Issue 41

Z. Li et alii, Frattura ed Integrità Strutturale, 41 (2017) 378-387; DOI: 10.3221/IGF-ESIS.41.49 385 web rises from 147.10 MPa in CH-6 to 405.53 MPa in CH-1, up by 175%. Fig. 14 (comparing CH-2 with CH-7) and Fig. 15 (comparing CH-3 with CH-8) show the same trend. Therefore, the peak residual stress will increase with the yield strength of the material if the cross-section remains the same. In short, the effect of material grade on residual stress is: for a given width-thickness ratio, the higher the yield strength, the larger the peak value of the residual stress. Figure 14: Comparison of residual stress distribution between CH-2 and CH-7. Figure 15: Comparison of residual stress distributions between CH-3 and CH-8. Influence of material size Fig. 16 compares the peak residual stresses of three groups of specimens. In each group, the specimens share the same material grade but differ in width-thickness ratio. Specifically, the first and second groups have different width-thickness ratios at the web; the third group have different width-thickness ratios at the flange. The first group of specimens are CH-1 and CH-2, both of which are made of the same material Q345; however, the two specimens differ in width-thickness ratio at the web (75 vs. 125). The second group of specimens are CH-7 and CH-8, both of which are made of the same material Q235; however, the two specimens differ in width-thickness ratio at the flange (125 vs. 100). The difference between the two groups of specimens is clearly illustrated in the above figure. For specimens of the same material grade, the peak value of residual stress at the web decreases significantly as the width-thickness ratio increases. For instance, the peak residual stress at the web drops from 405.53MPa in CH-1 to 274.52MPa in CH-2, down by 32%; the peak residual stress at the web falls from 275.23MPa in CH-8 to 251.48MPa in CH-7, down by 9%.