On the Fibre Pullout and Pushin Problem in Composite Materials with Controlled Interfaces

Abstract

Following the earlier work of Gao, Mai and Cotterell on fibre pullout using a shear lag model which includes friction at the debonded interface and the Poisson expansion of the fibre, we have solved the fibre-matrix debonding problem for fibre pushin. This gives the relationship between debonding stress and debonded length. Interfacial friction for coated and uncoated samples is shown to have a much more significant influence on debonding stress in fibre pushin than in fibre pullout particularly for long embedded fibre lengths. After debonding, the fibre initial pushin load is dependent on the embedded length and this relationship has been theoretically derived. Again, the interfacial friction, arising from the Poisson effect of the fibre is shown to have more influence on the fibre initial pushin load than the pullout load for the uncoated sample. However, in the case of the coated samples, the interfacial friction has insignificant influence on the fibre initial pullout and pushin loads. The average frictional or shear stress is a function of the embedded fibre length and is higher in pushin than in pullout due to the different Poisson effect of the fibre. It is also shown that the average shear stress varies significantly along the embedded fibre length of the uncoated samples but not the coated samples for both fibre pushin and pullout.