Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE This study shows that PMMA heats up in clear and informative ways as it is repeatedly compressed. Before it finally yields, its temperature passes through several distinct stages and leaves behind unrecovered heat after each cycle. These temperature stage patterns closely correspond to the changes in the material's deformation.

ABSTRACT
The thermal response of polymethyl methacrylate (PMMA) during deformation is highly relevant to its mechanical properties. In this study, temperature observation experiments were conducted on PMMA under uniaxial tiered cyclic loading. The temperature change characteristics and their mechanisms before yielding were investigated based on dissipated energy. The deformation of PMMA before yielding can be subdivided into four stages: linear elastic deformation, nonlinear deformation, pre–yielding, and yielding stage. Heat generation in loaded PMMA mainly includes the thermoelastic effect, viscous dissipation effect, and thermoplastic effect. Both viscous dissipation effect and thermoplastic effect cause the temperature and stress to deviate from linearity. The temperature decrease exhibits hysteresis relative to the stress under the unloading condition. The temperature hysteresis at low stress levels can be attributed to viscous deformation, while at high stress levels, it is primarily due to plastic deformation. Besides, some “irrecoverable temperature” cannot be recovered at the end of each cycle. The significant stage characteristics of the irrecoverable temperature are highly consistent with the deformation. This study suggests that temperature is an important parameter for reflecting the PMMA properties, and provides a new idea for monitoring and identifying the deformation regimes of the PMMA.