Homogeneous-internal damage detection in an epoxy-amine system through the use of the continuous relaxation spectrum

In the last 10 years, a new class of materials has been developed and is being further improved nowadays: the class of self-healing materials. This category of bio-inspired materials is potentially capable of repairing structural or functional damage in different ways, increasing the material lifetime. Polymers are the most studied material class in the field. For a better design of this material,it would be of enormous importance to detect and quantify the invisible internal damage occurring inside a polymer in order to value the healing efficiency before the ultimate failure. However, most of the avail??able scientific literature focuses on macroscopic and optically detectable damage. In this work, the continuous relaxation spectrum, obtained using rheology data, is used to analyze the dynamic behavior of an epoxy-amine system in both pristine and damaged states. The invisible damage is strain-induced, after the yield point, via tensile test. The spectrum was already used for the same purpose to analyze damage degree and damage restoration in a self-healing polymer network with dynamic sulfur??sulfur bonds, but some contradictions in the results were found. In order to understand the technique’s ability to detect damage and exclude it from results variation, the uncertainty due to experimental errors, and time-dependent effects of a non-healing system are examined. Material ageing, heterogeneity, and residual stresses from curing are found to be the most probable influence factors in CRS deviations. The technique confirms itself to be a very sensitive instrument and for this reason, better knowledge about the samples’ network (chemistry, defects, cross-linking %) would be necessary to really understand the obtained data. It is not excluded that a different interpretation of the curve (and curve parameters chosen to compare the spectra) could lead to a more detailed phenomena explanation.