numero25

Yu. G. Matvienko et alii, Frattura ed Integrità Strutturale, 25 (2013) 20-26; DOI: 10.3221/IGF-ESIS.25.04 25 Comparing the results of two types is performed for the fourth notch length increment with total notch length a 0 +a 4 = 27.2 mm. Finite element mesh consists of 162000 plane shell elements of CQUAD 4 type. Boundary conditions correspond to real geometry of the specimen shown in Fig. 3. Local area including a notch tip is simulated by two- dimensional notch tip element CRAC2D. This element is capable of SIF calculation accordingly to formula (7) only. Numerical SIF value 6.48 FEM I K MPa m  coincides with analogous experimental value 4 6.14 I K MPa m  within five per cent. This result proves a high accuracy and reliability of the developed approach. I NFLUENCE OF THE NOTCH WIDTH ON FRACTURE MECHANICS PARAMETERS eveloped approach is capable of determining fracture mechanics parameters for notches as well as cracks in both actual and residual stress field. It is also possible to estimate an influence of notch radius on SIF and T-stress values obtained through the use of formula (5) and relations (9)-(11), respectively. The first step in this way is made for actual stress field in specimen #4V, geometrical parameters and loading conditions of which completely coincide with scheme shown in Fig. 3. The main difference resides in using a saw of width b 3 = 1.0 mm (notch radius ρ 3 ~0.50 mm) for incremental crack length increasing. Dependences of SIF K I and T-stress T values obtained accordingly to formula (6) and relations (9)-(11) from total notch length for specimen #4V are also shown in Fig. 4. A difference in SIF values reaches 10 per cent with notch width increasing leads to SIF decreasing. Average T-stress values calculated for the first six steps are T n av = –67.2 MPa and T n av = –76.8 MPa for specimens #3V and #4V, respectively. Thus, notch width increasing gives a decrease of negative T-stress values by 12.5 per cent. A study of notch increase in residual stress field is performed for two welded thin plates of dimensions 200x100x4 mm 3 made from aluminium alloy ( E =72000 MPa, μ =0.33). These plates are denoted as specimen #015 (notch width b 2 = 0.6 mm, notch radius ρ 2 ~0.30 mm) and specimen #016 (notch width b 1 = 0.3 mm, notch radius ρ 1 ~0.15 mm). Weld seam of lengths 100 mm coincides with one from symmetry cross-section of each specimen. Notches in both specimens are increased from a centre of the weld along the second symmetry cross-section orthogonally to the weld direction. Preliminary determination of maximal residual stress values σ y max acting along the weld in both specimens serves for estimating an identity of residual stress fields. These values determined at points with co-ordinate x = 9 mm equal to σ y max = 130 and σ y max = 139 MPa for Specimen #015 and #016, respectively. Data are obtained by combining the hole drilling method and ESPI. Holes are drilled in specimen’s area, which does not contain a notch. (a) (b) Figure 5 : Dependences of SIF K I (a) and T-stress T (b) values form total notch length. Experimental technique and a procedure of SIF and T-stress determination completely corresponds to the approach described above. Dependences of SIF K I and T-stress T values from total notch length are shown in Fig. 5a and Fig. 5b, respectively. These results show that co-ordinate of points where K I = 0 and T = 0 do not depend on the notch radius and correspond to notch length a S = 16÷18 mm. Maximal SIF values for specimen #016 ( K I =17.8 MPa·m 0.5 ) and specimen D