Application Of Laser Speckle And Moire Photography To The Study Of Dynamic Fracture

The techniques of moire photography and high speed photography have been combined to measure transient displacement fields. Sequences of double exposure moire photographs of cracks moving through plates of polymethylmethacrylate (PMMA) were recorded with a rotating mirror camera at 2µs frame-1. One sequence was analysed in detail to reveal the time variation of both in-plane displacement components, and the dynamic stress intensity factor (Kld). An alternative approach, based on recording real-time moire fringes, allowed the spatial frequency of the specimen grating to be increased to 150 lines per mm (l mm-1), and was used to visualise the deformation caused by solid particle impact. Laser speckle photography with a double pulsed ruby laser has also been investigated as a noncontacting alternative to moire.