Properties of the interphase in organic matrix composites

The mechanical properties of the material surrounding a single carbon fiber in an epoxy matrix have been studied. Properties were determined within 100 nm of the fiber. A pronounced soft interphase was revealed adjacent to the fiber. A single fiber was embedded in a small supported disk of epoxy matrix. The fiber was loaded in tension. Examination of the surface displacements in the resin revealed that the matrix material within 250 nm of the fiber was substantially softer than the matrix far from the fiber. This interphase material was active in creep. Measurement of indentation properties of the matrix around a single fiber showed that the material close to the fiber exhibited an apparent high modulus due to restriction by the fiber. The implications of these findings are discussed. © 1990