Synchronous Biaxial Straining of Foils and Thin Films with In Situ Capabilities: Instruments

A common method to examine the reliability of thin films and small volumes of irradiated materials being used in aerospace, energy, and protective coating applications is biaxial straining. With such tests, the fracture and deformation mechanisms occurring under multi-axial stress states can be investigated, which can strongly differ from the simpler uniaxial one. However, devices that can apply a precise and synchronously applied biaxial strain tend to be too large for foils or thin films and do not allow for additional observation methods to be applied to examine film fracture or deformation during the test. A prototype device that can apply synchronous equi-biaxial and semi-biaxial strains and can be combined with multiple in situ methods is introduced. The device is light and compact in design, which allows it to be mounted on optical light microscopes, atomic force microscopes, inside scanning electron microscopes, and even on X-ray beamlines for reflection or transmission measurements. Additionally, digital image correlation was utilized in two geometries to measure strains on a local or global level. The possible errors associated with the device and experiments on polyimide foils and a 100 nm tungsten film on polyimide are presented.