reliability and limitations of impact-echo method for thickness measurement of orthotropic composite plates

In this paper, an impact-echo method has been used to numerically simulate low velocity impact of a steel ball on laminated composite plates in order to measure the plate's thickness. for the purpose of simulation, ls-dyna finite element code has been employed to express the behaviour of impact between steel ball and composite plates. furthermore, a single node near the impact area has been chosen and its displacement was demonstrated during the impact time on a graph by the software. after that, displacement-time graph was transformed to amplitude-frequency domain graph by means of fast fourier transform which was done by matlab software. the peak frequency was used to calculate the plate's thickness. the calculated thickness was verified by real plate thicknesses and this comparison shows an acceptable agreement between simulation and experimental results.