Meso-mechanical Study On Interfacial Transfer Behavior And Debonding Process Of The Steel Fiber Reinforced Concrete

The stress in fiber reinforced composites is transferred through the interface of the fiber and the matrix, so the mechanical properties of the interfacial region and the stress transfer behavior of the interface play an important role in the macroscopic mechanical properties of the whole composites. As a result, the interface of fiber reinforced composites has always been a critical part in engineering. This paper, focused on fiber-concrete composites, makes some experimental studies on the interfacial stress behaviors, analyzes the mechanism of the fiber reinforcement, toughness, and failure-resistance, and discusses the characteristics and patterns of the stress and strain near the interface, and therefore to provide some valuable experimental data for the setup of interfacial mechanical model of fiber-concrete composites.First, three-dimensional digital photo-elasticity method is used to test the interfacial residual stress distribution between the linear and specially designed hooked fiber and the resin matrix. The results show that the value of the interfacial residual shear stress reaches its peaks near the fiber's embedded ends in the interface of the single fiber and the matrix, and the interfacial residual stress transfer is also concentrated around the two ends of the fiber.Second, the three-dimensional interfacial shear stress near a straight fiber under the combined actions of pullout loading and thermal residual stress is studied. The interfacial shear stress has a parabolic distribution, and the transferring area mainly focuses on the region of the embedded end of the fiber where the stress reaches its critical point, causing the debonding of the interface, and then the shear stress transfers along the imbedded fiber length to the other end.In addition, the interfacial sheer stress transfer behavior near a specially designed hooked fiber under the combined actions of pullout loading and thermal residual stress is measured. The stress transfer mainly focuses on the region of the embedded end of the fiber where the stress reaches its critical point, causing the debonding of the interface. Before the debonding, as the pullout loading increases, the peak value of the shear stress transfers along the fiber from the imbedded top to the interior of the matrix, and then stops at the hooked part of the fiber. When the interface begins to debond as the load increases, the shear stress can be transferred to the fiber's hooked part.A direct measurement of both the whole field and the interfacial strain distributions and patterns is performed when the straight and specially designed hooked fibers are being pulled out from the concrete matrix using the digital image correlation method and the single fiber pullout experiment. The microscopic strain localization can result in the localization of the interfacial shear failure which includes the initiation, development and propagation of the interfacial debonding. This localization shows an apparent characteristic of time and spatial intervals.Finally, MARC finite element software is used to simulate the photo-elasticity experiment of the interfacial residual shear stress in the straight fiber and the specially designed hooked fiber composites, and the photo-elasticity experiment of the interfacial shear stress distributions along the fiber length under the combined actions of pullout loading and thermal residual stress. The simulation results are compared with the experiment results. The influence of the fiber's length and diameter on the interfacial shear stress is discussed. The change of the reinforced fiber's length and diameter does not influence the interfacial residual shear stress significantly. Under the combined actions of pullout loading and thermal residual stress, changing the fiber's length does not influence the interfacial shear stress much, but the change of its diameter leads to the change of the initial position of interfacial debonding and cracking. In addition, changing the fiber's length does not significantly influence the interfacial shear stress of the straight part of the hooked fiber, but it can reduce the stress concentrations at the hooked part; on the other hand, the change of the fiber's diameter has a significant influence on the interfacial shear stress—the smaller the diameter, the larger the interfacial shear stress.