An experimental investigation of guided wave propagation in corrugated plates

Non-planar surfaces are often encountered in engineering structures. Periodically corrugated boundaries can be found in aerospace structural components such as the surface formed by friction stir welding, and in civil structural components such as rebars used inside reinforced concrete beams and slabs. Engineers and architects also design periodically corrugated structures to create desired acoustic band gaps. For health monitoring of structures with periodic geometry a good understanding of the elastic wave propagation phenomenon through such periodic structures is necessary because crack initiation creates acoustic waves that propagate through the periodic geometry of the structure. These acoustic signals can be detected at remote locations and correctly interpreted only if the mechanics of elastic wave propagation through such periodic structures is well understood. With this application in mind the elastic wave propagation in three different plates with different degrees of corrugation is experimentally studied. The experimental results clearly show that elastic waves can propagate through the corrugated plate (waveguide) for certain frequencies and find it difficult to propagate for some other frequencies. Frequencies that allow the elastic waves to propagate through the plate are called pass band frequencies while the frequencies that block the wave propagation are called stop band frequencies. Pass band and stop band frequencies depend on the geometry of the corrugated plate as well as the phase velocity of the propagating guided wave. Stop bands increase with the degree of corrugation. Experimental results are compared with the theoretical predictions.