STRESS WAVES IN COMPOSITE-MATERIALS

The method of cells (MOC) developed by Aboudi provides a powerful mean s for studying the propagation of waves through systems having complic ated internal cell structure [Wave Motion 9, 141 (1987)]. Laminated ma terials are a common example. The method can handle harmonic waves and also transient waves arising from a finite duration impulse. The meth od is sufficiently robust to treat impact, as we show here. Both linea r and nonlinear elastic-stress-strain relations can be included. The p resent work generalizes the method to include viscoelastic materials ( such as polymers), systems with cell structure deviating from perfect periodicity (including random), and systems simulating actual impact e xperiments. We test the theory by comparing our results with measureme nts taken from a flat-plate impact experiment. The system investigated was a bilaminate composed of unit cells of epoxy and epoxy-graphite s ubcells. Using known and estimated material parameters, we find that t he MOC gives a reasonable representation of the data. We then address some features of the experimental data that have not yet been explaine d by other theoretical methods. The importance of unit cell periodicit y is tested by adding a random incremental width to each unit cell. Fi nally, the shortcomings of the MOC caused by using a truncated series expansion for the particle displacements, and neglecting plastic flow and nonadiabatic effects are discussed.