Computational Fracture Mechanics Anderson’s book, third ed. , chap 12

Elements of Theory Energy domain integral method: - Formulated by Shih et al. (1986): CF Shih, B. Moran and T. Nakamura, “Energy release rate along a three-dimensional crack front in a thermally stressed body”, International Journal of Fracture 30 (1986), pp. 79-102 - Generalized definition of the J- integral (nonlinear materials, thermal strain, dynamic effects). - Relatively simple to implement numerically, very efficient. Finite element (FE) code ABAQUS version 6.5 ABAQUS: - suite of powerful engineering simulation programs - based on the finite element method - for simple linear analyses and most challenging nonlinear simulations

products associated with Abaqus: Optional capabilities (offshore structures, design sensitivity calculations) Abaqus Standard : general-purpose analysis product that can treat a wide range of problems. Abaqus Explicit : intended for modeling brief, transient dynamic events (impact) uses an explicit dynamic finite element formulation. CAE : interactive, graphical environment allowing models to be created quickly. can be used for producing/ importing the geometry to be analyzed. is useful to monitor/control the analysis jobs and display the results (Viewer). creates input files (.inp) that will be processed by Abaqus standard. For details see the Getting Started Manual of Abaqus 6.5

Energy Domain Integral : In 2D, under quasistatic conditions, J may be expressed by The contour G surrounds the crack tip. The limit indicates that G shrinks onto the crack tip. n : unit outward normal to G. x1 , x2 Cartesian system q : unit vector in the virtual crack extension direction. w : strain energy density and, s : Cauchy stress tensor displacement gradient tensor H : Eshelby’s elastic energy-momentum tensor (for a non-linear elastic solid) For details see the Theory Manual of Abaqus 6.5, section 2.16

With q along x1 and the field quantities expressed in Cartesian components, i.e. Thus, In indexed form, we obtain The expression of J (see eq. 6.45) is recovered with The previous equation is not suitable for a numerical analysis of J. Transformation into a domain integral

Following Shih et al. (1986), (*) m : outward normal on the closed contour : the surface traction on the crack faces. A is a sufficiently smooth weighting function in the domain A. m = -n on G with Note that, A includes the crack-tip region as

(*) Derivation of the integral expression = = q → Line integral along the closed contour enclosing the region A. Noting that, since since

Using the divergence theorem, the contour integral is converted into the domain integral Under certain circumstances, H is divergence free, i.e. indicates the path independence of the J-integral. In the general case of thermo-mechanical loading and with body forces and crack face tractions: the J-integral is only defined by the limiting contour Introducing then the vector, in A or Using next the relationship, Contributions due to crack face tractions.

- Different contours are created: In Abaqus: - This integral is evaluated using ring elements surrounding the crack tip. - Different contours are created: First contour (1) = elements directly connected to crack-tip nodes. The second contour (2) are elements sharing nodes with the first, … etc Refined mesh Contour (i) nodes outside nodes inside Crack 2 1 8-node quadratic plane strain element (CPE8) Exception: on midside nodes (if they exist) in the outer ring of elements

J-integral in three dimensions Local orthogonal Cartesian coordinates at the point s on the crack front: J defined in the x1- x2 plane crack front at s L Point-wise value For a virtual crack advance l(s) in the plane of a 3D crack, T L : length of the crack front under consideration. : surface element on a vanishingly small tubular surface enclosing the crack front along the length L.

Numerical application (bi-material interface): SEN specimen geometry (see annex III.1): s a = 40 mm b = 100 mm h = 100 mm a/b = 0.4 Material 1 and h/b = 1 s = 1 MPa. Remote loading: 2h a b Materials properties (Young’s modulus, Poisson’s ratio): Material 1: E1 = 3 GPa n1 = 0.35 Material 2 x y Material 2: E2 = 70 GPa n2 = 0.2 s Plane strain conditions.

Typical mesh: Material 1= Material 2 Material 1 Material 2 Refined mesh around the crack tip Number of elements used: 1376 Type: CPE8 (plane strain)

Simulation of the stress evolution s22 (isotropic case)

Simulation of the stress evolution s22 (bi-material)

Results: Material 1 Material 2 Bi-material J (N/mm) Abaqus Isotropic 0.1641 0.0077 0.0837 (*) (*) same values on the contours 2-8 Isotropic Bi-material KI KII Annex III 0.746 0. / Abaqus 0.748 0.752 0.072 SIF given in for the isotropic case (i =1,2). Ones checks that:

KI and KII are defined here from a complex intensity factor, such that Relationship between J and the SIF’s for the bi-material configuration: - For an interfacial crack between two dissimilar isotropic materials (plane strain), where and plane strain, i = 1,2 KI and KII are defined here from a complex intensity factor, such that with - Extracted from the Theory Manual of Abaqus 6.5, section 2.16.2. H. Gao, M.Abbudi and D.M. Barnett, “Interfacial Crack-tip fields in anisotropic elastic solids thermally stressed body”, Journal of the Mechanics and Physics of Solids 40 (1992), pp. 393-416 Disagreement with the results of Smelser et al.