An experimental study with corresponding numerical simulations has been conducted to evaluate the response of E-Glass / Epoxy composite plates, including polyurea coating effects, subjected to near field underwater explosion (UNDEX) loading. Experiments are performed in a water filled blast tank in which the including transient plate response during the UNDEX loading is measured utilizing high speed photography coupled with Digital Image Correlation. The experimental results show that the transient response of the plate is improved through the use of a thicker plate or through the application of a polyurea coating, although there is a weight penalty associated with the additional material which should be considered. Corresponding computational models of the experiments have been conducted with the commercial finite element code LS-Dyna. The simulations are shown to have a high level of correlation to the experimental data.

Shape memory polymers (SMP) are used in the 3D printing field for different applications such as soft robotics or medical devices. Although this technology has expanded the capabilities of additive manufacturing, there still exists fundamental questions regarding the optimum condition for manufacturing these 3D printed parts. Various factors play a crucial role in the final quality of printed parts, such as deposition orientation, percentage infill, or environmental conditions. In this paper, we study the effect of humidity on commercially available SMPs (NinjaFlex©) at both micro- and macro-scale. By performing a 3-dimensional computational fluid dynamic model for the printing environment, it is found there are significant temperature and humidity fluctuations around the hot-end and printing bed. Macro-scale characterization through ASTM D638 tensile testing shows that for humidity levels higher than 60% there is 5-10% reduction in the strength of material (ultimate strength and tangent modulus). This study is verified by micro-scale characterization performed with atomic force microscopy on thin-films. It is shown that in addition to the effect of humidity on the stiffness of materials, there is an effect on the loss moduli of the matter as well. As humidity increases, these polymers become more viscoelastic. Simultaneously, it is shown higher humidity levels cause increased micro-level surface roughness, which can be the cause for the strength reduction for higher humidities.

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