Experimental conditions affecting the measured fracture toughness at the microscale: Notch geometry and crack extension measurement

Experimental fracture mechanics at the microscale became an indispensable tool for understanding and developing advanced material systems. In case of linear elastic fracture mechanics, stringent requirements are typically only warranted for very brittle materials. The material properties of semi-brittle materials might be accessible by elasto-plastic fracture mechanics. However, challenges exist in determining the crack length, in producing geometry and notch geometry, in defining of the initiation toughness and in extracting the size independent crack resistance curves. In this study, we assess current approaches of measuring the fracture toughness of semi-brittle materials by elasto-plastic fracture mechanics. We investigate the notch geometry (through thickness notch and bridge notch), the notch depth and the method of determining in situ the crack length for ultrafine grained tungsten. Further challenges due to the overlap of sample size and crack process zone are identified. Finally, we propose a workflow for analyzing the elasto-plastic fracture toughness of material systems at the microscale.