Investigation of the PLC Effect Using DIC

2010 ◽  
Author(s):  
Rebecca N. Storer ◽  
Armand J. Beaudoin ◽  
Peter Kurath
Keyword(s):  
Strain Rate ◽  
Plastic Flow ◽  
Local Strain ◽  
Image Correlation ◽  
Plastic Strain Rate ◽  
Type B ◽  
Time Curve ◽  
Serrated Flow ◽  
Jerky Flow ◽  
Stress Drops

In certain alloys non-homogeneous plastic flow is observed. A category of jerky flow, also called the Portevin-Le Chatelier (PLC) effect, is attributed to the competition between dislocation aging by solute atoms and plastic strain rate. In this study, the PLC effect was examined in an aluminum-magnesium alloy using digital image correlation (DIC) techniques. A cold rolling procedure was developed for Al5052-T0 specimens that resulted in repeatable jerky flow when tested in tension at nominal displacement rates that spanned three orders of magnitude. The tests were successful in producing repeatable propagating type bands of serrated flow, which resulted in serrations or stress drops on the stress versus time curve. Deforming specimens were photographed during testing, and the images were correlated using commercially available DIC software to determine local strains and local strain rates. The present study focuses upon type B, or hopping, bands. The DIC results revealed that the strain front moved along the length of the specimen and strains 1 to 2% higher were observed in the wake of the propagating bands. In addition, at least an order of magnitude increase in local strain rate corresponded to the band front as it moved through the specimen. At slower nominal displacement rates, the magnitude of the stress drops for type B bands was greater, but the number of stress drops was fewer for a given nominal displacement. The repeatability of this study shows that DIC provides an effective way to characterize this type of non-homogeneous or localized plastic flow.

Quantitative Detection of Hydrogen Gas Release during Slow Strain Rate Testing in Aluminum Alloys

2021 ◽  
Vol 1016 ◽  
pp. 568-573
Author(s):  
Keitaro Horikawa ◽  
Michiko Arayama ◽  
Hidetoshi Kobayashi
Keyword(s):  
Aluminum Alloys ◽  
Strain Rate ◽  
Local Strain ◽  
Hydrogen Sensor ◽  
Hydrogen Gas ◽  
Slow Strain Rate ◽  
Image Correlation ◽  
Quantitative Detection ◽  
Gas Release ◽  
Closed Chamber

We have developed a new testing device which is capable of detecting hydrogen gas release during slow strain rate tensile testing (SSRT) under ordinary pressure. The device is composed of an SSRT machine equipped with a closed chamber with an inspection window that is connected to gas chromatography with a semiconductor hydrogen sensor. Local strain distribution in the specimen during the SSRT is monitored dynamically with a digital image correlation (DIC) method. Hydrogen was pre-charged to aluminum alloys by means of friction in water process. Using the device, it was shown that hydrogen was released particularly in the stage of plastic deformation and fracture. In addition, the hydrogen gas release at the moment of fracture was clearly increased when the alloys were hydrogen-charged and tested at a slow strain rate. When we calculated hydrogen gas release from the fracture surface in Al-Zn-Mg base alloys tested at 3.3×10-6 s-1, the hydrogen amount was estimated to be 6.24×10-10 mol /mm2 in a hydrogen-uncharged alloy, and 1.30×10-9 mol / mm2 in a hydrogen-charged alloy.

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.

Deformation Band Velocities and Local Strain Rates in a Ni-Cr-Fe Alloy (Inconel)

2001 ◽  
Vol 683 ◽  
Author(s):  
Harry N. Jones ◽  
C. R. Feng
Keyword(s):  
Plastic Flow ◽  
High Velocity ◽  
Initial Period ◽  
Local Strain ◽  
Basic Mechanism ◽  
Deformation Bands ◽  
Dead Weight ◽  
Wire Sample ◽  
Serrated Flow ◽  
Thermally Activated

ABSTRACTNickel based alloys with nominal compositions similar to 78Ni -15Cr -7Fe, commonly referred to as “Inconel”, exhibit serrated flow (Portevin-LeChatelier effect) in the temperature interval of 230-730°C. Within this temperature range a series of thermally activated processes can also be observed when a wire sample of the alloy is heated with the direct resistance method under dead-weight loading while stressed above the room temperature yield. These processes include the expected initial period of plastic deformation at the start of heating followed by its complete arrest at a higher temperature, a behavior that is completely at odds with models for the thermal activation of plastic flow in metals. As the temperature is increased after this first arrest a cascade of two or three large plastic instabilities involving the high velocity propagation of narrow deformation bands is observed. Measurements of the band velocities using the time of flight within a 50.8 mm gage length extensometer indicate that they can exceed 2 m/s in some cases. Estimates of the maximum local strain rate attained within the deformation bands, obtained with a diametral extensometer, approach 15-18 s−1. The localization of plastic flow into narrow, high velocity bands in this material is the result of the collective behavior of dislocations interacting at a high density. As demonstrated by TEM examination of the complex dislocation structures associated with these various events, however, it is difficult to rationalize a specific mechanism for these effects. If one assumes that both serrated flow and the thermally activated strain bursts are manifestations of the same basic mechanism these observations pose a challenging problem for interpretation with models for the Portevin-LeChatelier effect in this material.

scholarly journals Experimental investigation of strain rate dependent damage mechanisms in DP1000 automotive steel

2021 ◽  
Vol 250 ◽  
pp. 03005
Author(s):  
Sarath Chandran ◽  
Patricia Verleysen
Keyword(s):  
Stress State ◽  
Strain Rate ◽  
Local Strain ◽  
Image Correlation ◽  
Plane Shear ◽  
Damage Mechanisms ◽  
Rate Dependent ◽  
Series Of Experiments ◽  
Stress States ◽  
Automotive Steel

Present study aims to investigate the effect of stress state and loading rates on the damage mechanisms in a DP1000 steel using a welldesigned series of experiments. A specimen family comprising of central hole, in-plane shear and plane strain samples is applied to characterise damage under well-controlled stress states. The optimization of the specimen geometries is achieved using finite element simulations. To assess the influence of strain rate, quasi-static, intermediate and dynamic tests are performed on the designed samples. Local strain fields are obtained by digital image correlation. After testing, scanning electron microscopy is employed to systematically analyse the micromechanisms driving the damage in the investigated material. The underlying damage mechanisms are ferrite-martensite interphase debonding, martensite cracking and debonding at ferrite-ferrite grain boundaries. Stress state and strain rate are found to have distinct influences on triggering the underlying damage mechanisms.

scholarly journals Closed system of coupling effects in generalized thermo-elastoplasticity

2016 ◽  
Vol 21 (2) ◽  
pp. 461-483 ◽  
Author(s):  
Z. Śloderbach
Keyword(s):  
Plastic Strain ◽  
Strain Rate ◽  
Plastic Flow ◽  
Yield Surface ◽  
Plastic Strain Rate ◽  
Generalized Function ◽  
Strain Rate Tensor ◽  
Field Equations ◽  
Coupling Effects ◽  
Thermodynamic Forces

Abstract In this paper, the field equations of the generalized coupled thermoplasticity theory are derived using the postulates of classical thermodynamics of irreversible processses. Using the Legendre transformations two new thermodynamics potentials P and S depending upon internal thermodynamic forces Π are introduced. The most general form for all the thermodynamics potentials are assumed instead of the usually used additive form. Due to this assumption, it is possible to describe all the effects of thermomechanical couples and also the elastic-plastic coupling effects observed in such materials as rocks, soils, concretes and in some metalic materials. In this paper not only the usual postulate of existence of a dissipation qupotential (the Gyarmati postulate) is used to derive the velocity equation. The plastic flow constitutive equations have the character of non-associated flow laws even when the Gyarmati postulate is assumed. In general formulation, the plastic strain rate tensor is normal to the surface of the generalized function of plastic flow defined in the the space of internal thermodynamic forces Π but is not normal to the yield surface. However, in general formulation and after the use the Gyarmati postulate, the direction of the sum of the plastic strain rate tensor and the coupled elastic strain rate tensor is normal to the yield surface.

scholarly journals Strain rate and temperature dependent strain localization of dynamically stretched lightweight bars: from metal to polymer

2021 ◽  
Vol 250 ◽  
pp. 05001
Author(s):  
Longhui Zhang ◽  
David Townsend ◽  
Nik Petrinic ◽  
Antonio Pellegrino
Keyword(s):  
Strain Rate ◽  
Strain Localization ◽  
Local Strain ◽  
Static Condition ◽  
Image Correlation ◽  
Constitutive Relationship ◽  
Dynamic Strain ◽  
Nominal Strain Rate ◽  
Nominal Strain ◽  
Local Strain Rate

This work studies the dynamic strain localization and constitutive relationship of a Ti3Al2.5V alloy in jet engine containment system and a transparent polycarbonate conceived for aircraft canopy application by Digital Image Correlation (DIC) technique from quasi-static condition to high strain rates at different temperatures. The responses of two materials show significant strain rate and temperature sensitivities. Observations of Ti3Al2.5V alloy show that the dynamic local strain rate can reach values up to 1000 % of the nominal strain rate in the necking zone. However, dynamic local strain rate of polycarbonate soars up during strain softening then decreases rapidly with necking propagation, and eventually becomes 20 % of the nominal strain rate until fracture. Appropriate viscoplastic constitutive models are determined for both materials, which are incorporated in finite element simulations to reveal the trend of dynamic local strain rate evolution in dynamic tensile tests. The present work shows two different kinds of strain localization in typical lightweight materials, which should be addressed carefully from Split Hopkinson Tension Bar (SHTB) tests.

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.

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