applied fracture mechanics

Higher Order Weight Functions in Fracture Mechanics of MultimaterialsHigher Order Weight Functions in Fracture Mechanics of Multimaterials 911to be easily proved by direct calculation. Using the same method, Chen and Hasebe [25, 27]derived the orthogonality property for an interface crack in an isotropic bimaterial and alsofor an orthotropic material with pure imaginary roots of the Stroh matrix. The cumbersomedirect calculations [13, 25, 27] are possible only for very simple cases and reveal neither thenature of the orthogonality relations nor their connection with the symmetry of the elasticityequations. Belov and Kirchner [28] suggested a proof of the orthogonality property for bothcracks and notches of finite opening angle in an elastically anisotropic media possessingarbitrary inhomogeneity of the elastic constants C ijkl (ω). In contrast to [13, 25], the proofgiven in [28] shows that the orthogonality property of the eigenfunctions (12) directly followsfrom the symmetry (5) of the operator ˆN(r).The idea of the proof [28] consists in the following. Integrating by parts an average of theweighted product of two ordered exponentials of arbitrary indices s and q, one finds∫ Ω∫ Ωq [ ˆV (s) (ω)] t ˆT ˆN(ω) ˆV (q) (ω)dω = [ ˆV (s) (ω)] t ˆT d00dω ˆV (q) (ω)dω (26)=[ˆV (s) (Ω)] t ˆT ˆV (q) (Ω) − ˆT∫ Ω− s [ ˆV (s) (ω)] t ˆN t (ω) ˆT ˆV (q) (ω)dω0So far only the fact that the ordered exponential ˆV (q) (ω) satisfies equation (14) has been used.Taking into account that the ’bulk’ operator ˆT ˆN(r) is symmetric (according to Eq.(5)), weobtain an important property of the ordered exponentials(s + q)∫ Ω[ ˆV (s) (ω)] t ˆT ˆN(ω) ˆV (q) (ω)dω =[ˆV (s) (Ω)] t ˆT ˆV (q) (Ω) − ˆT. (27)0This result is independent of the boundary conditions (17) specified at the notch faces. It takesplace for any indices s and q, which are not necessary roots of Eq. (19). Let us now considertwo roots s n and s p satisfying the condition s n + s p = 0. Then, according to Eq. (27), theweighted average can be represented as∫ Ω0[ ˆV (s p) (ω)]t ˆT ˆN(ω) ˆV (s n) 1((ω)dω = [ ˆV (s p) (Ω)]t ˆT ˆV (s )n) (Ω) − ˆT . (28)s p + s nNow let (h p , 0) and (h n , 0) be corresponding eigenvectors. Multiplying equation (28) fromthe right and from the left by these eigenvectors, one obtains the orthogonality relation in theform∫ Ω( )(h p , 0) t [ ˆV (s p) (ω)]t ˆT ˆN(ω) ˆV (s n) hn(ω)dω = 0,00(s n + s p = 0). (29)Details of the proof are clear from Eq. (28) and the identity( [ ( )] t) ( )ˆV (s p) hp(Ω) ˆT ˆV (s n) hn(Ω) − (hp , 0) ˆT00(=(h p ˆV (s p)1 (Ω), 0))0ˆV (s n) = 0.1 (Ω)h n(30)