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 controlled manner with a geometrically well-defined probe.
During the nanoindentation, a force is applied by the transducer and the resulting displacement is observed to produce a traditional force versus displacement curve. 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.
(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 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 near-instant observation of events or sample recovery.
Quasistatic nanoindentation from Hysitron is designed for maximum verstility. Standard with all Hysitron nanoindentation systems and equipped with a standard maximum force up to 10 μN and a noise floor of less than 30 nN, quasistatic nanoindentation covers a large range of sample testing possibilities.
How Quasistatic Nanoindentation Works
The Hysitron transducer is unique in its operation and is the only system in the world to use the patented three-plate capacitive design. Displacment 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.
Schematic showing explanantion of Hysitron's patented three-plate capacitive transducer operation for accurate 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 caluclated using an advanced analysis software package to ensure any variations in probe geometery are accounted for.
Analysis from quasistatic nanoindentation testing showing curve fit over increasing load indentation testing for calibration of probe shape.