Gerard C. Pardoen

Effect of Delamination on the Natural Frequencies of Composite Laminates

This paper presents the results of a study on the effect of prescribed delamination on the natural frequencies of laminated beam specimens. Experimental modal analysis was used to measure the effect of delamination length on the first four fre quencies of the simply supported test specimens. The experimental results were cor roborated with detailed finite element models as well as with simplified beam theory models. The presence of a delamination degraded the even numbered vibration modes much more rapidly than the odd numbered modes for a delamination centered at the speci men midspan. Delaminations which covered 1/3 of the specimen length had no more than a 20% effect on any of the first four frequencies.

Asymmetric vibration and stability of circular plates

Abstract The asymmetric vibration and stability of circular and annular plates using the finite element method is discussed. The plate bending model consists of one-dimensional circular and annular ring segments using a Fourier series approach to model the problem asymmetries. Using displacement functions which are the exact solutions of the static plate bending equation, the stiffness coefficients corresponding to the 1st and nth harmonics are used in closed form. By assuming that the static displacement function closely represents the vibration and stability modes, the mass and stability coefficient matrices for an annular and circular element are also constructed for the 1st and nth harmonics. Several numerical examples are presented to demonstrate the efficiency and accuracy of the finite element model with that of classical methods.

Achieving desirable stress states in thick rim rotating disks

Abstract The theoretical implications of varying the mass and stiffness properties in a search for desirable stress states in thick rim flywheels are investigated. In some cases, the variation of mass and stiffness properties to achieve desirable stress states facilitates consideration of thick rims with an inner radius to outer radius of 0.6 or lower. One thick rim concept investigated, namely that of variable mass density and stiffness, exhibits the same stress characteristics as does the thin rim concept in that the radial stress is zero throughout whereas the hoop stress is constant and equal to the product of the mass density times the peripheral speed squared.

Asymmetric bending of circular plates using the finite element method

Abstract The asymmetric bending of circular plates using the finite element method is discussed. The plate bending model consists of one-dimensional circular and annular ring segments using a Fourier series approach to model the problem asymmetries. Using displacement functions which are the exact solutions of the plate bending equation, the stiffness coefficients corresponding to the 0th, 1st, and n th harmonics are presented in closed form. These stiffness coefficients, which can be readily coded into any special or general purpose structural analysis computer program, represent the exact solution to any structural model consisting of nodal displacements and forces. An example indicating the technique is presented.

Vibration and buckling analysis of axisymmetric polar orthotropic circular plates

Abstract The vibration and stability analysis of polar orthotropic circular plates using the finite element method is discussed. In order to formulate the eigenvalue problems associated with the vibration and stability analyses, the clement stiffness, mass, and stability coefficient matrices are presented. By assuming the static displacement function, which is an exact solution of the polar orthotropic circular plate equation, approximates the vibration and buckling modes, the mass and stability coefficient matrices are readily derived from the given displacement function. Results showing the effects of orthotropy on natural frequencies and buckling loads are compared with their isotropic counterpart.

Effect of delamination on the flexural stiffness of composite laminates

Abstract This paper presents the results of a study on the effect of delamination on the flexural stiffness of advancedcomposite laminates. Three- and four-point bending tests were conducted on graphite-epoxy laminates with embedded delaminations. The experimental results were corroborated with finite element method results as well as with simple beam theory models. The delaminations did not cause any degradation of the four-point bending stiffness. However, the three-point bending stiffness test showed that the delamination did degrade the stiffness by as much as 34%.

The vibrational behaviour of three composite beam-slab bridges

Abstract This paper describes field measurements of the vibrational frequencies of three bridges with prestressed concrete beams and in situ concrete deck slabs. In each bridge, the beams are simply supported over each span while the composite deck is continous over three or four spans with short, full width, crumple slabs between the beam diaphragms over each pier. Analytical analyses were also carried out and compared with the field measurements. Values are also given for the damping determined from the tests.

Optoacoustical sensor to examine the structural integrity of transportation systems

We present the results of the analysis and experimental study of defect detection using whole field laser Doppler vibrometry (WFLDV). The nondestructive inspection (NDI) procedure is based on the vibrational mode evaluation for a test object with specified defect parameters. To evaluate the procedure, a clamped aluminum drum with radius R was selected as the test object. The introduced defect was a thickness loss of 2.5, 5.0, and 7.5% at the central part of the drum. The data from computational examination, based on finite element analysis, are compared with experimental data received from tests with LDV. Additionally, we present data from interrogation of a multilayer (carbon composite) element with present defects in a specific layer and examples of corrosion detection. The experiments show that the technique enables reliable defect detection, location, and quantification.

Improved Modelling of Electrical Substation Equipment for Seismic Loads

Publisher Summary This chapter discusses the improvement in modeling of electrical substation equipment for seismic loads. Improvements in the methods used for modeling electric substation equipment through a combination of experimental and analytical studies are explored. The experimental studies were a combination of in-situ field measurements of this equipment at four sites selected from Pacific Gas & Electric facilities and laboratory experimental modal analyses. The in-situ tests considered the transmissibility of the ambient and forced vibration ground motion to the support locations of the equipment, as well as the low level response of the equipment itself due to force-calibrated hammer excitation. The experimental modal analyses considered the linear response of the equipment under low level, force-calibrated hammer excitation. The analytical studies interpreted the vibration data using commercially available software in order to define the frequency, mode shape and damping characteristics of the equipment. Multiple degree-of-freedom, lumped parameter modal models were developed for the equipment. Simple analytical models were developed that closely matched the experimental data in order to predict the transformers dynamic response under dynamic loading. These modal models can be integrated with standard finite elements to model structural response modifications due to mass or stiffness changes resulting from support structures. The analytical studies recommend improved methods for modeling equipment and major components.

Experimental and Analytical Studies of Diaphragm to Shear Wall Connections

Publisher Summary The standard of practice for the lateral analysis and design of light framed timber structures has been changing to more closely consider the effects of wall stiffness in the distribution of forces in a structure. The stiffness of the shear wall system is a function of the sheathing, anchorage, and shear transfer connections. The experimental and analytical program builds on an earlier UC Irvine study that determined that the performance of some diaphragm to shear wall connections exhibited significant deformation within the region between the top plates of a shear wall and the underneath portion of a floor or roof diaphragm. This deformation is quite different depending on the orientation of the floor or roof joists. The 2.44 m x 6.00 m diaphragm to shear wall connection samples are constructed with dimensional lumber joists and oriented strand board sheathing. From these tests the structural characteristics of each connection type were analyzed. The test results show that the stiffness, strength, and degradation characteristics of shear transfer connections vary depending on the type of connector, the direction of flaming, and the existence of additional joist flaming toenails.