Method and device for measuring r-value of tube in circumferential direction

A method for measuring an r-value of a tube in a circumferential direction, comprising the following steps:

• step S1:
• determine a size of an annular sample according to a diameter and wall thickness of a to-be-measured tube, and cutting the annular sample from the tube;
• step S2:
• making speckles or printing circular grids on an outer surface of the annular sample;
• step S3:
• sleeving the annular sample in a middle of an outside of a ring segmented rigid die;
• step S4:
• filling a liquid bag with a fluid medium and controlling an internal pressure, and driving the ring segmented rigid die to move outward uniformly in a radial direction using a uniformly distributed load generated by pressurizing the liquid bag, so as to cause equal diameter bulging of the annular sample;
• step S5:
• measuring strain in width and circumferential directions on the annular sample in a single module region of the ring segmented rigid die;
• and
• step S6:
• determining the plastic strain ratio r-value of the tube in the circumferential direction according to the strain in the width and circumferential directions in combination with a condition of a constant volume for plastic deformation.