Numerical analysis of the single fiber fragmentation test including the effect of interfacial friction

Abstract: A numerical analysis of the single fiber fragmentation test is presented in this thesis. The aim of the numerical study is elucidating the influence of friction in the growth of the debond cracks along the fiber-matrix interface. Two distinct approaches and numerical techniques have been employed in the analysis. Firstly, debond growth is studied using Linear Elastic Fracture Mechanics for interface cracks. Thus, an accurate solution of the near-tip stresses and displacements is needed, which is obtained using a self-developed numerical tool, based on the Boundary Element Method. Energy Release Rate associated to debond growth is evaluated using a modified version of Irwin's Virtual Crack Closure Technique, which takes into account the presence of frictional stresses along the crack faces. Numerical results show that friction opposes to debond growth and, consequently, it has to be taken into account if quantitative values of the interfacial fracture toughness are going to be derived from test results. In the abovementioned approach, numerical solutions are obtained neglecting the influence of load history on the frictional contact solution. For that reason, a second approach has been employed in which debond onset and growth is simulated using cohesive elements, thus following the actual load history of the sample. A commercial Finite Elements code has been employed for the numerical simulation in this approach, since there is no need for such a high refinement in the mesh as in the previous analyses. Numerical results confirm that the influence of load history is negligible in the analysis, since analogous results are obtained with both approaches.