A new push-pull sample design for microscale mode 1 fracture toughness measurements under uniaxial tension

Schwiedrzik, J. J.; Ast, J.; Pethö, L.; Maeder, X.; Michler, J.

Fatigue and Fracture of Engineering Materials and Structures 41 (2018)

A sample geometry is proposed for performing microscale tensile experiments based on a push-pull design. It allows measuring mode 1 fracture toughness under uniform far-field loading. Finite element simulations were performed to determine the geometry factor, which was nearly constant for Young’s moduli spanning 2 orders of magnitude. It was further verified that mode 1 stress intensity factor KI is nearly constant over the width of the tension rods and an order of magnitude higher than KII and KIII. Notched samples with different a/w ratios were prepared in (100)-oriented Si by a combination of reactive ion etching and focused ion beam milling. The mode 1 fracture toughness KI,q was constant with a/w and in average 1.02 ± 0.06 MPa√m in good agreement with existing literature. The geometry was characterized and experimentally validated and may be used for fracture toughness measurements of all material classes. It is especially interesting when a uniaxial, homogeneous stress field is desired, if crack tip plasticity is important, or when positioning of the indenter is difficult.