Rheologically complex materials are described by function-valued properties with dependence on a timescale (linear viscoelasticity), input amplitude (nonlinear material behavior), or more generally both (nonlinear viscoelasticity). This complexity presents a difficulty when trying to utilize these material systems in engineering designs. Here, we focus on linear viscoelasticity and a methodolog...

In this work, and based on numerical optimization techniques, constitutive parameters for viscoelastic materials are determined using a inverse problem formulation. The optimization methodology is based on experimental results obtained in the frequency domain, for a CFRP-Carbon Fibre Reinforced Polymer, through DMA-Dynamic Mechanical Analysis. The relaxation modulus of viscoelastic materials is...

An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and c...

PURPOSE Fiber-reinforced composite (FRC) posts have gained much interest recently and understanding of their viscoelastic properties is important as they can be used in stress-bearing posterior restorations. The aim of this study was to evaluate the creep behavior and the viscoelastic properties of four commercial FRC posts under different temperatures and different storage conditions. METHOD...

We extend the linear “stick-slip” models of Doi-Edwards and Johnson-Stacer to nonlinear tube reptation models. We then show that such models, when combined with probabilistic formulations allowing distributions of relaxation times, provide a good description of dynamic experiments with highly filled rubber in tensile deformations. A connection to other applications including dielectric polariza...

In this thesis, we seek to outline a methodology to enable engineering design based on rheologically complex materials. Traditionally, engineers choose hard materials or simple uids for design. Complex materials (soft solids and non-Newtonian uids) greatly increase the design space. Additionally, these materials add functionality (viscoelasticity, nonlinearity) that can achieve diverse performa...

A general closed expression is given for the isothermal minimum free energy of a linear viscoelastic material with continuous spectrum response. Two quite distinct approaches are adopted, which give the same final result. The first involves expressing a positive quantity, closely related to the loss modulus of the material, defined on the frequency domain, as a product of two factors with speci...

Mesophase pitches are multicomponent discotic nematic liquid crystals (DNLCs), whose characteristic molecular weight is intermediate between low molar mass and polymeric nematic liquid crystals. The distinguishing features of the mechanical behavior can be summarized by stating that LC materials exhibit anisotropic, non-linear, viscoelastic behaviour quite distinct from Newtonian viscous materi...

In this paper, we present a theoretical analysis of the propagation of acoustic waves through elastic and viscoelastic two-dimensional phononic crystal structures. Numerical calculations of transmission spectra are conducted by extending the finite-difference-time-domain method to account for linear viscoelastic materials with time-dependent moduli. We study a phononic crystal constituted of a ...