Engineering Mechanics Commons^™

Coupled Dem-Fem For Dynamic Analysis Of Granular Systems In Bending, Kitti Rattanadit

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

Characterizing the dynamic behavior of granular materials is one of the great challenges in the mechanics of granular matter. Methods for evaluating the mechanical properties of granular matter have applications in a variety of industries, mining and geotechnical activities, defense and military operations. A coupled 2D Discrete Element Method-Finite Element Method (DEM-FEM) code, called "BobKit", is developed and implemented for analyzing the behavior of a 2D granular layer on top of an elastic beam under deforming (quasi-static) or vibrating (dynamic) of the beam. The explicit time-integration dynamic code is used to simulate quasi-static and dynamic bending of the granular layer …

Multiscale Transformation Field Analysis Of Progressive Damage In Fibrous Laminates, Yehia Bahei-El-Din, Ritesh Khire, Prabhat Hajela

Centre for Advanced Materials

As part of an ongoing effort to model uncertainty propagation across multiple scales in fibrous laminates, this paper presents a deterministic transformation field analysis for modeling damage progression under membrane forces and bending moments. In this approach, equivalent eigenstresses are computed in the phases and/or plies such that their respective stress components that satisfy the underlying failure criteria are reduced to zero. Superposition of the solutions found for the undamaged laminate under applied loads and under the eigenstress field provide the entire response. Failure criteria are based on stress averages in the fiber and matrix. Damage mechanisms considered are frictional …

Modified Sandwich Structures For Improved Impact Resistance Of Wind Turbine Blades, Yehia Bahei-El-Din, Mostafa Shazly, I. El-Habbal, Y. Elbahy

Centre for Advanced Materials

Wind turbine blades are susceptible to damage due to fatigue as well as impact by flying objects and parts broken off failed blades of nearby wind towers. Localized, permanent compression of the foam core and delamination of the fibrous composite face sheets are typical damage modes and can lead to progressive structural failure. Sandwich structures modified by inclusion of flexible polyurethane (PU) layers within the cross section are examined under both impact and dynamic loads. Finite element models of sandwich structures with conventional and modified designs show that sandwich designs modified with PU interlayes exhibit reduced foam core crushing and …

Studies Of Dynamic Crack Propagation And Crack Branching With Peridynamics, Youn Doh Ha, Florin Bobaru

Department of Engineering Mechanics: Faculty Publications

In this paper we discuss the peridynamic analysis of dynamic crack branching in brittle materials and show results of convergence studies under uniform grid refinement (m-convergence) and under decreasing the peridynamic horizon (δ-convergence). Comparisons with experimentally obtained values are made for the crack-tip propagation speed with three different peridynamic horizons.We also analyze the influence of the particular shape of themicro-modulus function and of different materials (Duran 50 glass and soda-lime glass) on the crack propagation behavior. We show that the peridynamic solution for this problem captures all the main features, observed experimentally, of dynamic crack propagation and branching, as well …

Indentation Creep Analysis For Self Similar Indenters, Sandeep V. Thube

Mechanical & Aerospace Engineering Theses & Dissertations

In indentation creep experiments, it is difficult to characterize the mechanical properties of small size specimens using conventional methods. This study uses finite element modeling to investigate rate-sensitive deformation of materials with different hardness and strain rate sensitivities for self similar indenter tip geometries. The simulation model is developed using commercially available finite element software Abaqus/Standard. Our study investigates the difference between strain rate sensitivity of hardness (vH) and of flow stress (vu) and their relation to the hardness/modulus ratio. It reveals that the commonly held assumption that vH = vu is violated except for materials with low hardness/modulus …

Multiscale Modeling Of Impact On Heterogeneous Viscoelastic Solids With Evolving Microcracks, Flavio V. Souza

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

Multiscale computational techniques play a major role in solving problems related to viscoelastic composite materials due to the complexities inherent to these materials. In the present work, a numerical procedure for multiscale modeling of impact on heterogeneous viscoelastic solids containing evolving microcracks is proposed in which the (global scale) homogenized viscoelastic incremental constitutive equations have the same form as the local scale viscoelastic incremental constitutive equations, but the homogenized tangent constitutive tensor and the homogenized incremental history dependent stress tensor depend on the amount of damage accumulated at the local scale. Furthermore, the developed technique allows the computation of the …

Identification Of Multiple Oscillation States Of Carbon Nanotube Tipped Cantilevers Interacting With Surfaces In Dynamic Atomic Force Microscopy, Mark Strus, Arvind Raman

Birck and NCN Publications

Carbon nanotubes (CNTs) have gained increased interest in dynamic atomic force microscopy (dAFM) as sharp, flexible, conducting, nonreactive tips for high-resolution imaging, oxidation lithography, and electrostatic force microscopy. By means of theory and experiments we lay out a map of several distinct tapping mode AFM oscillation states for CNT tipped AFM cantilevers: namely, noncontact attractive regime oscillation, intermittent contact with CNT slipping or pinning, or permanent contact with the CNT in point or line contact with the surface while the cantilever oscillates with large amplitude. Each state represents fundamentally different origins of CNT-surface interactions, CNT tip-substrate dissipation, and phase contrast …

Convergence, Adaptive Refinement, And Scaling In 1d Peridynamics, Florin Bobaru Ph.D., Mijia Yabg Ph.D., Leonardo F. Alves M.S., Stewart A. Silling Ph.D., Ebrahim Askari Ph.D., Jifeng Xu Ph.D.

Department of Engineering Mechanics: Faculty Publications

We introduce here adaptive refinement algorithms for the non-local method peridynamics, which was proposed (in J. Mech. Phys. Solids 2000; 48:175–209) as a reformulation of classical elasticity for discontinuities and long-range forces. We use scaling of the micromodulus and horizon and discuss the particular features of adaptivity in peridynamics for which multiscale modeling and grid refinement are closely connected. We discuss three types of numerical convergence for peridynamics and obtain uniform convergence to the classical solutions of static and dynamic elasticity problems in 1D in the limit of the horizon going to zero. Continuous micromoduli lead to optimal rates of …

Influence Of Van Der Waals Forces On Increasing The Strength And Toughness In Dynamic Fracture Of Nanofibre Networks: A Peridynamic Approach, Florin Bobaru Ph.D.

Department of Engineering Mechanics: Faculty Publications

The peridynamic method is used here to analyse the effect of van der Waals forces on the mechanical behaviour and strength and toughness properties of three-dimensional nanofibre networks under imposed stretch deformation. The peridynamic formulation allows for a natural inclusion of long-range forces (such as van der Waals forces) by considering all interactions as ‘long-range’. We use van der Waals interactions only between different fibres and do not need to model individual atoms. Fracture is introduced at the microstructural (peridynamic bond) level for the microelastic type bonds, while van der Waals bonds can reform at any time. We conduct statistical …

Statistical Interpretation Of Mohr-Coulomb Theory As Applied To Fracture In Brittle Materials Containing Cracks, Mudit J. Monsi

Mechanical & Aerospace Engineering Theses & Dissertations

Fracture in brittle materials containing pre-existing cracks was studied. The probability of of crack growth under both shear and tensile stresses was determined for an arbitrary distribution of crack sizes. Two different crack orientation distributions, random and uniform, as well as friction were also taken into account. The material's reliability was assumed to depend on the number of active cracks at a particular stress level, and this was expressed as an arbitrary 2-parameter Weibull distribution. Two new and efficient methods for calculating crack growth probabilities based on spherical triangles and spherical caps were developed. They utilized normalized stress coordinates and …

Matrix Structural Analysis, 2nd Edition, William Mcguire, Richard H. Gallagher, Ronald D. Ziemian

Faculty Books

The aims of the first edition of Matrix Structural Analysis were to place proper emphasis on the methods of matrix structural analysis used in practice and to lay the groundwork for more advanced subject matter. This extensively revised Second Edition accounts for changes in practice that have taken place in the intervening twenty years. It incorporates advances in the science and art of analysis that are suitable for application now, and will be of increasing importance in the years ahead. It is written to meet the needs of both the present and the coming generation of structural engineers.

KEY FEATURES …

Effect Of Temperature On Short-Term Creep Rupture Response In Polymer Matrix Pultruded Composites, Robert Harold Munson

Mechanical & Aerospace Engineering Theses & Dissertations

Polymer matrix pultruded composites have increasingly been used in applications where high strength-to-weight ratio and corrosion resistance are needed. Bridge and pier components are a couple of recent applications due the composite's resistance to corrosion from salt water. In applications of this sort, the material will commonly be subjected to sizable static loads while exposed to varying weather conditions. In using pultruded composites for these applications safely, a better understanding of the material's response to ambient conditions is necessary.

In this thesis, rectangular specimens of a polyester matrix glass reinforced pultruded composite sheet are subjected to both static tensile loading …

Triangulation Rangefinder And Sight Positioning System, Jeffrey Hargrove, William G. Wickham, John E. Briggs

Mechanical Engineering Patents

A rangefinder includes an angle sensitive transducer and a programmed data processor to calculate the distance to a target. In one embodiment, the rangefinder also includes a point-to-point measuring device. Another embodiment provides a linear actuator to selectively move a sight indicator vertically. A yet additional embodiment includes a liquid crystal display which displays information to the user.

Development Of Curved-Plate Elements For The Exact Buckling Analysis Of Composite Plate Assemblies Including Transverse-Shear Effects, David Michael Mcgowan

Mechanical & Aerospace Engineering Theses & Dissertations

The analytical formulation of curved-plate non-linear equilibrium equations including transverse-shear-deformation effects is presented. The formulation uses the principle of virtual work. A unified set of non-linear strains that contains terms from both physical and tensorial strain measures is used. Linearized, perturbed equilibrium equations (stability equations) that describe the response of the plate just after buckling occurs are then derived after the application of several simplifying assumptions. These equations are then modified to allow the reference surface of the plate to be located at a distance z_c, from the centroidal surface. The implementation of the new theory into the …

An Experimental Investigation Of Bolt Preload Relaxation In Pultruded Gfrp Composite Joints, Srinivas Ravi

Mechanical & Aerospace Engineering Theses & Dissertations

Mechanically fastened joints in pultruded composites are necessary for reasons of maintenance, repair, and assembly. Pultruded composites utilize polymers as matrices and therefore are susceptible to time-dependent effects. The positive effects of increasing the clamping force in bolted joints are well known. To maintain a safe operation of the assembly a minimum clamping force must be guaranteed. But since these materials show time-dependent effects, the bolt-preload relaxes over a period of time. The present study is aimed at investigating the bolt preload relaxation. In this study 1/2 in. thick pultruded sheets were first tested under compression in the thickness direction. …

Effects Of Elevated Temperature On The Physical Aging Of A High Temperature Thermoplastic Resin And Composite, Mark Feldman

Mechanical & Aerospace Engineering Theses & Dissertations

Development of a High Speed Civil Transport is considered by the commercial aviation industry to be one of the next big challenges for our national aircraft industry. Critical to the success of this aircraft is the development of advanced polymeric composites for both the primary and secondary structures and the predictive methodology necessary for assessment of long term durability. While polymeric composites offer an excellent strength to weight ratio a key disadvantage is the time dependent properties exhibited by the polymer matrix which can age and ultimately effect the resultant stiffness of a laminate.

Experimental studies were performed to determine …

Progressive Failure Analysis Methodology For Laminated Composite Structures, David Wayne Sleight

Mechanical & Aerospace Engineering Theses & Dissertations

A progressive failure analysis model has been developed for predicting the nonlinear response and failure of laminated composite structures. The progressive failure analysis uses C¹ plate and shell elements based on classical lamination theory to calculate the in-plane stresses. Several failure criteria, including the maximum strain criterion, Hashin's criterion, and Christensen's criterion, are used to predict the failure mechanisms and several options are available to degrade the material properties after failures. The progressive failure analysis model is implemented in COMET and can predict the damage and response of a laminated composite structures from initial loading to final failure.

Triangulation Rangefinder For Archers, Jeffrey Hargrove, William G. Wickham, John E. Briggs

Mechanical Engineering Patents

An archery rangefinder for use from an elevated position comprises a power supply for an electronic digital panel meter and a power supply for two voltage divider circuits that comprise the rangefinding circuit. One voltage divider provides a voltage signal proportional to the elevation distance. This signal acts to supply the second voltage divider to attenuate the voltage further by a factor proportional to the tangent of the inclination angle. A weighted pendulum arm is attached to a potentiometric element in the second voltage divider to effect feedback relevant to the angle of inclination. All circuits and components are housed …

An Investigation Of Hole Size Effects In A Composite Material During Tensile Fracture, David Floyd Moore

Mechanical & Aerospace Engineering Theses & Dissertations

An experimental investigation was conducted to evaluate the hole size effects, i.e., the reduction in strength with an increase in hole size at a constant stress concentration factor, for a glass fiber reinforced epoxy crossply laminate during tensile fracture. The characteristic dimension according to the point-stress and average-stress criteria of the two-parameter models proposed by Whitney and Nuismer were determined and compared for a circular hole, optimized circular hole, square hole with radiused corners and square hole with sharp corners. Modified versions of the two-parameter models proposed by Karlak and Pipes, Wetherhold, and Gillespie were also compared. On the basis …

Transverse Stress Effects For Laminated Composite Beams In Bending, Christine Chatterton Schleicher

Mechanical & Aerospace Engineering Theses & Dissertations

A higher-order theory and an associated finite element formulation are developed for analysis of laminated planar beams in bending. The higher-order theory incorporates both transverse normal stress and transverse shear stress, and is developed using two approaches. The first approach is based on assuming the transverse normal strain distribution to be a cubic function through the beam thickness, while the second approach is based on assuming the transverse normal stress distribution to be a cubic function through the beam thickness. In both approaches, the transverse shear strain distribution is assumed to be a quadratic function through the beam thickness. Theoretical …

Elastic Buckling Of Stiffened Composite Curved Panels, Navin R. R. Jaunky

Mechanical & Aerospace Engineering Theses & Dissertations

Continuous filament grid-stiffened structure is a stiffening concept that combines structural efficiency and damage tolerance. However, buckle resistant design of such structures using finite elements methods is expensive and time consuming. An analytical model of a general grid stiffened structure is developed using a smeared theory with a first order shear deformation theory to account for transverse shear flexibilities. The solution for buckling of a simply supported panel subjected to combined loading is developed using energy method and a Rayleigh-Ritz technique. The smeared theory results are compared with finite element results. The results smeared theory compare well with the finite …

Analysis Of Impact Damage Of Composite Laminates Using Five-Point Bending, Mark Edward Robeson

Mechanical & Aerospace Engineering Theses & Dissertations

The low-velocity impact of composite laminates can induce high transverse shear strains, resulting in severe damage within the laminate. This type of damage may be studied in a quasi-static manner by use of a multi-span beam shear test in five-point bending configuration. A five-point bending arrangement induces high transverse shear strains in sections of the laminate, causing failures, such as intraply cracks and delaminations, that are similar to those caused by low-velocity impact. Stress distributions in the laminate can be calculated using a potential energy approach, and these stress distributions can be correlated with failure locations in the five-point bending …

An Experimental Investigation Of Composite Sensors For Crack Length Measurement, Manickam Ramasamy

Mechanical & Aerospace Engineering Theses & Dissertations

Structural defects such as cracks can cause catastrophic failure in engineering components or structures. There are many techniques to measure the crack growth in materials and are commercially available. In this thesis, bondable crack length measurement gages have been investigated and these gages give electrical signal as the output and measure the crack length continuously. Silver paint, nickel powder impregnated epoxy and carbon powder impregnated polymer composite gages are investigated and tests are conducted by resistance measurement method with simple instrumentation and by potential drop method with a constant current output source. Rectangular shape gages have been investigated and as …

The Effectiveness Of Viscoelastic Damping Treatments On A Flexible Manipulator Subjected To Torsional Loads, Leah L. Remias

Mechanical & Aerospace Engineering Theses & Dissertations

The advent of new technology has led to an increasing number of missions in space. The space shuttle Remote Manipulator System (RMS) is a lightweight flexible manipulator currently used in NASA space missions. The future role of the RMS and similar flexible manipulators may include in-space construction and assembly tasks. Because these tasks require precise motion and short settling time of the end-point oscillations, effective vibration control schemes are being investigated.

Passive damping techniques have shown to provide a considerable amount of damping in controlling flexural vibrations. In this research passive damping via constrained viscoelastic damping treatments is explored as …

Determinations Of Molecular Weight And Molecular Weight Distribution Of High Polymers By The Rheological Properties, Joan Y. Z. Huang

Mechanical & Aerospace Engineering Theses & Dissertations

Several methods are reviewed by which the molecular weight (MW) and molecular weight distribution (MWD) of polymeric material were determined from the rheological properties. A poly (arylene ether) polymer with six different molecular weights was used in this investigation. Experimentally measured MW and MWD were conducted by GPC/LALLS (Gel Permeation Chromatography/Low Angle Laser Light Scattering), and the rheological properties of the melts were measured by a Rheometric System Four rheometer. It was found that qualitative information of the MW and MWD of these polymers could be derived from the viscoelastic properties, with the methods proposed by Zeichner and Pate1, and …

Stability Design Of A Slender Column With Curved Longitudinal Stiffeners, Mark S. Lake

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis presents the results of a stability design study of a slender column with curved longitudinal stiffeners for large space structure applications. The stiffened column concept is attractive because it allows the buckling load of a slender column to be increased at a fairly low cost in increased mass, and at no change in the column packaged size. Linear stability analyses are performed using a "linked-plate" representation of the stiffeners to determine stiffener local buckling stresses. Results from a set of parametric analyses are used to determine an approximate explicit expression for stiffener local buckling in terms of its …

Development Of Load Carrying Thermoplastic Components For An Automotive Emergency Braking System, Joseph Gerard Sikora

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis describes a classical approach to plastic parts' design leading to the development of load carrying fiber reinforced thermoplastic components for use in an automotive emergency braking system. The control arms that are the focus of this study are designed to withstand the static loads characteristic of the loads experienced by an automotive emergency braking system. The present study is particularly significant as a case study because the design involves development of load carrying components for use in the harsh automotive environment.

Beginning with a fundamental concept for the control arms, basic design criteria, and a limited insight into …

Optimal Cure Cycle Design Of A Resin-Fiber Composite Laminate, Jeenson Sheen

Mechanical & Aerospace Engineering Theses & Dissertations

High performance polymeric composites have been experiencing increasing usage in the aerospace and automobile industries. Such materials are commonly composed of long or chopped fibers embedded in the thermosetting resin matrix. Changes in physical and chemical properties of such composite materials during the cure process are rather complex. Thus, it is not a trivial task to properly design a cure cycle (temperature and pressure profiles) for a cure process. The material should be cured uniformly and completely with the lowest void content; the temperature inside the laminate must not exceed some maximum value; and the cure process should be completed …

Photoelastic Investigation Of Load Transfer In Eccentrically Loaded Single Lap Joints, Stephen Antrim Hann

Mechanical & Aerospace Engineering Theses & Dissertations

Photoelastic models of three eccentrically loaded single lap joints were analyzed. The adherends of each joint were identical and the bondlines differed in thickness and material properties. The adherends were analyzed for both cylindrical plate behavior and geometrical nonlinearity and the load transfer efficiency was examined. For all three models it was found that over 98% of the shank behaves as a cylindrical plate and that a geometrically nonlinear analysis yields bending stresses substantially lower than a linear analysis and that a relatively thick, low modulus bondline can increase load transfer efficiency.

Studies Of Fracture And Deformed Surfaces Of High Strength Aluminum Alloys By X-Ray Diffraction, Tamma K. Kumar

Mechanical & Aerospace Engineering Theses & Dissertations

X-ray observations of fatigue fracture and deformed surfaces of 7075-T6 aluminum were conducted in this study. The (111) and (222) diffraction peaks were obtained from the fractured and deformed surfaces. It was observed that in comparison with the base metal, the fracture exhibited line broadening similar to that due to cold working. The broadening is indicative of plastic deformation in the vicinity of the advancing crack tip during the fracture process. Also the different regions of fracture exhibited varying degrees of line broadening. With respect to the fatigue crack, the slow crack growth region showed a greater broadening, and, hence, …