Effect of high pressure salt water absorption on the mechanical characteristics of additively manufactured polymers

An experimental study has been performed to investigate the coupled effects of hydrostatic deep depth pressure and sustained salt-water immersion on the mechanical properties and material structure of additively manufactured (AM) polymer based materials. The materials that were evaluated in the study were produced by both the material extrusion and vat photopolymerization printing methods. The material extrusion materials consisted of Stratasys ULTEM 9085 and Markforged Onyx and the vat photopolymerization material was Accura ClearVue resin. Water immersion was conducted with 3.5% NaCl solution at room temperature under a pressure of 34.5 MPa in a novel test facility for long duration, high pressure water saturation. The respective materials were characterized in three conditions: (1) baseline with no water saturation, (2) 30 day water immersion, and (3) 60 day water immersion. The change in mechanical properties as a function of aging time was quantified through controlled laboratory testing, namely tension, compression, flexure, and in-plane fracture toughness. Additionally, a microscopic evaluation was performed to evaluate the physical material degradation between layer bonding due to the saline water absorption. The significant findings of the study highlight that salt water immersion has differing effects on additively manufactured materials based on the material composition of the base material and thus significant consideration must be given to material selection in marine environments.