Determination of rigidities of FRP laminates using holographic interferometry technique

Abstract

An experimental method for the measurement of the bending and torsional rigidities of fiber reinforced plastic (FRP) laminates and carbonlcarbon (CIC) composites is presented ill this paper. The present method consists of a four-point bending test and a resonance test by using laser holographic interferometry. The optical measurement technique enables us to visualize and to record the deflection in the order of the laser beam wavelength. By making the most of that advantage, in the four-point bending test, the ratio of the bending rigidities (DJD,) can be determined from the fringe patterns. As for the resonance test, after analyzing the lengthwise and chordwise deformed shapes of oscillated plates, two relational expressions between the rigidities and the natural frequencies are derived. Then the bending rigidities (Dl, and D,,) and the torsional rigidity (D,) can be calculated by using the measured frequencies. Experiments were conducted on test specinlens made of both carbon/epoxy crossply laminates and CIC composites. The adequacy of the measurement technique is first confirmed by comparing the measured rigidities of the FRP laminates with the theoretical values obtained from classical lamination theory (CLT). The results indicate that the present nlethod can be used to evaluate the rigidities of orthotropic laminates with reasonably good accuracy. Therefore, the bending and torsional rigidities of CIC composites were measured experimentally by using above mentioned technique. The results are also presented i n this paper.