Method and apparatus for analyzing nodal interference patterns vibrationally induced in semi-monocoque structure

摘要

Methods and apparatus for automatically analyzing anti-nodal patterns formed in the outer skin of a semi-monocoque structure when it is excited to vibrate at a resonant frequency at which out-of-plane displacement is optimized. The described principles of analysis may be utilized to analyze a recorded image of the anti-nodal patterns obtained by holographic interferometry, or to directly examine the anti-nodal pattern by scanning a test area of the surface with a beam of coherent radiation, e.g., a laser beam, and utilizing the Doppler effect, measuring, recording and displaying a contour map showing out-of-plane displacement of the surface for analysis. In the holographic record case, comparison of the fringe density of the anti-nodes against the density of any fringes which may occur along normally fringe-free lines of underlying structure reveals the type and location of any structural faults. In the laser Doppler system, faults are identified by comparing the surface displacement of the anti-nodes with any displacements occurring along lines of the underlying structure.