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Quasistatic Nanoindentation: An Overview
Quasistatic nanoindentation has become the standard technique used for nanomechanical characterization of materials. A quasistatic nanoindentation test is performed by applying and removing a load to a sample in a highly controlled manner with a geometrically well-defined probe.
During the nanoindentation process, a force is applied by the transducer and the probe displacement is continuously measured to produce a traditional force versus displacement curve. The resulting force vs. displacement curve serves as the 'mechanical fingerprint' of the material, from which quantitative nanoscale material properties can be determined. Hysitron measures the force and displacement of the nanoindentation probe with a unique patented three-plate capacitive transducer design. This transducer design provides an unsurpassed noise floor and ultra-low working force.
Figure 1: (A) Force versus displacement curve on fused quartz showing typical response of elastic-plastic material. (B) Resulting in-situ SPM image of quartz surface after quasistatic nanoindentation showing residual indent impression.
The tightly controlled construction and calibration standards used for the capacitive transducer in combination with the precisely machined, rigid nanoindentation probes produce quantifiable, reliable measurement on any material.
Analysis of the measured force versus displacement curve (particularly the unloading segment) provides the user with quantitative information regarding the mechanical properties of the sample. Values typically obtained from quasistatic nanoindentation testing are Reduced Modulus [Er] and Hardness [H]. However other information such as fracture toughness, stiffness, delamination force, and film thickness can also be obtained.
All Hysitron nanoindentation systems are capable of in-situ SPM imaging. Using the same probe to scan a sample surface immediately before and/or after a test allows for precise placement of the test as well as observation of deformation events or sample recovery after the test.
Quasistatic nanoindentation from Hysitron is designed for maximum versatility. Our capacitive quasistatic nanoindentation transducer technologies cover a force range from 2nN to 10μN, providing characterization capabilities on the widest range of materials.
How Quasistatic Nanoindentation Works
The Hysitron nanoindentation transducer is unique in its operation and is the only system in the world to use the patented three-plate capacitive design. Displacement is measured by running two AC signals that are 180 degrees out of phase with each other to the top and bottom plate of the three-plate capacitive sensor. The AC signals are observed by the center (floating) plate and the sum of the signals corresponds to a measured displacement. To apply a load, a DC offset is applied to the lower plate of the transducer that electrostatically attracts the center (floating) plate downward. The resulting difference in the sums of the AC signals results in an offset in the sum of the AC signals and thus a change in displacement.
Figure 2: Schematic showing an explanation of Hysitron's patented three-plate capacitive transducer operation for high accuracy force application during nanoindentation.
Hysitron nanoindentation systems include a quasistatic data analysis package that uses a standard model to fit the initial unloading portion of the force versus displacement curve to extract the Reduced Modulus [Er] and Hardness [H] values.
Quasistatic testing enables the nanoindentation probe area function to be calculated using an advanced analysis software package to ensure any variations in probe geometry are accounted for.
Figure 3. Analysis from quasistatic nanoindentation testing showing curve fit over increasing load indentation testing for calibration of probe shape.
Mechanical Properties Measured Using Nanoindentation
Nanoindentation is a powerful technique to quantitatively characterize the mechanical properties of small volumes of material. By fitting the appropriate models to the force vs. displacement curve obtained during the test, material properties such as elastic modulus, hardness, creep, stress relaxation, interfacial adhesion, and fracture toughness can be measured at the nanoscale and microscale.
For Additional Information on Nanoindentation Mechanical Property Measurements, see our Mechanical Properties webpage.
Nanoindentation Test Equipment
A wide variety of test equipment and application-specific techniques are available to perform nanoindentation testing. Three primary classes of nanoindentation equipment exist:
- Standalone Nanoindentation Equipment
- Nanoindentation Equipment Interfaced to Microscopy Systems
- High-throughput Nanoindentation Metrology Equipment
For general information about nanoindentation test equipment, see our Nanoindenter Overview