µTS Under-microscope Test System

 

The wavelength of visible light limits optical microscope resolution to 250 nm. Digital Image Correlation (DIC) is a powerful post-processing technique for resolving feature displacements down to 0.1 pixels. Combining DIC and optical microscopes gives 25 nm resolution of the full 2D displacement field. In this way, nano length scale research can be conducted without the need for an AFM or SEM. Moreover, optical microscopy offers the advantage of fast image acquisition.


The primary challenge with in situ materials testing under optical microscopes is out-of-plane specimen deflection. The high magnifications needed to achieve 25 nm displacement field resolution also mean a small depth of field. A few microns out-of-plane motion causes the image to go out of focus. Psylotech's µTS is specifically designed to keep a sample in- plane during testing. The result is a sophisticated instrument well suited for:
 

 

 

 

 

 

 

• Continuum Model Validation of finite element analysis through multi-scale testing
• Miniature Sample Testing to facilitate material development where quantities can be low
• Unprecedented Versatility to enable implementation of new experimental techniques testing

 

 

Continuum Model Validation

 

In finite element analysis (FEA), material mechanical properties are presumed uniform to limit the size of elements for reasonable computation times. Psylotech's µTS is a tool to validate continuum models over 6 length scales. Through digital image correlation (DIC) and optimized microscope optics, the full displacement field can be monitored down to 0.1 pixel resolution during a mechanical test. This means up to 25 nm resolution in the displacement field and 0.01% resolution in the strain field, depending on camera resolution.
Consider the example of a composite layup. Typically, FEA presumes uniform, anisotropic material behavior. Tests on a given layup must be experimentally determined in multiple directions. If the layup is modified or the matrix material is changed, new tests should be conducted to re-define material properties. Multi-scale testing offers a vehicle to better understand the interaction between fibers as well as between fibers and the matrix. With test data on smaller scales, continuum properties for any layup can be modeled, skipping an extra experimentation step and accelerating component development time. Moreover, better understanding of small scale interactions and small scale failure mechanisms can lead to fundamentally improved materials.