Figure 1.

Bending device. A, The stem (1) was equipped with a linear voltage displacement transducer (2) in order to monitor the diameter growth of the stem before, during, and after bending was applied. A moving arm (3) pushed the stem against a plastic tube; the stem was thus bent around the tube (4). Therefore, the stem was subjected to a controlled curvature in terms of strains. The moving arm was then driven back and the stem was reset to its initial position. B, Scheme of the stem in the bent state. Locally, the applied strain is the product of the curvature of the central line and the stem radius (r_stem). In the case of small curvature, the curvature of the central line is given by the inverse of the sum of the stem radius and of the radius of the plastic tube (r_tube).