Issue 35

T. Abe et alii, Frattura ed Integrità Strutturale, 35 (2016) 424-433; DOI: 10.3221/IGF-ESIS.35.48 432 Figure 19 : Position of the strain gauge near fillet weld. C ONCLUSIONS his study, observed crack initiation in a machine piece with welded filet joints, and crack propagation into the welding material. The aim was to clarify the fatigue properties of the filet weld and fatigue fracture. Our conclusions are summarized below. 1. Fatigue cracks in the test piece initiated from the tip of the unwelded portion and propagated into the welding materials, eventually leading to fracture. Macro fracture was independent of load amplitude. 2. Multiple welding defects were observed in the unwelded portion, but did not appear to be crack origins. Although these welding defects affected the direction of crack propagation, they exerted minimal influence. 3. The three-dimensional observations revealed that fatigue cracks initiate at an early stage of the fatigue development, and persist throughout the lifetime. We infer that the fatigue lifetime is chiefly governed by the crack propagation lifetime. 4. Cracks were initiated at multiple sites in the test piece. As the number of cycles increased, these cracks propagated and combined. 5. Considering the combination of cracks from multiple crack origins is important for a precise evaluation of fatigue damage. R EFERENCES [1] Bell, R., Vosikovsky, O., Bain, S. A., The significance of weld toe undercuts in the fatigue of steel plate T-joints, International Journal of Fatigue, 11(1) (1989) 3-11. [2] Carpinteri, A., Brighenti, R., Huth, H., Vantadori, S., Fatigue growth of surface crack in a welded T-joint, International Journal of Fatigue, 27 (2005) 59-69. [3] Chung, H.Y., Liu, S.H., Lin, R.S., Ju, S.H., Assessment of stress intensity factors for load-carrying fillet welded cruciform joints using a digital camera, International Journal of Fatigue, 30 (2008) 1861-1872. [4] Japanese Society of Steel Construction ed., Fatigue design recommendations for steel structures, Japanese Society of Steel Construction. [5] Kainuma, S., Mori, T., A fatigue strength evaluation method for load-carrying fillet welded cruciform joints, International Journal of Fatigue, 28 (2006) 864-872. [6] Kanvinde, A.M., Gomez, I.R., Roberts, M., Fell, B.V., Grondin, G.Y., Strength and ductility of fillet welds with transverse root notch, Journal of Constructional Steel Research, 65 (2009) 948-958. [7] Miki, C., Tateishi, K., Fan, H., Tanaka, M., Fatigue strengths of fillet-welded joints containing root discontinuities, International Journal of Fatigue, 15 (2) (1993) 133-140. [8] Mori, T., Influence of weld penetration on fatigue strength of single-sided fillet welded joints, Journal of Construction Steel of JSSC, 10(40) (2003) 9–15. T (a) Root tip 100μm (b) Narrow root tip Root tip 100μm Root tip