Highly Nonlinear Solitary Waves for Rail Buckling Prevention

One of the major structural problems in the railroads made of continuous welded rails is buckling in hot weather and breakage or pulling apart in cold weather. Buckling is usually caused by the high compressive stress due to thermal load or weak track conditions, and sometimes vehicle loads. The prevention of track buckling is related to the determination of the temperature, called rail neutral temperature, at which the net longitudinal force in the rail is zero. In the project presented in this thesis we investigated the capability of a novel sensing system to indirectly measure applied stress in rails and predict incipient buckling. This system consists of a simple and cost-effective transducer, recently developed at the University of Pittsburgh, which enables the generation and detection of highly nonlinear solitary waves (HNSWs), which are compact non-dispersive mechanical waves that can form and travel in highly nonlinear systems such as granular, layered, or porous materials, where they are conventionally generated by the mechanical impact of a striker. To prove the feasibility of this novel system to predict buckling temperature or measure applied stress, we investigated numerically and experimentally the interaction between solitary waves propagating along a chain of granular particles and slender beams of different shapes, lengths, and boundary conditions. We found that the geometric and mechanical properties of the beam or thermal stress applied to the beam alter certain features of the solitary waves. Overall, the work presented in this thesis was articulated in four main tasks: 1) literature review; 2) create a semi-analytical model; 3) design and test new transducers; and 4) conduct a series of experiments including a field test at the University of California, San Diego. This HNSWs approach does not require many electronic accessories and shows a good sensitivity to the properties of the material that is at the interface with the chain of particles. Moreover, it only observes the propagation of solitary waves within the transducer without the waves in the rail

Development of active microwave thermography for structural health monitoring

Active Microwave Thermography (AMT) is an integrated nondestructive testing and evaluation (NDT&E) method that incorporates aspects of microwave NDT and thermography techniques. AMT uses a microwave excitation to generate heat and the surface thermal profile of the material or structure under test is subsequently measured using a thermal camera (or IR camera). Utilizing a microwave heat excitation provides advantages over traditional thermal excitations (heat lamps, etc.) including the potential for non-contact, selective and focused heating. During an AMT inspection, two heating mechanisms are possible, referred to as dielectric and induction heating. Dielectric heating occurs as a result of the interaction of microwave energy with lossy dielectric materials which results in dissipated microwave energy and a subsequent increase in temperature. Induction heating is a result of induced surface current on conductive materials with finite conductivity under microwave illumination and subsequently ohmic loss. Due to the unique properties of microwave signals including frequency of operation, power level, and polarization, as well as their interaction with different materials, AMT has strong potential for application in various industries including infrastructure, transportation, aerospace, etc. As such, this Dissertation explores the application of AMT to NDT&E needs in these important industries, including detection and evaluation of defects in single- or multi-layered fiber-reinforced polymer-strengthened cement-based materials, evaluation of steel fiber percentage and distributions in steel fiber reinforced structures, characterization of corrosion ratio on corroded reinforcing steel bars (rebar), and evaluation of covered surface cracks orientation and size in metal structures --Abstract, page iv

Advanced Gas Turbine (AGT) powertrain system

A 74.5 kW(100 hp) advanced automotive gas turbine engine is described. A design iteration to improve the weight and production cost associated with the original concept is discussed. Major rig tests included 15 hours of compressor testing to 80% design speed and the results are presented. Approximately 150 hours of cold flow testing showed duct loss to be less than the design goal. Combustor test results are presented for initial checkout tests. Turbine design and rig fabrication is discussed. From a materials study of six methods to fabricate rotors, two have been selected for further effort. A discussion of all six methods is given

Advances in structural analysis and process monitoring of thermoplastic composite pipes.

Thermoplastic composite pipes (TCP) in comparison to other pipes have proven beneficial features due to its flexibility which includes being fit for purpose, lightweight and no corrosion. However, during the manufacturing of TCP which involves the consolidation process, certain defects may be induced in it because of certain parameters, and this can affect the performance of the pipe in the long run as the induced defects might lead to in-service defects. Current techniques used in the industry are facing challenges with on-the-spot detection in a continuous manufacturing system. In TCP manufacturing process, the pipe is regularly monitored. When a defect is noticed, the whole process stops, and the appropriate action is taken. However, shutting down the process is costly; hence it is vital to decrease the downtime during manufacturing to the barest minimum. The solutions include optimizing the process for reduction in the manufacturing defects amount and thoroughly understanding the effect of parameters which causes certain defect types in the pipe. This review covers the current state-of-the-art and challenges associated with characterizing the identified manufacturing induced defects in TCP. It discusses and describes all effective consolidation monitoring strategy for early detection of these defects during manufacturing through the application of suitable sensing technology that is compatible with the TCP. It can be deduced that there is a correlation between manufacturing process to the performance of the final part and selection of characterization technique as well as optimizing process parameters

Effect of wire diameter on ultrasonic enhancement of subcooled pool boiling

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.New methods for cooling of microelectronic elements have been recently developed, including application of ultrasonic fields. Ultrasonic fields enhance the heat transfer in two-phase cooling. The present work deals with ultrasonic enhancement of heat transfer from wires in sub-cooled pool boiling. The experiments have been carried out using three wires of different diameters: 0.05, 0.09, 0.2mm, submerged into a bath with water. The applied ultrasonic field was of frequency of 40 kHz and intensity of 0.5 W/cm2. The wire wall temperature was measured as a function of wire surface heat flux. When the ultrasonic field was applied, the wall temperature reduced in the range of measured heat fluxes. The temperature difference increased with the heat flux. It also increased with the wire diameter. At the smallest diameter only a small decrease of the wall temperature, about 10-15 degrees, was observed, while at larger diameters the decrease of the wall temperature was about 30 - 35 degrees.dc201

Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Characterization of concrete materials using non-destructive wave-propagation testing techniques

Non-destructive testing (NDT) of concrete members has been widely used for characterisation of material and assessment of functional structures without impairing their functions and performances. This thesis focuses on addressing critical challenges related to the practical implementation of NDT techniques based on wave-propagation approaches for characterisation of concrete members used in civil infrastructures. Specially, this research aims to achieve three interdependent objectives related to developing NDT techniques with piezoceramic-based transducers: monitoring of very early-age concrete hydration process, detection, and monitoring of cracking in concrete members of different complexity under loading. The concept of piezoceramic-based Smart Aggregate (SA) transducers is central to this research. Embedded SA transducers with an active sensing method have shown great potential for characterisation of construction materials such as concrete and concrete-steel composites. Based on the developed SA based approaches, an active sensing approach with appropriate arrangement of SAs in and on concrete members, and analysis of the received signal using the power spectral density, total received power and damage indexes is developed and applied in this thesis. To confirm its applicability for characterisation of very early-age concrete, a systematic investigation is performed into concrete specimens with different values of water-to-cement ratio due to slightly different initial water amounts, and different separation distances between the embedded SAs. For the detection and monitoring of cracking in concrete members under loading the mounted SA based approach is proposed and applied. It is shown that NDT systems, based on this approach, provide detection and monitoring of cracking in a variety of concrete members under loading, including relatively simple concrete beams and reinforced concrete beams under bending, and reinforced concrete slab as a part of a complex composite member under cyclic loading. Comparisons are provided between the proposed system and conventional load cell and strain gauge systems with each tested member

Post-Fire Assessment of Concrete Tunnel Structures

Although concrete tunnel structures can lose strength and long-term durability due to fire, the literature on the remaining capacity of structures after fire events is very scattered, and no published post-fire inspection protocols specifically for concrete tunnel structures are available. This work aims to summarize and synthesize the current state of knowledge of the deleterious effects of fire on the residual condition of concrete tunnel structures and how the extent and degree of fire damage can be assessed. The scope of this work includes an extensive literature review, heat testing of some common tunnel elements, and residual strength testing of a tunnel wall panel. The literature review includes a review of published standards, technical reports, academic papers, and a survey of post-fire inspection practices at other state DOTs and transit organizations. Topics covered in the review include the residual mechanical properties of concrete, steel, and the concrete/steel bond after fire, the residual strength and stiffness of structural members after fire, existing inspection tools and methods for assessing concrete structures after fire, and repair methods for fire-damaged concrete structures. The outcomes of the heat testing are presented, including the setup of a radiant heating system (which does not use a flame), procurement of sample specimens for testing, thermal and physical testing of specimens, and evaluation of results. Lastly, based on the literature review and experimental testing, recommendations for future work are presented