The stress relaxation (creep) rate of Mu2e straw tubes

We report on the material relaxation properties of the Mu2e straw tubes measured over a period of about 5 years under two conditions. One is a fixed tension condition: two straw tubes are under a constant tension, and the lengthening of the tubes is measured as a function of time. The other is a fixed length condition: the length of four straw tubes with different initial tensions is fixed, and the tension in the tubes is measured. For the latter case, a scaling behavior appears when the ratio of the tension to the initial tension of the four straws is plotted as a function of time. In both cases, we find that the creep rates can be well parameterized with a logarithmic function of time elapsed. This implies that, for example, the amount of creep from day 20 to 200 is the same as between day 200 and 2000.