Internal fiber orientation measurements and void distribution for large area additive manufactured parts using optical and SEM imaging techniques.

Abstract

The use of additively manufactured parts for industrial applications has grown is often limited by their structural performance and compromised thermal dimensional stability. The addition of carbon fiber reinforcements, to the polymer matrix, has the potential to mitigate both limitationsits. Quantification of the fiber orientation within the processed beads is required to correlate mechanical and thermal performance to processing variations. This study presents the sample preparation, image acquisition, and analysis methods to quantify the internal fiber orientation and void content. Imaging is performed through optical and scanning electron microscopy (SEM) of an additive manufactured bead with 13% by weight carbon fiber reinforced ABS, with SEM providing a higher resolution and contrast. Fiber orientation is measured using the Method of Ellipses (MoE). A new method using SEM to remove the ambiguity problem inherent to MoE is presented using electrical shadowing afforded by the semi-conductive behavior of the carbon fibers. The spatial change in fiber orientation across the deposited bead cross section is studied as a function of several process parameters, The thesis concludes with an investigation of the correlation between fiber orientation and void content, upwards of 10% by volume for the samples studied, on final part performance. This will hamper the final part performance by a nearly 40% knockdown factor, and void nucleation must be further studied.