Modelling of Creep and Stress Relaxation Test of a Polypropylene Microfibre by Using Fraction-Exponential Kernel

Abstract

A tensile test until breakage and a creep and relaxation test on a polypropylene fibre are carried out and the resulting creep and stress relaxation curves are fit by a model adopting a fraction-exponential kernel in the viscoelastic operator. The models using fraction-exponential functions are simpler than the complex ones obtained from combination of dashpots and springs and, furthermore, are suitable for fitting experimental data with good approximation allowing, at the same time, obtaining inverse Laplace transform in closed form. Therefore, the viscoelastic response of polypropylene fibres can be modelled straightforwardly through analytical methods. Addition of polypropylene fibres greatly improves the tensile strength of composite materials with concrete matrix. The proposed analytical model can be employed for simulating the mechanical behaviour of composite materials with embedded viscoelastic fibres.

Pullout modelling of viscoelastic synthetic fibres for cementitious composites

“…where Γ(m) = (m − 1)! is the Gamma function,λ = β(E 0 − E ∞ )/E 0 and α and β are two parameters which have been assessed by fitting properly the results provided by a creep test on PP macrofibres performed by Sorzia [27].…”

“…Similarly to the parameters involved in the Rabotnov model, the parameters ψ 0 , ψ ∞ and ν have been set on the basis of creep tests performed on PP macrofibres and reported in Sorzia [27]. The values of such parameters are shown in Tab. 3.…”

“…2.2 accounts for the elastic contribution of the displacement s L in debonding and pullout phase, but it does not account for the elastic contribution of the rigid motion s 0 at the pullout stage, which has been added apart. Eqn (27) allows evaluating straightforwardly the displacement of the end of the fibre based on the mapṡ 1.0 × 10 −5 1.0 × 10 −5 1.0 × 10 −5 0.003 17.5 mm and 27.5 mm respectively.…”

“…The first integral in eqn (27) can be evaluated by considering finite time instants. Let I(t) denote the first integral in eqn (27), namely…”

Finite Element Modeling of FRP‐Strengthened RC Beam under Sustained Load

“…In fact, under sustained load, concrete exhibits clear creep response, and the viscous property of adhesive is remarkable [4][5][6][7]. Related to the kind of fiber used and fiber content, some types of FRP products may also present noticeable viscoelasticity [8][9][10]. As time goes on, structure deformation increases and cracks further develop, which negatively affects the serviceability [11].…”