Experimental study on the tension and puncture behavior of spray polyurea at high strain rates

Polyurea is widely used as a protective coating material for structures subjected to impulsive loads. In this study, the mechanical properties of polyurea were investigated experimentally over a wide range of loading rates. Firstly, quasi-static tests were performed using conventional hydraulic machine at strain rates of 7.7 x 10(-4) - 7.3 x 10(-3) s(-1) for direct tension and at speeds of 1.67 x 10(-5 )- 1.67 x 10(-4) m/s for puncture. Then high-speed tests were carried out using a high-speed servo-hydraulic testing machine (INSTRON VHS 160/100-20) at strain rates of 3.3-500.3 s(-1) for direct tension and at speeds of 0.1-10 m/s for puncture. Deformation and failure processes of the polyurea specimens under high-speed tension were recorded with the aid of a high-speed camera. The testing results show that polyurea is a strain rate sensitive material. Under tensile loads, the initial yield stress and the strength increase with the increment of the strain rates while the fracture strain decreases. Under puncture loads, the yield force and the strength of the polyurea sheets also increase with loading rates. However, the strain rate effect on the failure deformation of the polyurea is only observed when the loading rate is less than 2 m/s. Based on the testing data, mechanism that causes the dynamic effect of polyurea material properties was discussed and some empirical relations were derived for engineering applications.