Issue 35

T. Abe et alii, Frattura ed Integrità Strutturale, 35 (2016) 424-433; DOI: 10.3221/IGF-ESIS.35.48 425 able to more accurately estimate the lifetime. To this end, we fabricated a test piece imitating the machine, and subjected it to fatigue tests. We also investigated the fatigue properties and fracture mechanism of a load carrying-type one-sided filet weld by three-dimensional observation. M ATERIALS AND METHODS Materials he base material was high strength steel SS400 (JIS) which is used in the attachment part of a hydraulic excavator. We joined this material to the “L” shape indicated in Fig.1 by one-sided filet welding. To prevent heat deformation of the plate during two-sided welding, we welded a grab section and stiffener plates (labeled (a) and (b), respectively, in Fig. 1) to the test piece. The welded part was cut into “L” shapes at 50mm intervals by wire cutting, excluding the welding start and end points. (see broken lines in Fig. 1). The welding rods were MX200 made by Kobe Steel, Ltd (Wire diameter φ=1.2mm). Tab. 1, 2, and 3 give the arc welding condition, the chemical composition of the welding rods and the mechanical properties of MX200, respectively. The chemical composition and mechanical properties of SS400 are listed in Tabs. 4 and 5, respectively. Grab plate (a) Stiffener plate (b) 6 30 64 6 14 6 50 176 50 4.5 30 14 15 Figure 1 : Manufacturing specimens. Figure 2 : Shapes and dimensions of specimens. Welding current (A) Arc Voltage 270 200 Material C Si Mn P S MX200 0.06 0.5 1.4 0.013 0.009 Table1 : Welding Condition. Table 2 : Chemical composition of MX200 [mass%]. Yield Strength  y (MPa) Tensile Strength  B (MPa) Elongation  (%) Absorbed Energy (J) 530 590 29 98 Table 3 : Mechanical properties of MX200. Material C Mn P S SS400 - - ≤ 0.05 ≤0.05 Yield Strength  y (MPa) Tensile Strength  B (MPa) Elongation  (%) 245 ≤ 400  510 29 ≤ Table 4 : Chemical composition of SS400 [mass%]. Table 5 : Mechanical properties of SS400. Experimental method The fatigue test was performed by a hydraulic servo-controlled fatigue strength-testing machine. The gray area in Fig. 2 was affixed to the jig, and the loading type of the machine was reproduced by applying a left and right cyclic load. When fixing the test piece to the jig, we also attached a strain gauge to the test piece and adjusted the test piece such that the T