STEEL FIBER BRIDGING

STEEL FIBER BRIDGING 

The fiber bridging, like the aggregate one, depends on many parameters and, for simplicity, an isolated fiber is investigated along a crack. The fiber contributes to dissipate energy to (1) matrix fracture and matrix spalling, (2) fiber‐matrix interface debonding, (3) post‐debonding friction between fiber and matrix (fiber pull-out), (4) fiber fracture and (5) fiber abrasion and plastic deformation (or yielding) of the fiber.

The mechanical behaviour of FRC depends surely on the amount of fiber , on the orientation of the fibers and largely on the pull‐out versus load (or load‐slip) behaviour of the individual fibers. In particular, the pull‐out depends on the type and the mechanical/geometrical properties of the fibers, on the interface's mechanical properties between fiber and matrix, on the angle of inclination of the fiber with respect to the direction of loading and on the mechanical properties of the matrix. A large amount of literature covers this subject.

The fiber pull‐out behaviour is the gradual debonding of an interface surrounding the fiber, followed by frictional slip and pull-out of fiber. The bond (responsible for the forces transmission between fiber and matrix) has different components:

• the physical and/or chemical adhesion between fiber and matrix;
• the frictional resistance;
• the mechanical component (arising from the fiber geometry, e.g. deformed, crimped or hooked‐end);
• the fiber‐to‐fiber interlock;
• the debonding criterion can be described with two different approaches:
• strength‐based criterion (or stress‐based) where it is assumed that the debonding initiates when the interfacial shear stress exceeds the shear strength;

Once debonding has taken place, stress transfer develops owing to frictional resistance that, in its turn, can be described, with the following different relationships:

• constant friction
• caying friction (or slip softening)
• slip hardening friction. 

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