Damage evaluation of composite beam in three point bending test by acoustic emission: frequency domain

Composite applications are very wide in most industrial fields. Today, polymer matrix composites are used in the automotive industry, aerospace, oil, gas and petrochemical Industries and etc. Glass / epoxy composite is one of the most useful composites that has special properties such as high strength-to-weight ratio, high hardness, high corrosion resistance, low thermal expansion, resistance to nuclear radiation and absorption of energy. Composite beams may be used as flexural elements. In flexural loading, the crack initiation and failure can occur in a variety of modes that each ones has special frequencies. In this research, acoustic emission method was used to evaluate and check the different failure mechanisms of glass epoxy composite beam under three point bending loading. In order to determine different failure mechanisms, wavelet transform analysis was used for acoustic signal processing by using only one sensor. Three types of dominant failure mechanisms (matrix fracture, debonding and fiber breakage) in composite beam under bending were identified and the frequency ranges corresponding to these failure mechanisms were determined. Wavelet transform results showed that these three types of dominant failure mechanisms (matrix fracture, debonding and fiber breakage) have frequency ranges of 0-125 KHz, 125-250 KHz and 375-500 KHz respectively. Finally, the observations of scanning electron microscope from fracture surface of specimen validated the obtained results. This research showed the possibility of acoustic emission technique as a monitoring tool of glass/epoxy composite beam in flexural failure.