Stiffness Degradation of PolyJet Printed Nano Embedded Configuration with Digital Material

Abstract

Introduction: Polymer-based additive manufacturing (AM) parts are used in a variety of engineering applications in the automotive, aerospace, and energy industries. However, AM printed parts are a new class of materials and the structural performance of these materials is not yet fully understood, and research on the exact performance of PolyJet printed parts and related digital materials under fatigue loading is still minimal. The present study provides insight into the fatigue damage state, cyclic performance, and comparison between pristine (baseline) and Carbon Nano Fibers (CNFs) modified embedded test coupons formed using tailored digital designs and printed with digital polypropylene from PolyJet printing. Methods: The investigations employed 3-dimensional (3D) test coupons formed using PolyJet printing. The nanomodified coupons were formed using digital design configurations for tailored deposition locations that allowed the integration in a 2-step process. The limitations of the conventional ASTM D638 2-dimensional (2D) test coupon for AM-treated materials caused by the process are eliminated by the homogeneous 3D test coupon used in this work. An analytical model of the accumulated damage state based on stiffness deterioration under cyclic loading is presented along with an empirical model of effective elastic modulus based on the analysis of fatigue data. Additionally, the predicted model and the actual damage accumulation due to cyclic loading are compared. Results: With a high correlation coefficient, R² of 0.9971 for the baseline and 0.9885 for the CNFs embedded configuration, it is observed that the linear function model can estimate fatigue life with an agreement to experimental results and can be used to extrapolate for other stress levels. CNFs modified resin embedded configuration showed lower fatigue life as compared to baseline. This reduction can be attributed to the stress concentration at the interfaces. Conclusion: This work fills the gap in the literature by characterizing the fatigue life, and cyclic performance of PolyJet printed parts and nano-modified systems with digital material.