Delamination in hybrid carbonglass fiber composites

Date of Award

2014

Degree Name

Ph.D. in Mechanical Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Advisor: Steven L. Donaldson

Abstract

Fiber reinforced composite materials have been used increasingly in primary and secondary structures in such applications as aircraft, satellites, automobiles, biomedical industries, marine, and sporting goods. This growth is due primarily to the characteristics of composite materials, which include high specific stiffness, high specific strength, and low density. Both carbon and glass fibers are often used as reinforcing fibers, embedded in polymer matrix material. The glass fibers are inexpensive, have high strength to weight ratio, but low stiffness. Carbon fiber is more expensive, but have a high strength to weight ratio and high stiffness.The delamination between composite layers is one of primary weaknesses in composite material structure. The mode I peeling, mode II shearing, and mixed-mode I/II are the most common delamination fracture crack driving modes between interfaces. Delamination can then lead to a reduction in the structural stiffness. If the structure has compression loading, buckling failure may ensue. The best design approach may find a compromise between less weight and less cost by using a hybrid material approach of both glass and carbon fibers.This research focused on a hybrid materials consisting of both glass and carbon fiber embedded in a polymer matrix, undergoing mode I, mode II, and mix mode I/II static interlaminar fracture. Glass fiber panels, carbon fiber panels, and hybrid panels were fabricated using the wet layup / vacuum bag technique. The non-hybrid all-glass, all-carbon, and hybrid glass/carbon were experimentally characterized by quasi-static testing in load frames. The specimen and material geometries (especially at material interfaces) were analyzed using the finite element method. The program Abaqus was utilized, including the cohesive zone method (CZM). Finally, the resulting fracture surfaces were investigated using a scanning electron microscope.The result showed the fracture toughness values of hybrid material (FG/CF) were between that of fiber glass and carbon fiber. Also, fracture toughness increased due to fiber bridging under static mode I, mode II, and mixed mode I/II . Fractographic imaging aided to study mechanical properties interface of hybrid (FG/CF) and comber with non-hybrid material of fiber glass and carbon fiber to investigate the differences between hybrid and non-hybrid.

Keywords

Composite materials Delamination, Fibrous composites Mechanical properties, Glass fibers Mechanical properties, Carbon fibers Mechanical properties, Composite materials Testing, Mechanical Engineering

Rights Statement

Copyright © 2014, author

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