Applicability of the time–temperature superposition principle in modeling dynamic response of a polyurea

Abstract

This paper addresses the applicability of the Time-Temperature Superposition Principle in the dynamic response of a polyurea polymer at high strain rates and different temperatures. Careful and extensive measurements in the time domain of the relaxation behavior and subsequent deduction of a master-relaxation curve establish the mechanical behavior for quasistatic deformations over a time range of 16 decades. To examine its validity in a highly dynamic environment, experiments with the aid of a split Hopkinson (Kolsky) pressure bar are carried out. The use of a two-material pulse shaper allows for stress equilibrium across the specimen during the compression process, to concentrate on the initial, small deformation part that characterizes linearly viscoelastic behavior. This behavior of polyurea at high strain rates and different temperatures is then investigated by comparing results from a physically fully three-dimensional (axisymmetric) numerical model, employing the quasistatically obtained properties, with corresponding Hopkinson bar measurements. The experimentally determined wave history entering the specimen is used as input to the model. Experimental and simulation results are compared with each other to demonstrate that the Time-Temperature Superposition Principle can indeed provide the requisite data for high strain rate loading of viscoelastic solids, at least to the extent that linear viscoelasticity applies with respect to the polyurea material.

High Strain Rate Mechanics of Polymers: A Review

“…Materials which have been well-studied in the literature are silicone elastomers [13,66,151], plasticized PVC [152,153] and polyureas [39,40,72,[154][155][156][157][158][159] and polyurethanes [160][161][162]. The rate dependence of these materials depends strongly on the glass transition, and in particular whether this transition affects the room temperature response at strain rates of interest.…”

Simulation of polyurea shock response under high-velocity microparticle impact

“…The EOS was fit to Hugoniot and quasi-isentrope data [8,[11][12][13][14] as well as thermophysical information [5]. The master relaxation curve describing thermo-viscoelasticity was fit to isothermal relaxation data [4,6]. The pressure-sensitivity was fit to shearing resistance data derived from pressure-shear plate impact (PSPI) experimental data [8], and was also guided by molecular dynamics simulations [15].…”

“…The current experimental database for polyurea P1000 is reasonably established for relatively simple loadings and up to just above room temperature [1][2][3][4][5][6], but characterization under extreme conditions is much more limited. A constitutive model has been specifically developed for this polyurea, with particular attention given in its development to features intended to address the aforementioned complexities seen in its shear response.…”

Structure Evolution in a Polyurea Segmented Block Copolymer Because of Mechanical Deformation

“…39 Such thermorheological complexity is apparently not evident in the corresponding stress relaxation measurements. 9 …”

“…21 Determination and interpretation of the morphological response to high strain rates are necessary for fundamental understanding of the performance. A number of studies have been carried out to measure the viscoelastic properties of PU: Boyce and co-workers 7,8 and Zhao et al 9 conducted split Hopkinson bar measurements at compressive strain rates as high as 10 4 s -1 on the material of interest herein. Jiao et al 6 used a pressure-shear impact plate to measure the response at shear rates between 10 5 and 10 6 s -1 .…”