Issue 41

Z. Li et alii, Frattura ed Integrità Strutturale, 41 (2017) 378-387; DOI: 10.3221/IGF-ESIS.41.49 384 (a) (b) Figure 12: Longitudinal residual stress distribution of CH-8. (a) Flage; (b) Web. Analysis of test results As shown in Figs. 5~12, the residual stress along the centerline in the cross-section obeys symmetric parabolic distribution. In all the specimens, the residual tensile stress descends from the near-weld region to the middle of the member, but the trend is not linear. The residual tensile stress peaks at the centerline of the member. Except for specimen CH-5, each of the specimens boasts a peak value of residual tensile stress so large as to exceed the yield strength of the material. The peaks of residual tensile stress at the web occur near the edge of weld instead of the flange. With only a few specimens surpassing the yield strength of the material, the web has a small residual tensile stress that essentially follows symmetric parabolic distribution similar to that of the cross-section of I-section members beyond the limits of width-thickness ratio. The stress distribution is basically linear in the middle of the web. Figs. 13, 14 and 15 make pair-wise comparison of residual stress distributions between CH-1 and CH-6, CH-2 and CH-7, as well as CH-3 and CH-8. Each pair includes two specimens of the same cross-sectional size but different materials. CH- 1, CH-2 and CH-3 are made of Q345B, while CH-6, CH-7 and CH-8 are made of Q235B. Figure 13: Comparison of residual stress distribution between CH-1 and CH-6. Influence of yield strength The material parameters stand for the important influencing factors of welding residual stress. This research mainly emphasizes on the yield strength of Q235B and Q345B in each pair of specimens. As mentioned above, out of the eight specimens CH-1~CH-8, CH-1~CH-5 are made of Q345B, and CH-6~CH-8 are made of Q235B. Fig. 13 compares the residual stress distributions between CH-1 and CH-6. The two specimens share same cross-sectional size.: 180  450  6  6mm. The materials of CH-1 and CH-6 are Q345B and Q235B, respectively. According to Fig. 13, the residual stress distribution of the two specimens are largely the same. The only difference lies in the peak residual stress, which is mainly attributable to the difference in materials. Moreover, the peak residual tensile stress at the flange increases from 253.38 MPa in CH-6 to 373.15 MPa in CH-1, up by 47%; the peak residual tensile stress at the