Residual stresses in plastic pipes by laser speckle technique

Laser speckle technique has been employed as a sensitive noncontact quantitative tool to measure the residual stress distribution developed in plastic pipes due to manufacturing processes. Pipes are classified into two main categories: thin-walled and thick-walled pipes. In thick-walled pipes, the laser technique has been combined with the layer removal method to describe accurately the stress distribution along the pipe thickness. A merit of the present investigation is the development of an empirical formula to assist the laser measurement in obtaining a more reliable stress distribution. Therefore, the need for the layer removal method has been eliminated, and the usual inaccuracy patterns resulting from excessive machining have been avoided. Since the results obtained are compared favorably with different techniques such as strain gages, ring slitting, and layer removal techniques, the proposed work possesses different advantages with respect to simplicity, practicality, and sensitivity.