Issue 48

M. K. Hussain et alii, Frattura ed Integrità Strutturale, 48 (2019) 599-610; DOI: 10.3221/IGF-ESIS.48.58 603 By minimizing the function  with respect to r and after some algebraic manipulations, r and 1 A can be obtained as [29]            1 1 1 2 I op I B r r A (14)        1 1 2 1 1 1 op I I FE r r op op op op v Ar Br A C r C r (15) Thus, by using the notch opening displacement  FE v at op r , 1 A can be obtained using the Eqn. (15) and hence I K using the Eqn. (5). Taking logarithm on both sides of Eqn. (8), one can write    1 1 1 ln ln ln I v r AC (16) It can be seen that, Eqn. (16) is a straight line equation whose slope is equal to  1 I . It can be shown that the slope of the plot of      ln FE v versus   ln / N r L (Eqn. (10)) becomes equal to  1 I at the optimal point opt r (Refer [29] for more details). Here N L is the notch tip element length as shown in Fig. (2). Similar to the mode I problems, estimation of the op r or opt r from u -displacement for mode II is not possible as    FE u (or    FE u ) contains the term II R u (Eqn. (9)). Therefore, to calculate the mode II NSIFs, it is presumed that the mode II u - displacements are also accurate at the optimal points obtained for the mode I problems using Eq. (14). To calculate both the constants 1 B and 2 B , two nearby points   op opt N r r L and     op op opt N r r r L are considered [29]. Therefore, from the FE u -displacements at the two close points op r and  op r , the Williams’ coefficient 1 B can be obtained as [29]               1 1 1 1 1 2 op op II II FE FE r op r op op op op op u r u r B C r r r r (17) Again, by substituting FE NSD  op FE r u and   op FE r u at op r and  op r , 1 B can be obtained using the Eqn. (17) and hence II K using the Eqn. (5). Finally, the NSIFs can be normalized as         ( ) 1 1 ( ) ( ) ( ) I II I II I II F K a and   ( ) 1 ( ) ( ) I II I II I II F K R F for the rectangular and circular plates, respectively. N UMERICAL E XAMPLES his section presents a numerical examination of the PSDT for the evaluation of the NSIFs under mode I and mixed mode (I/II) loading conditions. The FE analysis is carried out in ANSYS ® [32]. Throughout the domain conventional eight noded quadratic elements are used and no singular elements are utilized at the notch tip. At the notch tip, they are collapsed to form a spider web pattern. Four problems viz. (a) Mode I example of a single edge notched plate under uniform tension (SENT), (b) mode I example of a single edge notched plate under in-plane bending (SENB), (c) mixed mode problem of an angled single edge notched plate under uniform tension (ASENT) and (d) mixed mode problem of a sharp V-notched Brazilian disc (SV-BD) are considered for the demonstration of the efficacy of the PSDT. The notch length to width ratio  0.5 a w is considered for the single edged notch plates and the notch length to radius ratio  0.5 a R is considered for the Brazilian disc. It is assumed that all the specimens are under plane stress condition. Consistent units are employed in all the examples. The thickness of all the specimens is considered as unity. T