RESIDUAL-STRESSES IN PLASTIC PIPES BY LASER SPECKLE TECHNIQUE

Laser speckle technique has been employed as a sensitive noncontact qu antitative 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 re moval method to describe accurately the stress distribution along the pipe thickness. A merit of the present investigation is the developmen t of an empirical formula to assist the laser measurement in obtaining a more reliable stress distribution. Therefore, the need for the laye r removal method has been eliminated, and the usual inaccuracy pattern s resulting from excessive machining have been avoided. Since the resu lts obtained are compared favorably with different techniques such as strain gages, ring slitting, and layer removal techniques, the propose d work possesses different advantages with respect to simplicity, prac ticality, and sensitivity.