Issue 41

Z. Li et alii, Frattura ed Integrità Strutturale, 41 (2017) 378-387; DOI: 10.3221/IGF-ESIS.41.49 380 Figure 2: Specimens sizes Specimen b/t h w /t w b/mm h w /mm h/mm CH-1 14.5 75 180 450 462 CH-2 14.5 125 180 750 762 CH-3 24.5 100 300 600 612 CH-4 24.5 75 300 750 770 CH-5 41.2 100 500 1000 1020 CH-6 14.5 75 180 450 462 CH-7 14.5 125 180 750 762 CH-8 24.5 100 300 600 612 Table 3: Specimen sizes and width-thickness ratios. Fundamentals The principle of blind hole residual stress measurement is shown in Fig. 3. If a structural member is subjected to a residual stress field and an elastic strain field, the residual stress at any point inside the small blind hole will be released. As the original stress field falls out of balance, there will be a certain amount of strain release around the blind hole so that the original stress field reaches a new equilibrium. The formation of new stress and strain fields at the residual stress measuring points can be measured by the following formulas [9-11].     2 2 1 3 1,2 1 3 2 1 3 1 2 4 4 A B                (1)   1 2 1 2 cos 2 2 2 Z           (2)     1 3 2 1 3 2 2 tg           (3) 2 1 2 1 2 a A E r r    