The unusual effect of temperature on stress relaxation and mechanical creep of polycarbonate at low strain and stress levels

The effects of temperature, strain level during stress relaxation tests and stress level during mechanical creep tests on the viscoelastic characteristics of polycarbonate films were investigated. When the testing temperature increased the un-relaxed elastic modulus was found to increase during relaxation tests (at low strain levels <2.0%) and the initial strain was found to decrease during creep tests (at low stress levels <20 MPa), in an unusual behavior. A transition from poly-domain to a more coiled and more entangled chains poly-domain configuration took place at low strain and stress levels. At high strain and stress levels (⩾ 2.0% and ⩾20 MPa) a usual behavior of the un-relaxed stress and initial strain was observed and a transition from poly-domain to mono-domain configuration took place. The thermal energy required for the transition from poly-domain to another poly-domain and from poly-domain to the mono-domain during both relaxation and creep tests were calculated. Besides, both the relaxation and creep strengths were calculated and studied.

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► The un-relaxed elastic modulus increases with temperature at low strain levels (<2.0%).
► The relaxation strength increases linearly with increasing temperature.
► The initial strain increases with temperature at low stress levels (<20 MPa).
► The creep strength increases exponentially with temperature.