Irreversible thermodynamics of ideal plastic deformation

ABSTRACTThe characteristics of superplasticity are discussed from the viewpoint of irreversible thermodynamics, in particular, system evolution and the formation of dissipative structures. A mathematical model combining determinism with indeterminism is used to analyze plastic deformation and superplasticity in metals. Since the plastic deformation of a metal is in essence a dissipative process occurring in a system far away from thermodynamic equilibrium, the instability of the system resulting from structure fluctuations (defects) and thermodynamic bifurcations (possible thermodynamic states) will result in many deformation mechanisms being available to provide the deformation observed in the system. Thus it is virtually impossible to describe all the possible models in conventional terms i.e. by the application of the method of determinism. A new model is proposed, and is shown to account for much of the experimental data reported.

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Dislocation annihilation in plastic deformation: I. Multiscale irreversible thermodynamics

Acta Materialia ◽

10.1016/j.actamat.2012.01.027 ◽

2012 ◽

Vol 60 (6-7) ◽

pp. 2606-2614 ◽

Cited By ~ 26

Author(s):

P.E.J. Rivera-Díaz-del-Castillo ◽

M. Huang

Keyword(s):

Plastic Deformation ◽

Irreversible Thermodynamics ◽

Dislocation Annihilation

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Ideal plastic deformation of thick-walled tubes

10.1063/1.4912503 ◽

2015 ◽

Author(s):

Rostislav I. Nepershin

Keyword(s):

Plastic Deformation ◽

Ideal Plastic

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Sem Examinations of Glass Knives

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100068400 ◽

1970 ◽

Vol 28 ◽

pp. 282-283

Author(s):

J. Temple Black

Keyword(s):

Plastic Deformation ◽

Tensile Loading ◽

Resultant Force ◽

Stress Concentrations ◽

Edge Chipping ◽

Surface Flaws ◽

Edge Defects ◽

Microscopic Surface

There are two types of edge defects common to glass knives as typically prepared for microtomy purposes: 1) striations and 2) edge chipping. The former is a function of the free breaking process while edge chipping results from usage or bumping of the edge. Because glass has no well defined planes in its structure, it should be highly resistant to plastic deformation of any sort, including tensile loading. In practice, prevention of microscopic surface flaws is impossible. The surface flaws produce stress concentrations so that tensile strengths in glass are typically 10-20 kpsi and vary only slightly with composition. If glass can be kept in compression, wherein failure is literally unknown (1), it will remain intact for long periods of time. Forces acting on the tool in microtomy produce a resultant force that acts to keep the edge in compression.

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Stereo Electron Microscopy Applied to High Resolution Freeze-Etch Replicas

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100068527 ◽

1970 ◽

Vol 28 ◽

pp. 306-307

Author(s):

L. Andrew Staehelin

Keyword(s):

Electron Microscopy ◽

Plastic Deformation ◽

High Resolution ◽

Smooth Surfaces ◽

Small Particles ◽

Membrane Surfaces ◽

Wide Acceptance ◽

New Information ◽

Number Of Particles ◽

Small Holes

Freeze-etched membranes usually appear as relatively smooth surfaces covered with numerous small particles and a few small holes (Fig. 1). In 1966 Branton (1“) suggested that these surfaces represent split inner mem¬brane faces and not true external membrane surfaces. His theory has now gained wide acceptance partly due to new information obtained from double replicas of freeze-cleaved specimens (2,3) and from freeze-etch experi¬ments with surface labeled membranes (4). While theses studies have fur¬ther substantiated the basic idea of membrane splitting and have shown clearly which membrane faces are complementary to each other, they have left the question open, why the replicated membrane faces usually exhibit con¬siderably fewer holes than particles. According to Branton's theory the number of holes should on the average equal the number of particles. The absence of these holes can be explained in either of two ways: a) it is possible that no holes are formed during the cleaving process e.g. due to plastic deformation (5); b) holes may arise during the cleaving process but remain undetected because of inadequate replication and microscope techniques.

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Plastic Deformation in Microtomed Sections

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100066346 ◽

1971 ◽

Vol 29 ◽

pp. 458-459

Author(s):

J. Temple Black

Keyword(s):

Plastic Deformation ◽

Plastic Strain ◽

Applied Stress ◽

Elastic Strain ◽

High Strain ◽

Tool Material ◽

Cutting Edge ◽

Material Structure ◽

Geometrical Constraints

The output of the ultramicrotomy process with its high strain levels is dependent upon the input, ie., the nature of the material being machined. Apart from the geometrical constraints offered by the rake and clearance faces of the tool, each material is free to deform in whatever manner necessary to satisfy its material structure and interatomic constraints. Noncrystalline materials appear to survive the process undamaged when observed in the TEM. As has been demonstrated however microtomed plastics do in fact suffer damage to the top and bottom surfaces of the section regardless of the sharpness of the cutting edge or the tool material. The energy required to seperate the section from the block is not easily propogated through the section because the material is amorphous in nature and has no preferred crystalline planes upon which defects can move large distances to relieve the applied stress. Thus, the cutting stresses are supported elastically in the internal or bulk and plastically in the surfaces. The elastic strain can be recovered while the plastic strain is not reversible and will remain in the section after cutting is complete.

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Surface Structure in Microtomed Sections Caused by Glass and Diamond Knives

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100066334 ◽

1971 ◽

Vol 29 ◽

pp. 456-457

Author(s):

J. Temple Black ◽

William G. Boldosser

Keyword(s):

Plastic Deformation ◽

Epoxy Resin ◽

Carbon Coating ◽

Surface Damage ◽

Body Angle ◽

Normal Manner ◽

Bottom Side ◽

Cutting Direction ◽

Made In ◽

Diamond Knife

Ultramicrotomy produces plastic deformation in the surfaces of microtomed TEM specimens which can not generally be observed unless special preparations are made. In this study, a typical biological composite of tissue (infundibular thoracic attachment) infiltrated in the normal manner with an embedding epoxy resin (Epon 812 in a 60/40 mixture) was microtomed with glass and diamond knives, both with 45 degree body angle. Sectioning was done in Portor Blum Mt-2 and Mt-1 microtomes. Sections were collected on formvar coated grids so that both the top side and the bottom side of the sections could be examined. Sections were then placed in a vacuum evaporator and self-shadowed with carbon. Some were chromium shadowed at a 30 degree angle. The sections were then examined in a Phillips 300 TEM at 60kv.Carbon coating (C) or carbon coating with chrom shadowing (C-Ch) makes in effect, single stage replicas of the surfaces of the sections and thus allows the damage in the surfaces to be observable in the TEM. Figure 1 (see key to figures) shows the bottom side of a diamond knife section, carbon self-shadowed and chrom shadowed perpendicular to the cutting direction. Very fine knife marks and surface damage can be observed.

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Investigation of shock-wave deformation history from recovered structure

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100143754 ◽

1986 ◽

Vol 44 ◽

pp. 434-435

Author(s):

M.A. Mogilevsky ◽

L.S. Bushnev

Keyword(s):

Shock Wave ◽

Plastic Deformation ◽

Dislocation Density ◽

Shock Waves ◽

Shock Front ◽

Single Crystals ◽

Residual Deformation ◽

Deformation Structure ◽

Deformation History ◽

Deformation Velocity

Single crystals of Al were loaded by 15 to 40 GPa shock waves at 77 K with a pulse duration of 1.0 to 0.5 μs and a residual deformation of ∼1%. The analysis of deformation structure peculiarities allows the deformation history to be re-established.After a 20 to 40 GPa loading the dislocation density in the recovered samples was about 1010 cm-2. By measuring the thickness of the 40 GPa shock front in Al, a plastic deformation velocity of 1.07 x 108 s-1 is obtained, from where the moving dislocation density at the front is 7 x 1010 cm-2. A very small part of dislocations moves during the whole time of compression, i.e. a total dislocation density at the front must be in excess of this value by one or two orders. Consequently, due to extremely high stresses, at the front there exists a very unstable structure which is rearranged later with a noticeable decrease in dislocation density.

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