All ETDs from UAB

Advisory Committee Chair

Haibin Ning

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) School of Engineering


Additive manufacturing (AM) technologies are advantageous in small-batch manufacturing and prototyping functional parts, due to their cost-effectiveness and customizability. Using fiber-reinforced plastic composites (FRP) in extrusion-based AM can significantly improve the mechanical properties compared to neat thermoplastic. However, the two-fold anisotropy introduced by the multiple constituent materials and the layer-by-layer mesostructure can introduce undesired structural weaknesses. Investigating the mechanical behavior and failure mechanism is the key to understanding the synergistic effect of the constituents in FRP and assessing the structural integrity of AM-made FRP. This research work aims to experimentally, analytically, and numerically assess the mechanical behaviors of AM composite to aid in developing parts with better performance. Different loading scenarios were studied, including tensile, sing-lap shear, flexural, and mode I fracture. The failure mechanisms were identified with respect to the structural anisotropy using microscope and numerical simulation. Three studies were presented to address the effects of material and geometrical nonlinearity on the mechanical behavior of AM-made continuous and discontinuous fiber-reinforced polyamide-based thermoplastic composites. The effects of fiber orientation on tensile responses for the continuous and discontinuous FRP composites were first evaluated. The mechanical responses were systematically evaluated, incorporating seven reinforcing strategies for two continuous FRP materials: continuous glass and carbon fiber. The mechanical behavior of the anisotropic FRP under large deformation was successfully simulated using finite element analysis. Fracture morphologies of the samples were observed with microscope and analyzed with the corresponding reinforcing strategies in a case-by-case manner. A single-lap shear configuration was also designed and printed to investigate the mechanical behavior of AM composites under shear stress. Its failure mechanisms were evaluated using fractography to understand the complex stress field caused by the fiber orientation between interfaces. The stress distribution over the bonding interfaces was modeled and correlated to the observed fracture mode. Finally, a series of double cantilever beam samples were printed and tested to assess the interlaminar bonding based on fracture mechanics methodologies. The crack-initiation mode I fracture toughness (GIC) value for two continuous FRP was presented. The GIC for crack propagation was also reported and was found to correspond to geometrical anomalies such as fiber bridging and beam bending.

Included in

Engineering Commons



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.