AbstractsEngineering

The effect of ultraviolet radiation on the acoustic, thermal and dynamic mechanical properties of polyurea

by Ian Whitten




Institution: California State University – Northridge
Department: Department of Mechanical Engineering
Degree: MS
Year: 2015
Keywords: Polyurea; Dissertations, Academic  – CSUN  – Engineering  – Mechanical.
Record ID: 2060974
Full text PDF: http://hdl.handle.net/10211.3/134181


Abstract

Polyurea is used in military and civilian applications where exposure to the sun in long durations is common. Extended exposure to ultraviolet (UV) radiation from the sun can deteriorate its mechanical performance to suboptimal levels. This study reports on the acoustic, thermal and dynamic mechanical properties of polyurea as a function of ultraviolet radiation exposure duration. Six sets of samples were continuously exposed to ultraviolet radiation for different durations up to 18 weeks. Control samples were also tested that did not receive UV exposure. The acoustic properties were measured using high-frequency contact ultrasound transducers in pitch-catch configuration. The dynamic properties were measured using a Dynamic Mechanical Analyzer while thermal properties were measured using a Thermo Gravimetric Analyzer. All samples exhibited significant color changes from transparent yellow to opaque tan after 18 weeks of exposure. Changes of color were observed as early as 3 weeks of UV exposure. The effect of extended UV radiation on the acoustic properties was noted to be minimal, where elastic and shear moduli decreased monotonically after initial increase during the first 3 weeks of exposure. The attenuation and mechanical properties were measured at 23??C and 40??C. The p-wave attenuation did not show any notable change, while the s-wave attenuation monotonically decreased as the temperature and UV exposure duration increased. The elastic and shear moduli also decreased with an increase in temperature. The dynamic properties showed an initial increase in the dynamic modulus after 3 weeks of exposure, with no further significant change in the stiffness thereafter. The thermal stability was negatively affected by the UV radiation with an increase in the amount of decomposition seen at the upper end of the operating range for polyurea.