Loading-rate dependent Poisson's ratio of polyurethane auxetic foams at different loading strains; a user-defined material model and experimental verification

Behbahani, Ali; Nourani, Amir

doi:10.24200/sci.2025.64578.9043

Loading-rate dependent Poisson's ratio of polyurethane auxetic foams at different loading strains; a user-defined material model and experimental verification

Articles in Press

Document Type : Research Article

Authors

Ali Behbahani

Amir Nourani

Department of Mechanical Engineering, Sharif University of Technology, Azadi Ave, Tehran, Iran

10.24200/sci.2025.64578.9043

Abstract

This study investigated the combined effects of loading rate and applied strain on the behavior of auxetic materials and developed a user-defined material model to capture these effects during loading. First, test specimens were made of conventional polyurethane foams according to ASTM D-3574; then, with a thermo-mechanical process, the conventional foam was converted to auxetic polyurethane foam. Tensile experiments were conducted by applying different strains (i.e., 10, 40, and 80%) and loading rates (i.e., 0.01, 1, and 5 s^-1). Displacements were tracked during the tests by digital image correlation. Statistical analysis using analysis of variance (ANOVA) showed that both strain and loading rate significantly affect Poisson’s ratio (p˂0.0001). It was also found that transient strain auxeticity (TSA) depends on the applied loading rate. The user-defined material was developed from the experiments and used in a finite element model (FEM) to capture Poisson's ratio variations because of changing loading circumstances. The model's predictive ability (i.e., the model's validity) was examined by performing different experiments (i.e., different from those used for developing the model), showing a maximum difference of 10% compared to measured Poisson’s ratio-strain curves from experiments.

Keywords

Auxetic

Foam

Poisson’s ratio

Strain

Loading rate

Strain rate

Experiments

FEM

statistical analysis

Subjects