An interdisciplinary study exposes how structural flaws dictate failure strength and deformation in nanosized alloys with super-resilient properties.
A study from A*STAR reveals that designers of metallic-glass-based nanodevices must account for tiny flaws in alloy frameworks to avoid unpredictable catastrophic failure. Understanding how nanoscale metallic glass fractures and fails when subjected to external stress is critical to improving its reliability in devices and composites.
Experimental measurements (left and right) and molecular dynamics simulations (middle) of metallic glass nanopillars reveal that structural flaws play important roles in determining material strength.
Copyright : Adapted by A*STAR with permission from Ref. 1. Copyright 2014 American Chemical Society.
Recently, researchers have found evidence that artificial flaws — miniscule notches carved into the alloy — do not affect the material’s overall tensile strength. But other work has shown that such notches may actually induce the formation of localized cracks.
Mehdi Jafary-Zadeh and co-workers from the A*STAR Institute of High Performance Computing, in collaboration with researchers in the United States, used a combination of physical experiments and computational simulations to study nanoscale flaw tolerance with in-depth precision.
First, the researchers fabricated nickel–phosphorous metallic glass into narrow ‘nanopillars’ bearing tiny notches and mushroom-shaped endcaps that served as tension grips (see image). Guided by high-resolution scanning electron microscopy, they systematically pulled the structures apart until they cracked — an action that consistently occurred at the notched zone, and at failure strengths 40 per cent lower than those for unflawed nanopillars.
The team then turned to massive molecular dynamics simulations to explain these physical results. “Simulating failure modes in the nanopillar metallic glasses required large-scale, three-dimensional models containing millions of atoms,” says Jafary-Zadeh. “Performing simulations at these scales is pretty daunting, but we overcame this challenge with the help of the A*STAR Computational Resource Centre.”
When the researchers modeled atomic strain during nanopillar elongation, they found that the un-notched structures failed via a plastic type of deformation known as shear banding. However, the notched structures were brittle and failed through crack propagation from the flaw point at tensile strengths significantly smaller than the un-notched samples (see video). These observations suggest that ‘flaw insensitivity’ may not be a general feature of nanoscale mechanical systems.
“The theory of flaw insensitivity postulates that the strength of materials that are intrinsically brittle or have limited plastic deformation modes approaches a theoretical limit at the nanoscale, and does not diminish due to structural flaws,” explains Jafary-Zadeh. “However, our results show that failure strength and deformation in amorphous nanosolids depend critically on the presence of flaws.”
Jafary-Zadeh notes that the excellent agreement between experimental results and the simulations is exciting and demonstrates how such computations can bridge the knowledge gap between macroscopic mechanical fracturing and the hidden corresponding mechanisms taking place at atomistic time and length scales.
The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing.
1. Gu, X. W, Jafary-Zadeh, M., Chen, D. Z., Wu, Z., Zhang, Y.-W. et al. Mechanisms of failure in nanoscale metallic glass. Nano Letters 14, 5858–5864 (2014).
A*STAR Research | ResearchSEA
Further reports about: > Computing > High Performance Computing > computational simulations > crack propagation > electron microscopy > external stress > glass > metallic > metallic glasses > molecular dynamics > molecular dynamics simulations > nanopillars > nanoscale > physical experiments > plastic > plastic deformation > structures > tensile strength > tiny
Fighting myocardial infarction with nanoparticle tandems
04.12.2017 | Rheinische Friedrich-Wilhelms-Universität Bonn
Virtual Reality for Bacteria
01.12.2017 | Institute of Science and Technology Austria
DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.
Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
15.12.2017 | Power and Electrical Engineering
15.12.2017 | Materials Sciences
15.12.2017 | Life Sciences