BEM analysis of the single fiber fragmentation test

Sammanfattning: A Boundary Element analysis of micromechanical elastic fields in the single-fiber fragmentation test is presented in this thesis. The work carried out is roughly divided in two main tasks: the development of the BE code and the numerical simulation of the single-fiber fragmentation test. The numerical study is primarily concerned with the analysis of the initiation and growth of a debond crack along the fiber-matrix interface in the single fiber fragmentation test, although different configurations in which the crack propagates through the matrix have also been considered. The asymptotic behavior of the near-tip singular elastic solutions in the fiber cracks, the interface cracks and the matrix cracks are studied. Additionally, asymptotic behavior of the Energy Release Rate for a wide range of debond lengths is analyzed. Firstly, the numerical analysis is performed in the framework of the two linear elastic models of interface cracks, open model and frictionless contact model, and a discussion of their adequacy based on the numerical results presented is given. Finally, a frictional contact model is employed to elucidate the influence that the friction between the debond crack faces may have in the near-tip singular elastic solutions and crack propagation. Therefore, a Boundary Element code has been developed which allows the elastic analysis of axially symmetric bodies to be carried out, permitting the definition of multiple solids bonded or in contact, taking into account the residual stresses developed during the curing of the samples and allowing non conforming meshes to be used in the interfaces and contact zones. Moreover, a novel extremely accurate integration technique has been developed to allow the near-tip singular elastic solutions to be precisely obtained.