Possibility of a vortex mechanism of displacement of the grain boundaries under high-rate shear loading

1998 ◽  
Vol 34 (3) ◽  
pp. 366-368 ◽  
Author(s):  
S. G. Psakh’e ◽  
K. P. Zol’nikov
Keyword(s):  
Grain Boundaries ◽  
Shear Loading ◽  
High Rate

scholarly journals Strain rate and thermal softening effects in shear testing of AA7075-T6 sheet

2018 ◽  
Vol 183 ◽  
pp. 02037 ◽  
Author(s):  
Taamjeed Rahmaan ◽  
Ping Zhou ◽  
Cliff Butcher ◽  
Michael J. Worswick
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Rate Sensitivity ◽  
Thermal Conditions ◽  
Shear Loading ◽  
Image Correlation ◽  
High Rate ◽  
Strain Rates ◽  
Shear Testing ◽  
Plane Shear

Shear tests were performed at strain rates ranging from quasi-static (0.01 s-1) to 500 s-1 for AA7075-T6 sheet metal alloy at room temperature. A miniature sized shear specimen was used in this work to perform high strain rate shear testing. Digital image correlation (DIC) techniques were employed to measure the strains in the experiments. At maximum in-plane shear strains greater than 20%, the AA7075-T6 alloy demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the AA7075-T6 alloy showed mild positive rate sensitivity. The strain to localization (using the Zener-Holloman criterion), measured using the DIC technique, decreased with strain rate in shear loading. The strain at complete failure, however, exhibited an increase at the highest strain rate (500 s-1). The current work also focused on characterization of the thermal conditions occurring during high rate loading in shear with in situ high speed thermal imaging. Experimental results from the highest strain rate (500 s-1) tests showed a notable increase in temperature within the specimen gauge region as a result of the conversion of plastic deformation energy into heat.

Radiation-Induced Minor Element Segregation at Austenitic Stainless Steel Grain Boundaries

1996 ◽  
Vol 439 ◽  
Author(s):  
E. P. Simonen ◽  
S. M. Bruemmer
Keyword(s):  
Grain Boundaries ◽  
Neutron Irradiation ◽  
Ion Irradiation ◽  
Austenitic Stainless Steels ◽  
Minor Element ◽  
High Rate ◽  
Rate Theory ◽  
Minor Elements ◽  
Radiation Induced ◽  
Irradiation Behavior

AbstractMeasurement of minor element compositions at irradiated grain boundaries in austenitic stainless steels indicates that Si is the only element that significantly responds to radiation-induced segregation. Other minor elements, such as P or S, do not exhibit elevated grain boundary concentrations after irradiation. A rate theory evaluation of segregation is in accord with ioninduced Si enrichment, but reveals complexities in the interpretation of extrapolating behavior from ion-irradiation to neutron-irradiation behavior. The model calibrated to measured high-rate, ioninduced segregation greatly overestimates measured low-rate, neutron-irradiation segregation of Si.

Influence of the grain size and structural state of grain boundaries on the parameter of low-temperature and high-rate superplasticity of nanocrystalline and microcrystalline alloys

2010 ◽  
Vol 52 (5) ◽  
pp. 1098-1106 ◽  
Author(s):  
V. N. Chuvil’deev ◽  
A. V. Shchavleva ◽  
A. V. Nokhrin ◽  
O. É. Pirozhnikova ◽  
M. Yu. Gryaznov ◽  
...  
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Grain Boundaries ◽  
Structural State ◽  
High Rate

scholarly journals Particularities of changes in internal structure of nanocrystalline Ni under mechanical loading

2019 ◽  
Vol 221 ◽  
pp. 01025
Author(s):  
Dmitrij Kryzhevich ◽  
Aleksandr Korchuganov ◽  
Konstantin Zolnikov
Keyword(s):  
Grain Boundaries ◽  
Triple Junction ◽  
Shear Loading ◽  
Stacking Fault ◽  
Grain Sizes ◽  
Compressive Stresses ◽  
Nucleation Mechanisms ◽  
Constrained Conditions ◽  
Misorientation Angles ◽  
Nanocrystalline Sample

Molecular dynamics study of the plasticity nucleation mechanisms in a Ni nanocrystalline sample under shear loading in the constrained conditions was carried out. The studied Ni sample consisted of nine grains of the same size with large misorientation angles relative to each other. In one of the directions, grippers were simulated, to which compressive forces and shear with a constant velocity were applied. In two other directions, periodic boundary conditions were used. It is shown that plasticity nucleation occurs in the region of the triple junction. At the same time, in the region of the triple junction, in the zone of which the stacking fault will be formed, tensile stresses are realized along one of the adjacent grain boundaries, and compressive stresses occur along the other. An increase in stresses in the triple junction zone leads to the formation of a stacking fault, which moves to the volume of one of the grains. Another mechanism of plasticity in nanocrystalline nickel is the migration of grain boundaries, which leads to a significant change in grain sizes.

scholarly journals Formation of Nanolaminated Structure with Enhanced Thermal Stability in Copper

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2252
Author(s):  
Jianxin Hou ◽  
Xiuyan Li ◽  
Ke Lu
Keyword(s):  
Thermal Stability ◽  
Ambient Temperature ◽  
Grain Boundaries ◽  
Shear Deformation ◽  
Stacking Faults ◽  
High Rate ◽  
Nanostructured Metals ◽  
Partial Dislocations ◽  
Boundary Spacing ◽  
High Microhardness

Nanolaminated structure with an average boundary spacing of 67 nm has been fabricated in copper by high-rate shear deformation at ambient temperature. The nanolaminated structure with an increased fraction of low angle grain boundaries exhibits a high microhardness of 2.1 GPa. The structure coarsening temperature is 180 K higher than that of its equiaxial nanograined counterpart. Formation of nanolaminated structure provides an alternative way to relax grain boundaries and to stabilize nanostructured metals with medium to low stacking faults energies besides activation of partial dislocations.

Anomalously high rate of grain boundary displacement under fast shear loading

1997 ◽  
Vol 23 (7) ◽  
pp. 555-556 ◽  
Author(s):  
S. G. Psakh’e ◽  
K. P. Zol’nikov
Keyword(s):  
Grain Boundary ◽  
Shear Loading ◽  
High Rate ◽  
Boundary Displacement

scholarly journals Regularities of Structural Rearrangements in Single- and Bicrystals Near the Contact Zone

2020 ◽  
pp. 301-322
Author(s):  
Konstantin P. Zolnikov ◽  
Dmitrij S. Kryzhevich ◽  
Aleksandr V. Korchuganov
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Contact Zone ◽  
Boundary Migration ◽  
Shear Loading ◽  
Structural Defects ◽  
Grain Boundary Migration ◽  
Boundary Motion ◽  
Symmetric Tilt ◽  
Grain Boundary Motion

AbstractThe chapter is devoted to the analysis of the features of local structural rearrangementsin nanostructured materialsunder shear loadingand nanoindentation. The study was carried out using molecular dynamics-based computer simulation. In particular, we investigated the features of symmetric tilt grain boundary migration in bcc and fcc metals under shear loading. The main emphasis was on identifying atomic mechanisms responsible for the migration of symmetric tilt grain boundaries. We revealed that grain boundaries of this type can move with abnormally high velocities up to several hundred meters per second. The grain boundary velocity depends on the shear rate and grain boundary structure. It is important to note that the migration of grain boundary does not lead to the formation of structural defects. We showed that grain boundary moves in a pronounced jump-like manner as a result of a certain sequence of self-consistent displacements of grain boundary atomic planes and adjacent planes. The number of atomic planes involved in the migration process depends on the structure of the grain boundary. In the case of bcc vanadium, five planes participate in the migration of the Σ5(210)[001] grain boundary, and three planes determine the Σ5(310)[001] grain boundary motion. The Σ5(310)[001] grain boundary in fcc nickel moves as a result of rearrangements of six atomic planes. The stacking order of atomic planes participating in the grain boundary migration can change. A jump-like manner of grain boundary motion may be divided into two stages. The first stage is a long time interval of stress increase during shear loading. The grain boundary is motionless during this period and accumulates elastic strain energy. This is followed by the stage of jump-like grain boundary motion, which results in rapid stress drop. The related study was focused on understanding the atomic rearrangements responsible for the nucleation of plasticity near different crystallographic surfaces of fcc and bcc metals under nanoindentation. We showed that a wedge-shaped region, which consists of atoms with a changed symmetry of the nearest environment, is formed under the indentation of the (001) surface of the copper crystallite. Stacking faults arise in the (111) atomic planes of the contact zone under the indentation of the (011) surface. Their escape on the side free surface leads to a step formation. Indentation of the (111) surface is accompanied by nucleation of partial dislocations in the contact zone subsequent formation of nanotwins. The results of the nanoindentation of bcc iron bicrystal show that the grain boundary prevents the propagation of structural defects nucleated in the contact zone into the neighboring grain.

Experimental analysis of airbag seam design: high-rate shear testing for skin abrasions

2011 ◽  
Vol 226 (4) ◽  
pp. 468-478 ◽  
Author(s):  
S M Duma ◽  
J M Cormier ◽  
W J Hurst ◽  
J D Stitzel ◽  
I P Herring
Keyword(s):  
Experimental Analysis ◽  
Shear Loading ◽  
High Rate ◽  
Post Mortem ◽  
Porcine Skin ◽  
Shear Testing ◽  
Skin Injury ◽  
Injury Threshold ◽  
The Usa ◽  
New System

Approximately 66 per cent of all airbag deployments in the USA result in at least one skin injury, with 47 per cent of these skin injuries attributed directly to the airbag deployment. The purpose of the present study was to evaluate the risk of skin abrasions from the airbag fabric seam design by using a new shear testing methodology. High-rate shear loading was performed with a pneumatic impactor that propelled a section of airbag fabric across porcine skin at 85 m/s. Twenty-seven tests (three control and 24 with fabric) were performed using eight different seam designs. A 40 cm × 10 cm section of airbag fabric with each seam was forced across a 5 cm × 5 cm section of fresh porcine skin that was acquired within 2 h post-mortem. No abrasions were observed in the three control tests, but abrasions were observed in all 24 of the tests conducted using airbag fabric. The unturned, sewn seam orientation resulted in significantly more severe abrasions than the woven, unturned seam orientation ( P = 0.01). This new system and results illustrate that different seam designs can result in different skin abrasion risk. Moreover, the data show that severe abrasions can be caused by normal pressures well below the 1.75 MPa injury threshold previously published.

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