Issue 41

Z. Li et alii, Frattura ed Integrità Strutturale, 41 (2017) 378-387; DOI: 10.3221/IGF-ESIS.41.49 381   2 2 2 2 1 1 2 2 2 2 1 2 1 2 1 2 1 1 4 a r r r r a B E r r r r                (4) The symbols are explained as below [12]: 1  , 2  and 3  : the relieved strain measured by each of the rosettes in the strain (  ); A, B: the strain release coefficients obtained based on tensile experimental calibration or theoretical calculation formulas based on aperture, hole depth, geometry size of strain rosette and elastic modulus; θ : the clockwise angle between the maximum principal stress and the stress reference axis of 1# rosette; 1  , 2  : the principle stresses (MPa). E: the elasticity modulus; μ : the Poisson’s ratio; d, 1 r , 2 r : the aperture of the blind hole, the distance from the blind hole center to the near end of the strain gauge, and the distance from the blind hole center to the far end of the strain gauge (mm). Figure 3: Principle of blind hole drilling method Residual stress test Test Methods Targeted at measuring the distribution of longitudinal residual stress in the I-section members, the rosettes are arranged along the centerline of the cross-section of each specimen [13-21]. For the sake of simplicity, only the rosettes at the upper flange and web are taken into consideration because the cross-section is symmetrical. The rosette arrangement is shown in Figure 3. The spacing between the rosette and the flange is 1/4b; the spacing between the rosette and the web is: 1/6hw (CH-3, CH-4), 1/8hw (CH-5), and 1/4hw (others). The distance from the flange to the edge of the member is 10m, and the distance from the web to the edge of the member is 20mm. (a) Paste strain rosettes (b) Weld the wires (c) Drill the holes Figure 4: Strain rosettes cementing, wire welding and drilling