# Novel test method to measure time-cure superposition shift factors of filled-thermoset under isocure testing conditions

## TL;DR

This paper introduces a new method to accurately measure time-cure superposition shift factors under isocure conditions, improving the reliability of the theoretical model.

## Contribution

A novel test method is proposed to measure TCS shift factors under isocure conditions, solving issues with existing techniques.

## Key findings

- The proposed method produces excellent overlaps in master curves across the entire curing range.
- The validity of time-cure superposition and applicability of time–temperature superposition to partially-cured specimens are confirmed.
- The method is implemented successfully for an epoxy-based molding compound.

## Abstract

Despite the solid theoretical foundation of time-cure superposition, the time-cure superposition (TCS) shift factors reported in the literature do not support the theory very well. The discrepancy stems from the non-isocure test conditions used in the tests. This study proposes a novel method to eliminate the inherent problems of existing techniques to measure the TCS shift factors, i.e., to measure them under isocure test conditions. The proposed method optimizes a test procedure while offering sufficient relaxation but producing no or negligible additional curing during testing. Optimization requires a complete understanding of curing behavior not only in the chemically-controlled domain but also in the diffusion-controlled domain. The method is implemented for an epoxy-based molding compound. Portions of the storage master curves are obtained at four partially-cured states \documentclass[12pt]{minimal}
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\begin{document}$$(p = 0.6, 0.7, 0.8, 0.9)$$\end{document}(p=0.6,0.7,0.8,0.9), and they are normalized by the corresponding equilibrium modulus. The normalized curves are subsequently shifted to determine the TCS shift factors using the master curve of fully-cured specimen as a reference. The results show excellent overlaps over the entire curing range after shifting, corroborating that the proposed method is accurate and effective. Validity of the time-cure superposition and applicability of the time–temperature superposition to partially-cured specimens are also confirmed using the test data used to determine the TCS shift factors as well as additional test data.