Some problems in the measurement of stress-strain curves for thermoplastics are considered and the importance of measuring true stress-strain curves is emphasized. However, an increasing number of suitable curves have now been published of which the large majority have been found to comply with the following Gaussian equation: Otru? = Y+ Gp(22 - !/,~) where atrue is the true stress, Y is the extrapolated yield stress, Gp is the strain hardening modulus and 2 is the extension ratio. It is shown that the Considere condition for necking requires that Y/Gp> 3 and the available results support the proposition that this is a necessary condition for necking to occur. High values of Gp are observed in polymers with an extended chain conformation.
Посилання на статтю:
The derivation of a strain hardening modulus from true stress-strain curves for thermoplastics / R. N. Haward // Polymer. – 1994. – Vol 35. – P. 3858-3862.