Surface formation energy in plastic deformation of solids in media

1986 ◽  
Vol 21 (5) ◽  
pp. 468-470
Author(s):  
V. V. Popovich ◽  
V. N. Yuzevich
Keyword(s):  
Plastic Deformation ◽  
Formation Energy ◽  
Surface Formation ◽  
Surface Formation Energy

scholarly journals Minimum Surface Formation Energy for Three-Dimensional Intergranular Fracture

1998 ◽  
Vol 539 ◽  
Author(s):  
E. A. Holm ◽  
G. N. McGovney
Keyword(s):  
Fracture Surface ◽  
Cross Section ◽  
Intergranular Fracture ◽  
Formation Energy ◽  
Boundary Energy ◽  
Surface Formation ◽  
Minimum Surface ◽  
Specimen Cross Section ◽  
Fracture Area ◽  
Surface Formation Energy

AbstractThe minimum expended energy for fracture is the free energy required to form two new surfaces. For intergranular fracture, the minimum surface formation energy is complicated by the rough fracture surface, with area greater than the specimen cross-section. We utilize network optimization algorithms (max-flow/min-cut) to determine the minimum surface formation energies and surfaces for intergranular fracture in 3D polycrystals. For equiaxed grains and uniform boundary strength, the minimum energy fracture area is independent of grain size and is 45% larger than the specimen cross-section, and intergranular fracture will occur when surface energy is less than 1.6 times the grain boundary energy. The 3D fracture area is larger than projected from 2D systems. In systems with microcracked boundaries, the fracture surface deviates to preferentially include microcracked boundaries, creating interlocking grain configurations. Two-dimensional percolation of microcracks occurs at about 80% microcracked boundaries.

Grinding of WC-Co Cemented Carbides

1980 ◽  
Vol 102 (3) ◽  
pp. 209-220 ◽  
Author(s):  
O. Zelwer ◽  
S. Malkin
Keyword(s):  
Plastic Deformation ◽  
Plastic Flow ◽  
Dissociation Energy ◽  
Chip Formation ◽  
Material Removal ◽  
Formation Energy ◽  
Cemented Carbides ◽  
Grinding Process ◽  
Energy Limit ◽  
Wheel Topography

An investigation is reported on the grinding process for WC-Co cemented carbides with diamond wheels. SEM examination of the grinding detritus revealed that material removal occurs mainly by flow-type chip formation. A grinding model is proposed whereby the total grinding energy is partitioned into a chip formation component for material removal, and a plowing component causing plastic deformation of the workpiece by a force along the engaged cutting edges. With many wheel-workpiece combinations, the specific chip formation energy was found to be comparable to the dissociation energy of WC, suggesting chip formation by constrained adiabatic plastic flow to the energy limit. Wheel topography measurements showed an increasing number of cutting points with coarser grit size, which is attributed to coarser grains having more cutting points per grain and less of a tendency to dislodge. Finished surfaces exhibited grooves along the grinding direction with valleys depleted of cobalt and ridges along the sides of the grooves rich in cobalt.

Computer Simulation of the Interaction of Junction Disclinations in Nanomaterials with Grain Boundary Vacancies

2008 ◽  
Vol 137 ◽  
pp. 1-8
Author(s):  
Ayrat A. Nazarov ◽  
Ramil’ T. Murzaev
Keyword(s):  
Computer Simulation ◽  
Plastic Deformation ◽  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Formation Energy ◽  
Nanostructured Metals ◽  
Formation Energies ◽  
Magnitude Increase ◽  
Junction Disclinations

Junction disclinations are important elements of the structure of nanostructured metals produced by severe plastic deformation (SPD). Effect of these defects on the formation energy of vacancies in grain boundaries (GBs) is studied by means of atomistic computer simulations. Estimates based on the calculations of vacancy formation energies suggest that at least two orders of magnitude increase of the GB diffusion coefficient can be expected due to junction disclinations in nanostructured metals.

Sem Examinations of Glass Knives

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.

Stereo Electron Microscopy Applied to High Resolution Freeze-Etch Replicas

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.

Plastic Deformation in Microtomed Sections

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.

Surface Structure in Microtomed Sections Caused by Glass and Diamond Knives

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.

Investigation of shock-wave deformation history from recovered structure

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.

Sign in / Sign up

Export Citation Format

Share Document