Strain Rate Dependent Behavior of Pure Aluminum and Copper Micro-Wires

Abstract

In order to shed light on the role that grain boundaries and dislocations play in anelastic relaxation of thin films and small-scale structures, we measured the effective elastic moduli of 99.99% pure Al and Cu 10 m m diameter micro-wires in the as-received (drawn and slight tempered) and annealed states. Moduli were determined using microtensile tests at various strain rates (6.7x10-6s-1, 1.3x10-5s-1, 2.6x10-5s-1, 4.5x10-5s-1, 2.5x10-4s-1, 4.5x10-4s-1). Focused-ion beam scanning electron microscopy was used for imaging grain sizes. Results from the as-received wires are compared with the annealed wires to illustrate the effects of grain size and dislocation density on effective moduli, which closely relates to grain boundary sliding and dislocation motion, respectively. We conclude that microstructure is more significant than scale in inducing anelasticity in small-scale wires and, by extension, thin films.

Strain rate effects on the mechanical behavior of nanocrystalline Au films

“…El-Deiry and Vinci [32] reported a 25 GPa modulus reduction at 10 − 6 s − 1 strain rate for Al and Cu wires, which was explained on the basis of anelastic relaxations. At the same strain rates Kalkman et al [33] reported 20% difference between the bulk and thin film moduli, which was attributed to grain boundary sliding as a result of small grain size.…”

Experimental Evidence that the Onset of Mechanical Softening in Nanocrystalline Metals is Strain Rate Dependent

“…Fig. These results may, in part, shed some light on the wide variability of yield strengths and Hall-Petch relationships of nanocrystalline gold reported by many researchers [9][10][11][12][13][14]. The average strain rate at each displacement rate is indicated on the plot and listed in Table 1.…”

“…In this regard, if grain size drops too far into the nanoscale regime the material undergoes a mechanical softening process, whereby further decreases in grain size result in more softening, known as the inverse Hall-Petch effect [6][7][8]. One of the more important loading conditions that has received recent attention is low applied strain rates that have been shown to induce considerable diffusion-based deformation at room temperature in nanostructured gold and other metals [9][10][11][12][13][14]. One of the more important loading conditions that has received recent attention is low applied strain rates that have been shown to induce considerable diffusion-based deformation at room temperature in nanostructured gold and other metals [9][10][11][12][13][14].…”

Numerical Investigation of Size Effects in Tension and Torsion of Micro-scale Copper Wires using a Strain Gradient Modified Johnson-Cook Constitutive Model

“…(5) Substituting ( 3) and ( 5) into (4), the flow stress is now [3]: (6) where is defined as material characteristic length l. is introduced to represent the density of GNDs needed to accommodate the strain gradient in the deformation zone. Equation ( 6) describes the material constitutive model which combines the JC and the SGP theories.…”