Tension Test of Fiber-Reinforced Polymeric Materials

Overview

Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA

Fiber-reinforced polymeric materials (FRP) are composite materials that are formed by longitudinal fibers embedded in a polymeric resin, thereby creating a polymer matrix with aligned fibers along one or more directions. In its simplest form, the fibers in FRP materials are aligned in an orderly, parallel fashion, thus imparting orthotropic material characteristics, meaning that the material will behave differently in the two directions. Parallel to the fibers, the material will be very strong and/or stiff, whereas perpendicular to the fibers will be very weak, as the strength can only be attributed to the resin instead of the whole matrix.

An example of this unidirectional configuration is the commercially available FRP reinforcing bars, which mimic the conventional steel bars used in reinforced concrete construction. FRP materials are used both as stand-alone structures such as pedestrian bridges and staircases, and also as materials to strengthen and repair existing structures. The thin, long plates are often epoxied to existing concrete structures to add strength. In this case, the FRP bars act as external reinforcement. The FRP bars and plates are lighter and more corrosion resistant, so they are finding applications in bridge decks and parking garages, where de-icing slats lead to rapid deterioration of conventional bars.

In this laboratory exercise, the tensile behavior of a unidirectional specimen will be studied, with emphasis on its ultimate strength and deformation capacity. The behavior of the specimen is expected to be elastic until failure, which is expected to occur in a sudden and explosive manner. This behavior should be contrasted with those of ductile steels, which exhibit extensive deformation capacity and strain hardening before failure.

Procedure

Take proper safety precautions, and wear eye protection because the explosive failure typical of these specimens sends many small, sharp shards flying.
Obtain four FRP specimens. Two will be from a unidirectional 0.5-inch E-glass FRP plate cut into 1" x 8" specimens, one along the direction of the fibers and one perpendicular to the fibers. The third specimens will be a 0.25-inch carbon FRP rebar, and the fourth will be a 0.25 FRP E-glass rebar. The rebar specimens should be about 24 inches long.
Attach hol

Results

Typical stress-strain curves for the E-glass FRP plate specimens are shown for the plate with the two uniaxial layers aligned longitudinally (Fig. 1) and respectively perpendicularly (Fig. 2) to the direction of loading. For the case of the load applied parallel to the fibers (Fig. 1), the maximum force was 12.32 kips, corresponding to a tensile strength of 98.6 ksi. The failure occurred at a strain of 2.98% and the modulus of elasticity, calculated from a line tangent at 30% of the ultim

Application and Summary

FRP materials are light, strong composites used extensively in both civil, mechanical, and aerospace applications. They are made up of strong fibers embedded in a resin or similar matrix, and they are manufactured in many forms, including prepeg strips and laminates. Their strength and stiffness can be tailored by varying the amounts, types, and directionality of the fibers. FRP materials have a much smaller deformation capacity than metals or polymers and give little warning of failure, thus are important to study th