Duncan Cree

Tensile and Lap-Splice Shear Strength Properties of CFRP Composites at High Temperatures

AbstractCarbon fiber–reinforced polymer (CFRP) composites are used to retrofit or reinforce existing civil infrastructure. When a new combination of carbon fiber/epoxy system is to be implemented, elevated temperature requirements must be evaluated to determine performance in fire or hot climates. This article presents experimental results conducted on small-scale CFRP laminates produced by the hand layup technique to determine tensile strength and single lap-splice shear strength at temperatures from 23 to 200°C. Two curing regimes were evaluated: room temperature (23°C) and elevated temperature (120°C). The dynamic mechanical analyzer was used to determine the glass transition values from each curing regime. Strength tests were performed at steady-state (heat, then load to failure) and transient (hold load, increase temperature to failure) temperatures. Loss of tensile strength and modulus at elevated temperature is thought to be due to polymer resin matrix softening and loss of load transfer capability...

Enhancement of Mechanical Properties of Bio-Resin Epoxy/Flax Fiber Composites using Acetic Anhydride

Chemically treated acetic anhydride (AA) flax fiber mats were investigated. Bio-based epoxy resin and conventional epoxy resin unidirectional fiber composites were manufactured using a vacuum bagging technique. Flax fibers in the bio-resin composites were chemically treated with 1, 2, 3 and 4% (AA), while the fibers used with the conventional resin were not treated. The composites with the conventional resin were compared with the bio-resin in an untreated condition. A 2% AA treatment improved the bio-resin composite tensile strength, stiffness and bond shear strength by 55%, 58% and 7%, respectively. These three properties were evaluated and the results statistically analyzed using ANOVA. The AA reduced moisture absorption intake and improved adhesion of the fiber/matrix interface. The composites treated with 1–2% AA were most successful with a 65% moisture resistance. The scanning electron microscope was used to observe the fiber surface and fractured surfaces of the untreated and treated flax fibers. A chemical pre-treatment has improved the composite mechanical and moisture resistance over the non-treated fiber composites.

Thermal behaviour of unstressed and stressed high strength concrete containing polypropylene fibers at elevated temperature

Purpose The purpose of this paper is to evaluate high strength concrete (HSC) containing polypropylene fibers (PP-fibers) at high temperature under a compressive load. Design/methodology/approach The use of PP fibers in HSC is known to reduce and at times eliminate the risk of spalling. HSC containing 0, 1 and 2 kg/m3 of PP-fibers were subjected to various temperatures from 20°C to 150°C, 300°C and 450°C and evaluated in a “hot condition”. One group of specimens was in a non-stressed condition during heating (unstressed hot), while a second group was subjected to an initial preload of 40 per cent of the room temperature compressive strength during the heating (stressed hot). Findings Results showed that stressed concrete containing PP-fibers had lower thermal gradients (the temperature difference between the surface and center temperatures as a function of radial distance) and a decrease in relative porosity. However, the compressive strength of stressed specimens was improved with or without fibers as compared to that of the unstressed HSC. The increased stress levels due to concrete expansion at elevated temperature were also reported. The PP-fibers did not have a significant effect on the compressive strength of stressed concrete as compared to the unstressed state. Originality/value This paper reports the compressive strength of PP-fibers in HSC at elevated temperature with and without a pre-load.