Interfacial partial debonding and its influence on the elasticity of a two-phase composite

A dual effective-medium and finite-element study is carried out to examine the influence of interfacial partial debonding on the elastic stiffness of a two-phase composite containing aligned elliptic fibers. In the effective- medium approach double debonding on the top and bottom of the elliptic inte rface is considered, but in the finite-element approach both double and sin gle debonding are examined. The effective-medium approach makes use of the concept of a fictitious fiber whose load-carrying capacity is taken to be l ost in the debonding direction but remains intact in the transverse directi on. The finite-element analysis allows one to examine further the influence of debonding angle on the stiffness of the composite and it also provides the needed magnitude for this angle at which the effective-medium approach applies. It is found that the angle has to be sufficiently wide, but not so wide as to lead to a potential complete debonding. Such an angle also incr eases when the fibers become more ribbon-like, but it decreases with increa sing volume concentration. The basic assumption that the fictitious fiber h as zero, or very low, load-carrying capacity along the debonding direction is also verified by the finite-element results. For both double and single debonding the Young's modulus of the composite along the debonding directio n can be significantly reduced as the debonding angle increases. The local stress distributions inside the fiber and the matrix are also illustrated f or both types of debonding. (C) 2000 Elsevier Science Ltd. All rights reser ved.