Issue 35

Takamasa Abe et alii, Frattura ed Integrità Strutturale, 35 (2016) 196-205; DOI: 10.3221/IGF-ESIS.35.23

9kN －② 1 ． 5 × 10 5 cycles

9kN －① 1 ． 4 × 10 5 cycles

4mm 5 m

4mm 5 m

8kN －② 2 ． 1 × 10 5 cycles

8kN －① 1 ． 9 × 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 －② 6 ． 7 × 10 5 cycles

6kN －③ 1 ． 1 × 10 6 cycles

6kN －① 6 ． 4 × 10 5 cycles

4mm 5 m

4mm 5 m

4mm 5 m

Figure 10 : Macro observation.

root region

The Length of

(c)

(a)

(A) Macroscopic fracture surface of Fa=6kN 4mm 5m

(b)

Fillet welded

50μm (d) Ductile fracture surface

Base metal

0.5mm

(a) Fatigue fracture surface

(d)

0.5mm (c) Ductile fracture surface

0.5mm (b) Fatigue fracture surface

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.

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