An anti-fatigue smart paste, which consists of fine alumina particles and silicone grease with low viscosity, was applied to a bolt hole (and its periphery in some cases) in a steel plate specimen, and the effects of the smart paste on automatic restraint and visual detection of fatigue crack growth were experimentally investigated through fatigue tests. Fractographic observations using a SEM (Scanning Electron Microscope) were also carried out. As a result, approximately 20∼410% increase in failure life was produced by the wedge effect of the alumina particles in the smart paste. When the smart paste was applied, remarkable black color developed in the white paste along the paths of crack growth, exceedingly facilitating the visual detection of the crack growth.
A series of fatigue experiments and elastic analysis were carried out for investigating fatigue characteristics of patch plate joints assembled by fillet welding assisted with bonding. In the case that fatigue cracks occurred at the weld toe by the 4-points bending fatigue experiment, the fatigue life of joints assembled by welding and bonding (WB specimens) were almost the same as those by only welding (W specimens). The elastic analysis simulating the 4-point bending loaded situation on W and WB specimens was performed for elucidating its reason. The stress concentration at the weld toe was even high in the WB specimens. Therefore, the fatigue life of WB specimens was not longer than that of W specimens. On the other hand, the stress around the weld root of WB specimen was around 30% of that of W specimen. The possibility of stress reduction effect by bonding was indicated around the weld root rather than around the weld toe. In order to verify this possibility, the 4-point bending fatigue experiment was performed by setting the specimens so that the tensile stress was applied on the weld root. It was confirmed that the fatigue cracks occurred from the weld root in both of W and WB specimens. The fatigue life defined in this study of WB specimens was from 4 to 8 times longer than that of W specimens when the applied nominal stress range was under 175 MPa. The fatigue life defined in this study of WB specimens was from 2 to 3 times longer than that of W specimens when the applied nominal stress range was over 200 MPa. The results indicated the fatigue life improvement of patch plate joints by fillet welding assisted with bonding when the fatigue cracks occurred at the weld root.