In-Situ SEM Material Testing

Large scale tensile testing is a commonly used test to quantify the elastic modulus, yield- , ultimate-, and fracture-strength of materials. However, while these tests provide valuable insights into the overall material properties, they average out the effects of each constituents such as the different phases or interfaces.

To quantify the properties of a single phase or interface, micro-tensile testing is required as shown in the image sequence on the left. Furthermore, by scaling down these experiments event more, single plastic deformation mechanisms can be detected and investigates.

For sample preparation, focused-ion beam (FIB) can be used to create dog-bone shaped samples with a uniform cross-section that remain attached to the original substrate. FIB can also be used to machine a griper shape into the tip of the silicon force-sensing probe. This gripper shape enables the interlocking with the dog bone sample in order to conduct micro-tensile tests.

During tensile test, linear elasticity is observed in the initial loading stage, before yielding, plasticity and, eventually fracture.

A critical testing requirement to measure the full stress-strain curve is true displacement-controlled testing. As a result, the material’s behavior after the ultimate strength, with decreasing slope of the stress-strain curve can be optioned.

By combining this micro-tensile testing method with the deposition of speckles or line markers (shown here) along the sample, digital image correlation (DUIC) can be used to obtain the local strain along the samples axis.

Z. Fu, L. Jiang, J. L. Wardini, B. E. MacDonald, H. Wen, W. Xiong, D. Zhang, Y. Zhou, T. J. Rupert, W. Chen, E. J. Lavernia, “A high-entropy alloy with hierarchical nanoprecipitatesand ultrahigh strength.” Science Advances, 2018