Title: Deflection-Softening and Deflection-Hardening FRC Composites: Characterization and Modeling
Author(s): A.E. Naaman
Publication: Symposium Paper
Appears on pages(s): 53-66
Keywords: deflection; deflection hardening; deflection softening; fiber-reinforced concrete; strain hardening; strain softening; polypropylene fibers; steel fibers
The load-deflection response of fiber reinforced cement composites generally starts by an initial portion that is linear elastic up to a certain load at which it deviates from linearity; this is often identified as the onset of first cracking in the matrix. If the cement matrix is not reinforced, first cracking is followed by a sudden drop in the load-deflection curve, and failure occurs. The addition of fibers mostly influences the response of the composite after cracking. For all practical purposes, the load-deflection response of fiber reinforced cement composites after first cracking can be simply classified as either "deflection-softening" or "deflection-hardening." This paper describes first the different types of load-deflection curves observed in various experimental tests and illustrates the influence of some fiber reinforcing parameters with steel and polymeric fibers. Then, an analytical formulation is suggested to predict the value of the critical volume fraction of a given fiber to achieve deflection-hardening behavior. Several parameters influence the “deflection-hardening” portion of the curve and include the fiber content, fiber aspect ratio, and fiber to matrix bond.