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Fatigue Properties of Fiberglass Bolted, Bonded Joints in Marine Structures
Testing of Glass-Fiber Reinforced Polymer Composite Joints Determines Environmental Stressors' Effect on Fatigue Life

Feature Author
K. Turgut Gürsel

Feature Author
Gökdeniz Neşer

The fatigue testing device.
Glass-fiber reinforced polymer (GFRP) composites have been used in boatbuilding and marine construction for decades because of their optimal durability, workability and cost. These materials offer better resistance to marine environmental agents, such as ultraviolet rays, seawater, organisms and fatigue loading, as well as the advantages of a better strength-to-weight ratio (specific tensile strength) compared with conventional materials. Understanding how GFRP behaves under environmental stresses during a set period as it ages has become a necessity for the cost-effective design of marine structures and their life-cycle assessment.

For structures subject to environmental cyclic loading, fatigue characteristics are important indicators of structural limits. The fatigue design methodology of GFRP compared to that of metallic structural materials is still limited in terms of the availability of methods and the insufficiency of existing models to reliably assess fatigue behavior.

The reason for this is the inherent inhomogeneity of GFRP as well as various damage mechanisms, such as matrix cracking, fiber and matrix debonding, fiber fracture, interlaminar delamination and the interactions of these mechanisms.

The applications of GFRP to naval and other vessels have often been accompanied by the application of conservative design safety factors due to limited durability data and to account for underwater shock loading. It should be recognized that fatigue behavior is strongly related to the interface properties of the fiber and resin.

Tests were performed at the Research Institute for Construction Equipment and Technology in Romania from late 2009 to early 2010, and the resulting data were later used to study the tensile-release fatigue performance of stitched multilayer (noncrimp) E-glass GFRP, which is believed to enable the production of lighter structures by using less layers or, alternatively, achieving higher levels of strength for the same weight of material.

GFRP joint manufacturing methods often decrease the mechanical properties of this material. However, the main factor that deters the producer from using stitched multilayer reinforcements is their higher cost. Although less layers will reduce production cost, the material cost is still high in developing countries. Therefore, the use of stitched multilayer reinforcements is generally limited to the inner and outer shell (2 to 3 millimeters) of sandwich-type hulls, where high strength and stiffness are required.

There were three types of specimens used in the fatigue tests: jointless (flat) tensile bars, bolted and adhesive-bonded. The specimens came from panels of two different thicknesses: 5 and 10 millimeters, manufactured by hand-laying processes and cut from one direction of 0 degrees. To continue this article please click here.

K. Turgut Gürsel studied naval architecture and marine engineering at Istanbul Technical University in Turkey and at University of Hamburg in Germany, and completed his Ph.D. at Berlin University of Technology. He is a professor of mechanical engineering at Ege University, and his research interests are mechanics and construction.

Gökdeniz Neşer is a naval architect and marine engineer who graduated from Istanbul Technical University. He received a master's and Ph.D. in naval architecture from the Institute of Marine Sciences and Technology, Dokuz Eylül University (DEU) in Turkey. He is an associate professor and director of DEU's Boat Building Research Center.

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