Abstract: The nature of the birefringence fringe and the relationship between the birefringence fringe and the residual stress induced by machining in PMMA were investigated by means of experiment.A mew method--birefringence measurement has been established for the quantitative determination and nondestructive evaluation of the machining stress in PMMA plates and the transparent pieces of airplane cabines. Besides, it has been discussed how to separate the birefringence induced by machining from the initial one quantitatively and how to get the distribution of the birefringence induced by machining through thickness. Birefringence measurement has been used in engineering.

Key words: machining stress, polymethylmethacrylate （PMMA）, birefringence measurement, photoelasticity, canopy