Browsing by Author "Winston O Soboyejo"

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    Pull-out behavior of natural fiber from earth-based matrix
    (Journal of Composite Materials, 2016) Kabiru Mustapha; Salifu T Azeko; Ebenezer Annan; Martiale G Zebaze Kana; Leo Daniel; Winston O Soboyejo
    This paper presents the results of a combined experimental and analytical study of the pull-out behavior of natural fiber (grass straw) from an earth-based matrix. A single fiber pull-out approach was used to measure interfacial properties that are significant to toughening brittle materials via fiber reinforcement. This was used to study the interfacial shear strengths of straw fiber-reinforced earth-based composites with a matrix that consists of 60 vol. % laterite, 20 vol. % clay and 20 vol. % cement. The composites that were used in the pull-out tests included composites reinforced with 0, 5, 10 and 20 vol. % of straw fibers. The toughening behavior of fiber-reinforced earth-based matrix was analyzed in terms of their interfacial shear strengths and bridging zones, immediately behind the crack tip. This approach is consistent with microscopic observations that reveal intact bridging fibers behind the crack tip, as a result of debonding of the fiber–matrix interface. Analytical models were used to study the debonding of fiber from the matrix materials, as well as the toughening due to crack-tip shielding via bridging. The results show that increasing the fiber embedment length and the fiber volume fraction (in the earth/cement matrix) increases the peak pull-out load. The debonding process was also found to be associated with a constant friction stress. The combined effects of multiple toughening mechanisms (debonding and crack bridging) are elucidated along with the implications of the results for the design of earth-based composites for potential applications in robust building materials for sustainable eco-friendly homes.
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    Strength and fracture toughness of earth-based natural fiber-reinforced composites
    (Journal of Composite Materials, 2015) Kabiru Mustapha; Ebenezer Annan; Salifu T Azeko; Martiale G Zebaze Kana; Winston O Soboyejo
    This paper presents the results of a combined experimental and theoretical study of the strength, fracture toughness, and resistance-curve behavior of natural fiber-reinforced earth-based composite materials. The composites, which consist of mixtures of laterite, clay, and straw, are stabilized with controlled levels of Ordinary Portland cement. The compositional dependence of compressive, flexural/bend strength, and fracture toughness are explored for different proportions of the constituent materials using composites and crack-tip shielding models. The underlying crack-microstructure interactions associated with resistance-curve behavior were also studied using in situ/ex situ optical microscopy. This revealed evidence of crack bridging by the straw fibers. The measured resistance-curve behavior is also shown to be consistent with predictions from small- and large-scale bridging models. The implications of the results are then discussed for potential applications in the design of robust earth-based building materials for sustainable eco-friendly homes.