Residual stress measurement on a tube using EN2718

Hill Engineering was recently asked to perform a residual stress measurement on a tube specimen in accordance with EN2718, which defines the calculation of circumferential residual stress in circular tubes with a ratio D/a ≥ 10, where D is the tube outer diameter and a is the tube wall thickness.

Before splitting the tube section open, the residual stress within the tube wall is in equilibrium. After the tube section is split, the residual stress redistributes, and the tube either springs open or pinches closed, depending on the internal stress state. Measuring the diametral change in the tube section provides some insight regarding the magnitude and sign of the original circumferential stress state.

The following is a summary of the EN2718 tube splitting test.

1. Cut three adjacent test specimens a long tube.
2. Mark two parallel reference lines and measure the distance between them.
3. Measure the outer diameter and thickness of each test specimen.
4. Cut each test specimen directly between the two parallel reference lines and measure the new distance between them.
5. Measure the new outer diameter of each test specimen.
6. Compute the residual stress from the measured deformation data according to the equations in EN2718.

For more information about this type of measurement, or any of our other residual stress measurement techniques, contact us.