large Strain Testing

A Shear-Tension Specimen for Large Strain Testing

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