PSI - Issue 42

F. Cesarano et al. / Procedia Structural Integrity 42 (2022) 1282–1290 F. Cesarano, M. Maurizi, C. Gao, F. Berto, F. Penta, C. Bertolin / Structural Integrity Procedia 00 (2019) 000 – 000

1289

8

The results obtained from the second experimental method were compared with the numerical method presented in the previous step. For each simulation, the maximum displacement of the associated experiment was obtained by applying the external forces along the z-direction via a trial-and-error process. Since viscoelastic behaviour and its related deformation generally do not develop linearly with time and temperature, these FEA simulations made it possible to search for a linear development of the phenomenon attributable to the SME. From the comparison results, we obtained that for the curve referring to a time of three minutes; there was an almost negligible error, i.e. < 5%, thus suggesting that the phenomenon of residual stress release can be considered linear with temperature (Fig. 8b). However, with increasing time, for high temperatures, the error between the numerical and experimental results increases; this is because, with time, the viscoelastic behaviour of the PLA is likely to have a more significant influence on the final deformation of the component.

a

b

Fig. 8a: First experimental method - Plot: Curvature-Temperature

Fig. 8b: Second exp. Method vs FEA - Plot: Curvature-Temperature

4. Conclusions and outlooks In conclusion, it can be stated that the correct experimental methodology to address the SME has been understood, understanding that placing the specimens in the oven directly at the target temperature allows a broader range of analysis of the curvatures. This first analysis also understood the non-linearity of the shape memory effect associated with viscoelastic behaviour. It was concluded that the overall deformation phenomenon is due to a term related to the SME, which with good approximation (looking at the FEA results) can be considered linear, and an exponential term caused by the viscoelastic behaviour. The next step in future research will be to report in detail the experiments carried out to study the modification of the curvature as a function of the specimen geometric parameters (fill-angle, fill density, and thickness using a more accurate fitting tool to process the results. Doing so will make it possible to understand the phenomenon better and thus exploit it to realize application concepts such as passive sensors. References [1] A. Subash and B. Kandasubramanian, "4D printing of shape memory polymers," European Polymer Journal , vol. 134, p. 109771, Jul. 2020, https://doi.org/10.1016/j.eurpolymj.2020.109771. [2] T. van Manen, S. Janbaz, and A. A. Zadpoor, "Programming 2D/3D shape-shifting with hobbyist 3D printers," Materials Horizons , vol. 4, no. 6, pp. 1064 – 1069, 2017, https://doi.org/10.1039/c7mh00269f. [3] A. Lantada and M. Rebollo, "Towards low-cost effective and homogeneous thermal activation of shape memory polymers," Materials , vol. 6,