applied fracture mechanics

376Applied Fracture MechanicsFrom these figures, it also observed that the different between mode II SIF and mode I SIF isreduced as the a/W decreases. In the context of crack interaction limit (CIL) based onKI , in,Dand KII , in,D, by considering the convergence level as the indicator of CIL. It can beseen that the degree and speed of CIL achievement not only depends heavily on theincreased of b/a , the reduction of a/W from a/ W 0.5 0.05 also provides significantimpact on CIL determination.KFig. 8 shows the variation of I , in , DKand II , in , Dfor ( a/ W 0.05 0.2) . It can be observedKthat at smallest a/ W 0.05 , the value of I , in , Dvalue and stabilize.Kand II , in , Dis almost hold at constantThe identification of CIL in this condition is absent because the value of KI , in,Dand KII , in,Dare about the same value for all b/a . This equalization condition may be referred to theidentification of crack unification limit (CIL). Overall, it can be concluded that the higherratio of b/a and a/W , the more the realization of CIL. Inversely, the lower ratio of b/aand a/W , the more indication to CUL can be realized.5. ConclusionThe numerical solution based on displacement extrapolation method (DEM) has proved tobe more consistent in SIF prediction comparedd to for both crack tips. However, the DEMable to predict the SIF for Mode I and Mode II fracture behaviour. The FE results concludethat the interaction of two cracks is directly influence the reduction of SIF magnitude and Iat the crack tips. The parallel cracks have experienced decrease shielding effect as the cracksinterval b/a decrease. The identification of crack interaction limit (CIL) and crack unificationlimit (CUL) has been accomplished. The SIF of Mode I is found more significant comparedto Mode II in higher or lower b/a and a/W ratio. Mode II SIF can be neglected due to itssmall effect to the stress shielding effect. The FFS codes rules that define the combination oftwo cracks as single crack are well translated as CIL and CUL.Author detailsRuslizam Daud, Ahmad Kamal Ariffin, Shahrum Abdullah and Al Emran IsmailUniversiti Kebangsaan Malaysia, Malaysia6. ReferencesAndersson, B., Blom, A. F., Falk, U., Wang.G.S, Koski, K., Siljander, A., et al. (2009). A casestudy of multiple site fatigue crack growth in the F-18 Hornet bulkhead. Paper presented atthe 25th ICAF Symposium.ASME. (1998). ASME Boiler and Pressure Vessel Code, Section XI. New York, USA.