DETECTING DAMAGE IN CARBON FIBRE COMPOSITES USING NUMERICAL ANALYSIS AND VIBRATION MEASUREMENTS

Abstract

IN THIS WORK, CARBON FIBRE REINFORCED POLYMER (CFRP) PLATES HAVE BEEN TESTED UNDER FREE IMPACT VIBRATION TESTS IN PRISTINE AND DAMAGED CONFIGURATIONS. EACH DAMAGED PLATE INVOLVED ONE CRACK OF SPECIFIC ORIENTATION (HORIZONTAL, VERTICAL, AND DIAGONAL). THE PLATES WERE SUSPENDED AS CANTILEVERS AND VIBRATED USING AN IMPACT HAMMER. TWO ACCELEROMETERS AND ONE MICROPHONE WERE USED TO OBTAIN THE VIBRATION RESPONSE DATA SIGNALS FROM THE PRISTINE AND DAMAGED PLATES, AND THE FREQUENCY RESPONSE FUNCTION (FRF) WAS PLOTTED. THE CFRP PLATES WERE ALSO SUBJECTED TO A TENSILE TEST AND TO SCANNING ELECTRON MICROSCOPY (SEM), THEREBY ESTIMATING THEIR MECHANICAL PROPERTIES AND EVALUATING THEIR CARBON FIBRE MICROSTRUCTURES. THE CURRENT TECHNIQUE FOCUSED ON THE DETECTED SIGNAL FROM MORE THAN ONE VIBRATION SENSOR TO ENSURE THE MEASUREMENT'S ACCURACY. COMPARISONS BETWEEN THE EXPERIMENTAL VIBRATION TEST AND THE FINITE ELEMENT ANALYSIS (FEA) SIMULATION SHOWED THAT THE RESULTS AGREED. THE DAMAGE ORIENTATION SIGNIFICANTLY AFFECTED THE COMPOSITES’ DYNAMIC
PROPERTIES. THE FRF MEASURES OF THE DAMAGED CFRP COMPOSITES SHOWED THE LOWEST EIGENVALUES FOR THE EXCITED MODE SHAPES' RESONANT FREQUENCIES. THE 0/90 LAYUP LAMINATE COMPOSITE EXHIBITED GREATER FLUCTUATIONS IN RESONANT FREQUENCIES ACROSS THE VARIOUS MODE SHAPES THAN DID THE QUASI-ISOTROPIC LAMINATES. THE RESONANT FREQUENCY FLUCTUATIONS IN THE 0/90 LAYUP LAMINATE REACHED A 2.85% DIFFERENCE COMPARED TO THE QUASI-ISOTROPIC LAMINATE COMPOSITES.