An experimental study on the evolution of modal damping with damage in carbon fiber laminates

Many of the techniques developed to assess structural damage are based on experimental modal analysis. This paper presents a study to extend the current understanding of how increasing damage in a carbon fiber reinforced plastic affects the modal damping factor of a laminated structure. Damage is introduced and quantified in terms of the dissipated energy. It is shown that there is a tendency for the overall damping to increase whereas there is a tendency for the overall stiffness to decrease. While these results are not novel, the former is quite relevant, since the authors are not aware of many other experimental studies on the evolution of the modal damping factor with damage in carbon fiber reinforced plastic. At the same time, a modal-based damage location technique that combines both the natural frequencies and the modal damping factors as damage sensitive features is discussed. The hypothesis that different damage morphologies on composite materials have different contributions to the damage features is drawn. The methods are illustrated with both numerical and experimental examples. One of the problems observed is that, although damping is consistently found to increase globally with damage, the determination of the individual changes of the modal damping factors is still very uncertain. This may be due to concurrent damage types being present at the same time, but most certainly due to uncertainties involved in the identification of the modal damping factors