Effect of aspect ratio on the compressive deformation and fracture behaviour of Zr-based bulk metallic glass

Zhang, Z. F.; Zhang, H.; Pan, Xiangnan; Das, J.; Eckert, J.

doi:10.1080/09500830500395237

Cited by 152 publications

(80 citation statements)

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“…They relate this difference in behavior to the density of the specimens which, for the denser materials, add inertia effects to the dynamic compression process. The threshold aspect ratio, L/D=1, according to [7], is the limiting case for the intersection of the shear planes with the cylinder wall, as was suggested by ZHANG et al [12] for the failure behavior of their Zr-based bulk metallic glass specimens. Moreover, the titanium specimens failed through a large number of planes inclined at about 45° to the specimen faces.…”

Section: Resultsmentioning

confidence: 99%

The effect of specimen dimensions on the propensity to adiabatic shear failure in Kolsky bar experiments

Rosenberg

Ashuach

Kreif³

2010

Matéria (Rio J.)

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The issue of adiabatic shearing is discussed in this work and a new interpretation is given to some failure phenomena which are usually termed as adiabatic shears. We propose that only a few materials undergo a truly inherent failure which is due to thermal softening at the shearing zone and that the interplay between microvoids, cracks and narrow shear bands should be taken into account through the temperature rise at the front of advancing cracks. Also, the size of the plastic zone ahead of a crack plays an important role in determining the brittleness of a given specimen and should be taken into account when specimens of different sizes are tested. Experimental results for several alloys in the Kolsky bar system support our approach.Keywords: Kolsky bar, SHPB, adiabatic shear banding. INTRODUCTIONAdiabatic shear banding is one of the major failure mechanisms of solids subjected to high rate loading. Extensive research on this subject has been conducted over the past 50 years, both experimentally and theoretically, much of which is summarized in BAI and DODD [1]. The most common explanation of this dynamic instability is based on the competing tendencies of the solid to strengthen at high strains (and strain rates) and, on the other hand, to soften with the temperature increase under adiabatic loading conditions. Although many materials seem to behave accordingly, the basic mechanism which causes this softening is still unresolved. Recent work on the subject is focused on the basic physics behind this process, as can be found in [2-5], for example. These works emphasize the link between adiabatic shearing and ductile fracture by the coalescence of microvoids, since the shear zones act as precursor sites for eventual failure by cracks (see [2]). GIOVANOLA [3,4] conducted a careful experimental study on 4340 steel specimens, in order to follow the evolution of strain localization and failure which he finds to proceed in two stages. He found that the first stage of localization (deformed bands) results in the formation of local perturbations for the strain field, such as machining marks. These perturbations grow as a result of the imbalance between strain hardening and thermal softening. In the second stage, softening is due to the nucleation and growth of microvoids, leading to the shear fracture within the band. GIOVANOLA [3,4] suggested that this process can take place under other conditions, including quasi-static loading. He also emphasized the role of the compressive stress which acts on the shear plane to reduce the microvoid nucleation process.FLOCKHART et al.[5] used numerical simulations to follow the shear band in dynamically compressed specimen, by analyzing the loci of velocity discontinuities within the specimen. They also claim that "the distinction between shear fracture and adiabatic shear failure is not clear", and that "material susceptibility to adiabatic shear alone does not guarantee that failure occurs by this mechanism, as shear fracture may intervene". This interplay between shear...

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Section: Resultsmentioning

confidence: 99%

The effect of specimen dimensions on the propensity to adiabatic shear failure in Kolsky bar experiments

Rosenberg

Ashuach

Kreif³

2010

Matéria (Rio J.)

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“…Efforts have been made to enhance the plasticity of BMGs, mostly focusing on the fabrication of BMG composites. [23][24][25][26][27] Very recently, Liu et al 28 succeeded to prepare several Zr-based BMGs which show an exceptional deformability and a high strain as revealed by compression tests. The samples which were able to endure maximum deformation ͑yielding at 1690 MPa, maximum true strain of 160%͒ had a composition of Zr 64.13 Cu 15.75 Ni 10.12 Al 10 .…”

Section: Introductionmentioning

confidence: 99%

Strain distribution in Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass investigated by in situ tensile tests under synchrotron radiation

Stoica

Das

Bednarčı́k

et al. 2008

Journal of Applied Physics

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We report on the evolution of the atomic-scale strain tensor of ductile Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass under tensile loading by using x-ray synchrotron radiation. The same kind of samples was previously investigated under compressive loading and revealed yielding at 1690 MPa together with large deformability of up to 160% strain. In tension the samples fracture at a lower stress, 1500 MPa, with no sign of yielding or plastic deformation. With no macroplasticity observed under tension, large differences in the elastic constants obtained from the strain tensor and from ultrasonic sound velocity measurements are revealed. This paper presents in detail the measuring procedure as well as the calculation of the tensile tensor and pair distribution functions of Zr64.13Cu15.75Ni10.12Al10 at different stages of deformation. The results are discussed in comparison with other reported data obtained from x-ray diffraction measurements using synchrotron radiation.

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“…Because the partially relieved local heating and hindrance of the propagation of shear bands, both the strength and the ductility of a Zr-based BMG are enhanced at cryogenic temperatures [12]. A compressive strain as large as 80% for a previously brittle BMG was obtained under constrained conditions, by tuning the strain rate and aspect ratio [13]. Large plasticity has also been obtained by shot-peening [16], electrodeposition [17,18] and use of a metal sleeve [19].…”

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confidence: 97%

“…So to enhance the plasticity of BMGs, it is necessary to promote the activation of multiple shear bands [2][3][4][5][6][7][8][9][10] and hinder the localization and rapid propagation of shear bands [11][12][13][14][15][16][17][18][19]. Indeed much important progress has been made in enhancing the ductility of BMGs by various ways [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], such as by introducing second phase particles on the nanoscale/microscale [2][3][4][5] or solid solution particles [6] which restrict the severe localization and rapid propagation of shear bands, the as-prepared BMG composites could exhibit a global plasticity of about 7% [7].…”

mentioning

confidence: 99%

“…Indeed much important progress has been made in enhancing the ductility of BMGs by various ways [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], such as by introducing second phase particles on the nanoscale/microscale [2][3][4][5] or solid solution particles [6] which restrict the severe localization and rapid propagation of shear bands, the as-prepared BMG composites could exhibit a global plasticity of about 7% [7]. Because the partially relieved local heating and hindrance of the propagation of shear bands, both the strength and the ductility of a Zr-based BMG are enhanced at cryogenic temperatures [12].…”

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Work toughening effect in Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass

2011

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Work hardening is a well-known phenomenon occurring in crystalline metals during deformation, which has been widely used to increase the strength of metals although their ductility is usually reduced simultaneously. Here we report that the plastic strain of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 (at.%) bulk metallic glasses has been increased from 0.3% for the as-cast sample to 2.5%-8.0% for samples that have experienced pre-deformation under constrained conditions. The pre-deformed glassy alloys possess more free volume and abundant introduced shear bands, which are believed to promote the activation of shear bands in post-deformation and result in an increase in plasticity. The orientation of the pre-introduced shear bands relative to the loading direction will affect the deformation behavior of pre-deformed samples. The present results show that pre-deformation of this glassy alloy will result in work toughening. This work toughening effect can be removed by isothermal annealing at a sub-T g (glass transition) temperature, which causes annihilation of free volume and healing of shear bands. It is well known that most bulk metallic glasses (BMGs) possess super-high strength but very low global plasticity. The accepted reason for the limited plasticity of BMGs is that BMGs possess a tendency to form highly-localized shear bands which result in early fracture of the materials. It is obvious that deformation behavior of BMGs is quite different from crystalline metals, in which plastic deformation corresponds to the generation and motion of large numbers of dislocations. As the dislocation density increases with the plastic deformation, the interactions among dislocations are also increased, resulting in an increase in the resistance to dislocation movement. Then, further deformation requires an increase in the applied stress. This is the so-called "strain hardening" or "work hardening". However, since there are no dislocations in glassy alloys, absolutely no strain hardening resulting from interactions among dislocations can be observed in BMGs. So it is very difficult for glassy alloys to deform uniformly. Instead, highly localized shear bands [1] form easily during the deformation process, resulting in limited global plasticity of BMG. So to enhance the plasticity of BMGs, it is necessary to promote the activation of multiple shear bands [2-10] and hinder the localization and rapid propagation of shear bands [11][12][13][14][15][16][17][18][19]. Indeed much important progress has been made in enhancing the ductility of BMGs by various ways [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], such as by introducing second phase particles on the nanoscale/microscale [2][3][4][5] or solid solution particles [6] which restrict the severe localization and rapid propagation of shear bands, the as-prepared BMG composites could exhibit a global plasticity of about 7% [7]. Because the partially relieved local heating and hindrance of the propagation of shear bands, both the strength and the ductility of a Zr-bas...

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Effect of aspect ratio on the compressive deformation and fracture behaviour of Zr-based bulk metallic glass

Cited by 152 publications

References 23 publications

The effect of specimen dimensions on the propensity to adiabatic shear failure in Kolsky bar experiments

The effect of specimen dimensions on the propensity to adiabatic shear failure in Kolsky bar experiments

Strain distribution in Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass investigated by in situ tensile tests under synchrotron radiation

Work toughening effect in Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass

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