Compression test. The compression testing was performed using a universal mechanical testing machine (Zwick/Roell, Ulm, Germany), equipped with a flat steel base and a tiltable flat punch for self-alignment, according to the sample tilt. Measurements were performed with a constant crosshead speed of 0.2 mm/min, until a defined load was reached. Maximum loads were increased in 500N steps after each measurement to investigate the effects of previous loading on the mechanical response. To partially correct for the frame compliance of the testing machine, the elongation of the system was measured under the same loading conditions without any sample and subtracted from the data collected during sample measurement, to derive the actual sample response.