A study on time dependent properties of aluminum alloy by nanoindentation technique

Abstract

Purpose

Lightweight alloys are of major concern, due to their applicability, in transport and industry applications. The purpose of this paper is to perform a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique, through investigation of creep behavior. Additionally, possible explanations on the time dependent behavior and the influence of the hold period at maximum load and the loading rate on the elastic modulus and hardness results are also analyzed and discussed.

Design/methodology/approach

In this work, a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique was performed, by varying the loading rate, the maximum applied load and the loading time. The stress exponent values are derived from the displacement‐holding time curves. The present experimental setup includes three different approaches: variation of loading rate, maximum applied load and loading time. The creep deformation mechanisms of the alloy, which are dependent on experiment setup, are discussed and the characteristic “elbow” behavior in the unloading part of the curves is also reported.

Findings

The authors found that the stress exponent values obtained are dependent on the applied peak loads and indentation loading rates. Nanoindentation creep testing of aluminum AA6082‐T6 revealed significant creep displacements, where the strain rate reached a steady state after a certain time and the stress decreased with time as the displacement increased during the creep process. The slopes of strain rate versus stress curves (exponent of power‐law creep) for different maximum loads and various holding times, were investigated.

Originality/value

The stress exponent of the constant‐load indentation creep, in all three types of experiments, was found to reduce at low load region. In case of different holding load and time, the stress exponent increased almost linearly and increased very rapidly as the indent size increased, exhibiting an intense size effect.

Citation

Charitidis, C.A., Dragatogiannis, D.A. and Koumoulos, E.P. (2013), "A study on time dependent properties of aluminum alloy by nanoindentation technique", International Journal of Structural Integrity, Vol. 4 No. 1, pp. 33-54. https://doi.org/10.1108/17579861311303618