Issue 39

S. K. Kudari et alii, Frattura ed Integrità Strutturale, 39 (2017) 216-225; DOI: 10.3221/IGF-ESIS.39.21 219 magnitudes of 3D maximum stress intensity factors (at the center of the specimen) are compared with the analytical 2D value computed by Eq. (3). I K Y a    (3) Typically, such comparison for a specimen with a/W=0.65 is shown in Fig.3. It is estimated that magnitude of 2D K I is about 10% lower than 3D K I . It is well known that variation of stress intensity factor against   a 1/2   for various specimen thickness (B) is linear, slopes of K I-max vs.   a 1/2   obtained for various a/W are plotted in Fig 4. As the relation between K I-max /   a 1/2   and a/W (Fig.4) is nonlinear, the data is fit with a suitable polynomial. In such exercise, it is found that a polynomial equation of third order fits the 3D FEA results with least error (Regression co-efficient=0.998). This polynomial fit (Eq. (4)) is superimposed on the 3D FEA results plotted in Fig.4 and shows an excellent agreement. From this third order polynomial fit, the relation between K I-max , a/W and  can be expressed as: I K a a a W W W a 2 3 max 4.48287 14.99985 20.44016 3.85185                          (4) Let, a a a C W W W 2 3 1 4.48287 14.99985 20.44016 3.85185                       (5) Figure 4 : Variation of slopes, K I-max /   a 1/2   vs. a/W. The Eq. (4) reduces to: I K C a max 1     (6) Eq. (6) is similar to Eq. (3) and the constant C 1 shown in Eq. (5) is similar to the geometric factor, Y as used in Eq. (3). Hence, C 1 in this work is referred as 3D geometric factor. Eq. (6) can be used to estimate magnitudes of K I-max for the CT specimen. To validate the proposed formulation given in Eq. (6), the computed values of K I-max using Eq.(6) for various a/W are compared with the present 3D FEA results and the results computed by Eq.(1) proposed by Kwon and Sun [7] in Fig.4. The figure shows that the results computed by Eq. (6) are in good agreement with the results obtained by