Interfacial cracks in isotropic and anisotropic media with friction.

摘要

The thrust of the thesis work is to investigate and determine the fracture parameters of interface cracks. Both the oscillatory model and the contact model are used to study the fracture behavior of interface cracks for small scale contact condition and large contact condition with friction, respectively.; For interface cracks with their surfaces in small scale contact, the existing solutions for interfacial cracks in bimaterial media obtained from the contact model and oscillatory model were compared. The oscillatory neartip stress field was found to agree very well with that of the contact model except for the extremely small contact zone. Using the oscillatory solution, Mode I and Mode II "strain energy release rates" for finite crack extensions were obtained in terms of the stress intensity factors and the assumed crack extension {dollar}Delta a{dollar} for interface cracks lying between three different kinds of media, i.e.. two dissimilar isotropic materials; two dissimilar general orthotropic media with one plane of material symmetry in {dollar}xsb1 - xsb2{dollar} plane; and two dissimilar monoclinic media. Finite elements in conjunction with the crack closure method were used to calculate these "strain energy release rates" from which accurate stress intensity factors were obtained. An alternative method based on crack surface displacement ratio was also introduced to obtain stress intensity factors. Numerical examples were studied to show their accuracy and implementation.; For interface cracks with friction, the concept of strain energy release rate for interfacial cracks in the presence of friction is reexamined. A finite element based numerical procedure is introduced to calculate the strain energy release rate and energy dissipation due to friction for a finite crack extension. Thus, the finite extension strain energy release rate with a fixed crack extension can be used to represent the magnitude of the singular stress field and, therefore, to quantitatively characterize the intrinsic fracture toughness. For numerical examples, a center crack in an infinite bimaterial media under pure shear and combined compression and shear were studied to understand the neartip singularity nature and concept of strain energy release rates. Both fiber pull-out and push-out tests were simulated for illustration of this application.