Mechanical properties
The developed SH-SPC was experimentally tested for different over-pressures of the air chamber. The resulting deformations of the SPC were captured using a digital camera. The cell was tested for over-pressures starting from 0 bar up to 0.36 bar. A zoomed image is presented, showing the deformation of the SPC for an over-pressure of 0.36 bar. For this over-pressure the width of the cubic cell increases with 40%.
The force exerted by the top plane of the SH-SPC was measured using a force sensor. These are steady state forces, the constant force applied by the SH-SPC on the force sensor over a long time. The steady state force is represented as a function of over-pressure. The forces are in the range of a few newtons and are, compared to values measured in literature, suitable for SPA applications.
The combination of forces in the range of newtons that can be applied by the SH-SPC and the high deformation response for over-pressures lower than 0.5 bar, indicate that the mechanical properties of the DA-materials, DPBM-FGE-J4000 and -J2000, are adequate for small actuation in soft robotic.
Self-healing properties
After the validation of the mechanical properties of the SH-SPC, the cell was pushed to its limits: the over-pressure was increased until a small perforation occurred in the cell at a maximum over-pressure of 0.46 bar. The location of the perforation is presented in figure below. At this location the open cube, created entirely out of -J4000 material, is connected to the -J2000 sheet. The -J4000 is more elastic and when the air chamber is put under overpressure, the cubic cell starts to deform. -J2000 on the other hand, is less elastic and will only deform only a little. This causes stress concentrations at the connection between the two polymer materials. The perforation of the SH-SPC took place on the location where failure was theoretically expected. From this it can be concluded that the sides of the 3D cubic cell were well-sealed in the manufacturing process, using the new developed technique: "shaping through folding and self-healing".
To evaluate the SH-property of the SPC, an incision was made with a scalpel in one of the planes of the cubic part. The dimensions of this
incision are: a length of 4.43 mm, a thickness of 0.30mm (blade) and all the way through the wall of the cell. Subsequently this incision as well as the perforation were self-healed in an external furnace using the SH-procedure. This procedure had a maximum temperature of 70 °C and a duration of 30 hours.
In order to determine whether the initial mechanical properties of the SH-SPC were recovered after the SH-procedure, the steady state force was again measured as a function of the over-pressure. The results of this test were plotted in figure Below, together with the data measured before the incision was made. As the results for the two experiments are the same within the scatter of the data, the SH-SPC has the same mechanical
performance before and after the SH-procedure. After these experiments, the SH-SPC was again pushed to its limits. A perforation took place at 0.48 bar, at the same location it did before. This indicates that the incision was completely cured and no weak spots were created during and after the SH-procedure. In addition, comparing the maximal over-pressure before (0.46 bar) and after (0.48 bar) the SH-procedure, it can be concluded that the puncture, created before the incision was made, was also entirely healed.
