Mechanics of cracking failure in a silver layer deposited by inkjet printing on a flexible substrate

This work intends to investigate strain fields around cracks in thin metallic film deposited on flexible substrate through an experimental approach. The studied sample consists of a pre-cracked silver nanoparticles inkjet printed layer with a thickness of 2 µm deposited on 125 µm thick polyimide substrates. The mechanical induced failure experiments are performed on a tensile testing device installed under a scanning electron microscope (SEM) allowing in situ cracking observations through digital images correlation (DIC). The samples are deformed up to 2 %. In order to follow the deformation during the test though DIC, speckle patterns of 100 nm wide and 50 nm depth are milled on the film surface with focused ions beam (FIB). The displacement field is obtained experimentally with DIC, the strain field being too noisy to be exploited. These experimental results are compared with finite elements models (FEM). Three-dimensional models are developed using the ABAQUS code and allow assessing the strain distribution in a cracked film around the crack tip. These FEM results agree with the experimental strain in front of the crack tip. The crack disturbs the imposed homogeneous strain at a distance of 200 µm laterally and 70 µm ahead.