ABSTRACT Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples ... more ABSTRACT Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples and the fracture surface features were analyzed in detail to understand the underlying physical processes. Wallner lines, which result from the interaction between the propagating crack front and shear waves emanating from a secondary source, were observed on the fracture surface and geometric analysis of them indicates that the maximum crack velocity is ∼800 m s−1, which corresponds to ∼0.32 times the shear wave speed. Fractography reveals that the sharp crack nucleation at the notch tip occurs at the mid-section of the specimens with the observation of flat and half-penny-shaped cracks. On this basis, we conclude that the crack initiation in brittle BMGs is stress-controlled and occurs through hydrostatic stress-assisted cavity nucleation ahead of the notch tip. High magnification scanning electron and atomic force microscopies of the dynamic crack growth regions reveal highly organized, nanoscale periodic patterns with a spacing of ∼79 nm. Juxtaposition of the crack velocity with this spacing suggests that the crack takes ∼10−10 s for peak-to-peak propagation. This, and the estimated adiabatic temperature rise ahead of the propagating crack tip that suggests local softening, is utilized to critically discuss possible causes for the nanocorrugation formation. Taylor’s fluid meniscus instability is unequivocally ruled out. Then, two other possible mechanisms, viz. (a) crack tip blunting and resharpening through nanovoid nucleation and growth ahead of the crack tip and eventual coalescence, and (b) dynamic oscillation of the crack in a thin slab of softened zone ahead of the crack-tip, are critically discussed.
The mode I fracture toughness, KIc, of ductile bulk metallic glasses (BMGs) exhibits a high degre... more The mode I fracture toughness, KIc, of ductile bulk metallic glasses (BMGs) exhibits a high degree of specimen-to-specimen variability. By conducting fracture experiments in modes I and II, we demonstrate that the observed high variability in mode I, vis-à-vis mode II, is a result of highly variable propensity for the conversion of shear bands into cracks in mode I whereas in mode II, crack growth direction is fixed. Thus, the measured variability in KIc is intrinsic to the nature of BMGs.
ABSTRACT Significant progress in understanding the mechanical behavior of metallic glasses (MGs) ... more ABSTRACT Significant progress in understanding the mechanical behavior of metallic glasses (MGs) was made over the past decade, particularly on mechanisms of plastic deformation. However, recent research thrust has been on exploring the mechanics and physics of fracture. MGs can be very brittle with \(K_{Ic}\) values similar to silicate glasses and ceramics or very tough with \(K_{Ic}\) akin to high toughness crystalline metals. Even the tough MGs can become brittle with structural relaxation following annealing at temperatures close to glass transition temperature \((T_{g})\) . Detailed experimental studies coupled with complementary numerical simulations of the recent past have provided insights on the micromechanisms of failure as well as nature of crack tip fields, and established the governing fracture criteria for ductile and brittle glasses. In this paper, the above advances are reviewed and outstanding issues in the context of fracture of amorphous alloys that need to be resolved are identified.
Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples and the f... more Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples and the fracture surface features were analyzed in detail to understand the underlying physical processes. Wallner lines, which result from the interaction between the propagating crack front and shear waves emanating from a secondary source, were observed on the fracture surface and geometric analysis of them indicates that the maximum crack velocity is 800 m s1, which corresponds to 0.32 times the shear wave speed. Fractography reveals that the sharp crack nucleation at the notch tip occurs at the mid-section of the specimens with the observation of flat and half-pennyshaped cracks. On this basis, we conclude that the crack initiation in brittle BMGs is stress-controlled and occurs through hydrostatic stress-assisted cavity nucleation ahead of the notch tip. High magnification scanning electron and atomic force microscopies of the dynamic crack growth regions reveal highly organized, nanoscale periodic patterns with a spacing of 79 nm. Juxtaposition of the crack velocity with this spacing suggests that the crack takes 1010 s for peak-to-peak propagation. This, and the estimated adiabatic temperature rise ahead of the propagating crack tip that suggests local softening, is utilized to critically discuss possible causes for the nanocorrugation formation. Taylor’s fluid meniscus instability is unequivocally ruled out. Then, two other possible mechanisms, viz. (a) crack tip blunting and resharpening through nanovoid nucleation and growth ahead of the crack tip and eventual coalescence, and (b) dynamic oscillation of the crack in a thin slab of softened zone ahead of the crack-tip, are critically discussed
Some bulk metallic glasses (BMGs) exhibit high crack initiation toughness due to shear band media... more Some bulk metallic glasses (BMGs) exhibit high crack initiation toughness due to shear band mediated plastic flow at the crack tip and yet do not display additional resistance to crack growth due to the lack of a microstructure. Thus, at crack initiation, the fracture behavior of BMGs transits from that of ductile alloys to that of brittle ceramics.
ABSTRACT Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples ... more ABSTRACT Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples and the fracture surface features were analyzed in detail to understand the underlying physical processes. Wallner lines, which result from the interaction between the propagating crack front and shear waves emanating from a secondary source, were observed on the fracture surface and geometric analysis of them indicates that the maximum crack velocity is ∼800 m s−1, which corresponds to ∼0.32 times the shear wave speed. Fractography reveals that the sharp crack nucleation at the notch tip occurs at the mid-section of the specimens with the observation of flat and half-penny-shaped cracks. On this basis, we conclude that the crack initiation in brittle BMGs is stress-controlled and occurs through hydrostatic stress-assisted cavity nucleation ahead of the notch tip. High magnification scanning electron and atomic force microscopies of the dynamic crack growth regions reveal highly organized, nanoscale periodic patterns with a spacing of ∼79 nm. Juxtaposition of the crack velocity with this spacing suggests that the crack takes ∼10−10 s for peak-to-peak propagation. This, and the estimated adiabatic temperature rise ahead of the propagating crack tip that suggests local softening, is utilized to critically discuss possible causes for the nanocorrugation formation. Taylor’s fluid meniscus instability is unequivocally ruled out. Then, two other possible mechanisms, viz. (a) crack tip blunting and resharpening through nanovoid nucleation and growth ahead of the crack tip and eventual coalescence, and (b) dynamic oscillation of the crack in a thin slab of softened zone ahead of the crack-tip, are critically discussed.
The mode I fracture toughness, KIc, of ductile bulk metallic glasses (BMGs) exhibits a high degre... more The mode I fracture toughness, KIc, of ductile bulk metallic glasses (BMGs) exhibits a high degree of specimen-to-specimen variability. By conducting fracture experiments in modes I and II, we demonstrate that the observed high variability in mode I, vis-à-vis mode II, is a result of highly variable propensity for the conversion of shear bands into cracks in mode I whereas in mode II, crack growth direction is fixed. Thus, the measured variability in KIc is intrinsic to the nature of BMGs.
ABSTRACT Significant progress in understanding the mechanical behavior of metallic glasses (MGs) ... more ABSTRACT Significant progress in understanding the mechanical behavior of metallic glasses (MGs) was made over the past decade, particularly on mechanisms of plastic deformation. However, recent research thrust has been on exploring the mechanics and physics of fracture. MGs can be very brittle with \(K_{Ic}\) values similar to silicate glasses and ceramics or very tough with \(K_{Ic}\) akin to high toughness crystalline metals. Even the tough MGs can become brittle with structural relaxation following annealing at temperatures close to glass transition temperature \((T_{g})\) . Detailed experimental studies coupled with complementary numerical simulations of the recent past have provided insights on the micromechanisms of failure as well as nature of crack tip fields, and established the governing fracture criteria for ductile and brittle glasses. In this paper, the above advances are reviewed and outstanding issues in the context of fracture of amorphous alloys that need to be resolved are identified.
Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples and the f... more Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples and the fracture surface features were analyzed in detail to understand the underlying physical processes. Wallner lines, which result from the interaction between the propagating crack front and shear waves emanating from a secondary source, were observed on the fracture surface and geometric analysis of them indicates that the maximum crack velocity is 800 m s1, which corresponds to 0.32 times the shear wave speed. Fractography reveals that the sharp crack nucleation at the notch tip occurs at the mid-section of the specimens with the observation of flat and half-pennyshaped cracks. On this basis, we conclude that the crack initiation in brittle BMGs is stress-controlled and occurs through hydrostatic stress-assisted cavity nucleation ahead of the notch tip. High magnification scanning electron and atomic force microscopies of the dynamic crack growth regions reveal highly organized, nanoscale periodic patterns with a spacing of 79 nm. Juxtaposition of the crack velocity with this spacing suggests that the crack takes 1010 s for peak-to-peak propagation. This, and the estimated adiabatic temperature rise ahead of the propagating crack tip that suggests local softening, is utilized to critically discuss possible causes for the nanocorrugation formation. Taylor’s fluid meniscus instability is unequivocally ruled out. Then, two other possible mechanisms, viz. (a) crack tip blunting and resharpening through nanovoid nucleation and growth ahead of the crack tip and eventual coalescence, and (b) dynamic oscillation of the crack in a thin slab of softened zone ahead of the crack-tip, are critically discussed
Some bulk metallic glasses (BMGs) exhibit high crack initiation toughness due to shear band media... more Some bulk metallic glasses (BMGs) exhibit high crack initiation toughness due to shear band mediated plastic flow at the crack tip and yet do not display additional resistance to crack growth due to the lack of a microstructure. Thus, at crack initiation, the fracture behavior of BMGs transits from that of ductile alloys to that of brittle ceramics.
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Papers by Parag Tandaiya
in detail to understand the underlying physical processes. Wallner lines, which result from the interaction between the propagating
crack front and shear waves emanating from a secondary source, were observed on the fracture surface and geometric analysis of them
indicates that the maximum crack velocity is 800 m s1, which corresponds to 0.32 times the shear wave speed. Fractography reveals
that the sharp crack nucleation at the notch tip occurs at the mid-section of the specimens with the observation of flat and half-pennyshaped
cracks. On this basis, we conclude that the crack initiation in brittle BMGs is stress-controlled and occurs through hydrostatic
stress-assisted cavity nucleation ahead of the notch tip. High magnification scanning electron and atomic force microscopies of the
dynamic crack growth regions reveal highly organized, nanoscale periodic patterns with a spacing of 79 nm. Juxtaposition of the crack
velocity with this spacing suggests that the crack takes 1010 s for peak-to-peak propagation. This, and the estimated adiabatic temperature
rise ahead of the propagating crack tip that suggests local softening, is utilized to critically discuss possible causes for the nanocorrugation
formation. Taylor’s fluid meniscus instability is unequivocally ruled out. Then, two other possible mechanisms, viz. (a) crack
tip blunting and resharpening through nanovoid nucleation and growth ahead of the crack tip and eventual coalescence, and (b) dynamic
oscillation of the crack in a thin slab of softened zone ahead of the crack-tip, are critically discussed
in detail to understand the underlying physical processes. Wallner lines, which result from the interaction between the propagating
crack front and shear waves emanating from a secondary source, were observed on the fracture surface and geometric analysis of them
indicates that the maximum crack velocity is 800 m s1, which corresponds to 0.32 times the shear wave speed. Fractography reveals
that the sharp crack nucleation at the notch tip occurs at the mid-section of the specimens with the observation of flat and half-pennyshaped
cracks. On this basis, we conclude that the crack initiation in brittle BMGs is stress-controlled and occurs through hydrostatic
stress-assisted cavity nucleation ahead of the notch tip. High magnification scanning electron and atomic force microscopies of the
dynamic crack growth regions reveal highly organized, nanoscale periodic patterns with a spacing of 79 nm. Juxtaposition of the crack
velocity with this spacing suggests that the crack takes 1010 s for peak-to-peak propagation. This, and the estimated adiabatic temperature
rise ahead of the propagating crack tip that suggests local softening, is utilized to critically discuss possible causes for the nanocorrugation
formation. Taylor’s fluid meniscus instability is unequivocally ruled out. Then, two other possible mechanisms, viz. (a) crack
tip blunting and resharpening through nanovoid nucleation and growth ahead of the crack tip and eventual coalescence, and (b) dynamic
oscillation of the crack in a thin slab of softened zone ahead of the crack-tip, are critically discussed