Effects of stress ratio on fatigue crack propagation properties of submicron-thick free-standing copper films

Fatigue crack closure in submicron-thick freestanding copper films

“…3(a). The fatigue crack propagation accompanied with intrusions/extrusions was similar to the reported results [39]. In the loading process, the fatigue crack remained closed from the minimum K ¼0.38 MPam 1/2 (K/K max ¼ 0.11, Fig.…”

“…11(b)). The da/dN vs. ΔK relationships at R¼ 0.1, 0.5, and 0.8 obtained in the previous study [39] are shown by the dotted regions in Fig. 11.…”

“…2) due to the cyclic frequency limitations imposed by the complex displacement transfer mechanism. Therefore, we employed another piezoelectric actuator-driven fatigue testing machine in ambient air, which was previously developed [39], to conduct fatigue crack propagation experiments at high frequencies. The experimental conditions for the fatigue crack propagation experiments are listed in Table 1.…”

“…Although several studies have been conducted on the fatigue in metallic thin films fixed on substrates [25][26][27][28][29][30][31][32] and freestanding films [33][34][35][36], fatigue crack propagation of freestanding submicron-thick films have rarely been studied [37][38][39]. Thin films have a structure with a large surface area to volume ratio, and those formed by physical vapor deposition generally consist of fine columnar grains.…”

“…In a previous study, the authors investigated the fatigue crack propagation properties of approximately 500-nm-thick freestanding copper (Cu) films [39]. In the high-K max region (maximum stress intensity factor K max Z 4.5 MPam 1/2 ), the fatigue crack propagated by tensile fracture mode accompanied by a necking deformation in the thickness direction irrespective of R, and da/dN was dominated by K max .…”