Issue 35

H. Dündar et alii, Frattura ed Integrità Strutturale, 35 (2016) 360-367; DOI: 10.3221/IGF-ESIS.35.41 362 0 1 1 1 0 1 1 0 1 ( , , ) ( , , ) ( , , ) ( , , ) ( , , ) ( ) ( , , ) ( , , ) ( , , ) ( ) ( , , ) ( , , ) ( , , ) ntip m m i j j w j wj i I j j i ntip m i w j wj i II j i m w j wj j w N w Z f N f N K Z g N g N K Z h N h N                                                                                     1 ( ) ntip i i III i K          (3) Figure 1 : Work scheme of FCPAS finite element software for analysis of multiple cracks. In Eqs. 1-3,  ,   and   are local coordinates in enriched elements, u j , v j , and w j are the nodal displacement, N j are regular finite element shape functions, Z 0 is a zeroing function which varies between 0 and 1, m is number of nodes in the element, f j , g j and h j represent the mode I, II and III components of crack tip displacements, K I , K II and K III are the unknown SIFs. Finally  is the local isoparametric coordinate along the crack front that varies between -1 and 1. After FE solution and SIF calculation, cracks are propagated taking into account crack interaction effects. A modified form of Paris-Erdoğan equation (Eq. 4) is used for this process. max max n i i K a a K           (4) In the next step, if cracks are to be represented in elliptical form, a best ellipse fit method is applied to propagated crack tip nodes. Then ellipse parameters are given to ANSYS software as new crack dimensions. For through the thickness cracks in thin walled structures, there is no need for ellipse fitting and any crack tip node coordinates are used for new crack locations. After all propagation analyses are completed, a crack growth law such as Paris-Erdoğan formulation (Eq. 5) is used for prediction of crack propagation life [10].   n da C K dN   (5)