Type of Document	Master's Thesis
Author	Phifer, Stephan (Steve) 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 J. Jack Lesko Committee Chair David Y. Gao Committee Member Rakesh Kapania 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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