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Study of edge effects in laminated sandwich specimens
Title
Study of edge effects in laminated sandwich specimens.
Creator
Mankuzhy, Pradeep Prabhakaran., Florida Atlantic University, Merry, Stephanie L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Different methods have been employed to calculate the interlaminar stresses and to study the edge effect in a laminated sandwich specimens under uniaxial tension. However, Finite Element Analysis and Force Balance Method produced stress values which disagreed in both magnitude and sign, a controversy which exists in the case of composite laminates also. Experimental methods, photoelastic coating method and strain gaging, were attempted to obtain the strain distribution on the top surface of a...
Show moreDifferent methods have been employed to calculate the interlaminar stresses and to study the edge effect in a laminated sandwich specimens under uniaxial tension. However, Finite Element Analysis and Force Balance Method produced stress values which disagreed in both magnitude and sign, a controversy which exists in the case of composite laminates also. Experimental methods, photoelastic coating method and strain gaging, were attempted to obtain the strain distribution on the top surface of a sandwich specimen in three point bending. However, these conventional methods failed to show the sharp strain gradient that exists near the free edge. The Force Balance Method was simplified for sandwich specimens by considering the face laminate as a homogeneous and orthotropic material with averaged properties. Simplified expressions were also obtained for calculating the boundary layer thickness. The boundary layer thickness was found to vary linearly with core thickness for the cases considered.
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Date Issued
1989
PURL
http://purl.flvc.org/fcla/dt/14523
Subject Headings
Sandwich construction--Fatigue, Composite materials, Strains and stresses, Structural analysis (Engineering)
Format
Document (PDF)
Development of a Comprehensive Design Methodology and Fatigue Life Prediction of Composite Turbine Blades under Random Ocean Current Loading
Title
Development of a Comprehensive Design Methodology and Fatigue Life Prediction of Composite Turbine Blades under Random Ocean Current Loading.
Creator
Suzuki, Takuya, Mahfuz, Hassan, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A comprehensive study was performed to overcome the design issues related to Ocean Current Turbine (OCT) blades. Statistical ocean current models were developed in terms of the probability density function, the vertical profile of mean velocity, and the power spectral density. The models accounted for randomness in ocean currents, tidal effect, and ocean depth. The proposed models gave a good prediction of the velocity variations at the Florida Straits of the Gulf Stream. A novel procedure...
Show moreA comprehensive study was performed to overcome the design issues related to Ocean Current Turbine (OCT) blades. Statistical ocean current models were developed in terms of the probability density function, the vertical profile of mean velocity, and the power spectral density. The models accounted for randomness in ocean currents, tidal effect, and ocean depth. The proposed models gave a good prediction of the velocity variations at the Florida Straits of the Gulf Stream. A novel procedure was developed to couple Fluid-Structure Interaction (FSI) with blade element momentum theory. The FSI effect was included by considering changes in inflow velocity, lift and drag coefficients of blade elements. Geometric non-linearity was also considered to account for large deflection. The proposed FSI analysis predicted a power loss of 3.1 % due to large deflection of the OCT blade. The method contributed to saving extensive computational cost and time compared to a CFD-based FSI analysis. The random ocean current loadings were calculated by considering the ocean current turbulence, the wake flow behind the support structure, and the velocity shear. The random ocean current loadings had large probability of high stress ratio. Fatigue tests of GFRP coupons and composite sandwich panels under such random loading were performed. Fatigue life increased by a power function for GFRP coupons and by a linearlog function for composite sandwich panels as the mean velocity decreased. To accurately predict the fatigue life, a new fatigue model based on the stiffness degradation was proposed. Fatigue life of GFRP coupons was predicted using the proposed model, and a comparison was made with experimental results. As a summary, a set of new design procedures for OCT blades has been introduced and verified with various case studies of experimental turbines.
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Date Issued
2017
PURL
http://purl.flvc.org/fau/fd/FA00005931
Subject Headings
Dissertations, Academic -- Florida Atlantic University, Turbines--Blades--Design and construction., Turbines--Blades--Materials., Composite construction--Fatigue., Ocean currents--Mathematical models.
Format
Document (PDF)