Date of Award

5-2005

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Habib J. Dagher

Second Committee Member

Roberto Lopez-Anido

Third Committee Member

Michael L. Peterson

Abstract

This thesis is divided into two parts. For the first part, the variability of tensile mechanical properties of a polymer matrix composite material with woven fabric reinforcement is studied using both experimental work and numerical simulations. Four (1.2 m x 1.8 m x 4.9 mm) E-glass / vinyl ester composite plates were fabricated using the Vacuum-Assisted Resin Transfer Molding (VARTM) by a US Navy contractor. The materials and process selected are representative of marine grade composites typically used by the US Navy. Standard ASTM D3039 tensile coupons were obtained from the plates and the laboratory results were compared with those of a 3D probabilistic finite element analysis (FEA). In the probabilistic FEA model, elastic properties I E22, G12 VI~)s,t rength parameters ( F" 7 F ~ c 9 F 2 ~9 F 2 ~9 F 6 ' 1 1 9 'IC 7 ' 2 1 3'2, ' 1 2 ) and geometric properties (thickness, fiber misalignment) of woven fabric E-glass / vinyl ester coupons were considered as random fields, and generated using Monte Carlo simulations. These material properties were obtained from laboratory test data of [0]4sf lay-ups, and in turn used to predict the properties' of the [0/90]2sf lay-ups. The study evaluates the effects of spatial correlation, finite element size, probability distribution functions (PDF) and failure criteria on statistical strength properties of the [0/90]2sf tension coupons. Comparisons of experimental and probabilistic FEA results provide useful observations on how to assign mean, COV and PDF of material properties to individual finite elements within a mesh. The second part investigates the size effects of tensile strength of marine grade polymer matrix composites (PMC) using both probabilistic finite element analysis and laboratory testing. Woven [0/90]2sf E-glass 1 vinyl ester material specimens with different lengths were evaluated to predict the effect of specimen size on the tensile strength. In the probabilistic FEA models, elastic properties (Ell, E229G129V12) strength parameters ( 41 7 F,c 7 F2~ 3 F 2 ~ 9 F6 '11 9 ' 1 ~ 9 '21 9 ' 2 c I '12 ) and geometric (thickness, fiber misalignment) of the woven fabric E-glass / vinyl ester ASTM D3039 coupons were considered as random fields, and generated using Monte Carlo simulations. These material properties were obtained from laboratory test data of [0]4sf lay-ups. The FEA models also considered properties of the tabbing materials and gage pressure. The relationship between the tensile strength and specimen size for the [0/90]2,f lay-up was also evaluated experimentally. 48 material specimens were prepared and tested according to ASTM D3039 using three gauge lengths: % the standard gauge length, the standard gauge length, and twice the standard gauge length. The probabilistic FEA model tensile strength predictions are compared with both the Weibull weakest link theory and. the experimental results.

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