The nonlinear viscoelasticity and its asymmetry of UV-cured resin under large amplitude oscillatory axial (LAOA) loading

Abstract

Solid viscoelastic materials often undergo large amplitude oscillatory axial (LAOA) loading and exhibit complex asymmetric nonlinear viscoelasticity in many practical applications. The methods used to analyze the nonlinear viscoelasticity of non-Newtonian fluid under large amplitude oscillatory shear (LAOS) cannot be directly applied to the corresponding situation of solid viscoelastic materials due to strict symmetry of LAOS. In this work, a typical UV-cured resin mainly used for 3D printing is chosen to investigate the nonlinear viscoelasticity and its asymmetry under LAOA loading. Based on Fourier transform, the geometric description of stress–strain curve is used to quantitatively characterize the asymmetric nonlinear viscoelasticity. Further, the global asymmetry ratios of nonlinear viscoelasticity under LAOA loading are developed based on the sequence of physical process (SPP) approach throughout the entire oscillatory cycle. We also define an asymmetric ratio of nonlinear viscoelasticity with clear physical meaning from the perspective of energy, which can comprehensively characterize the nonlinear elastic and viscous behavior during the tensile and compressive phases within an oscillatory cycle. Besides, the influences of oscillatory frequency and UV exposure time on asymmetric nonlinear viscoelasticity of UV-cured resin under LAOA loading can be captured as well. These approaches are suitable for evaluating the asymmetric nonlinear viscoelasticity of a large category of viscoelastic solid materials under LAOA loading, which is crucial for analyzing the nonlinear viscoelastic mechanism and for corresponding engineering applications.