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Elmushyakhi, AbrahamIn-Plane Fatigue Characterization of Core Joints in Sandwich Composite Structures
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Materials Engineering
In practice, adjacent preform sandwich cores are joined with a simple butt joint without special precautions. When molded, this gap is filled with resin and creates a resin rich area. Stress risers will be amplified under cyclic load, and consequently, the serviceability of the structure will be affected. Designers and researchers are aware of this problem; however, quantifying this effect and its intensity and consequence on the service life of the structures has not yet been developed. Despite pervious findings, limited experimental data backed by a comprehensive root cause failure analysis is available for sandwich under axial static, fatigue and post-fatigue. If such a comprehensive experimental characterization is conducted, specifically understanding the nature of the damage, intensity, and residual strength, then a valid multi-scale damage model could be generated to predict the material state and fatigue life of similar composite structures with/without core joints under in-plane static and fatigue load. This research study characterized the effect of scarf and butt core joints in foam core sandwich structures under in-plane static and fatigue loads (R=0.1 and R= -1). Post-Fatigue tensile tests were also performed to predict the residual strength of such structures. Nondestructive Evaluation Techniques were used to locate the stress concentrations and damage creation. A logical blend of experimental and analytical prediction of the service life of composite sandwich structures is carried out. The testing protocol and the S-N curves provided in this work could be reproducible and extrapolated to any kind of core material. This research study will benefit composite engineers and joint designers in both academia and industry to better apprehend the influence of core joints and its consequence on the functionality of sandwich structures.

Committee:

Elias Toubia (Advisor); Paul Murray (Committee Member); Thomas Whitney (Committee Member); Youssef Raffoul (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Civil Engineering; Composition; Design; Engineering; Materials Science; Mechanical Engineering; Polymers

Keywords:

Sandwich Composite Structures; Design; Fatigue; Damage; Joints; Lightweight Materials; E-glass-vinyl ester; GFRP Laminate; Modeling; Prediction; Nondestructive Testing

Choamnak, SitdhichaiNondestructive and destructive testing of covered timber bridge members
Master of Science (MS), Ohio University, 1997, Civil Engineering (Engineering)
Nondestructive and destructive testing of covered timber bridge members

Committee:

Eric Steinberg (Advisor)

Subjects:

Engineering, Civil

Keywords:

Nondestructive Testing; Destructive Testing; Ultrasonic Wave

Fernandes, BertrandDevelopment of a Magnetic Field Sensor System for Nondestructive Evaluation of Reinforcing Steel in Prestressed Concrete Bridge Members
Doctor of Philosophy in Engineering, University of Toledo, 2012, Electrical Engineering
Nondestructive evaluation of prestressed concrete mainly includes inspection of the condition of the prestressing strands for load rating. This thesis presents a magnetic inspection system to measure main magnetic flux (MMF) and magnetic leakage flux (MFL) signals, to evaluate the condition of prestressing stands. A proof-of-concept has been established using a prototype electromagnet-sensor, showing a direct relationship between the cross-sectional area of the strand and the magnitude of magnetic field induced in it. A field test of a box-beam bridge was conducted using both MMF and MFL detection techniques separately. This led to the realization of a comprehensive MMF-MFL electromagnet-sensor system for inspection of prestressed steel in concrete. A computer aided simulation model was created to model the magnetic field signals and aid in better understanding of the electromagnet-sensor. This model is also useful for generating expected magnetic field signals from magnetization of different strand size and configuration setups and thus, helps in making corrosion estimations. The MMF-MFL signal detection concept was evaluated using the existing electromagnet-sensor in a laboratory setup and on prestressed box-beams obtained from a demolished bridge. It was able to identify corrosion and defects such as breaks or fractures in prestressing strands. For this magnetic inspection system to become practical, certain modifications such as redesign of the magnetic field generated by the magnet to have higher resolution have been suggested. Other features such as accurate measurement of pole face to strand distance and weight reduction have been discussed. The overall outcome of this research has shown that magnetic field signals can be useful to detect hidden corrosion in prestressed box-beams.

Committee:

Vijay K. Devabhaktuni, PhD (Committee Chair); Douglas K. Nims, PhD (Committee Co-Chair); Mansoor Alam, PhD (Committee Member); Roger J. King, PhD (Committee Member); Brian W. Randolph, PhD (Committee Member)

Subjects:

Civil Engineering; Electrical Engineering

Keywords:

Box-Beam Bridge; Nondestructive Testing and Evaluaiton; Prestressed Strand; Electromagnet Sensor; Main Magnetic Flux; Magnetic Flux Leakage

Wade, James DavidMagnetic Sensor for Nondestructive Evaluation of Deteriorated Prestressing Strand
Master of Science in Civil Engineering, University of Toledo, 2010, Civil Engineering
The objective of this thesis was to develop a non-destructive in-situ magnetic technique to investigate the remaining cross-sectional area of prestressing strands. Corrosion is the predominate failure-mechanism in box-beam bridges. The current method, visual inspection, is not sufficient as the strands may not be exposed to the investigator. An inaccurate estimate of the remaining area of strands can lead to an overestimated strength of the bridge. A new technique involving an electromagnet and magnetic theories was researched for this thesis. The experiments conducted have shown that it is possible to distinguish between different cross-sectional areas using an electromagnet and Hall sensors. Experiments with an air-gap were first used to simulate concrete cover and provide viability of the technique. These experiments showed that as the cross-sectional area increased so did the induced magnetic field. To further the research, concrete blocks were used in place of the air-gap to better simulate field conditions. Again, these experiments showed an increase in the induced magnetic field as the cross-sectional area was increased. Using the data from the air-gap and concrete block experiments, an approach to determine the cross-sectional area of a corroded strand under concrete cover was investigated.

Committee:

Douglas Nims, PhD (Committee Chair); Vijay Devabhaktuni, PhD (Committee Member); Brian Randolph, PhD (Committee Member)

Subjects:

Civil Engineering; Electromagnetism; Engineering; Transportation

Keywords:

Nondestructive testing; corrosion detection; prestressing strand; magnetic flux; electromagnet; cross-sectional area; bridge; concrete

Susinskas, Larisa DianaField Observation of Installation and Performance of Repair Materials
Master of Science in Civil Engineering, Cleveland State University, 2016, Washkewicz College of Engineering
The state of Ohio is in a region that commonly experiences drastic changes in weather. States with similar climates are susceptible to pavement cracking and failures due to the frequent or extreme freeze-thaw cycles. Freeze-thaw cycles, paired with de-icing chemicals that are frequently placed on roadways during the winter months will most likely lead to pavement cracks and failure. Ohio Department of Transportation (ODOT) routinely repairs and replaces sections of concrete roadways and bridge decks. Therefore, ODOT is seeking durable, cost-effective materials to repair smaller pavement failures. The purpose of this study is to determine which high performance repair materials would be suitable for implementation in ODOT’s construction practices. This includes selecting a variety of high performance repair materials, installing said materials in the field, conducting laboratory testing, and determining which materials are the most efficient and cost-effective. The activities that occurred during this study consist of visual inspections of previously installed high performance repair material patches, the nondestructive testing of each patch, and the installation of two types of selected repair materials. These repair materials are MG Krete and RepCon 928. The results of this study will help determine which of these materials would be optimal to implement in areas with extreme climates.

Committee:

Norbert Delatte, Ph.D. (Committee Chair); Mehdi Jalalpour, Ph.D. (Committee Member); Jacqueline Jenkins, Ph.D. (Committee Member)

Subjects:

Civil Engineering

Keywords:

civil engineering; pothole patching; pothole installation; Ohio Department of Transportation; acoustic concrete tester; rebound hammer; roadway repair materials; patch installation process; patch inspection; nondestructive testing

Shah, Nilesh D.Quantification and Improvement of Stiffness Measurement Techniques of Trabecular Bone Using Porcine Mandibular Condyles
Master of Science (MS), Ohio University, 2014, Mechanical Engineering (Engineering and Technology)
This study improves the agreement between two stiffness measurement techniques of trabecular bone harvested from porcine mandibular condyles. The previous method of Zaylor (2013) measured stiffness with digital finite element and experimental compression tests using 2 mm bone cubes. The current study improves the agreement between methods by examining the effect of sample size using 3 mm and 4 mm cubes, the effect of strain range used in compression tests, and investigating the geometric accuracy of the digital finite element models. It was found that larger specimens improved the stiffness agreement in mediallateral, and superior-inferior directions of the condyles, (R² > 49). The agreement was not affected by the strain limits of 0.4-0.5%, 0.5-0.6%, and 0.4-0.6%. The average digital cube lengths were 2% smaller than the physical lengths. The improved agreement justifies digital modeling of trabecular bone to measure the stiffness of mandibular condyles.

Committee:

John Cotton (Advisor)

Subjects:

Biomedical Engineering; Mechanical Engineering

Keywords:

Trabecular bone cubes; Finite element analysis; nondestructive testing; porcine mandibular condyles

RUIZ, ALBERTOSURFACE ACOUSTIC WAVE VELOCITY MEASUREMENTS ON SURFACE-TREATED METALS BY LASER-ULTRASONIC SPECTROSCOPY
PhD, University of Cincinnati, 2004, Engineering : Aerospace Engineering
SAW velocity spectroscopy has been long considered to be one of the leading candidates for nondestructive characterization of surface-treated metals because of its ability to probe the material properties at different penetration depths depending on the inspection frequency. This research effort is directed towards the use of a highly accurate laser-ultrasonic technique to study the feasibility of SAW dispersion spectroscopy for residual stress assessment on shot-peened metals. Unfortunately, surface acoustic waves are sensitive to spurious parameters, which are byproducts of the surface treatment, i.e., surface roughness and cold work The experimental results obtained on rough surfaces were compared to both theoretical and computational simulations for surface wave induced dispersion from the literature. It was found that experimental results were consistent with the numerical simulations, but neither of them showed conclusive evidence of the high frequency positive dispersion suggested by earlier models. Also, we studied the effect of gradually relaxed shot-peened aluminum specimens on the SAW velocity. Finally, we investigated the individual contribution of residual stress by determining the acoustoelastic constants of the material and we present numerical predictions of the effect of texture on the surface wave dispersion. We detail that the dispersion of the surface wave arises from three different sources, namely, (a) there is an apparent dispersion on smooth surfaces due to the diffraction of the surface acoustic wave as it travels over the surface of the specimen, (b) there is a real but spurious dispersion caused by SAW scattering on the rough surface, and (c) there is the principal dispersion caused material effects of the surface treatment, including the primary compressive residual stress effect and the secondary cold work effect. The results of this investigation revealed some important aspects of SAW propagation on surface treated metals and confirmed that in aluminum SAW dispersion is mainly sensitive to cold work effects and much less to residual stress effects. It still can be a very useful NDE tool since quantitative assessment of the level and distribution of cold work in surface-treated metals is of primary importance from the point of thermo-mechanical stability of the beneficial residual stresses.

Committee:

Dr. Peter Nagy (Advisor)

Keywords:

Ultrasonic Surface Waves; Spectroscopy; Nondestructive Testing; Shot Peening