Repeated stress relaxation tests are used to characterize the macroscopic time dependent behavior in metals. During stress relaxation, the mobile dislocation density and internal stress vary continuously with time. The phenomenological models available do not provide a comprehensive mathematical framework to account for transient effects during stress relaxation accurately. An advanced stress relaxation model based on the logarithmic model is proposed in the present work to overcome the limitations of existing models. The proposed model is found to fit the experimental data of SS 316 better than the available models. The proposed model in combination with Kocks–Mecking type dislocation density model is utilized to predict the rate of strain hardening during relaxation © 2019 Elsevier Ltd

K Hariharan

Department of Mechanical Engineering

Anand Varma

Jayant Jain

Myoung-Gyu Lee

Frédéric Barlat

Strain hardening

Strain rate

Testing

ACTIVATION VOLUME

DISLOCATION DENSITY MODEL

LOGARITHMIC MODELS

Mathematical frameworks

MOBILE DISLOCATION DENSITY

Phenomenological models

STRESS RELAXATION TESTS

time dependent behavior

stress relaxation

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Mechanics of Materials

In a recent paper, Mishra et al.&nbsp;[Effect of obstacle strength and spacing on the slope of Haasen plot. Mater Sci Technol. 2019;1–6. doi:10.1080/02670836.2019.1567043], discrepancy between theoretical and experimental results in the slope of the Haasen plot between pure metals and alloys were reported. The discrepancy arises from a common belief that when Haasen plot for pure metals is extended to metals with multiple strengthening mechanisms, the inverse of activation volume components can be linearly superposed. It is conjectured that the slope of the Haasen plot should remain the same for both the pure metals and alloys, as it is governed only by dislocation–dislocation interaction. The purpose of this note is to clarify that the conjecture of invariant Haasen slope is only a special case. © 2019, © 2019 Institute of Materials, Minerals and Mining.

Materials Science and Technology (United Kingdom)

Comments on ‘Effect of obstacle strength and spacing on the slope of Haasen plot’

The mechanical behaviour during stress relaxation of metals has generated considerable interest in the recent years owing to its contribution to ductility. Most of the past studies were focused on ferrous alloys. In the present work, an attempt is made to systematically quantify the improvement in ductility during stress relaxation in AA 8011 aluminium alloy. Room temperature uni-axial tensile tests with single relaxation step were performed under different combinations of pre-strain, strain rate and relaxation time. The ductility was found to increase in all the cases. The parametric dependence of ductility improvement can be assessed using an empirical equation. It was found that the ductility improvement in aluminium is significant compared to SS 316 under similar conditions. The stress-time data obtained is modelled using a recently proposed logarithmic law and is found to fit the experimental data well. The underlying transient mechanisms responsible for ductility improvement are explored by conducting image based fractography analysis of the samples post failure. The fractography was complemented with nano-indentation technique to characterize the homogenization of internal stress. © 2017 Elsevier B.V.

Journal of Materials Processing Technology

Leveraging transient mechanical effects during stress relaxation for ductility improvement in aluminium AA 8011 alloy

Electroplasticity refers to the application of controlled electric pulses during plastic deformation of materials. The electroplasticity phenomenon in metallic materials has led to the development of electrically assisted forming (EAF) process with improved formability. The lack of a suitable constitutive model to describe this electroplastic behaviour is a serious limitation in modelling and optimizing the EAF process. In the present work, a dislocation – density based constitutive model is developed for electroplastic deformation and is capable of predicting the effect of continuous and pulsed electric current during plastic deformation. Single- pulse electroplastic deformation experiments conducted on Al 5052 reveal similar mechanical behaviour as that predicted by the proposed model. The proposed model is also validated against published results for multiple electric pulses using Al 5052. The predicted results correlate well with the experimental data. Based on the predicted results, it is demonstrated that the long range softening observed in certain experiments results from the frequent application of electric pulses and is not due to any other internal softening mechanism. © 2017 Elsevier Ltd

Materials and Design

Electroplastic behaviour in an aluminium alloy and dislocation density based modelling

International Journal of Plasticity

Effects of the grain size and shape on the flow stress: A dislocation dynamics study

Size and stress dependences in the tensile stress relaxation of thin copper wires at room temperature

Stress-level-dependency and bimodal precipitation behaviors during creep ageing of Al-Cu alloy: Experiments and modeling

Advanced constitutive model for repeated stress relaxation accounting for transient mobile dislocation density and internal stress

Journal	Data powered by TypesetMechanics of Materials
Publisher	Data powered by TypesetElsevier B.V.
ISSN	01676636
Open Access	No