Experimental Study on the Effect of Humidity on the Mechanical Properties of 3D-Printed Mechanical Metamaterials

TL;DR

This study explores how humidity affects the mechanical properties of 3D-printed materials and metamaterials, showing significant changes in strength and behavior under different humidity levels.

Contribution

The study systematically validates the impact of humidity on 3D-printed mechanical metamaterials, identifying critical thresholds for material behavior.

Findings

Water absorption in polymers occurs in three stages with Nylon showing the highest uptake.

Material properties like Poisson’s ratio shift abruptly at high humidity levels.

Mechanical metamaterials exhibit predictable behavior at low-to-moderate humidity but become unpredictable at high humidity.

Abstract

In this study, six common fused filament fabrication (FFF) polymers—PEEK, PLA, PETG, ABS, Nylon, and TPU—were acclimatized at 15%, 45%, and 95% relative humidity (RH) to characterize tensile behavior, including Young’s modulus, maximum strain, and ultimate tensile strength. Separately, mechanical metamaterial samples at relative densities (RD) of 25%, 35%, and 45% were tested in compression at the same RH levels to evaluate stiffness, strength, and Poisson’s ratio. The water absorption process can generally be divided into different stages—rapid uptake (0–12 h), a plateau (12–60 h), and a late rebound (60–100 h)—with a total uptake ranking of Nylon > PETG > PLA ≈ ABS > TPU ≈ PEEK. Samples under tensile and compressive tests show a great difference between properties at different RD and RH levels. Poisson’s ratio indicates that material responses remain predictable at low-to-moderate RH, whereas high RH serves as a critical threshold inducing abrupt Poisson’s ratio behavioral shifts. This study provides systematic validation for the application of 3D-printed metamaterials under varying humidity conditions, such as biomedical implants in human body.

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