How to Characterize Damage in DMA Measurements

The storage modulus can be influenced by many factors, for example morphological damage or the time- and stress-dependent behavior of polymers. In this report, we investigate how DMA can be used as simple and effective tool to distinguish between these effects.

For long-term applications of polymers, there are several causes for the loss of mechanical integrity. On the one hand, components under constant loading can suffer from creep effects, which are ultimately caused by the time-dependent behavior of polymers. On the other hand, the slow accumulation of microscopic damage can also lead to the loss of mechanical performance. Defects such as micro-cracks, crazes etc. reduce the internal load-bearing cross-section, so that stiffness and strength on a macroscopic level are reduced. Additionally, polymeric materials can have a non-linear viscoelastic response to elevated stresses. As a result, the measured storage modulus, Eʹ, is reduced when a certain stress limit is surpassed. Distinguishing between these mechanisms and investigating each one separately is no easy task. However, in this report we utilize DMA as simple and effective tool to characterize different mechanisms, that lead to the reduction of the Eʹ.

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