TY  - CHAP
AV  - none
ID  - eprints2071
TI  - A nonlocal cohesive zone model for studying crack propagation in mechanical systems with finite thickness interfaces
UR  - http://eprints.imtlucca.it/2071/
N2  - Finite thickness regions between heterogeneous material constituents are often simplified as zerothickness
interfaces. Then, the cohesive zone model (CZM) is employed, establishing a constitutive relation between tractions and displacement discontinuities. The shape of the CZM is usually chosen as simple as possible for numerical reasons, rather than being physically meaningful. Therefore, the reliability and the predictive capabilities of these models are a serious concern. In this contribution, the complex nonlinear damage phenomena occurring in finite thickness interface regions are modeled using damage mechanics. The derived nonlinear relation between cohesive
tractions and anelastic displacements is then reinterpreted as a new nonlocal CZM. Depending on
the ductility of the material, different shapes of the CZM can be recovered, from linear and bilinear
softening curves, typical of brittle materials, to bell-shaped curves typical of ductile materials. It is
also shown that the parameters of the damage law can be tuned according to molecular dynamics simulations.
The implementation of the proposed nonlocal CZM in the finite element method is then presented. Special attention is given to the numerical treatment of the related nonlocality and to the computation of the tangent stiffness matrix to be used in the Newton-Raphson method for the solution of the nonlinear boundary value problem.
The numerical model is applied to polycrystalline materials and it is shown that the nonlocal CZM is able to reproduce realistic statistical distributions of Mode I fracture energies, as a consequence of the interface thickness distribution. Finally, we demonstrate that the relation between interface thickness and grain size can also be used to explain the grain size effects on the material
tensile strength, namely the Hall-Petch law and its inversion at the nanoscale.
SN  - 978-88-906340-0-0
PB  - Publi&Stampa Edizioni
EP  - 10
Y1  - 2011///
SP  - 1
T2  - Atti del XX Congresso Associazione Italiana di Meccanica Teorica e Applicata
A1  - Paggi, Marco
A1  - Wriggers, Peter
ER  -