Issue 35

Takamasa Abe et alii, Frattura ed Integrità Strutturale, 35 (2016) 196-205; DOI: 10.3221/IGF-ESIS.35.23 196 Focussed on Crack Paths Fatigue properties and fracture mechanism of load carrying type fillet joints with one-sided welding Takamasa Abe Kobelco Construction Machinery CO.,LTD, Japan abe.takamasa@kobelco.com Hiroyuki Akebono, Masahiko Kato, Atsushi Sugeta Department of Mechanical Science and Engineering, Hiroshima University, Japan akebono@hiroshima-u.ac.jp, mkato@hiroshima-u.ac.jp, asugeta@hiroshima-u.ac.jp A BSTRACT . The structures of the hydraulic excavator and the crane have numerous one-sided welded joints. However, attachments with box like structures are difficult to weld at both sides. Therefore, high accurate evaluation method is needed. In this study, the fatigue properties and the fracture mechanism of the load carrying type fillet joints with one-sided welding were investigated experimentally to evaluate its fatigue damage with high accuracy based on the experimental results. As the results, f atigue cracks in the test piece initiated from the tip of the unwelded portion and propagated into the welding materials. 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. The three-dimensional observations revealed that fatigue cracks initiate at an early stage of the fatigue development. We infer that the fatigue lifetime is chiefly governed by the crack propagation lifetime. Cracks were initiated at multiple sites in the test piece. As the number of cycles increased, these cracks propagated and combined. So considering the combination of cracks from multiple crack origins is important for a precise evaluation of fatigue damage. K EYWORDS . The filet joint with One-sided welding; Crack Propagation; 3-Dimensional Observation. I NTRODUCTION ydraulic excavators and cranes are major heavy equipment with numerous one-sided welded joints. Although fillet weld joints are easily implemented and economical, the unwelded portion frequently initiates crack propagation. Therefore, the unwelded portion is reduced by both side welding and by adding a groove. However, attachments with box like structures are difficult to weld at both sides, and grooving cannot completely remove the unwelded portion because high-quality full penetration welds are difficult to achieve. Despite the need for an accurate evaluation method of crack propagation, the fatigue fracture mechanism and the fatigue damage in practical fillet joints with one-sided welding remains poorly understood [1 - 13]. While the fatigue strength of the unwelded portion of load- carrying cruciform-welded joints has been extensively investigated, few studies have reported on one-sided welding. Moreover, few load-carrying types are suitable for one-sided welding. Most of the existing studies evaluate the lifetime from the S-N curve and stress intensity factor, without referring to the crack development behavior. At the beginning of this study, we believed that if we could understand the crack propagation behavior in the interior structure, we would be