Global Plasticity Research Articles

Industrial wastes as alternative raw materials to produce eco-friendly fired bricks

This work focuses on the incorporation of sugarcane bagasse ash (SCBA) and silica fume (SF) wastes as an alternative raw material into clay bricks, replacing clay by up to 40 wt.%. Fly ash (FA) was used as reference. The plasticity of the batches was determined by Atterberg’s consistency limits. Bricks were produced by uniaxial pressing and fired a 900 and 1000°C. Physical properties (fired shrinkage, water absorption, apparent porosity and Initial water absorption rate) and mechanical properties (compressive strength and flexural strength) as function of the firing temperature and type waste were investigated. The results showed that wastes into clay body increase its global plasticity. 80%Clay-20%SCBA mixture has the lower linear shrinkage. After firing process, the brick produced with clay-SCBA show the higher water absorption and apparent porosity, regardless of the firing temperature. The brick produced with 60%clay-40%SF show the water absorption and apparent porosity similar to control bricks. The SCBA waste additions tend to decrease the mechanical strength of the clay bricks, therefore amounts of 40% SCBA waste should be avoided because it reduce the mechanical strength of the red fired bricks. The fired bricks with 40% SF, firing a 900°C show mechanical properties similar control bricks.

Microscopic mechanism on the evolution of plasticity in nanolamellar γ-Ni/Ni5Zr eutectic composites

The evolution of microstructure and the mechanical properties of a series of (Ni0.912Zr0.088)100-xAlx (0≤x≤4) eutectic composites, constitute of γ-Ni and Ni5Zr nanolamellar phases, have been presented. Al dissolves in γ-Ni phase preferentially, decreases its hardness and refines the microstructure. Strain rate jump test was performed in order to investigate the rate sensitivity. It has been found that activation volume increases from 39b3 to 46b3 upon Al addition. The strain rate sensitivity of the composites has been estimated to be ~0.008. The scanning and transmission electron microscopic studies have confirmed that dislocation meditated flow in nano-lamellar phases dominates the plastic deformation mechanism. Analysis based on Stroh's pile-up model suggests that the required shear stress for slip decreases and that for cleavage crack nucleation increases around a dislocation pile-up at the lamellae interface, upon Al addition. The nano-lamellar Ni5Zr strengthen the composite, whereas, dislocation slip endorses the global plasticity of high strength Ni-Zr-(Al) nanoeutectic composites.

Stagnation accommodated global plasticity in nanoglass composites

To reveal mechanical effects of intersecting shear flow in metallic nanoglass composites, thin film structured with layers of Al–Zr glass and columnar hexagonal grains of Cu–Zr glass has been studied with molecular dynamics. Pronounced homogeneous deformation beyond 10% of applied strain can be achieved at room temperature, either by impeding shear band formation through intergranular flow stagnation or by accommodating multiple shear banding flow through intragranular flow stagnation. Highly localized inhomogeneous flow or shear band can be suppressed effectively.

Achieving the desirable compressive plasticity by installing notch cluster in metallic glass

In this work, the compressive global plasticity depending on different settings of notch cluster was investigated on Zr-based metallic glass by experiment and finite element simulation. In experiment, it was found that a large plasticity could be generated by changing the distance of notch pairs which could make the shear bands (SBs) interact with each other and block the rapid shear banding. By introducing the Mohr–Coulomb yielding criterion and the associated flow rule, an elastic–plastic model was built up to describe deformation process for all specimens by means of finite element method (FEM). Combined with the experimental results, it demonstrated that the large plasticity was attributed to the intersection of multiple SBs which was caused by V-shaped plastic strain regions according to FEM results. Finally, conclusive parameters were tentatively proposed to work as the direct and fundamental basis for fabrication of new metallic glass based porous materials or composites.

Ductility enhancement in nanoglass: role of interaction stress between flow defects

Using a thermodynamically consistent non-local plasticity model, the mechanistic origin of enhancement in ductility and suppression of dominant shear banding in nanoglasses (NGs) is analysed. It is revealed that the interaction stress between flow defects plays a central role in promoting global plasticity of NGs. Specifically, we find that the intrinsic length associated with this stress provides a scaling for the shear band width and its coupling with grain size governs the level of enhancement in the deformation behaviour of NGs. The present work may provide useful insights in developing highly ductile NGs for practical engineering applications.

Coupled glide-climb diffusion-enhanced crystal plasticity

This paper presents a fully coupled glide-climb crystal plasticity model, whereby climb is controlled by the diffusion of vacancies. An extended strain gradient crystal plasticity model is therefore proposed, which incorporates the climbing of dislocations in the governing transport equations. A global–local approach is adopted to separate the scales and assess the influence of local diffusion on the global plasticity problem. The kinematics of the crystal plasticity model is enriched by incorporating the climb kinematics in the crystallographic split of the plastic strain rate tensor. The potential of the fully coupled theory is illustrated by means of two single slip examples that illustrate the interaction between glide and climb in either bypassing a precipitate or destroying a dislocation pile-up.

An atomistic investigation of structural evolution in metallic glass matrix composites

Metallic glass matrix composites may have unique mechanical properties and potential for practical applications. Deformation mechanisms governing the structural evolution process of these mixed structures remain poorly understood. In this article, we elucidate the effect of the crystalline second phase on the tension behavior of metallic glass matrix composites by using large-scale atomistic simulations. We identify that the interaction between the crystalline second phase and the local shear bands is dominated by the cooperative activation of lattice dislocations on the glass–crystal interfaces and discrete shearing events in the neighboring glass matrix. By tailoring the morphology of the crystalline second phase, one observes deflection, bifurcation and suppression of local shear bands and succeeds in enhancing the global plasticity of the composite structure. Guiding principles aimed at designing effective crystalline second phases in metallic glasses are proposed as conclusions.

Pressure and temperature effects on tensile strength andplasticity of metallic glasses

The effects of superimposed hydrostatic pressure and test temperature on the strength and plasticity of two different bulk metallic glasses have been determined. The effects of superimposed hydrostatic pressure on the global tensile strength and plasticity at test temperatures well below the Tg of the metallic glass are negligible, consistent with the minor effects of superimposed pressure on the elastic constants at these temperatures. However, increasing the test temperature produces tensile strength reductions and an increase in the global plasticity at 0.1MPa. Superposition of hydrostatic pressure produces significant increases in strength and reduced ductility at temperatures approaching Tg for both a Zr-based and La-based bulk metallic glass. Potential source(s) of the pressure-induced changes in strength and global plasticity of the bulk metallic glasses are provided, and relate to pressure-induced increases in viscosity near Tg.

Structural origins for the high plasticity of a Zr–Cu–Ni–Al bulk metallic glass

The structural origins for the high plasticity of a Zr53Cu18.7Ni12Al16.3 (at.%) bulk metallic glass are explored. Under plastic flow conditions, in situ synchrotron high-energy X-ray diffraction reveals that the atomic strain saturates to the closest packing in the longitudinal direction of the applied load while atoms yield in the transverse plane. Scanning electron microscopy investigation reveals that global plasticity benefits from abundant shear band multiplication and interactions. Atomic level flows are seen to accompany profuse shear bands. The plasticity enhancement of this metallic glass benefits from such atomic level flows. Atomic level flow facilitates the activation of shear transformation zones that further self-assemble to promote shear band multiplication. On the other hand, it also mitigates the shear band propagation that prevents catastrophic shear band extension.

Microhardness characterisation in developing high strength, high toughness and superior ballistic resistance low carbon Ni steel

To develop new steels that exceed the ballistic resistance, strength and toughness of current naval ship steel plates, we designed optimally quenching–lamellarising–tempering treated low carbon 10%Ni steel plates. These plates displayed exceptional properties in all aspects; when compared to the widely used HSLA-100 steel plates, they showed superior toughness and an improvement of over 15% in strength and 20 mm fragment simulation projectile ballistic limit V50. A preliminary vibrating sample magnetometer study on the effect of quenching–lamellarising–tempering process and dynamic deformation on the microstructure evolution of the 10%Ni steel during ballistic impact was valuable to our understanding of the steel. The data led us to conclude that dynamic deformation during ballistic perforation induced an austenite to martensite phase transformation, which improves the global dynamic plasticity and ballistic resistance of the steel target. This mechanism, similar to the transformation induced plasticity effect, can be appropriately named ballistic induced plasticity. Characteristics of the microhardness maps of the sectioned craters created by ballistics are consistent with ballistic induced plasticity.

Nanocrystallization enabled tensile ductility of Co-based amorphous microwires

Melt-extracted amorphous Co68.15Fe4.35Si12.25B15.25 microwires were drawn at ambient temperature into different diameters and the dependence of tensile properties and microstructural evolution on the degree of deformation was investigated. The cold-drawn wire with 51% area cross-section reduction exhibits a tensile ductility of 1.64%, with a tensile strength exceeding 4000 MPa. Deformation-induced Co-rich nanocrystals were observed in the cold-drawn wires and proved to be capable of arresting the quick extension of shear bands and leading to the enhanced global plasticity of the microwires.

Enhanced plasticity of Fe-based bulk metallic glass by tailoring microstructure

The room temperature compressive plasticity of Fe75Mo5P10C8.3B1.7 bulk metallic glass (BMG) was improved from 0.5% to 1.8% by increasing the sample diameter from 1.5 mm to 2.0 mm. With increasing the sample diameter to 2.0 mm, a heterogeneous microstructure with in-situ formed α-Fe dendrite sparsely distributed in the amorphous matrix can be attained. This heterogeneous microstructure is conceived to be highly responsible for the enhanced global plasticity in this marginal Fe-based BMG.

Tensile Plasticity in Metallic Glasses with PronouncedβRelaxations

Metallic glasses are commonly brittle, as they generally fail catastrophically under uniaxial tension. Here we show pronounced macroscopic tensile plasticity achieved in a La-based metallic glass which possesses strong β relaxations and nanoscale heterogeneous structures. We demonstrate that the β relaxation is closely correlated with the activation of the structural units of plastic deformations and global plasticity, and the transition from brittle to ductile in tension and the activation of the β relaxations follow a similar time-temperature scaling relationship. The results have implications for understanding the mechanisms of plastic deformation and structural origin of β relaxations as well as for solving the brittleness in metallic glasses.

Compressive Plasticity of Zr-Based Bulk Metallic Glass at Low Temperature

The mechanical properties of a new Zr-based bulk metallic glass at low temperatures were investigated. The results indicate that the fracture strength increases significantly (4.9%) and the global plasticity increases somewhat when testing temperature is lowered to 123K. The stress-strain curve of the sample deformed exhibits more serrations and smaller stress drop due to formation of more shear bands at low temperature than at room temperature.

Compartmentalized versus Global Synaptic Plasticity on Dendrites Controlled by Experience

Synapses in the brain are continuously modified by experience, but the mechanisms are poorly understood. In vitro and theoretical studies suggest threshold-lowering interactions between nearby synapses that favor clustering of synaptic plasticity within a dendritic branch. Here, a fluorescently tagged AMPA receptor-based optical approach was developed permitting detection of single-synapse plasticity in mouse cortex. Sensory experience preferentially produced synaptic potentiation onto nearby dendritic synapses. Such clustering was significantly reduced by expression of a phospho-mutant AMPA receptor that is insensitive to threshold-lowering modulation for plasticity-driven synaptic incorporation. In contrast to experience, sensory deprivation caused homeostatic synaptic enhancement globally on dendrites. Clustered synaptic potentiation produced by experience could bind behaviorally relevant information onto dendritic subcompartments; global synaptic upscaling by deprivation could equally sensitize all dendritic regions for future synaptic input.

Observations on Clustered Synaptic Plasticity and Highly Structured Input Patterns

In this issue of Neuron, Makino and Malinow and Kleindienst etal. present evidence of a behaviorally induced form of synaptic plasticity that would encourage the development of fine-scale structured input patterns andthe binding of features within single neurons.

Effect of solid solution elements on nanoindentation hardness, rate dependence, and incipient plasticity in fine grained magnesium alloys

The effect of solid solution alloying elements on the plastic deformation of fine grained Mg alloys was studied in five binary systems: Mg–0.3 at.% X (X=Al, Ca, Li, Y or Zn). All the alloys were produced by extrusion and had an average grain size of ∼2–3μm. Solid solution strengthening is observed for all of the alloys subjected to hardness tests with a scale much larger than the grain size, and the efficacy of the various solutes is in line with expectations based on recent solution strengthening models. The different alloying elements also have an impact on the rate dependence of deformation, with activation volumes ranging between 20 b3 and 80 b3 being consistent with cross-slip as a rate limiting mechanism. For nanoscale indentations the yield point is identified by a pop-in event, and this event is found to have a dramatically different rate dependence and activation volume than does global plasticity. Specifically, the dislocation generation mechanism associated with pop-in has an activation volume of scale ∼0.2–1 b3, and is far less affected by solute content than is global plasticity.

Learning-stage-dependent, field-specific, map plasticity in the rat auditory cortex during appetitive operant conditioning

Cortical reorganizations during acquisition of motor skills and experience-dependent recovery after deafferentation consist of several distinct phases, in which expansion of receptive fields is followed by the shrinkage and use-dependent refinement. In perceptual learning, however, such non-monotonic, stage-dependent plasticity remains elusive in the sensory cortex. In the present study, microelectrode mapping characterized plasticity in the rat auditory cortex, including primary, anterior, and ventral/suprarhinal auditory fields (A1, AAF, and VAF/SRAF), at the early and late stages of appetitive operant conditioning. We first demonstrate that most plasticity at the early stage was tentative, and that long-lasting plasticity after extended training was able to be categorized into either early- or late-stage-dominant plasticity. Second, training-induced plasticity occurred both locally and globally with a specific temporal order. Conditioned-stimulus (CS) frequency used in the task tended to be locally over-represented in AAF at the early stage and in VAF/SRAF at the late stage. The behavioral relevance of neural responses suggests that the local plasticity also occurred in A1 at the early stage. In parallel, the tone-responsive area globally shrank at the late stage independently of CS frequency, and this shrinkage was also correlated with the behavioral improvements. Thus, the stage-dependent plasticity may commonly underlie cortical reorganization in the perceptual learning, yet the interactions of local and global plasticity have led to more complicated reorganization than previously thought. Field-specific plasticity has important implications for how each field subserves in the learning; for example, consistent with recent notions, A1 should construct filters to better identify auditory objects at the early stage, while VAF/SRAF contribute to hierarchical computation and storage at the late stage.

Strain localization in annealed Cu 50Zr 50 metallic glass

A molecular dynamics simulation technique was used to investigate the atomic structural changes in Cu 50Zr 50 metallic glass during isothermal annealing, with the aim of clarifying the mechanism responsible for the reduction of the plasticity experimentally observed during uniaxial loading of heat-treated Cu 50Zr 50. The atomic strain during shear deformation was calculated for the as-cast and annealed samples to evaluate the degree of strain localization, which affects the global plasticity of the alloys. The validity of the normalized relaxation heat parameter used to evaluate the degree of strain localization has been verified during elastostatic compression. The variation of the potential energy in the elastic regime, which was found to be correlated to the degree of strain localization, is proposed as parameter to evaluate by computational simulation the ability of an amorphous alloy to deform plastically.

In Situ Nanomechanics of GaN Nanowires

The deformation, fracture mechanisms, and the fracture strength of individual GaN nanowires were measured in real time using a transmission electron microscope-scanning probe microscope (TEM-SPM) platform. Surface mediated plasticity, such as dislocation nucleation from a free surface and plastic deformation between the SPM probe (the punch) and the nanowire contact surface were observed in situ. Although local plasticity was observed frequently, global plasticity was not observed, indicating the overall brittle nature of this material. Dislocation nucleation and propagation is a precursor before the fracture event, but the fracture surface shows brittle characteristic. The fracture surface is not straight but kinked at (10-10) or (10-11) planes. Dislocations are generated at a stress near the fracture strength of the nanowire, which ranges from 0.21 to 1.76 GPa. The results assess the mechanical properties of GaN nanowires and may provide important insight into the design of GaN nanowire devices for electronic and optoelectronic applications.