Abstract
A recently proposed cohesive-zone model which effectively combines damage, friction and mechanical interlocking has been revisited and further validated by numerically simulating the pull-out test, from a concrete block, of a ribbed steel bar in the post-yield deformation range. The simulated response is in good agreement with experimental measurements of the bond slip characteristics in the post-yield range of deformed bars reported in the literature. This study highlights the main features of the model: with physically justified and relatively simple arguments, and within the sound framework of thermodynamics with internal variables, the model effectively separates the three main sources of energy dissipation, i.e. loss of adhesion, friction along flat interfaces and mechanical interlocking. This study provides further evidence that the proposed approach allows easier and physically clearer procedures for the determination of the model parameters of such three elementary mechanical behaviours, and makes possible their interpretation and measurement as separate material property, as a viable alternative to lumping these parameters into single values of the fracture energy. In particular, the proposed approach allows to consider a single value of the adhesion energy for modes I and II.
Highlights
C ohesive‐zone models (CZMs) are widely used to simulate initiation and propagation of cracks along structural interfaces. They represent an effective alternative approach to fracture-mechanics-based methods for a wide variety of problems at very different scales, such as crack growth in dams, mortar-joint failure in brick masonry, bond-slip response of reinforcing bars in concrete, debonding of adhesive joints, delamination or fibre‐matrix debonding in composites, among many others. Many of such problems entail combination of de-cohesion and frictional sliding, which is often accompanied by dilatancy, in turn associated with the interlocking effect created by the asperities of the fracture surface
A different strategy was followed by Alfano and Sacco [6], Alfano et al [7] and, more recently, Sacco and Toti [8], where interface damage and friction have been combined in a cohesive zone model based on a simplified micromechanical formulation
To simulate dilatancy and interlocking this approach was adopted by Serpieri and Alfano [9], within a multi-scale framework in which, at a small scale, the asperities of the interface are represented in the form of a periodic arrangement of distinct inclined planes, denominated Representative Interface Area (RIA)
Summary
C ohesive‐zone models (CZMs) are widely used to simulate initiation and propagation of cracks along structural interfaces. Many studies have revealed the significant role played by complex mechanisms including the progressive development of primary transversal and secondary inclined cracks [15], the influence of stress triaxiality on the formation of inclined struts in the concrete surrounding the steel bar [16], the fact that with increasing confinement the failure mode changes from being more brittle (splitting) to more ductile (pull out) [17] All these studies revealed that, for ribbed bars (the only ones nowadays used), interlocking is the predominant mechanism of stress transfer between concrete and steel with respect to adhesion and friction (the latter intended as the theoretical friction that would be obtained if the fracture surfaces were flat). This makes calibration of the model easier and gives more confidence in the robustness of the validation
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