Application of the grating objective speckle method to composite materials

The grating objective speckle method has been applied in whole-field strain analysis of carbon-fiber-woven polyimide-composite materials. A sequence of rosette fringe patterns was obtained from one single specklegram, indicating displacement components along four different directions with a 45-deg interval. The spatial frequencies, which represent the sensitivities of the fringe intervals, were 2400 ℓ/mm forU _x ,U _y and 1697 ℓ/mm forU ₄₅ andU ₁₃₅. Normal strain components, ɛ _x , ɛ _y , ɛ₄₅, and ɛ₁₃₅, were trasformed to quantitative topographic representations by coupling to a digital computer system. Shear strain can be determined by the rosette equations.