### Abstract

Many models use the equilibrium stress, also sometimes known as the back stress, in characterizing the response of both polymeric and non-polymeric materials. We study the characteristics of the equilibrium and show that the tangent modulus and local Poisson's ratio at equilibrium both are rate independent for common modeling assumptions. This fact is used to propose a method based on uniaxial tension or compression to measure the equilibrium stress, and the associated point's tangent modulus and local Poisson's ratio. The method is based on cyclic loading and identification of similar states with vastly different loading rates. The method is used to characterize the equilibrium stress in glassy polycarbonate, and the results are studied in regard to the possible error for such a measurement. The method is faster than most other proposed methods for calculating the equilibrium stress, and provides additional measurements of parameters at equilibrium that are normally not obtained.

Original language | English (US) |
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Pages (from-to) | 709-716 |

Number of pages | 8 |

Journal | Proceedings of the Society for Experimental Mechanics, Inc. |

Volume | 67 |

State | Published - 2010 |

### Keywords

- Back stress
- Compression
- Cyclic loading
- Equilibrium stress
- Error analysis
- Glassy polymers
- Local Poisson's ratio
- Polycarbonate
- Tangent modulus
- Uniaxial testing

### ASJC Scopus subject areas

- Mechanics of Materials
- Mechanical Engineering

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## Cite this

*Proceedings of the Society for Experimental Mechanics, Inc.*,

*67*, 709-716.