Fatigue crack propagation properties of submicron-thick freestanding copper films in vacuum environment

AbstractFatigue crack propagation experiments were conducted in approximately 500 nm thick freestanding copper (Cu) films in both air and vacuum environments to clarify the effects of vacuum environment on fatigue crack propagation properties. First, we newly developed an experimental setup for fatigue crack propagation experiments of the freestanding Cu films inside a vacuum chamber of a field-emission scanning electron microscope (FESEM). Fatigue crack propagation experiments were conducted in ambient air and vacuum environment of the FESEM chamber (˜10-4 Pa) under load-control conditions with constant maximum stress and at a stress ratio R of 0.1. In situ FESEM observations of fatigue crack propagation confirmed that preceding intrusions/extrusions were formed ahead of the fatigue crack tip, and the fatigue crack then propagated preferentially through these intrusions/extrusions in the lower stress intensity factor range (ΔK). In the higher ΔK, the fatigue crack propagated in tensile fracture mode. These mechanisms of fatigue crack propagation were similar to those in air. The relationships between fatigue crack propagation rate (da/dN) and stress intensity factor range (ΔK) in both environments were roughly within a narrow band in the region of ΔK ≳ 4—5 MPam1/2. On the other hand, da/dN in vacuum became smaller than that in air in the region of ΔK ≲ 4—5 MPam1/2. FESEM observations confirmed that the fracture surfaces morphologies depended on the environments in ΔK ≲ 4—5 MPam1/2: flat fracture surface were mainly observed in air, whereas, in vacuum environment, blunt fracture surface with fine roughness were mainly observed. This suggests that reversible cyclic slip deformation and rewelding occurred in vacuum environments, resulting in smaller da/dN in vacuum than air

Effects of optical diameter of intraocular lenses with intrascleral fixation on higher-order aberrations

Abstract Background Intrascleral fixation of an intraocular lens (IOL) is used in eyes that lack capsular support. The aim of the study is to determine whether a larger optical diameter IOL will decrease the higher-order aberrations (HOAs) when the haptics are extended for intrascleral fixation than a smaller diameter IOL. Methods Three-piece acrylic IOLs with 6.0 mm optics (X-60, VA-60BBR) and 7.0 mm optics (X-70, VA-70 AD) were fixed at lengths of 13, 14, 15, 16, or 17 mm. A wavefront analyzer was used to measure the HOAs within the central 3.0 and 5.2 mm optic diameter. Results The astigmatic aberration within the central 5.2 mm was greater than that within the central 3.0 mm for all IOLs. The HOAs increased significantly with an extension of the IOLs with both optical diameters (P < 0.001). The coma aberration within the central 5.2 mm was greater than that within the central 3.0 mm but it did not increase with an extension of the haptics. The astigmatic aberration of the X-60 IOL was significantly greater than that of the X-70 only at an extension of 17 mm. The astigmatic aberration of the VA-70 AD was not significantly different from that of the VA-60BBR. The cylindrical power changed from 0.047 D in the X-60 to 0.118 D in the VA-70 AD when the IOLs were extended from 13 to 17 mm. Conclusion When three-piece IOLs are highly extended for intrascleral fixation, the astigmatic aberration increases significantly. However, IOLs with 7 mm optics do not have less astigmatic and coma aberrations than IOLs with 6 mm optics