Structural Materials Commons^™

Morphing Shape Metastructures Using The Hybrid Position Feedback Control And Bistable Structural Elements, Mehmet Simsek, Thomas E. Alberts, Onur Bilgen

Mechanical & Aerospace Engineering Faculty Publications

This research introduces a new multi-degree-of-freedom metastructure concept utilizing a hybrid position feedback controller. An arbitrary number of bistable segments, or structural elements, are connected serially or in parallel to form a distributed bistable structure, or a so-called metastructure. The hybrid controller, an unstable-then-stable second-order single-degree-of-freedom system, leverages the resonant mode of a bistable system to destabilize it and dynamically induce snap-through between equilibria. The metastructure inherits multiple bistable positions, maintaining equilibrium shapes without consuming power and enabling many equilibrium configurations. Two geometric configurations are proposed and analyzed using a modified hybrid feedback control approach, which rejects forces from neighboring …

Rheology Of Alumina Suspensions Subjected To Alternating Current Electric Fields For Freeze-Casting, Sivakumar Chithamallu, Ruksana Baby, Jacob L. Jones, Dipankar Ghosh

Mechanical & Aerospace Engineering Faculty Publications

Alternating current (AC) electric field can extrinsically tune freeze‐cast microstructure, originating from field‐induced increase in viscosity of ceramic suspensions. However, the changes that occur in a ceramic suspension and rheological behavior, ultimately affecting freeze‐cast microstructure, are not well understood. Moreover, the effects of AC electrokinetic forces and temperature on viscosity need to be decoupled. The viscosity and temperature of ceramic suspensions subjected to AC field and direct heating were measured, revealing that the increase in viscosity is due to AC dielectrophoretic forces rather than field‐induced heating of suspension. The shear thinning behavior of suspensions characterized using a power‐law model reveals …

Predicting Compressive Strength Of Concrete Incorporating Fly Ash, Blast Furnace Slag, And Superplasticizer Using Machine Learning Techniques, Muhammad Faisal Yaqub

2024 REYES Proceedings

Concrete is the second most essential element in the construction industry, and its strength requirements vary based on the specific conditions of each project. However, determining the compressive strength of concrete involves laboratory tests, which wastes a lot of time and money. Researchers have developed machine learning models that predict the compressive strength of cement-based concrete having various mixes. In this research, the compressive strength of concrete incorporating fly ash, blast furnace slag, and superplasticizer is predicted using different machine learning models, namely, Linear Regression, Random Forest Regression, Decision Tree Regression, Extreme Gradient Boosting, Light Gradient Boosting, AdaBoost, and CatBoost …

Architecture Of Heptagonal Metallo-Macrocycles Via Embedding Metal Nodes Into Its Rigid Backbone, A.M.Shashika D. Wijerathna, He Zhao, Qiangqiang Dong, Qixia Bai, Zhiyuan Jiang, Jie Yuan, Jun Wang, Mingzhao Chen, Markus Zirnheld, Rockwell T. Li, Yuan Zhang, Yiming Li, Pingshan Wang

College of Sciences Posters

Metal-organic macrocycles have received increasing attention not only due to their versatile applications such as molecular recognition, compounds encapsulation, anti-bacteria and others, but also for their important role in the study of structure-property relationship at nano scale. However, most of the constructions utilize benzene ring as the backbone, which restricts the ligand arm angle in the range of 60, 120 and 180 degrees. Thus, the topologies of most metallo-macrocycles are limited as triangles and hexagons, and explorations of using other backbones with large angles and the construction of metallo-macrocycles with more than six edges are very rare.

In this study, …

Influence Of Defects On In-Plane Dynamic Properties Of Hexagonal Ligament Chiral Structures, Ning An, Xunwen Su, Dongmei Zhu, Mileta M. Tomovic

Engineering Technology Faculty Publications

Although the six-ligament chiral structure has many unique properties, due to its special structure, the stress concentration is prone to defects. In addition, additive manufacturing is also prone to defects. This paper studies the effect of defects, which is helpful for the better application of the six-ligament chiral structure. Several new six-ligament chiral structures with random and concentrated defects were designed to explore the effects of the defects on the in-plane dynamic properties. The structures were studied with the finite element ANSYS/LSDYNA numerical simulation and experimental methods. According to the defect-free six-ligament chiral structures exhibiting different deformation modes at different …

Method For Reducing Warping Stresses In Torsionally Loaded I-Section Members Using Cfrp Plates, Mamadou Konate, Zia Razzaq

Civil & Environmental Engineering Faculty Publications

This paper presents a method for reducing warping normal stresses in torsionally loaded I-section members by utilizing carbon fiber-reinforced polymer (CFRP) plates. The CFRP plates are bonded to the outer surfaces of the flanges with a view to reducing warping normal stresses. The maximum warping normal stress in the flanges of a steel I-shaped member without the CFRP plates is compared to those obtained with the CFRP plates having various thicknesses. It has been found that the use of CFRP plates bonded to both flanges of the I-section result in a substantial reduction of the warping stresses. For the study …

Mechanism Of Compaction With Wrinkle Formation During Automatic Stitching Of Dry Fabrics And The Size Effect Of Compression Molded Discontinuous Fiber-Reinforced Composites, Anibal Benjamin Beltran Laredo

Mechanical & Aerospace Engineering Theses & Dissertations

With an ever-increasing demand for composites, more ways of manufacturing them are becoming popular and widely used. Stitching of dry fabrics is an efficient method for improving delamination resistance. Discontinuous fiber reinforced composites can be used as a lightweight alternative material for metals through a process of compression molding, which allows for complex shape manufacturing while offering structural grade mechanical properties.

This study demonstrates how the stitching of dry fabrics can be adapted to more complex surfaces. The consequences of stitching of curvilinear surfaces can result in defect formation. Therefore, to understand the physical formation of possible defects, experimental characterization …

N-I-P Nanocrystalline Hydrogenated Silicon Solar Cells With Rf-Magnetron Sputtered Absorbers, Dipendra Adhikari, Maxwell M. Junda, Corey R. Grice, Sylvain X. Marsillac, Robert W. Collins, Nikolas J. Podraza

Electrical & Computer Engineering Faculty Publications

Nanocrystalline hydrogenated silicon (nc-Si:H) substrate configuration n-i-p solar cells have been fabricated on soda lime glass substrates with active absorber layers prepared by plasma enhanced chemical vapor deposition (PECVD) and radio frequency magnetron sputtering. The cells with nanocrystalline PECVD absorbers and an untextured back reflector serve as a baseline for comparison and have power conversion efficiency near 6%. By comparison, cells with sputtered absorbers achieved efficiencies of about 1%. Simulations of external quantum efficiency (EQE) are compared to experimental EQE to determine a carrier collection probability gradient with depth for the device with the sputtered i-layer absorber. This incomplete …

Direct Strength Approach To Predict The Flexural Strength Of Cold-Formed Z-Section Purlins On Sloped Roofs, Ali Parva, Michael W. Seek

Engineering Technology Faculty Publications

In this study, the strength of cold-formed Z-section purlins is predicted considering the effects of roof slope in real roof systems. The study applies to simple span purlins with torsion restraints at support locations and at paired locations along the length of the member. A previously developed method has shown through comparisons to base tests that when the biaxial bending and torsion stresses are incorporated into the analysis, the Direct Strength Method can accurately predict the strength of a purlin. These stress distributions can deviate substantially from the constrained bending approximation typically assumed in analysis and therefore impacts the local …

Behavior And Strength Of Rc Spandrel Members Under Unsymmetrical Bending And Torsion Including Cfrp Retrofitting, Muhammad Fahim

Civil & Environmental Engineering Theses & Dissertations

This dissertation presents the outcome of an experimental and theoretical investigation of the behavior and strength of reinforced concrete spandrel members both with and without carbon fiber reinforced polymer (CFRP) retrofitting. Both isolated spandrel members with L-shaped cross section as well as those integrated with reinforced concrete slabs are studied. A series of isolated spandrel members were tested under separate and combined actions of unsymmetrical bending and torsion. Six of these specimens were retrofitted externally with high-strength CFRP strips. Materially nonlinear analysis procedures are also formulated and programmed for the spandrel members with and without CFRP retrofitting. Furthermore, ultimate bending-torsion …

Flexural Rigidity Characterization Of Retrofitted Frp Plates, Steven J. Makonis Jr., Stella B. Bondi, Zia Razzaq

Civil & Environmental Engineering Faculty Publications

Presented herein is a procedure and numerical results for flexural rigidity characterization of Fiber Reinforced Polymer (FRP) plates retrofitted with various types of fabrics. The FRP plates were retrofitted with Kevlar® 49 (Aramid), Carbon Fiber (Harness-Satin H5), and Unidirectional Carbon Fiber (T700 Aerospace Grade) fabrics, respectively. The FRP plate flexural rigidity values were calculated with a central finitedifference iterative scheme while utilizing the experimental load-deflection relations based on bending tests. The tests were performed on each plate by applying a concentrated load at the center. A fourth-order partial differential equation of plate equilibrium was adopted to estimate the plate flexural …

Steel Angle Section Members Under Combined Axial Load And Unsymmetric Bending, Maheshchandra Rajasekharan Phanibhushan

Civil & Environmental Engineering Theses & Dissertations

This thesis presents the outcome of an investigation into the experimental and theoretical behavior of steel angle section members under combined axial load and unsymmetric bending. Tests are conducted on a series of six angle section members provided with biaxial pinned-end boundaries about the cross-sectional non-principal axes. The end bending moments and axial load are applied in a quasi-static manner until the member load-carrying capacity is reached. The experimental load-deflection and load-strain curves are recorded. The theoretical analysis is based on a system of both elastic as well as materially nonlinear differential equations. The equations were solved using an iterative …

Plain And Steel-Reinforced Concrete Shear Walls With And Without Cfrp Retrofitting, Ali Mohammed Salih Al Aloosi

Civil & Environmental Engineering Theses & Dissertations

This thesis presents the outcome- of a study of the behavior and strength of plain and steel-reinforced concrete shear walls with and without a window opening and Carbon Fiber-Reinforced Polymer (CFRP) retrofitting. A total of seven tests were conducted using six different shear walls. Each wall was subjected to a gradually increasing static load at one of it's top corners until the maximum load was reached. The load-deflection relations and the walls' failure patterns were observed and recorded. It was found that the window opening in the plain concrete wall reduced the wall load capacity by 18 percent. For the …

Validation Of Finite Element Beam Models, Pavan R. Madhineni

Mechanical & Aerospace Engineering Theses & Dissertations

Finite Element (FE) methods these days are becoming very popular to predict the responses of structures in industries, such as the aerospace and automobile industries. When there is a new design or modification of an existing design, the product must be tested to fulfill the criterion projected by the industry or external agencies before it can be launched. The product must be checked for each and every aspect, and every minute detail of each of the external forces. Hence, it becomes very important to carry out the model validation on the product.

This thesis describes validation of finite element (FE) …

A Substructuring Technique With Application To Spot Weld Placement Design, Yang Wang

Mechanical & Aerospace Engineering Theses & Dissertations

It is quite common in the industry to use various interface methods, such as welding, fasteners, bolts, adhesive bonding, etc., to join substructures together. The quality of the assembled structure is directly related to the type of the interface methods used in the manufacturing process. Thus, it is important to include the interface conditions as part of design variables in any design process. To this end, this work develops a reanalysis method that can efficiently analyze structures with variations on the interface conditions. This reanalysis method is based upon a new two-step substructuring technique. The first step performs substructural level …

Flexural Behavior Of Thermoplastic Beams With And Without Frp Reinforcement, Hilmi Coskun

Civil & Environmental Engineering Theses & Dissertations

This thesis presents the results of an experimental and theoretical study of the flexural behavior of thermoplastic beams with and without fiber-reinforced plastic (FRP) rebars. Tests are conducted on commercially available thermoplastic beams known as Seatimber. The normal stress-strain relations of both the thermoplastic material and FRP rebars are obtained in tension and compression experimentally. These mechanical property curves are then used as part of the input for developing the theoretical moment-curvature relations using an iterative equilibrium procedure. The moment-curvature relations are in turn used for predicting the beam load-deflection curves via the central finite-difference procedure. Behavior predictions are made …

Finite Element Analysis Of Structures With Constrained Viscoelastic Layer Damping, Yung Chen

Mechanical & Aerospace Engineering Theses & Dissertations

It has been demonstrated that constrained viscoelastic layer damping treatments provide an effective means of passive control for structural vibration. These treatments dissipate vibrational energy by inducing shear strain in a thin layer of viscoelastic material. Our interest is in adding passive damping to a structure as an augmentation to active control. For such applications it is desirable to achieve high damping performance in a given frequency range with a minimum of added weight. Most damping treatments employ spatially continuous constraining layers over the entire viscoelastic layer. Plunkett and Lee have shown that the effectiveness of the damping treatment can …

A Systematic Procedure For The Analysis And Design Of Deployable Space Structures, Praveen Kumar

Mechanical & Aerospace Engineering Theses & Dissertations

An integrated graph theory and a symmetry-based approach have been developed for the type synthesis of deployable truss structures. Using this systematic approach, a bay of a deployable structure may be looked upon as being built around an axis or a plane of symmetry, including anti-symmetry. By providing a fictitious joint along this axis, the problem of structural design and analysis can be reduced to the study of one plane or face of the given structure. Each face is considered to be an assemblage of structural links connected by joints which form a closed kinematic chain. The conventional graph representation …

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 …

The Use Of Complex Versus Normal Modes In Structural Model Improvement, Chih Lin

Mechanical & Aerospace Engineering Theses & Dissertations

In the past, normal modes approximation to complex modes was employed by most researchers or users in the process of identification or modification of structural systems. This is true, of course for simple structures with no or proportional damping. For complex structures with nonproportional damping, even level of which is small, it will be shown that applying this approximation is inadequate. Use of complex modes instead of approximated normal modes is justified.

An algorithm is presented that computes a set of normal modes from the corresponding measured complex modes. The computed normal modes are then used in the Berman's technique …

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, …

An Experimental Study Of Lateral Soil Pressures And Moments On Flexible Sheet Piles, James H. Donahue

Civil & Environmental Engineering Theses & Dissertations

In order to study the effect compaction has on lateral earth pressures exerted on and bending moments in steel sheet pile bulkheads, an experimental study was undertaken which employed the placement of a non-cohesive soil at two specific densities against three model piles of varying thicknesses. The soil was placed both in a loose and a dense state and the bending strains and deflections of the sheet piles were measured at various stages of backfill. Surface loadings were then placed after completion of the backfilling to observe the effects these loads had on the bending moments. The results of the …