Fig. 6. Force–length isotherms are plotted to demonstrate the force correction for a typical thermoelastic test of Araneus MA silk at an extension of 27%. (A) The force on a fibre at a relative length of 1.27 is plotted for temperatures of 283 K (reference temperature) and at 298 K. The dashed line shows the regression between the force measured at 298 K and a relative length of 0.99, which was calculated based on the thermal swelling coefficient of 1x10^–4°C^–1 for Araneus MA silk. Owing to the small value of the correction, the uncorrected and corrected isotherms are difficult to distinguish. (B) The force at a relative length of 1.27 is measured at 283 K (reference temperature) and at 298 K. At the reference temperature of 283 K, the relative length at zero force is 1.0 and a relative length of 1.27 is equivalent to an extension of 27%. However, with a thermal swelling coefficient of –1x10^–2°C^–1, the zero force length at 298 K is reduced to 0.85. This occurs because, at 298 K, the initial length has decreased because of a thermal de-swelling, and thus the extension of the fibre has increased. At 298 K, an extension of 27% occurs at a relative length of 1.08. The linear regression between the measured force and the zero force length (dashed line) is solved at 1.08 to determine the force at a constant extension of 27%, and is represented by the black triangle. An exaggerated thermal swelling coefficient of –1x10^–2°C^–1 was chosen to better demonstrate the correction process.