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In this work, the stress relaxation behavior of 3D printed PLA was experimentally investigated and analytically modeled. First, a quasi-static tensile characterization of additively manufactured samples was conducted by considering the effect of printing parameters like the material infill orientation and the outer wall presence. The effect of two thermal conditioning treatments on the material tensile properties was also investigated. Successively, stress relaxation tests were conducted, on both treated and unconditioned specimens, undergoing three different strains levels. Analytical predictive models of the viscous behavior of additive manufactured material were compared, highlighting and discussing the effects of considered printing parameters. [ABSTRACT FROM AUTHOR]

Predictive models play an important role for increasing the reliability of composite structures over time, but a great deal of experimental data is requested. In this paper, results from creep experiments on uniaxial E‐glass fiber reinforced polymer (FRP) single ply laminates, performed at different stress levels, are presented. The tests duration was of 42 months. Analytical modeling of the viscous behavior of the tested GFRP composite, under linear and nonlinear viscoelastic hypotheses, is reported. A discussion on the comparison of creep strain response by Burgers model, with parameters obtained from fitting of data for different test duration, is also proposed. Finally, predictive finite element method (FEM) simulations were carried out for discussing the deferred behavior induced by creep, for composite layers used for repair purposes in hydrogen transportation pipes. Numerical results highlighted a non‐negligible difference in creep strain values, pointing out that a model based on experimental tests with shorter duration leads to a conservative composite design. [ABSTRACT FROM AUTHOR]