Strain ratio and thickness effects on plasticity and crack patterns of Nickel thin films

International audienceThe influence of the strain ratio (equibiaxial or uniaxial) and the strain path (equibiaxial or sequenced uniaxial) on the cracking of metallic thin films is studied. We used 20, 100 and 600 nm Nickel films deposited onto flexible substrates, analysed with in-situ X-ray diffraction and digital image correlation, and post-mortem optical microscopy. It is shown that the thickness and the loading ratio effects are interweaved. In particular, 600 nm films show a small (1.9%) von Mises fracture strain and straight cracks when strained equibiaxially, but a larger (2.7%) fracture strain and more tortuous cracks when strained uniaxially. On the contrary, 20 and 100 nm thin films show different von Mises ultimate tensile strengths, though their von Mises fracture strain and theirs cracks tortuosity hardly depend on the test