Time-dependent nanoindentation behavior of high elastic modulus dental resin composites

Abstract

Nanoindentation and the viscous-elastic-plastic (VEP) model developed by Oyen and Cook for lightly filled thermoplastic polymer composites were used to characterize the elastic modulus, hardness, and viscoelastic response of a new high elastic modulus dental resin composite. The VEP model was used because loading rate studies indicated a viscous component in the loading/unloading response of our highly filled, thermosetting acrylic resin composites. Increasing the volume fraction of our high modulus filler increased the elastic modulus and hardness and decreased the viscous response in our composites. Coupling the filler and resin matrix with a commercial coupling agent like Metaltite or MPTMS (3-methacryloxypropyltrimethoxysilane) that ionically bonds to the filler and covalently bonds to the matrix decreases the viscous response and increases the hardness of the composite. The coupling agents did not affect the elastic modulus. The ability of the VEP model to predict load-displacement trajectories and the correlation of the elastic modulus and hardness values determined from the VEP model with those from the direct continuous stiffness measurement mode nanoindentation measurements indicate that the VEP model can be extended to highly filled, thermosetting systems. This is valuable since the potential to predict elastic, plastic, and viscous contributions to behavior should be valuable in the design and understanding of future highly filled resin composite systems.

Using the Kelvin–Voigt model for nanoindentation creep in Sn-C/PVDF nanocomposites

“…The moduli presented in Table 1 are within these ranges, with the observed variation possibly associated with variations in the local volume fraction of the carbon. The values for viscosity reported in Table 1 are consistent with a previous study regarding creep measurements of PVDF solid films, which provided stress/strain rate ratios, suggesting a viscosity in the range of 10 11 –10 12 Pa s. 21…”

“…1 Significant focus from the mechanics community is given on using this technique for determining the hardness of materials, 2,3 dislocation motion, 4 fracture of thin films 5 and the effect of the tip on the hardness. 6,7 Recent nanoindentation studies [8][9][10][11] focus on capturing and modelling creep in a variety of materials. The present study is concerned with Sn-C nanopowders that are mixed with polyvinylidene fluoride (PVDF) polymer to prepare a slurry and then left to dry on a Cu foil.…”

Mapping viscoelastic and plastic properties of polymers and polymer-nanotube composites using instrumented indentation

“…The quadratic Maxwell VEP model above was reasonably successful in a quantitative sense: the material properties H , M , and τ inferred from fits of the model to triangular load spectra, specifically fits to the unloading response in which all three displacement components are distinct, were in agreement with other measurements; 1,2,5 the ability of the model to predict loading behavior from unloading behavior was excellent; 1,2,4,5,8 and, the material properties inferred using a triangular load spectrum at a reference time- or load-scale could be used to predict the triangular responses for indentation time scales factors of three shorter or longer than the reference and indention load scales factors of ten different from the reference. 1,2,4,8 The limitations of the quadratic Maxwell VEP model are apparent in comparisons of observed and predicted behavior during constant-load creep, a test method that focuses on the time-dependent constitutive behavior.…”

“…(10)) were developed. Similar validations are often performed, 1,2,4,8,18–20 but often not, especially when viscoelastic correspondence methods are used to analyze measurements. 3,9,12,13,16,17 In this regard, it is to be noted that for non-simple loading protocols or those with multiple stages, the integrand of the general displacement integral (Eq.…”

“…1,2,4,8 The limitations of the quadratic Maxwell VEP model are apparent in comparisons of observed and predicted behavior during constant-load creep, a test method that focuses on the time-dependent constitutive behavior. The free viscous element, meaning that it has no element constraining it in parallel, of the quadratic Maxwell VEP model leads to unbounded displacement increasing linearly with time for an imposed constant load and an instantaneous displacement recovery on load removal.…”