A methodology to measure the interface shear strength by means of the fiber push-in test

Abstract

A methodology is presented to measure the fiber/matrix interface shear strength in composites. The strategy is based on performing a fiber push-in test at the central fiber of highly-packed fiber clusters with hexagonal symmetry which are often found in unidirectional composites with a high volume fraction of fibers. The mechanics of this test was analyzed in detail by means of three-dimensional finite element simulations. In particular, the influence of different parameters (interface shear strength, toughness and friction as well as fiber longitudinal elastic modulus and curing stresses) on the critical load at the onset of debonding was established. From the results of the numerical simulations, a simple relationship between the critical load and the interface shear strength is proposed. The methodology was validated in an unidirectional C/epoxy composite and the advantages and limitations of the proposed methodology are indicated.

Influence of plastic deformation on single-fiber push-out tests of carbon fiber reinforced epoxy resin

“…Following the considerations made in [12,25], we assume ܴ ௧ଵ ൌ ܴ ௧ଶ and ܴ to be negligible for the present case. Therefore, equation 6 can be written solely in terms of one critical stress value ܴ .…”

“…Interfacial crack growth is modeled following the work of Rodriguez et al [12] using an implementation for cohesive zone modeling in Comsol. The boundary condition "thin elastic layer" was chosen for the interface between fiber and matrix.…”

“…and the internal separation of the thin elastic layer nodes δ Following the recommendation of [12] we implemented a quadratic interaction criterion to derive the critical stress value ܴ for crack initiation. This is written in terms of the critical interfacial strengths in normal (ܴ ) and transverse directions (ܴ ௧ଵ and ܴ ௧ଶ ) as…”

“…The onset of this non-linearity is often interpreted as crack initiation followed by crack growth [7][8][9][10][11]. Various models were proposed to deduce the interfacial shear strength based on this non-linear behavior [9][10][11][12]. Most of the analytical models rely on assumptions concerning the stress distribution along the interface and, therefore, are restricted to special push-out geometries and types of loading.…”

Fabrication and properties of 3D oxide fiber-reinforced Al2O3–SiO2–SiOC composites by a hybrid technique based on sol–gel and PIP process

“…The push-in test [19] was used to determine the bonding strength between the fibers and matrix. Indentations were performed with an Ultra Nano-indentation Tester equipped with a flat punch of 3 μm in diameter.…”