Title page for ETD etd-013199-185939


Type of Document Master's Thesis
Author Phifer, Stephan Paul
Author's Email Address sphifer@vt.edu
URN etd-013199-185939
Title Quasi-Static and Fatigue Evaluation of Pultruded Vinyl Ester/E-Glass Composites
Degree Master of Science
Department Engineering Mechanics
Advisory Committee
Advisor Name Title
Lesko, John Jack Committee Chair
Gao, David Y. Committee Member
Kapania, Rabesh K. Committee Member
Keywords
  • Fatigue
  • Composite
  • Residual Strength
  • Pultrusion
Date of Defense 1998-12-17
Availability unrestricted
Abstract
QUASI-STATIC AND FATIGUE EVALUATION OF PULTRUDED VINYL ESTER/E-GLASS COMPOSITES

Stephan P. Phifer

(ABSTRACT)

The quasi-static strength, stiffness, and fatigue properties of cross-ply, angle-ply, and quasi-isotropic vinyl ester/E-glass non-woven tricot stitched fabric composite laminates fabricated from the Continuous Resin Transfer Molding (CRTM) pultrusion process were the focus of this research. The tricot stitch and the 6% vinyl ester matrix cure shrinkage were found to play key roles in the quasi-static and fatigue strength and stiffness properties of these laminates. Laminates tested transverse to the pultrusion axis had greater fiber undulation and maximum of 44% quasi-static strength reduction and 8% stiffness reduction compared with axially tested specimens. While the matrix failure strain was 1.9%, failure strain of these laminates range over 1.91 to 2.08% when tested along the pultrusion axis and as low as 1.29% transverse to the pultrusion axis. Fatigue evaluation, in load control mode, evaluated laminate S-N, stiffness reduction, and residual strength. Measured S-N curves and residual strength curves compared with literature were found most like woven fabric laminates, well below aerospace grade laminates. Residual strength and life analysis using Reifsnider’s methodology [43], revealed that the choice of quasi-static strength and stiffness, S-N curve, laminate stiffness reduction, and residual strength shape parameter, J, strongly affect predicted life. Predictions at high fatigue stress/low cycle were more exact than at low stress; the S-N curve was steep initially but at low stress/high cycle was nearly horizontal. The best predictions utilized separate off-axis stiffness reductions of E2 obtained from cross-ply and G12 from angle-ply laminates, the quasi-static strength and stiffness of the laminate predicted, and the average S-N and residual strength curves.

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