Experimental R-Curves for Assessment of Toughening in Fiber Reinforced Cementitious Composites


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Title: Experimental R-Curves for Assessment of Toughening in Fiber Reinforced Cementitious Composites

Author(s): B. Mobasher, C. Y. LI, and A. Arino

Publication: Special Publication

Volume: 155


Appears on pages(s): 93-114

Keywords: aluminum oxide; carbon; composite materials; concretes; cracking (fracturing); fiber reinforced concretes; fibers; fracture properties; mortars (material); polypropylene fibers; toughness; Materials Research

Date: 8/1/1995

Procedures to obtain the experimental R-curves using a compliance calibration technique are revisited in this paper. R-curves provide a convenient means to study the process of fracture and the brittle-ductile transition in materials. Single edge notched beam specimens are tested under closed loop crack mouth opening control. The procedure to obtain the R-curves using loading/unloading compliance and the residual displacements are discussed. An elastically equivalent toughness K R as a function of crack extension is defined to compare the R-curves with the available data in the literature. The developed test method is applied to fiber reinforced concrete (FRC) composites with up to eight percent by volume of short, chopped alumina, carbon, and polypropylene (PP) fibers. Significant strengthening of the matrix due to the addition of short carbon and alumina fibers was observed. R-curves in these composites are characterized by an increase in the steady state fracture toughness. In PP-FRC composites, energy dissipation due to fiber pullout increases the ascending rate of the R-curve well after the main crack has formed. The work of fracture is computed from the cyclic loading/unloading tests and the results compared with the R-curves.