Surface Effects in Crystal Plasticity: General Overview

Latanision, R. M.

doi:10.1007/978-94-011-9691-8_1

Cited by 26 publications

(17 citation statements)

References 47 publications

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“…A ltogether the literature on surface e ects on plasticity is enormous, including the proceedings of at least two specialized conf erences (Westwood andStolo 1966, Latanision andFourie 1977). Most signi® cant for the purposes of the present paper is the evident extreme sensitivity of plastic deformation to stored energy that is demonstrated by the discussed e ects, as mere fractions of an electronvolt per atom ic length and a width of b or less of surf ace ledge can have a noticeable impact.…”

Section: Slip Lam Ellae In`wavy Glide' and Surf Ace E Ects In Plasticitymentioning

confidence: 93%

The theory of dislocation-based crystal plasticity

Kuhlmann‐Wilsdorf

1999

Philosophical Magazine A

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A bstract An overview of the low-energy dislocation structure (LEDS) theory of lowtemperature, that is non-creep, dislocation-based crystal plasticity is presented, as systematically developed over the past 35 years. It is ultimately based on G. I. Taylor's 1934 theory of work hardening wherein he assumed that stress application causes the essentially instantaneous athermal generation of dislocation structures which are in equilibrium with the applied stress and which on stress release and reversal are stable up to the previously highest stress magnitude. As will be shown, at least in principle even though many details are still lacking, the following phenomena of crystal plasticity are readily explained by means of the LEDS theory: ( 1) the four stages of work hardening; ( 2) the shape of the stress± strain curve; ( 3) the temperature dependence of work hardening; (4) the low-temperature strain rate dependence of the¯ow stress; (5) the di erence between`planar' and`wavy' glide materials ( as exempli® ed by a -brass and copper respectively); (6) the empirical relationship D KGb/ ¿ between dislocation cell size and¯ow stress; (7) grain-boundary hardening; ( 8) alloy hardening including solid-solution, precipitation and phase-boundary hardening; ( 9) slip lines and slip bands; ( 10) the evolution of the dislocation structures from stages I to IV; (11) deformation texture evolution; (12) work softening; (13) the thermodynamics of dislocation storage; (14) recovery, creep and recrystallization; (15) the development of dislocation structures in f atigue. A ll these are explained e ortlessly on the basis of only the known properties of glide dislocations and the second law of thermodynamics, as expressed in the LEDS hypothesis, to wit that, am ong the structures which are in equilibrium with the applied tractions and accessible to the dislocations, those are form ed which m ost nearly m inimize the stored energy. (See Note added in proof at end of this paper.) The alternative`self-organizing dislocation' model of crystal plasticity assumes plastic deformation to be due to individual thermally activated processes, which are treatable by the thermodynamics of energy-¯ow-through systems. It can be traced back to the early theory by R . Becker in 1925 and 1926 and still has to yield signi® cant results. §1. IntroductionLargely unobserved by solid-state physicists and materials scientists, the development of the theoretical fundamentals of dislocation-ba sed non-creep crystal plasticity is nearing completion, and it seems appropriate to outline brie¯y the present state of understandin g. It is ultimately based on the theory of Taylor (1934). A ccording to that theory, the imposition of stresses in excess of the previously highest evoke almost instantaneou s dislocation multiplication and glide by which dislocation patterns are formed that support the stresses, or else the material fails through fracture. Since 1986 it has been called the low-energy dislocation structure (LEDS) theory and before that was known as the`mesh-le...

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Section: Slip Lam Ellae In`wavy Glide' and Surf Ace E Ects In Plasticitymentioning

confidence: 93%

The theory of dislocation-based crystal plasticity

Kuhlmann‐Wilsdorf

1999

Philosophical Magazine A

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“…Plastic deformation and the rebinder effect. Through a variety of processes collectively termed the Rebinder effect, water adsorbed onto the surfaces of ionic and covalent solids can give rise to dislocation-controlled indentation creep [Latanision, 1977]. To see if the Rebinder effect contributed to convergence in our experiments, we conducted an additional control experiment in air at high humidity and loads of 4.07-4.23 N. The lenses for this experiment (PSH 34) were exposed to laboratory air at 41% relative humidity for 27 hours and then sealed in this air in the microscope stage at room temperature.…”

Section: Measurement Of Deformation At the Contactmentioning

confidence: 99%

Kinetics of pressure solution at halite‐silica interfaces and intergranular clay films

Hickman¹,

Evans²

1995

J. Geophys. Res.

172

126

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of pressure solution at halite-silica interfaces and intergranular clay films" (1995). by diffusion through an intergranular film with a very high diffusion coefficient (• 10 -5-10 -7 cm2/s). The data further suggest that the diffusion coefficient and/or thickness of this film increases with decreasing normal stresses, at least for normal stresses less than about 4 MPa. As no island-channel boundary structures were observed, we propose that this film consists of a continuous layer of strongly adsorbed (i.e., structured) water that is maintained between the halite and silica lenses during deformation. Convergence rates in similar experiments conducted at a constant load of 0.11 N but at 8.3 ø, 50.2 ø, and 90.2øC were approximately constant at a given normal stress and contact spot size. The cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation. An experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0.8-/•m-thick film of Na-montmorillonite in brine. This clay film produced an approximately fivefold increase in convergence rates over those observed in a halite/ silica experiment conducted without clay at the same load and temperature. The strong sensitivity of IPS rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine-grained, clay-rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust.

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“…The effect has traditionally been attributed to either "microcracks" on the workpiece surface promoting a physicochemical effect (21,22) or a fundamental change in the dislocation structure near the surface (20). Besides the speculative nature of these explanations, the reports of the force reductions have been inconsistent (23,24). Sinuous flow provides a natural explanation for this effect-any surface application, including volatile CCl 4 , will modify the surface mechanical state of the workpiece and inhibit initial bump formation ahead of the tool.…”

mentioning

confidence: 99%

Sinuous flow in metals

Yeung

Viswanathan

Compton

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Annealed metals are surprisingly difficult to cut, involving high forces and an unusually thick "chip." This anomaly has long been explained, based on ex situ observations, using a model of smooth plastic flow with uniform shear to describe material removal by chip formation. Here we show that this phenomenon is actually the result of a fundamentally different collective deformation mode-sinuous flow. Using in situ imaging, we find that chip formation occurs via large-amplitude folding, triggered by surface undulations of a characteristic size. The resulting fold patterns resemble those observed in geophysics and complex fluids. Our observations establish sinuous flow as another mesoscopic deformation mode, alongside mechanisms such as kinking and shear banding. Additionally, by suppressing the triggering surface undulations, sinuous flow can be eliminated, resulting in a drastic reduction of cutting forces. We demonstrate this suppression quite simply by the application of common marking ink on the free surface of the workpiece material before the cutting. Alternatively, prehardening a thin surface layer of the workpiece material shows similar results. Besides obvious implications to industrial machining and surface generation processes, our results also help unify a number of disparate observations in the cutting of metals, including the so-called Rehbinder effect.folding | plasticity | metal cutting | instability | deformation

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Surface Effects in Crystal Plasticity: General Overview

Cited by 26 publications

References 47 publications

The theory of dislocation-based crystal plasticity

The theory of dislocation-based crystal plasticity

Kinetics of pressure solution at halite‐silica interfaces and intergranular clay films

Sinuous flow in metals

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