Temperature, loading rate and stress triaxiality effects on tensile failure of polymethyl methacrylate (PMMA)

Due to its low density and excellent transparency, polymethyl methacrylate (PMMA) is increasingly employed in structural components such as aircraft canopies, spacecraft viewports, and automotive windows. During service, PMMA structures are subjected to varying temperatures, loading rates, and stress states, which can significantly affect their mechanical integrity. Therefore, a failure investigation on two typical PMMAs is conducted under a wide range of conditions, including temperatures (293 K, 333 K and 373 K), strain rates (10^-3 s⁻¹, 10^-1 s⁻¹, and 10⁰ s⁻¹), and multiple stress triaxialities achieved via different tensile specimen geometries. The results indicate that the ultimate tensile strength decreases linearly with increasing temperature, with a temperature sensitivity that is strongly influenced by the prevailing stress triaxiality. Both PMMA grades exhibit clear strain rate sensitivity, where the ultimate strength correlates linearly with the logarithm of the strain rate. Fractographic analysis using scanning electron microscopy (SEM) reveals distinct failure mechanisms that depend on temperature, strain rate, and stress state. Based on the experimental data, a comprehensive failure model for PMMA is proposed, incorporating these coupled effects. This study can provide valuable insights for the mechanical testing and engineering application of PMMA under complex service conditions.