Analytical Determination of Localized Heat Damage in Fiberglass Reinforced Resin Beams Using the Frequency Response Shifting

The dynamic response of a localized, heat-damaged, fiberglass-reinforced epoxy cantilever beam is obtained as a function of damaged length and damage severity. A heat-damaged area causes a reduction in the local stiffness of the beam and introduces a complex damping in the damaged zone. These variations in the local mechanical properties could result in changing vibration characteristics of the beam. The variations in the system characteristic could then be used to assess the structural integrity of the composite beam. A cantilever beam made of a glass fiber-resin composite material and damaged by a hot tip contact element and a laser beam is evaluated for its dynamic response using numerical methods. The laser beam caused local melting of many fibers in the damaged area and thus reducing the stiffness of the beam in the damaged area. The beam is analyzed by modeling it as a lumped system and a continuous system and by a finite element. The goal of the research is to find out whether the changes in the frequency response of the damaged beam can be used as a diagnostic tool for estimating the severity of the damage. The results show that the size and location of damage are equally as important as the local stiffness and damping of the damaged region in terms of their effects on the beam resonant frequencies. The results indicate that the resonance frequencies may not be suitable parameters for estimating the residual tensile strength of the composite. A 50% reduction in the local bending rigidity produced relatively little change in the system first resonance frequency. In contrast, it significantly reduced the residual tensile strength of the composite.