Właściwości mechaniczne oraz zmiany temperatury polimeru z pamięcią kształtu w procesie rozciągania

摘要

W pracy zawarto opis podstawowych właściwości, przykłady zastosowań oraz wyniki badań efektów sprzężeń termomechanicznych poliuretanu z pamięcią kształtu w procesie rozciągania. Otrzymane charakterystyki mechaniczne i temperaturowe wskazują na dużą wrażliwość tego polimeru na prędkość deformacji. Wykorzystując efekt termosprężysty wyznaczono granice odwracalnego odkształcenia (plastyczności) dla różnych prędkości odkształcania. Pokazano, że metoda bazująca na minimum temperatury próbki pozwala na wyznaczenie granicy plastyczności z dużą dokładnością, w tym materiałów wykazujących nieliniową sprężystość.%Mechanical properties and temperature changes of a new multifunctional material - polyurethane shape memory polymer (PU-SMP) subjected to tension at room temperature with various strain rates are presented (Figs. 1-3), [1, 2], The stress and strain data were recorded by an MTS 858 testing machine. The temperature changes were measured by a fast and sensitive infrared camera ThermaCam Phoenix. Basing on the obtained mechanical and corresponding temperature data, experimental effects of thermomechanical couplings occurring in the SMP during loading were studied (Figs. 4-7). The stress and temperature changes vs. strain obtained for tension with strain rates 2×10~(-1)s~(-1) and 2×10~0s~(-1) until the sample rupture show that the SMP exhibits a hardening-like behavior and its elongation limit is over 180 % in case of the true strains (Figs. 4, 5). The higher strain rate, the higher temperature changes were recorded, since the mechanisms of deformation occurred very fast and the process was more close to adiabatic conditions. The significant temperature changes, accompanying the SMP loading with higher strain rate, influence the SMP mechanical behavior. Namely, a maximum of the stress value was recorded at the advanced loading stage, followed by its drop and increase preceding the sample rupture (Fig. 5). The initial reversible tension of any solids is accompanied by a temperature decrease, called thermoelastic effect, whereas the following plastic deformation is always related to energy dissipation and increase in the sample temperature [3-5]. Thus, the maximum drop in temperature of the sample subjected to tension indicates a limit of the reversible material deformation. The higher strain rate, the higher drops in temperature for the SMP were recorded and the larger values of the yield point for the polymer were obtained (Figs. 6, 7), [9,10].