David Taggart

• University of Rhode Island

A novel finite element topology optimization procedure is presented based on the application of probability density and cumulative distribution functions. The procedure utilizes a family of Beta functions with constant probability mean which provide a smooth transition from a uniform to a bi-modal density distribution while conserving constant mean...

Two types of defects normally occur in ultrasonically consolidated parts: (i) Defects that occur between mating foils in successive layers ("type 1" defects) and (ii) defects that occur within a layer between two foils laid side-by-side ("type 2" defects). While some success has been achieved in minimizing type 1 defects, type 2 defects, however, h...

An iterative finite element based topology optimization method based on prescribed material redistribution (PMR) has recently been demonstrated to effectively identify optimal topologies for single material structures. Through the application of a family of Beta probability density and cumulative distribution functions, the method provides a gradua...

A general minimum-weight cylindrical structural layout for the support of any combination of axial and torsional loading has been developed. The principal intention in this work is to provide a test case for 3-dimensional numerical topological optimization. It is anticipated that the solution may present a challenge, since for the small angular spa...

Optimized, lightweight, high strength structures are needed in many applications from aerospace to automotive. In pursuit of such structures, there have been proposed analytical solutions and some specialized FEA solutions for specific structures such as automobile frames. However, generalized 3D optimization methods have been unavailable for use b...

Determining the unknown material parameters of intact ventricular myocardium can be challenging due to highly nonlinear material behavior. Previous studies combining a gradient-search optimization procedure with finite element analysis (FEA) were limited to two-dimensional (2D) models or simplified three-dimensional (3D) geometries. Here we present...

In this paper we present the results of a detailed study of a systematic numerical scheme for estimating material parameters for ventricular myocardium. The numerical scheme combines a real encoded genetic algorithm with nonlinear finite element analysis. The primary objective of this study was to determine optimal population size for the genetic a...

The estimation of material parameters in constitutive models for soft biological materials such as myocardium is a challenging problem due to the complex behavior of the material. Here we present a systematic scheme to solve the inverse problem of estimating material parameters from experimentally observed deformation. This scheme couples a genetic...

A finite element method that uses shell element face sheets that are tied appropriately to a brick element core to model sandwich composites is presented. This method is more computationally efficient than using brick elements alone and allows examination of local deformations that are normally lost due to the high level of kinematic assumptions in...

Nozzle wear dependence on abrasive water jet system, parameters and nozzle geometry is experimentally investigated. Experimental procedures for evaluating long term and accelerated nozzle wear are discussed. Accelerated wear tests are conducted to study the effects of nozzle length, inlet angle, diameter, orifice diameter. abrasive flow rate, and w...

Winter maintenance of pavement surfaces consists of plowing and the application of corrosive deicing agents. These chemicals are hazardous to the environment, and thus their use should be minimal. More than 20 years ago, the Connecticut Department of Transportation (ConnDOT) investigated the use of 2.1 MPa (300 psi) pressurized salt brine jets to e...

In this project, concepts of engineering graphics, mechanical design, numerical simulation, rapid prototyping and product testing are integrated in project experiences performed by interdepartmental teams of sophomores, juniors, seniors and graduate students. Working in vertically integrated teams, students were asked to design components using a c...

Parameters that influence nozzle wear in abrasive water jetting environment are identified and classified. Regular and accelerated wear test procedures are developed to study wear under actual and simulated conditions, respectively. In addition to exit diameter growth, nozzle weight loss and bore profiles are shown to better characterize and explai...

A micromechanical model is utilized to estimate the elastic-plastic deformation characteristics of a discontinuously reinforced composite consisting of an elastic-plastic matrix material reinforced with a dilute concentration of axisymmetric elastic inclusions. By neglecting interactions between neighbouring inclusions, the composite is modeled by...

A three-phase self-consistent model is developed for particulate composites consisting of spherical inclusions in an elastic-plastic matrix. The effective properties are estimated for a three-phase geometry that consists of a composite sphere (a spherical inclusion in a spherical matrix shell) embedded in an infinite unknown effective material subj...

A micromechanical modeling approach is used to study stresses induced during processing and their effect on the subsequent elastic-plastic behavior of particle reinforced composite materials. A three phase, self-consistent model is developed to determine the effective (macroscopic) composite behavior as well as internal stress histories during proc...

This paper summarizes the results of a recent study [1] funded by the National Science Foundation to investigate the feasibility of woven fabric composite materials for automotive applications. By identifying the advantages and limitations associated with woven fabric composites and by comparison with current automotive materials, the potential for...

The behavior of polymeric materials reinforced by discontinuous. Descriptors for the planar and axial orientation distributions are discussed. Predictions of micromechanical models and experimental data are presented to illustrate the influence of orientation state upon elastic constants, thermal coefficients of expansion and tensile strength. Resu...

Standard test methods ASTM D-651 for determining tensile properties and ASTM D-790 for flexure properties are evaluated. Heterogeneous fiber distributions due to molding flow conditions are shown to yield test specimens wherein fiber orientation near surfaces is highly collimated while orientations in central regions are oriented approximately tran...

The mechanical properties of five glass fiber sheet molding compounds are investigated in this research program. The materials studied are SMC-25, SMC-3O, SMC-65, SMC-C20/R3o and XMC-3. The specific properties include the tensile, compressive and shear response, as well as the strain rate sensitivity, impact resistance, notch sensitivity, statistic...

Determining the unknown material parameters of intact ventricular myocardium can be challenging due to highly nonlinear material behavior. Previous studies combining a gradient-search optimization procedure with finite element analysis (FEA) were limited to two- dimensional (2D) models or simplified three-dimensional (3D) geometries. Here we presen...

This study includes an experimental investigation into the effects of surface geometry on the interfacial strength of carbon fiber reinforced polymer (CFRP) rods embedded in a high strength concrete. In the experimental phase of the study, a series of pullout tests are conducted on CFRP reinforcing bars with different surface configurations. The su...

Analytical methods exist for the identification of minimum weight structural topologies for certain loading and support configurations (Dewhurst et al, 2003). These topologies, referred to as Michell layouts, follow lines of maximum and minimum strain magnitude in virtual strain fields defined by the appropriate optimality criterion (Michell, 1904;...

Aerospace designers seek lightweight, high-strength structures to lower launch weight while creating structures that are capable of withstanding launch loadings. Most “light-weighting” is done through an expensive, time-consuming, iterative method requiring experience and a repeated design/test/redesign sequence until an adequate solution is obtain...

Use of carbon fiber reinforced plastic (CFRP) rebars as a replacement for ordinary steel reinforcement is examined. Specifically, the effect of the pitch length of the spiral surface indentations of CFRP's on the interfacial load transfer is studied. Direct bond strength tests of samples with various pitch lengths are carried out. Tests with smooth...

Analysis of sintering of a powder compact around a rigid spherical inclusion are presented based on constitutive equations that include the effect of elasticity, nonlinear viscoplasticity, and sintering on the deformation. The presence of the inclusion causes a build up of stress that retards sintering, while creep will eventually relax this stress...