Dynamic characterization of Portevin–Le Chatelier instabilities occurring in depth-sensing microhardness tests

2003 ◽  
Vol 18 (12) ◽  
pp. 2874-2881 ◽  
Author(s):  
G. Bérces ◽  
J. Lendvai ◽  
A. Juhász ◽  
N.Q. Chinh
Keyword(s):  
Dynamic Model ◽  
Contact Surface ◽  
Indentation Depth ◽  
Loading Rate ◽  
Experimental Setup ◽  
Dynamic Characterization ◽  
Depth Sensing ◽  
Constant Loading ◽  
Constant Loading Rate

Characteristic properties of plastic instabilities were studied using depth-sensing microhardness experiments on an Al–3.3 wt.% Mg alloy and computer simulations based on a macroscopic dynamic model of the experimental setup. A stepwise increase was observed in the indentation depth versus load (d-F) curves measured in constant loading rate mode, indicating hardness oscillations around a nearly constant value of the conventional dynamic microhardness. These oscillations were correlated with plastic instabilities starting from the contact surface between the sample and the indenter head. Taking into account the experimentally determined connection between the hardness oscillations and the indentation velocity, a dynamic model was proposed for the characterization of instability steps.

The strain-rate dependence of the nanoindentation stress of gold at 300 K: A deformation kinetics-based approach

2009 ◽  
Vol 24 (4) ◽  
pp. 1456-1465 ◽  
Author(s):  
Vineet Bhakhri ◽  
Robert J. Klassen
Keyword(s):  
Strain Rate ◽  
Indentation Depth ◽  
Loading Rate ◽  
Cold Work ◽  
Constant Load ◽  
Constant Loading ◽  
Dislocation Glide ◽  
Deformation Kinetics ◽  
Cold Worked ◽  
Constant Loading Rate

Indentation tests involving a constant-loading rate stage followed by a constant-load stage were performed on annealed and 20% cold-worked Au to investigate the effect of indentation depth and initial dislocation density on the indentation deformation process. The indentation strain rate data were analyzed in terms of an obstacle-limited dislocation glide mechanism. The apparent activation energy was of the order of 0.16 μb3 and was neither a function of initial indentation depth nor cold work. The results of Haasen plot activation analysis and direct transmission electron microscopy (TEM) observations indicate that more mechanical work must be applied during the constant-loading rate stage due to the large amount of work hardening compared with the constant-load stage where considerably more dislocation recovery occurs.

Critical concentration of Mg addition for plastic instabilities in Al–Mg alloys

2000 ◽  
Vol 15 (5) ◽  
pp. 1037-1040 ◽  
Author(s):  
N. Q. Chinh ◽  
F. Csikor ◽  
Zs. Kovács ◽  
J. Lendvai
Keyword(s):  
Room Temperature ◽  
Loading Rate ◽  
Critical Concentration ◽  
Solute Concentration ◽  
Mg Alloys ◽  
Depth Sensing ◽  
Solute Content ◽  
Mg Addition ◽  
Constant Loading Rate ◽  
Al Mg Alloys

Plastic instabilities were investigated by the depth-sensing microhardness test in binary high-purity Al–Mg alloys with different Mg contents. During the tests the applied load was increased from 0 to 2000 mN at constant loading rate. The instabilities appeared as characteristic steps in the load–depth curves during indentation. It was shown that the occurrence and development of the plastic instabilities depend strongly on the solute content. Furthermore, the plastic instabilities occurred only when the solute concentration was larger than a critical value, C0. From room-temperature tests on Al–Mg alloys, C0 was found to be 0.86 wt% Mg. The critical concentration, which is necessary to get plastic instabilities, was also interpreted theoretically.

Molecular Dynamics Simulation of Nanoindentation on Folded Chain Crystal of Polyethylene

2005 ◽  
Vol 297-300 ◽  
pp. 2247-2252 ◽  
Author(s):  
Kisaragi Yashiro ◽  
Atsushi Furuta ◽  
Yoshihiro Tomita
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Loading Rate ◽  
Dynamics Simulation ◽  
Delayed Response ◽  
Berkovich Indenter ◽  
Orthorhombic Crystal ◽  
Constant Loading ◽  
Constant Loading Rate ◽  
The Ideal

Nanoindentation tests on a folded chain crystal of polyethylene are implemented with the molecular dynamics simulation. The orthorhombic crystal is made of the planar zig-zag chains and has the thickness of about 10nm. The ideal Berkovich indenter is plunged into upper surface of the crystal down to 2nm with the constant loading rate of 200m/s or 2000m/s. After the holding time of 1000fs at the maximum depth, the indenter is then pulled up with the same speed. The results are summarized as follows; a) The indentation of 2000m/s remains the residual depression while that of 200m/s recovers the hollow, b) No elastic component is found in the deformation under the both rate of 200m/s and 2000m/s, c) The crystal deforms statically under the indentation of 200m/s while that of 2000m/s shows delayed response.

Method of testing glass for strength with constant loading rate

1982 ◽  
Vol 39 (6) ◽  
pp. 277-279
Author(s):  
D. L. Orlov ◽  
�. A. Abramyan ◽  
A. A. Perova ◽  
R. Leiterits
Keyword(s):  
Loading Rate ◽  
Constant Loading ◽  
Constant Loading Rate

scholarly journals Constant Loading Rate Consolidation Test

1970 ◽  
Vol 10 (1) ◽  
pp. 43-56 ◽  
Author(s):  
Hisao Aboshi ◽  
Hiroshi Yoshikuni ◽  
Seiichiro Maruyama
Keyword(s):  
Loading Rate ◽  
Constant Loading ◽  
Consolidation Test ◽  
Constant Loading Rate

Dynamic Crushing Behavior of the High-Density Closed-Cell Foams

2011 ◽  
Vol 306-307 ◽  
pp. 485-488
Author(s):  
Wei Chen ◽  
Zi Xing Lu
Keyword(s):  
Aspect Ratio ◽  
Loading Rate ◽  
High Density ◽  
Stress Strain ◽  
Constant Loading ◽  
Closed Cell ◽  
Crushing Behavior ◽  
Strain Model ◽  
Constant Loading Rate ◽  
Dynamic Crushing

The face-centered cubic model is used to investigate the dynamic crushing behavior of high density closed-cell foams. The influences of the constant loading rate and the specimen aspect ratio on the crushing stress were discussed. It is demonstrated that the crushing stress is more sensitive to the constant loading rate than the specimen aspect ratio. To describe the dynamic crushing behavior of the foam theoretically, the idealized rigid-perfectly plastic-locking (RPPL) stress-strain model is extended to a more general case, in which both the density and the cross-section area are discontinuous. The good agreement between the finite element results and theoretical results confirms that the dynamic crushing behavior of foam can be described by the modified RPPL stress-strain model.

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