Simple fatigue testing machine for fiber-reinforced polymer composite

Abstract

Fiber-reinforced polymer (FRP) composites seem to be the best options in many structural applications. Such applications are often exposed to fatigue loads, and therefore, the fatigue behavior of the composites must be studied in order to achieve a proper design. This is fulfilled by means of an experimental characterization, in which a lot of specimens are tested because of the several parameters involved (i.e., fiber/matrix ratio, fiber orientation, staking sequence, etc.). Besides, the fatigue tests must be carried out at low frequencies, in order to avoid temperature increments in the polymer matrix, which would change the mechanical properties of the composite. Consequently, considerable time is consumed to perform a complete set of tests and, when using conventional servohydraulic testing machines, costs rise notably. A machine to perform fatigue tests of composite materials under constant amplitude load cycles and a wide range of load ratios is presented in this paper. This machine exhibits as main goals the fulfillment of the corresponding standard requirements, a very low cost compared to conventional servohydraulic testing machines and, consequently, makes reasonably priced to have several machines testing specimens simultaneously, in order to reduce the necessary time to complete the whole characterization.