Hybrid effect and pseudo-ductile behaviour of unidirectional interlayer hybrid FRP composites for civil engineering applications

Abstract

An experimental study on the tensile stress-strain curves of interlayer (layer-by-layer) unidirectional hybrid FRP composites was conducted aiming at evaluating the corresponding hybrid effect and pseudo-ductility of this innovative solution. Different combinations of the following dry unidirectional fabric materials, also varying the number of layers, were adopted in tests: high-modulus carbon, standard carbon, E-glass, and basalt. The composites were produced layer-by-layer by hand lay-up method, using an epoxy-based resin as matrix. The results have shown a strain increase at failure of both standard carbon and high-modulus carbon fibres with the volume decrease of these materials in hybrid combinations. It was also concluded that combining high-modulus carbon with E-glass, high-modulus carbon with basalt, or high-modulus carbon with standard carbon can lead to very good pseudo-ductile tensile behaviour. Finally, it should be highlighted that an existing analytical model in the literature was satisfactorily adopted to predict the tensile response of these hybrid composites.

Hybrid FRP jacketing for enhanced confinement of circular concrete columns in compression

“…Aiming at achieving pseudo-ductile tensile response (so called to describe a mechanical non-linear behaviour characterized by presenting a flat-topped stress-strain curve in monotonic tensile tests), exhaustive work has been carried out with a combination of different unidirectional FRP composites [13,14,[17][18][19][20][21][22]. This type of combination consist of two types of fibres, namely low strain (LS) and high strain (HS) fibres, within the same polymeric matrix.…”

“…Ribeiro et al [14] conducted an experimental study on the tensile stress-strain curves of interlayer (layerby-layer) unidirectional hybrid FRP composites, aiming at evaluating the corresponding hybrid effect and pseudoductility of this innovative solution. A maximum hybrid effect of circa 45% was achieved, by combining unidirectional fabrics of high-modulus carbon with standard-modulus carbon.…”

“…The strategy passed by combining commercially available unidirectional dry fabrics of different materials in the same matrix obtained a hybrid composite that promotes synergies between the involved reinforcing materials, conducting, for instance, a pseudo-ductile tensile response (characterized by fragmentation in the low strain material and dispersed delamination, please see details in [13]), and an increase (until 50% [13,24]) of the apparent failure strain of low strain fibres, known as 'hybrid effect'. The present research focus on the results of pure compression tests, performed on small-scale plain concrete columns confined with 16 unidirectional interlayer hybrid composite combinations, exploiting the demonstrated hybrid effect and pseudo-ductility of this confining material [14]. All the unidirectional hybrid composites used in the jacketing has been tensile characterized before in [14].…”

“…The present research focus on the results of pure compression tests, performed on small-scale plain concrete columns confined with 16 unidirectional interlayer hybrid composite combinations, exploiting the demonstrated hybrid effect and pseudo-ductility of this confining material [14]. All the unidirectional hybrid composites used in the jacketing has been tensile characterized before in [14]. This paper aims at demonstrating that the hybrid effect can maximize the efficiency of the FRP jackets and pseudo-ductility can avoid abrupt failures, and thus, improve safety.…”

“…To the best of the authors' knowledge, it is the first time that fragmentation of low strain material and dispersed delamination is explored in this type of applications. Moreover, it is intended to prove that the model of Jalalvand et al [13] and the bilinear rule of mixtures (ROM) [14] can be used to predict satisfactorily the confining pressure of hybrid composites. A new design-oriented model to predict the ultimate condition of hybrid FRP-confined concrete is proposed in this paper.…”