Digital and optical moiré detection of flaws applied to holographic nondestructive testing

Superposition of two double-exposure holographic interferograms creates moiré patterns that can be used to detect flaws. Relative magnification can be used to correct for imprecise replication of loading when the second interferogram is formed; it also can be used to detect flaws when only a single interferogram is used if the basic deformation field is radially symmetric. Digital image processing is a rapid and versatile technique for forming such moiré patterns.