Date of Award

12-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

Garrett Pataky, Committee Chair

Committee Member

Huijuan Zhao

Committee Member

Hongseok Choi

Abstract

Geometric defects play a significant role in affecting both material properties and material behavior. Defects occur in a material due to manufacturing imperfections as well as undesired loading such as incidental impacts. With the popularity of composites and additively manufactured metals in structural applications and component design, the effects of their material-specific defects are important to understand to have confidence in the safety of their intended uses. The use of additive manufacturing (AM) in metals has become a popular choice due to its ability to create geometrically complex parts. In this study, the effect of printed defects and build plate location on the material behavior of AM 316 stainless steel (SS) was examined. Tapered tubular specimens manufactured with intentional defects consisting of a through hole, quarter crack, or internal void were tested in tension and compared to a pristine specimen. The through hole and quarter crack defects resulted in a reduction in the ultimate tensile strength and global fracture strain. Fracture toughness experiments were performed on two different notch types to determine an effective KIC value on thin, AM printed specimens. Compression experiments were performed to analyze the effect of distance from the build plate and build plate location on the compressive yield strength and Young’s Modulus. It was found that both material properties improved as distance from the build plate decreased. A variance in material properties dependent on the build plate location was observed for all experiments. Composites have become widely used due to their high specific strength and stiffness. During compression loading, composites can experience ply separation, or delamination, due to buckling behavior both locally and globally. An embedded delamination occurs when there is ply separation within the composite. This can result from manufacturing defects or incidental impacts. In this study, the effect of embedded delaminations on the buckling behavior of Carbon Fiber/Epoxy laminate composite plates was examined experimentally. A study was performed to examine the effect of the size of a single artificially embedded delamination on the load carrying capacity and surface strain field of laminate composite plates. This testing was compared to that of laminate composite plates made without the use of artificially embedded delaminations. Results of this study indicated there was a critical size of an embedded delamination that resulted in a significant reduction in load carrying capacity subjected to buckling. This led to further testing to examine the behavior of laminate composite plates artificially embedded with double delaminations of the same total area with varied spacing. This revealed that there was no discernible difference in the load carrying capacity of embedded single delaminations compared to embedded double delaminations of the same area due to increased scatter.

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