| Fibre reinforced cementitious material(FRC)with random-distributed short fibres has higher strength and toughness than normal cementitious materials,and is widely used in civil engineering constructions.To meet engineers’ requirements in practice,optimization of the composite is greatly desired,so that the key parameters including fibre volume fraction,fibre slenderness,strengths of the interfaces and matrix can be fine-tuned.This can only be achieved after a thorough understanding of the reinforcing behaviors of fibres in the composites,thus numerical analysis at the micro/meso-scale is highly needed.The sigle fibre pullout test is carried out to study interfaces between the fibres and matrix at meso-scale.This present work reviews the analytical pullout models for both aligned and inclined fibres and discusses the effects of fibre inclinations and geometries on the pullout behaviors.Furthermore,many numerical models of single fibre pullout test are introduced,during which the modeling of interfaces and the gradual damage of the matrix are highlighted.Then the approaches to model FRC specimens with a number of fibres are reviewed,including direct/indirect ways and the corresponding advantages and disadvantages.We firstly introduce a discrete-continuum coupled finite element model to simulate the complex fracture process in the straight steel fibre reinforced composites.At present,this model is mainly applicable to high-rigidity steel fibre reinforced compact SFRC.The cementitous matrix is represented using continuum damaged plasticity mechanics and a Python script is applied to obtain the conforming mesh between fibre and the matrix.Then a MATLAB code is used to insert the zero-thickness cohesive elements to connect the cementitious matrix element and fibre element.Single fibre pullout tests are simulated and the pullout force-slip curves are well captured followed by an extensive parametric study using two kinds of models(corresponding to pre-and post-cracking).Effects of those parameters are explored,especially on the fibre reinforcing capability and crack development during fibre pullout.Secondly,the developed model is further validated against specimens with multiple random fibres,such as FRC beam bending test,UHPFRC three-point bending beam test and UHPFRC direct tensile test,the former two using notched specimen and the last one un-notched specimen.It is indicated that this model is capable of reproduce the complex fracture and cracking process in the specimens with random fibres.Many micro-mechanisms that may occur can be well captured,including the fibre bending,yielding and rupture,interfacial bonding and debonding,matrix damage,cracking and spalling.A numerous parametric analysis is also performed and discussed,the results of which indicated that the parameters do not function independently and their effects are connected,and thus an overall consideration is necessary.Finally,a new finite element model is developed with the interfacial shear stress characterized as a combination of physical and chemical bonding,internal friction regardless of the fibre inclination,and the Coulomb’s friction.The full-length pullout force-slip curves for fibres oriented at any angle can be achieved,and after validation this model is also used for another parametric analysis.The present work includes numerical simulation with validation against experiments and theoretical conductions,aiming to increase the knowledge of FRC composite.The main purpose is to provide feasible methods on how to simulate the fracture process of the straight steel fibre reinforced cementitious composites.The results obtained after the parametric analysis are of certain significance for the design and optimization of the micro component of the composite. |
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