Impact Testing on the Nano-Scale - Principles and Methods of Nano-Impact Testing Available by Micro Materials

 

Topics Covered

Impact Testing
Impact Testing on the Nano-Scale
How Does Nano-Impact Testing Work?
High Cycle Nano-Impact Testing
Low Cycle Nano-Impact Testing
Correlation Nano-Impact Testing with Macro Scale Testing
End Milling vs Nano-Impact
High Temperature Nano-Impact Testing

Impact Testing

Impact testing is a well established method of measuring a samples ability to withstand high strain-rate loading. It determines the amount of energy which can be absorbed by a material before a fracture event or plastic deformation occurs. It also gives information on the effect of cyclic loading on the properties of materials. Traditionally, such tests have been carried out on the macro-scale. While qualitatively these tests can be informative, they lack detailed quantitative information, and also result in destruction of the sample. Furthermore, macro scale method of impact testing requires bulk samples and sufficient sample preparation.

Impact Testing on the Nano-Scale

Impact testing on the nano-scale can overcome all of these limitations. It gives valuable quantitative data on the performance of the sample, and impact sites are small enough to be classed as non-destructive. This means that the mechanical properties of a sample are not compromised, thus allowing it to go on to be tested by other complimentary means such as nanoindentation or nanoscratch testing. Sample size is limited only by the practicality of handling the sample. Highly localised individual structures of sizes in the order of microns may be targeted successfully. Automation enables repetitive impacts at the same position on the sample surface with a set frequency. Information such as cycles and time to failure can easily be obtained.

How Does Nano-Impact Testing Work?

High Cycle Nano-Impact Testing

Two methods of nano-impact are available; high cycle and low cycle. Both use the pendulum system of the NanoTest system (Micro Materials, Wrexham UK). The first method oscillates a sample in the horizontal plane, causing it to strike an indenter (typically made of diamond) of known geometry. This allows high cycle fatigue conditions to be replicated. Sample oscillation frequencies up to 500 Hz and amplitudes up to 5 µm are available, dependent on indenter angle.

Low Cycle Nano-Impact Testing

The second low cycle method releases the pendulum at speed into the sample, allowing a single impact or repeated impacts on the same sample. This allows investigation of low cycling fatigue, work hardening, yield stress and dynamic hardness. Solenoid actuation enables the probe to be accelerated over a precisely known distance (typically 10µm) and hence the energy delivered to be determined. The NanoTest (with the swinging pendulum analogous to conventional macro-scale impact tests) can accelerate the indenter fast enough to produce true high strain rate impacts up to 300s-1. Again, this is dependent on indenter geometry.

Correlation Nano-Impact Testing with Macro Scale Testing

The energy range produced by the NanoTest during nano-impact tests correlates well with wear rates during macro scale activities, spanning the range from 1nJ to 1mJ. Using the impact module in conjunction with the MicroTest (high load) loading head, this energy range can be extended up to 100mJ. This correlates well with the energy deposited during the operation of MEMS devices, hard disk drives, slurry pumps, ultrasonic abrasion and shot blasting of glass and steel.

End Milling vs Nano-Impact

Cutting tool coatings need to be optimised for toughness rather than hardness, meaning nanoimpact is a superior technique to nanoindentation for such an application. Cutting tool coatings are often characterised using end milling tests, which are laborious and time consuming, and also require bulk samples.

A five minute nanoimpact test on a small sample can predict the same wear pattern as an industrial wear test undertaken on the macro scale. (Results have been submitted for publication and are available on request)

High Temperature Nano-Impact Testing

A further advantage of the Micro Materials nanoimpact capability is that it may be used in conjunction with the high temperature testing option, allowing nanoimpact tests to be carried out at temperatures up to 750°C, thus allowing the replication of true service conditions.

About Micro Materials

Established in 1988, Micro Materials Ltd are manufacturers of the innovative NanoTest system, which offers unique nanomechanical test capability to materials researchers for the characterisation and optimisation of thin films, coatings and bulk materials. The current model, the NanoTest Vantage was launched on June 1st 2011.

This information has been sourced, reviewed and adapted from materials provided by Micro Materials.

For more information on this source, please visit Micro Materials.

Source: Micro Materials Ltd.

For more information on this source, visit Micro Materials.

Date Added: Oct 30, 2008 | Updated: Apr 18, 2013
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