Strain Hardening Of Metals Research Articles

An informatics method for inferring the hardening exponent of plasticity in polycrystalline metals from surface strain measurements

The investigation of strain hardening in metals is complex, with the outcome depending on experimental conditions, that may involve microstructural history, temperature and loading rate. Hardening is commonly measured, after mechanical processing, through controlled mechanical testing, in ways that either distinguish elastic (stress) from total deformation measurements, or by identifying plastic slip contributions. In this paper, we conjecture that hardening effects can be unraveled through statistical analysis of total strain fluctuations during the evolution sequence of profiles, measured in-situ, through digital image correlation. In particular, we hypothesize that the work hardening exponent is related, through a power-law relationship, to a particular exponent arising from principal component analysis. We demonstrate a scaling analysis for synthetic data produced by widely applicable crystal plasticity models for polycrystalline solids.Graphical

Dislocation kinetics explains energy partitioning during strain hardening: Model and experimental validation by infrared thermography and acoustic emission

The energy dissipation and storage during strain hardening of metals have been investigated by means of complementary in situ techniques - infrared thermography (IRT), digital image correlation (DIC) and acoustic emission (AE). Inspired by experimental results obtained in the present work and data available in literature, we proposed the analytically tractable thermodynamic modelling approach, which is conceptually based on a single-variable dislocation evolution approach with a total dislocation density serving as a principal variable governing the strain hardening process. Unified by the kinetic approach involving generation, annihilation and motion of dislocations, the models accounting for the acoustic emission behaviour and heat dissipation under load have been proposed and verified experimentally. For the first time, we were able to demonstrate that the key parameters governing the dislocation storage and annihilation rates can be, in principle, recovered from independent AE and IRT measurements. These results agree favourably with the predictions of the dislocation-based constitutive strain hardening models of the Kocks-Mecking type. The self-consistency, versatility and predictive capacity of the proposed modelling approach are demonstrated in the examples of Cu–Zn alloys with different concentrations of Zn varied from 0 to 30% and correspondingly different stacking fault energies.

Simulation of dislocation evolution in microparticle impacts over a wide range of impact velocities

The dynamic loading environment created by high velocity microparticle impacts is very difficult to model. The extremely high strain rates, large deformations, and high temperatures affect the flow stress of the material in ways that standard flow stress models cannot capture. Plastic deformation and strain hardening in metals is controlled by the motion of dislocations. Dislocations can be nucleated, stored as forest dislocations, or be annihilated as loading progresses. A comprehensive accounting of dislocation density change is needed to accurately describe rate and temperature dependent dislocation glide and evolution across the wide rage of loading conditions present in microparticle impact problems. Therefore, we implement and apply a newly proposed flow stress model (Hunter and Preston, 2015, 2022) that is then coupled with mobile and immobile dislocation density evolution equations. This model is implemented in Los Alamos National Laboratory’s hydrodynamics code, FLAG, to model copper-on-copper microparticle impacts. This new strength model allows for accurate simulation of particle rebound and flattening across a wide range of impact velocities.

Stored and dissipated energy of plastic deformation revisited from the viewpoint of dislocation kinetics modelling approach

In the present work, we revisited the classical topic of elastic energy storage during strain hardening of metals from a perspective of the analytically tractable thermodynamic modelling framework inspired by the widely accepted phenomenological single-variable dislocation evolution approach. The model versatility has been extended towards predicting the energy partitioning during plastic flow. With a total dislocation density serving as a principal variable governing strain hardening during constant strain rate tensile tests, we have been able to demonstrate a very good predictive capability of the proposed analytical solutions. Besides the simplicity, the flexibility and predictive power of the obtained analytical solutions suggest that the entire approach can be used for further modelling, where the emphasis should be placed on the integration of various possible mechanisms of heat dissipation into the proposed framework. Although the examples of successful application of the model refer to the low-carbon austenitic stainless 316L steel, their adaptation to other fcc, bcc or hcp metals is rather straightforward.

Strain Hardening in Metals at Different External Parameters

Strain Hardening in Metals at Different External Parameters

Plastic Flow Localization and Strain Hardening of Metals

The plastic flow macrolocalization in single crystals and polycrystalline alloys at various stages of strain hardening is considered. The macrolocalized plastic flow at these stages is shown to be an autowave self-organization process. The ultrasound velocity is found to be an informative parameter of autowave plastic deformation.

Hardening by slip-twin and twin-twin interactions in FeMnNiCoCr

To enhance strain hardening of alloys beyond levels accessible by forest hardening slip-twin interactions and twin-twin interactions have been proposed. The high entropy alloy FeMnNiCoCr constitutes a prominent example of exceptionally pronounced strain hardening instigated by profuse slip-twin/twin-slip and twin-twin interaction at cryogenic temperatures. In the current study, we perform uniaxial straining experiments on single crystals at 77 K. The <144>Tension crystal shows the potential ease of twin progression for slip-twin interaction (softening) in contrast to the difficulty for twin advancement in <122>Tension, <111>Tension and <001>Compression cases (hardening). The corresponding self and latent hardening coefficients derived from the data reveal that slip-twin latent moduli are much smaller than twin-twin latent moduli. Unlike previous undertakings, this study demonstrates a novel approach to assess latent hardening where plastic straining is implemented in a monotonic fashion and primary and latent systems operate simultaneously. To predict the flow stress depending on crystal orientation and as a function of strain a numerical model is proposed using the obtained hardening moduli. It emerges that the magnitude of residual Burgers vectors originating from twin-related reactions can explain the experimental hardening/softening trends. These results hold considerable promise for a quantitative description of strain hardening in metals and alloys.

Локализация пластического течения и деформационное упрочнение металлов

Локализация пластического течения и деформационное упрочнение металлов

Using the Hollomon Model to Predict Strain-Hardening in Metals

Stress – strain values obtained from tensile tests of aluminium and steel is used to evaluate the true stress – true strain values. The Hollomon’s model is then used to predict the strain-hardening behavior in the two specimens. It is clearly seen that the strain-hardening behavior in metals can be described using the Hollomon’s model. However, we have assumed that the onset of strain-hardening is at the yield point up until the ultimate tensile strength. The correlation between the experimental true stress – true strain values of aluminium and the calculated values using the Hollomon equation is much better than that of steel.

Effect of strain hardening on the electromagnetic radiation during plastic deformation of metals and alloys beyond yield point

This paper presents a theoretical model to analyze and predict the electromagnetic radiation (EMR) during the strain hardening of metals with negligible Peierls stress. The model developed is validated by comparing it with the experimental results on the ASTM B265 grade 2 titanium reported earlier. It is observed that inclusion of time-varying stress is essential to studying EMR occurring during strain hardening. The model confirms the observation that the amplitude of oscillatory EMR is generally much larger than the amplitude of exponential EMR. Further, the variation in viscous damping as a function of strain during strain hardening too has been incorporated in the model. The nature as well as amplitude of the EMR calculated by this model matches well with the earlier reported results on titanium. The model is thus suitable for studying the EMR during plastic deformation of metals and alloys with negligible Peierls stress.

Some basic results in the mathematical analysis of dislocation storage and annihilation in stage II and stage III strain hardening

Eighty years since G.I. Taylor presented the first empirical explanation for the yield stress and strain hardening of metals, generally accepted formalisms to explain strain hardening have been established. The most important of these empirical laws have eluded full mathematical analysis until now. The Taylor equation provides a relationship between yield stress and strain. The semi-empirical Kocks–Mecking model provides a description of the physical phenomena of dislocation storage and annihilation, but lacks information on the formation of substructure and its effects. Here, a recently developed mathematical analysis of the corresponding phenomena is presented, which reproduces the essential equations in strain hardening. The first important result is the proof that the Taylor equation is the unique solution of a fundamental evolution equation for dislocation density. The second one demonstrates that dislocation storage and annihilation are exactly additive. The latter conclusion is independent of substructure, explaining the success of the Kocks–Mecking model during stages II and III.

The structure and properties of thin aluminum coatings

Mechanical properties and structure of a thin aluminum coating were investigated. Experimental methods of measuring yield stress, strength and fracture strain of ultrathin coatings were developed. Yield stress, strength and fracture strain of aluminum increase with decrease in the coating thickness. The increase of yield stress and strength was explained by reduction of the crystal size and by strain-hardening of metal.

Dislocation Dynamics Simulations

Dislocation Dynamics (DD) simulations are used to study the evolution of a pre-specified dislocation structure under applied stresses and imposed boundary conditions. These simulations can handle realistic dislocation densities ranging from 1010to 1014m-2, and hence can be used to model plastic deformation and strain hardening in metals. In this paper we introduce the basic concepts of DD simulations and then present results from simulations in thin copper films and in bulk zirconium. In both cases, the effect of orientation on deformation behaviour is investigated. For the thin film simulations, rigid boundary conditions are used at film-substrate and film-passivation interfaces leading to dislocation accumulation, while periodic boundaries are used for bulk grains of Zr. We show that there is a clear correlation between strain hardening rate and the rate of increase of dislocation density.

Structure and properties of nanosized coatings deposited onto polymers

Results of studies aimed at developing a new approach to measuring stress-strain properties of nanosized solids (strength, yield stress, and the value of plastic deformation at uniaxial tension) are generalized. This approach is based on the analysis of the parameters of microrelief arising upon the deformation of polymer films with thin coatings. It is demonstrated for the first time that the stress-strain properties of aluminum coatings deposited onto Lavsan substrates depend on the level of stresses in the substrate, the value of its deformation, and the thickness of the coating. The evolution of these parameters is related to the strain hardening of metal and the effect of nanostructuring of crystalline materials in the range of small thicknesses. When precious metal (Au, Pt) nanosized films are deposited onto polymers by ion-plasma sputtering, in the course of metal deposition, polymer surface layers interact with cold plasma. Stress-strain properties of polymer surface layers modified by plasma are quantitatively estimated for the first time. The model is proposed that makes it possible to take into account the contribution of the properties of precious metal and plasma-modified polymer surface layer to the strength of the coating.

Strain hardening of metals and alloys in the superconducting state

The strain hardening of single crystals of pure Al and a Pb–In alloy in the normal (N) and superconducting (S) states is investigated. It is found that the strain hardening coefficients satisfy the inequality θS&amp;gt;θN irrespective of whether the SN transition is brought about by an external magnetic field or temperature.

Investigation of the formation of dislocation cell structures and the strain hardening of metals by computer simulation

In order to explain the appearance of stage IV strain hardening and to understand the development of dislocation cell structure, a computer simulation was carried out for a two-dimensional crystal. Based on several dislocation reactions, the conditions for the formation of stable cell structures were investigated. The resulting cell structures were analysed by a geometric method and a correlation between their development and the strain hardening was found. The most important advantage of this work is that several dislocation processes and the assumptions of physical models can be considered as direct functions of deformation. It is a possible alternative to transmission electron microscopy investigations.

Structure and strain hardening of metals with a complex stressed state

Strain hardening features for steels of the austenitic, martensitic, and maraging classes in stable and metastable states in relation to structural parameters in complex biaxial loading conditions have been studied, including prior and repeated (with intermediate unloading) deformation with different principal stress ratios. The structural sensitivity of the Bauschinger effect is studied, structural dependences for yield stress with compression after prior tension are obtained, and generalization of the yield stress under repeated biaxial loading is substantiated by experiment. In the relationships presented there is quantitative consideration of the regularities revealed for the change in structural parameters of deformed metal during repeated loading in relation to the principal stress ratio. Classification of the test steels is suggested according to structural state characteristics caused by preferred isotropic and anisotropic strain hardening.

Features of hydrogen-phase strain hardening of metals as a controllable physical phenomenon

Features of hydrogen-phase strain hardening of metals as a controllable physical phenomenon

Microflow and strain-hardening of metals under cyclic loading

Microflow and strain-hardening of metals under cyclic loading