Abstract
Nonlinear material response is analysed with the Fourier transform (FT) of the raw signal measured by a high-frequency dynamic mechanical analyzer (HF DMA). It is known from rheological behaviour of elastomers that reinforcing fillers additionally induce nonlinearity in an already inherently nonlinear system. This behaviour is often described in terms of a mechanical response of strain sweeps, essentially the transition from the linear viscoelastic (LVE) to the nonlinear viscoelastic (NVE) region. In the current investigation, the NVE region could be observed with respect to frequency under low-amplitude deformation. A foldover effect was observed, whereby the material exhibited a nonlinear dependency in relation to the increment of the filler amount above the percolation threshold. In addition, an apparent superharmonic resonance was observed within higher orders of vibrational modes which is further indication of nonlinearity. In this paper, the analytical approach is presented as a novel method to characterise the behaviour of the polymer–filler interaction by HF DMA.
Highlights
Rubber is one of the most prevalent among the materials in our daily life that exhibit mechanical nonlinearity
The main advantage of this device is the ability to measure frequencies up to 10 kHz, which is not possible with a traditional dynamic mechanical analyzer (DMA) device. This DMA is a type of forced vibration resonant system, according to ASTM D5992 [12], essentially using the resonance principle to evaluate the mechanical response of the material
The nonlinear material response induced by the nanocomposite fillers was analysed by a high-frequency DMA
Summary
Rubber is one of the most prevalent among the materials in our daily life that exhibit mechanical nonlinearity. Even with this familiarity, deep understanding of this material remains a substantial challenge to this very day. After a certain strain threshold the modulus drops significantly with respect to the applied amplitude. This is mainly due to the rearrangement of the polymer chains with respect to the external applied force, and is reflected in the stress–strain curve, where the mechanical response portrays a non-Hookean behaviour [2]. The breakdown of this filler network is described as the so-called “Payne effect” [4]
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