Monday  |  Salon 10  |  01:50 PM–02:10 PM

#15798, Inverse Identification of Time-Domain Linear Viscoelastic Constitutive Parameters in Polymers with the Image Based Inertial Impact Test

Polymers typically exhibit a strong time dependence in their mechanical response and are often used in applications in which they may be subjected to impulsive loading. Thus, understanding the viscoelastic constitutive response on the timescales relevant to impact loading is critical for the design and evaluation of these polymer structures. However, direct measurement of these viscoelastic constitutive parameters on microsecond timescales at room temperature has proven challenging. Typical dynamic viscoelastic characterization experiments, such as dynamic mechanical analysis, often rely on assumptions such as an assumed form of time-temperature superposition to extract viscoelastic parameters on these short time scales. Additionally common high-rate characterization experiments, such as Kolsky-bars, must satisfy stringent requirements like dynamic force equilibrium, making them poorly suited to the characterization of viscoelastic properties. In recent years, the Image Based Inertial Impact (IBII) test has been used to characterize linear elastic materials, at high strain rates, through leveraging inertial effects measured with quantitative full-field imaging techniques with the virtual fields method (VFM). Additionally, a computational investigation utilizing a digital virtual twin approach has demonstrated the ability of the IBII experiment to determine viscoelastic material parameters on microsecond timescales without the need to assume a time-temperature superposition. Here we present an experimental validation of viscoelastic constitutive parameter identification with the IBII test. IBII experiments were performed on two polymers, polymethyl methacrylate (PMMA) and Acrylonitrile butadiene styrene (ABS), and the viscoelastic response was modelled using the generalized Maxwell model for viscoelasticity. Specimen deformation was measured using ultra-high-speed imaging and the grid method, and viscoelastic parameter identification was performed with the stress gauge formulation of VFM. These experiments demonstrate the ability of the IBII technique to directly measure viscoelastic constitutive parameters at room temperature and on impact-relevant time scales without the need to satisfy the stringent experimental requirements and assumptions of classical dynamic tests.

Andrew Matejunas   Colorado School of Mines
Lloyd Fletcher   United Kingdom Atomic Energy Authority
Leslie Lamberson   Colorado School of MInes