Dynamic properties of ultraviolet-exposed polyurea

Polyurea is used for military and civilian applications and long-term exposure to the sun is coming. Long-term exposure to solar ultraviolet radiation will reduce its mechanical properties to sub-optimal levels. This study reports the relationship between the dynamic mechanical properties of polyurea and the duration of UV exposure. I continued to irradiate the samples of 6 groups for up to 18 weeks. Control samples that were not exposed to ultraviolet radiation were also tested. Dynamic characteristics were measured using a dynamic mechanical analyzer. After 18 weeks of exposure, the exposed samples showed significant color change from clear yellow to opaque tan. Changes in color were observed as early as 3 weeks. The kinetics showed an initial increase in dynamic modulus after three weeks of exposure, followed by no further significant change in stiffness. Ultraviolet irradiation has a significant influence on the relatively short loading time or low temperature, for example up to 60 years. Ultraviolet exposure and performance effects on temperature become closely related as performance time increases or as polyurea operates at high temperature.

Polyurea is widely used for military and civilian use and is generally exposed to sunlight for a long time. Long-term UV exposure can reduce the mechanical properties of the material to sub-optimal levels. This study reports the relationship between the superelastic behavior of polyurea and the duration of ultraviolet rays. Initially, five groups of samples were continuously exposed to ultraviolet radiation for different periods up to 15 weeks. Other sets of samples were not exposed to report the properties of the as-cast polyurea control. Then uniaxially stretch the sample with a quasi-static loading speed (\ (\ dot {\ epsilon} = 0.0127 {s} ^ {- 1} \)) using a standard loading frame. All exposed samples showed an increase in color change in the range from clear yellow in the first sample to opaque tan after 15 weeks exposure. Changes in color were observed as early as 3 weeks after UV irradiation

This study shows that the mechanical properties of polyurea's low strain rate are a function of the duration of ultraviolet irradiation. The polyurea sample was cast and continuously exposed to UV radiation for 15 weeks to simulate direct sunlight exposure of about 9,200 hours. Each sample (unexposed and exposed) was uniaxially tested according to ASTM D 638-8 with semi-static tension. Stress-strain data were used to calculate the elastic modulus of polyurea, 0.2% offset yield stress, shear modulus and stress at 250% strain. In addition, the optical properties and surface topology change of polyurea were investigated using ultraviolet - visible spectroscopy (UV - Vis) and scanning electron spectroscopy (SEM), respectively. Finally, we apply stress-strain data to Ogden's superelastic model. The change in Ogden's fitting parameter is due to the duration of UV exposure

Polyurea is used for military and civilian applications and long-term exposure to the sun is coming. Long-term exposure to solar ultraviolet radiation will reduce its mechanical properties to sub-optimal levels. This study reports the relationship between the dynamic mechanical properties of polyurea and the duration of UV exposure. I continued to irradiate the samples of 6 groups for up to 18 weeks. Control samples that were not exposed to ultraviolet radiation were also tested. Dynamic characteristics were measured using a dynamic mechanical analyzer. After 18 weeks of exposure, the exposed samples showed significant color change from clear yellow to opaque tan. Changes in color were observed as early as 3 weeks. Dynamic properties show an initial increase in dynamic modulus after 3 weeks of exposure, after which there is no significant change in stiffness any more.