Direct observation of the thickness effect on critical crack tip opening displacement in freestanding copper submicron-films by in situ electron microscopy fracture toughness testing

Microstructural dependence of the fracture toughness of metallic thin films: A bulge test and atomistic simulation study on single-crystalline and polycrystalline silver films

“…A preliminary study [10] evidenced that this low toughness is connected to the strong confinement of the plastic deformation in front of the notch, which strongly limits the energy dissipation during crack initiation and propagation. It was also observed that crack growth in polycrystalline thin films is usually intercrystalline [2,10]. This second observation, consistent with previous reports in the literature [11,12,13,14,15], suggests that grain boundaries (GBs) are easy crack propagation paths, as expected from the lower energy required to produce surfaces compared with an intracrystalline crack [16].…”

“…As an example, the fracture toughness of 200-nm-thick gold membranes was measured to be only ;2 MPa m 1/2 [6], far off from the 50-100 MPa m 1/2 reported in the literature for standard bulk specimens [7]. The scaling relationship between thickness and fracture toughness of thin films has already been investigated in detail in [1,2,3,4,8,9]. The focus of the present study is, therefore, on identifying additional factors contributing to the low toughness of thin metallic films.…”

“…Thin films, even when made out of the most ductile metals, exhibit an extremely low fracture toughness compared with their bulk counterparts [1,2,3,4,5]. As an example, the fracture toughness of 200-nm-thick gold membranes was measured to be only ;2 MPa m 1/2 [6], far off from the 50-100 MPa m 1/2 reported in the literature for standard bulk specimens [7].…”

Influence of a thin surface oxide layer on fracture toughness of copper films

“…In situ field emission scanning electron microscope (FESEM) fracture toughness experiments were conducted using an in situ FESEM tensile testing machine (2), (3) . Crack tip opening displacement (CTOD) was evaluated by measuring the notch width before loading (δ0), notch opening displacement (δa) and crack mouth opening displacement at the notch root (δnr) from FESEM images.…”

“…Crack tip opening displacement (CTOD) was evaluated by measuring the notch width before loading (δ0), notch opening displacement (δa) and crack mouth opening displacement at the notch root (δnr) from FESEM images. The CTOD was calculated using the following equations (2), (3) , and the critical CTOD was determined as δ just after crack initiation.…”