Application Note | Nano Compression
Compression on Soft, Flexible Materials
Low-Load, Large-Displacement Compression for MEMS and Spring-Like Structures
Research & Experimental Testing
NANOVEA Laboratory
Visual Design & Editorial
Andrew Shore
Introduction
An example of very soft and flexible samples is a microelectromechanical system. MEMS are used in everyday commercial products like printers, mobile phones, and cars [1]. Their uses also include special functions, such as biosensors [2] and energy harvesting [3]. For their applications, MEMS must be able to reversibly transition between their original configuration to a compressed configuration repeatedly [4]. To understand how the structures will react to mechanical forces, compression testing can be conducted. Compression testing can be utilized to test and tune various MEMS configurations as well as testing upper and lower force limits for these samples.
Why Low-Load, Large-Displacement Compression Matters
The NANOVEA Mechanical Tester Nano Module’s ability to accurately collect data at very low loads and travel over 1mm of distance makes it ideal for testing the soft and flexible samples. By having independent load and depth sensors, large indenter displacement does not affect the readings by the load sensor. The ability to carry out low-load testing over a range of more than 1mm of indenter travel makes our system unique compared to other nanoindentation systems. In comparison, a reasonable travel distance for a nanoscale indentation system is typically below 250μm.
ℹ️ Learn more about nanoindentation and mechanical testing lab services.
Mobile phones are among the everyday products that rely on MEMS.
Measurement Objective
In this case study, NANOVEA conducted compression testing on two uniquely different flexible, spring-like samples. We showcase our ability to conduct compression at very low loads and record large displacement while accurately obtaining data at low loads and how this can be applied to the MEMS industry. Due to privacy policies, the samples and their origin will not be revealed in this study.
NANOVEA PB1000 Large Platform
Mechanical Tester
Measurement Parameters
| Test parameter | Sample A | Sample B |
|---|---|---|
| Maximum force (mN) | 0.075 | 8.00 |
| Loading rate (V/min) | 1.00 | 15.00 |
| Unloading rate (V/min) | 1.00 | 15.00 |
| Indenter type | Flat | Flat |
| Indenter radius (µm) | 50 | 50 |
Table 1: Test parameters for compression testing on the flexible samples.
Note: The loading rate of 1 V/min is proportional to approximately 100μm of displacement when the indenter is in the air.
Results and Discussion
The sample’s response to mechanical forces can be seen in the load vs depth curves. Sample A only displays linear elastic deformation with the test parameters listed above. Figure 2 is a great example of the stability that can be achieved for a load vs. depth curve at 75μN. Due to the load and depth sensors stability, it would be easy to perceive any significant mechanical response from the sample.
Sample B displays a different mechanical response from Sample A. Past 750μm of depth, fracture-like behavior in the graph begins to appear. This is seen with the sharp drops in load at 850 and 975μm of depth. Despite traveling at a high loading rate for more than 1mm over a range of 8mN, our highly sensitive load and depth sensors allow the user to obtain the sleek load vs depth curves below.
The stiffness was calculated from the unloading portion of the load vs depth curves. Stiffness reflects how much force is necessary to deform the sample. For this stiffness calculation, a pseudo Poisson’s ratio of 0.3 was used since the actual ratio of the material is not known. In this case, Sample B proved to be stiffer than Sample A.
| Max depth (µm) | Unloading stiffness (mN/nm × 10⁶) | |
|---|---|---|
| Sample A | 29.20 ± 0.71 | 2.552 ± 0.319 |
| Sample B | 1084.33 ± 18.49 | 7.470 ± 0.204 |
Table 2: Results from compression testing on soft, flexible samples.
Conclusion
Two different flexible samples were tested under compression using the NANOVEA Mechanical Tester’s Nano Module. The tests were conducted at very low loads (<80μN) and over a large depth range (>1mm). Nano-scaled compression testing with the Nano Module has shown the module’s ability to test very soft and flexible samples. Additional testing for this study could address how repeated cyclical loading affects the elastic recovery aspect of the spring-like samples via the NANOVEA Mechanical Tester’s multi-loading option.
References
“Introduction and Application Areas for MEMS.” EEHerald, 1 Mar. 2017, www.eeherald.com/section/design-guide/mems_application_introduction.html.
Louizos, Louizos-Alexandros; Athanasopoulos, Panagiotis G.; Varty, Kevin (2012). “Microelectromechanical Systems and Nanotechnology. A Platform for the Next Stent Technological Era”. Vasc Endovascular Surg. 46 (8): 605–609. doi:10.1177/1538574412462637. PMID 23047818.
Hajati, Arman; Sang-Gook Kim (2011). “Ultra-wide bandwidth piezoelectric energy harvesting”. Applied Physics Letters. 99 (8): 083105. doi:10.1063/1.3629551.
Fu, Haoran, et al. “Morphable 3D mesostructures and microelectronic devices by multistable buckling mechanics.” Nature Materials 17.3 (2018): 268.
Frequently Asked Questions About Low-Load Compression Testing
Why compression-test MEMS structures?
MEMS must reversibly transition between their original and compressed configurations, repeatedly. Compression testing shows how a structure reacts to mechanical force and can be used to tune MEMS configurations and to find upper and lower force limits.
How much indenter travel can the Nano Module cover?
More than 1 mm of indenter travel while still testing at low loads. A reasonable travel distance for a nanoscale indentation system is typically below 250 µm.
Why do independent load and depth sensors matter?
With independent sensors, large indenter displacement does not affect the load sensor reading, so stable load-depth curves can be recorded at loads as low as 75 µN.
What did the load-depth curves show?
Sample A deformed only linear-elastically up to 75 µN. Sample B, loaded to 8 mN, showed fracture-like drops in load at 850 and 975 µm of depth, beyond 750 µm.
How was stiffness calculated?
From the unloading portion of the load-depth curves, using a pseudo Poisson’s ratio of 0.3 because the material’s actual ratio is not known. Sample B proved stiffer than Sample A.
Which NANOVEA instrument was used?
The NANOVEA Mechanical Tester with its Nano Module, fitted with a 50 µm radius flat indenter.
