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Dissertation - Nisrin.pdf (8.75 MB)

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Effects of Voids on Delamination Behavior Under Static and Fatigue Mode I and Mode II

Abdelal, Nisrin Rizek
http://rave.ohiolink.edu/etdc/view?acc_num=dayton1365418463

Abstract Details

2013, Doctor of Philosophy (Ph.D.), University of Dayton, Aerospace Engineering.
Composite materials have become materials of choice for wind turbine blade manufacturing due to their high specific stiffness, strength and fatigue life. Glass fiber composites are used extensively in light-weight structural components for wind turbines, aircrafts, marine craft and high performance automobile because glass fiber is inexpensive and usually provides high strength to weight ratio and good in-plane mechanical properties. The high cycle fatigue resistance of composite materials used in wind turbine blades has been recognized as a major uncertainty in predicting the reliability of wind turbines over their design lifetime. Blades are expected to experience 108 to 109 fatigue cycles over a 20 to 30 year lifetime. Delamination or interlaminar failure is a serious failure mode observed in composite structures. Even partial delamination will lead to a loss of local stiffness, which can preclude buckling failure. Manufacturing process defects such as voids and fiber waviness degrade the fatigue life and delamination resistance of the blade’s composite. This research describes the effect of voids on static and fatigue interlaminar fracture behavior under mode I and mode II loading of wind turbine glass fiber composites. Samples with different void volume fractions in the 0.5%-7% range were successfully obtained by varying the vacuum in the hand layup vacuum bagging manufacturing process. Void content was characterized using four different methods; ultrasonic scanning, epoxy burn off, serial sectioning and X-Ray computed tomography. The effect of voids on both mode I and mode II interlaminar fracture toughness under static and fatigue loading was investigated. Finally, fractographic analysis (using optical and scanning electron microscopy) was conducted. The results showed that voids leads to slight reduction in static modes I and II interlaminar fracture toughness. In addition, voids lead to a decrease in modes I and II maximum cyclic strain energy release rates and fatigue life. Fractographic features allowed relations to be drawn between fracture surfaces and mechanical properties of the composite, and to investigate the differences in the fractographic features between panels fabricated at different vacuum levels, and between static and fatigue modes I and II.
Steven Donaldson (Advisor)
176 p.
Aerospace Engineering; Aerospace Materials; Materials Science; Mechanical Engineering; Mechanics
composites; voids; mode I; mode II; fatigue; static; glass fiber; delamination; fractographic analysis

Recommended Citations

Citations

  • Abdelal, N. R. (2013). Effects of Voids on Delamination Behavior Under Static and Fatigue Mode I and Mode II [Doctoral dissertation, University of Dayton]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1365418463

    APA Style (7th edition)

  • Abdelal, Nisrin. Effects of Voids on Delamination Behavior Under Static and Fatigue Mode I and Mode II . 2013. University of Dayton, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=dayton1365418463.

    MLA Style (8th edition)

  • Abdelal, Nisrin. "Effects of Voids on Delamination Behavior Under Static and Fatigue Mode I and Mode II ." Doctoral dissertation, University of Dayton, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1365418463

    Chicago Manual of Style (17th edition)

dayton1365418463
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This open access ETD is published by University of Dayton and OhioLINK.