scholarly journals Scaling in the Local Strain-Rate Field during Jerky Flow in an Al-3%Mg Alloy

Metals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 134 ◽  
Author(s):  
Mikhail Lebyodkin ◽  
Youcef Bougherira ◽  
Tatiana Lebedkina ◽  
Denis Entemeyer
Keyword(s):  
Strain Rate ◽  
Scale Invariance ◽  
Spatial Organization ◽  
Local Strain ◽  
Power Laws ◽  
Jerky Flow ◽  
Self Organized Criticality ◽  
Fluctuation Scaling ◽  
Strain Rate Field ◽  
Local Strain Rate

Jerky flow in alloys, or the Portevin-Le Chatelier effect, presents an outstanding example of self-organization phenomena in plasticity. Recent acoustic emission investigations revealed that its microscopic dynamics is governed by scale invariance manifested as power-law statistics of intermittent events. As the macroscopic stress serrations show both scale invariance and characteristic scales, the micro-macro transition is an intricate question requiring an assessment of intermediate behaviors. The first attempt of such an investigation is undertaken in the present paper by virtue of a one-dimensional (1D) local extensometry technique and statistical analysis of time series. The data obtained complete the missing link and bear evidence to a coexistence of characteristic large events and power laws for smaller events. The scale separation is interpreted in terms of the phenomena of self-organized criticality and synchronization in complex systems. Furthermore, it is found that both the stress serrations and local strain-rate bursts agree with the so-called fluctuation scaling related to general mathematical laws and unifying various specific mechanisms proposed to explain scale invariance in diverse systems. Prospects of further investigations including the duality manifested by a wavy spatial organization of the local bursts of plastic deformation are discussed.

Quantitative analysis of in situ straining experiments in the case of strong frictional forces

1978 ◽  
Vol 36 (1) ◽  
pp. 570-571
Author(s):  
F. Louchet ◽  
L.P. Kubin
Keyword(s):  
Strain Rate ◽  
Radiation Effects ◽  
Dislocation Line ◽  
Critical Length ◽  
Local Strain ◽  
Local Flow ◽  
Double Kink ◽  
Dislocation Densities ◽  
Frictional Forces ◽  
Local Strain Rate

Investigation of frictional forces -Experimental techniques and working conditions in the high voltage electron microscope have already been described (1). Care has been taken in order to minimize both surface and radiation effects under deformation conditions.Dislocation densities and velocities are measured on the records of the deformation. It can be noticed that mobile dislocation densities can be far below the total dislocation density in the operative system. The local strain-rate can be deduced from these measurements. The local flow stresses are deduced from the curvature radii of the dislocations when the local strain-rate reaches the values of ∿ 10-4 s-1.For a straight screw segment of length L moving by double-kink nucleation between two pinning points, the velocity is :where ΔG(τ) is the activation energy and lc the critical length for double-kink nucleation. The term L/lc takes into account the number of simultaneous attempts for double-kink nucleation on the dislocation line.

A Microscopic Study on Local Strain Rate Sensitivity of Polypropylene Syntactic Foam with Microballoons

2010 ◽  
Vol 160-162 ◽  
pp. 1280-1284
Author(s):  
En Yang Wang ◽  
Masaki Omiya
Keyword(s):  
Strain Rate ◽  
Microscopic Study ◽  
Strain Rate Sensitivity ◽  
Syntactic Foam ◽  
Rate Sensitivity ◽  
Local Strain ◽  
Local Strain Rate

A Microscopic Study on Local Strain Rate Sensitivity of Polypropylene Syntactic Foam with Microballoons

Strain Rate Evolution in Aluminium Alloy Measured by ESPI during Tensile Test

2009 ◽  
Vol 614 ◽  
pp. 155-162 ◽  
Author(s):  
Johann Petit ◽  
Guillaume Montay ◽  
Manuel François
Keyword(s):  
Tensile Test ◽  
Strain Rate ◽  
Aluminium Alloy ◽  
Speckle Pattern ◽  
Local Strain ◽  
Plastic Instability ◽  
Electronic Speckle Pattern Interferometry ◽  
The Moment ◽  
The One ◽  
Strain Rate Field

The original and significant achievement of this work is to analyse strain rate field in aluminium alloy sheets during micro tensile test. In-plane Electronic Speckle Pattern Interferometry is used to follow the evolution of the local strain in real time. This paper is based on the detection of the localization on a relatively small area of the analysed specimen: less than 5mm × 4mm area. Moreover the speed of the tensile machine is very low, 0.2 to 0.1µm/s. The phase shifting technique is used to obtain the fringes representative of the material displacement. We can therefore get a very good accuracy in the material displacement. A heterogeneity in strain rate field can be noticed from a deformation stage which doesn’t coincide with the one calculated by the classic Considère’s criterion (dF=0) for the diffuse neck initiation (or plastic instability). We also show, the moment when one of the two slip bands systems becomes predominant, and even only one band continues to exist, this occurring widely before fracture. Finally, the fracture of the specimen occurs across this remaining band. The total strain is measured with a second camera, in white light, and is correlated together with the strain rate field to study the localization.

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