Issue 35

Takamasa Abe et alii, Frattura ed Integrità Strutturale, 35 (2016) 196-205; DOI: 10.3221/IGF-ESIS.35.23 200 Figure 10 : Macro observation. Figure 11 : Microscopic fracture surface. Observation of crack initiation behavior In this subsection, we consider the influence of welding defects on fatigue crack initiation and propagation behavior by observing the crack from the root tip of the unwelded portion. The observation results for part of the unwelded portion are presented in Figs. 12 and 13. These images were captured under a load amplitude of 9kN. The test was terminated before it had gone to completion, and the test piece was cut axially to the load and observed near the unwelded portion. 9kN －② 1 ． 5 × 10 5 cycles 9kN －① 1 ． 4 × 10 5 cycles 4mm 5 m 4mm 5 m 8kN －① 1 ． 9 × 10 5 cycles 8kN －② 2 ． 1 × 10 5 cycles 4mm 5 m 4mm 5 m 7kN －① 2 ． 4 × 10 5 cycles 7kN －② 6 ． 6 × 10 5 cycles 7kN －③ 9 ． 9 × 10 5 cycles 4mm 5 m 4mm 5 m 4mm 5 m 6kN －① 6 ． 4 × 10 5 cycles 6kN －② 6 ． 7 × 10 5 cycles 6kN －③ 1 ． 1 × 10 6 cycles 4mm 5 m 4mm 5 m 4mm 5 m (A) Macroscopic fracture surface of Fa=6kN 4mm 5m The Length of root region (a) (c) Base metal Fillet welded (b) 0.5mm (a) Fatigue fracture surface 0.5mm (b) Fatigue fracture surface 0.5mm (c) Ductile fracture surface (d) 50μm (d) Ductile fracture surface