A computer program for interconversion between creep compliance and stress relaxation

Numerical interconversion of linear viscoelastic functions is an important problem in rheology. This work focuses on interconversion between creep compliance (J) and relaxation modulus (G) via the convolution relation. A discrete spectrum or Prony series is used to describe both the source (G or J) and the target (J or G) of the interconversion. A previously developed numerical template [Loy et al.,J. Rheol.59(5), 1261 (2015)] is modified to bypass singularities. It is released as an open-source computer program called PSI (Prony series interconversion). PSI is tested on a variety of materials including viscoelastic solids and liquids and used for both G→J and J→G interconversions. It is fast and numerically stable for input data that span over 20 decades in time. It fills a gap in the existing software landscape for conversion of linear viscoelastic functions.