31-40 of 63 results

  • Behavior of superalloys subjected to fatigue loads under high temperature

    PI Alberto Mello

    CO-I Paulina De La Torre Morales

    CO-I Open Position - New students are welcome

    This study is evaluating what initial conditions can activate cubic slip planes, then the level of accommodation and strain homogenization within the grain, and how a given initial condition affects the material behavior when subjected to operational cyclic loads under high temperature.

    Ni-based super alloys are widely used in turbine engines mainly due to its high strength and fatigue resistance at elevated temperatures. One hypothesis to explain its atypical characteristic among metals is that a cross-slip mechanism is in place. The activation of {100} cubic slip systems along of the octahedral slip planes {111} in Ni-based superalloys has been verified when under high strain and  temperature. The material would exhibit a more homogeneous strain distribution and less strain localization. We seek for the ideal precondition that will improve the endurance of Ni-based superalloy (IN 718) samples subjected to operational loading. We evaluate the initial conditions that activate cubic slip planes, the level of accommodation, and strain homogenization within the grain. With focus on the deformation mechanism, the sample microstructure can be fully characterized by electron backscatter diffraction (EBSD) and the slip systems, after the applied pre-condition, can be tracked via digital image correlation (DIC).

    Accomplished tasks:

    (a) samples’ manufacturing, (b) sample polishing and preparation, (c) furnace installation and operational tests, (d) development of laboratory procedures, equipment and microscopes (optical and SEM), (d) calibration and controller fine tuning for the MTS tensile testing machine, and (e) fatigue test with several specimens, including control samples and modified pre-conditions

    Next steps:

    Characterization of the microstructure of tested specimens under special conditions via EBSD to identify the slip planes and confirm or not the activation of cubic slip systems.

    Categories: Faculty-Staff

  • Influence of cold expansion and aggressive environment on crack growth in aluminum alloy

    PI Alberto Mello

    CO-I Christopher Leirer

    CO-I Ken Shishino

    CO-I Open Position - New students are welcome

    This research aims to establish the effect of hole cold expansion on fatigue life of pre-cracked material under aggressive environment.

    This research investigates the relationship between crack propagation and secondary crack initiation in aluminum alloys with cold worked holes subjected to cyclic loads to determine the impact on fatigue life of joints in presence of aggressive environment. We work with experiments and analysis of fatigue life of bolted joints with coldworked holes in presence of galvanic corrosion. This investigation is examining the effect of local plastic deformation and localized galvanic corrosion on small cracks and fatigue life of bolted joints. The benefits of cold work are well known and its application is widely used in new and repaired structures, even in crack arrester holes. However, coldworked holes are usually fastened to dissimilar materials, what may induce localized galvanic corrosion. When applied in the field, damaged material removal in a cold work procedure may be limited to a maximum allowable diameter for reaming and finishing, what may leave micro/small cracks on the strained region. To completely understand the effect of initial cracks as a function of initial plastic deformation level in a coldworked hole it is necessary to fully evaluate strain distribution during and post cold work with microscopic detail. In a first approach, we have analyzed (FEM and classic analysis) and measured strain distribution during the process using digital image correlation (DIC). In the next step, we have tested specimens under fatigue. Pre cold work induced micro cracks was monitored in-situ via digital optical microscopy. In sequence, the coldworked holes were filled with a dissimilar material fastener in saline environment and the impact of galvanic corrosion on crack growth rate was determined for AA 2024-T3.

    In a next step, we will further investigate the formation of critical secondary cracks. The probable cause could be a local corrosion around cathodic precipitates, but a detailed study is necessary to confirm this hypothesis. The tested samples must be prepared for use in scanning electron microscope (SEM) to identify the local pit formation at the plate edge, find the point of crack initiation, and determine the propagation path. Using striation counting technique, we may be able to estimate the number of cycles to failure and, consequently, the time necessary for the crack initiation under aggressive environment. Additionally, we will plan to use and analyze a special ceramic coating to mitigate galvanic corrosion effect on loaded components. 

    Categories: Graduate

  • Damage Control Measures in Composites: Focus on Damage Tolerance of Aerospace Structures

    PI Alberto Mello

    CO-I Kais Jribi

    CO-I Doug Neill (C.E.S. LLC)

    CO-I Jon Gosse (C.E.S. LLC)

    The focus of this research is to provide advanced methods and tools to address damage tolerance in composite structure 

    This study is in partnership with Computational Engineering Software, LLC (http://icmedesign.com).

    Critical damage within metallic structure usually takes the form of cracks. The main issue is continued growth of the cracks as a function of in-service loading conditions. Often crack growth due to cyclic loading is of interest. Damage within composite structure has a higher number of factors to represent how critical the damage is. It must be considered that:

    • Single cracks rarely exist in composite laminates, if they exist do it is usually as a delamination between adherents.
    • Damage usually manifests itself as a network of inter-connected delaminations and transverse cracks.
    • Unlike metals, Fracture mechanics is generally not applicable to laminated damage. The Mode I, Mode II and Mode III single crack failure modes require satisfaction of similitude to be realized in composite structures.

    The main question to be answered is this study is when will the damage perimeters begin to grow under operational cyclic load. To do that, we expect to accomplish the following main steps:

    Obtain limiting critical values for one or more material systems.

    Develop a sequence of tests to simulate damage and then measure limits to catastrophic failure in compression and/or tension.

    Model each of the test articles and apply the Onset approach to predict whether (for a given applied loading environment) the damage will or will not begin to propagate.

    Compare prediction of the onset of propagation to measured ultimate failure. The criterion of success is that the numerical methodology can conservatively, but realistically predict a load level below which propagation does not occur.

    Categories: Graduate

  • Bird Strike - The Effect of the Leading Edge Radius on the Behavior of the Bird Upon Impact

    PI Alberto Mello

    CO-I Kiran Kumar Avula

    CO-I James Pembridge

    This project is in partnership with Gulfstream Aerospace Corporation under MMSE program.

    Birds pose a major threat to aviation. Bird impact can lead to significant damage of the aircraft and can be sometimes catastrophic. For a damage tolerant design of an aircraft structure, the structure has to fulfill the airworthiness specifications prescribed by FAA or EASA. 



    According to FAR 25, Sub-part 25.571, leading-edge structures of large transport aircraft have to withstand an impact with a 4 lb (1.81 kg) bird (8 lb (3.62kg) for empennage leading edge) when the velocity of the airplane relative to the bird along the airplane's flight path is equal to its cruising speed (Vc) at sea level or 0.85 (Vc) at 8,000 feet, whichever is more critical.

    When a bird impacts the structure, it either slides off of the impacted surface causing less damage or it creates a dent or hole due to penetration into the structure, causing significant damage. The behavior of the bird upon the impact depends on the geometrical characteristics of the structure and the velocity at which the bird impacts. When split upon impact, it results in low impact forces and thus less damage. The impact forces are higher when the bird doesn’t split upon the impact which causes more damage to the target structure as the impact forces are directly proportional to the mass of the bird.

    Bird strike tests are very expensive and their number in the engine development programs should be minimized. Numerical simulations help reduce a significant amount of testing by providing valuable information in the design process. This thesis aims to develop a model using smooth particle hydrodynamics (SPH) method for analyzing aircraft leading edges for bird strikes that will correlate well with the test results and subsequently, apply the method to study the effect of the leading edge radius on the behavior of the bird (split/not split) upon the impact.

    The objective is to generate sufficient data through numerical analysis to confirm the “one inch radius split/no split dividing line”, and to validate the empirical formulas used to calculate the impact forces. Overall, the goal is to save both time and money for the future generation aircraft by minimizing or eliminating the bird strike tests. 

    Categories: Graduate

  • Pilot-in-the-Loop UAS Mobile Research Test-Bed

    PI Hever Moncayo

    CO-I May Chan

    CO-I Ashwini Agrawal

    CO-I Agustin Giovagnoli

    This project aims to develop and implement a Mobile UAV Ground Control Station (GCS) supporting aviation safety research with pilot-in-the-loop capabilities using unmanned aerial systems platforms, in which flight conditions, such as systems failures, could be simulated in real-time to characterize pilot response, control laws performance, and human-machine and control laws interactions.

    ​A fruitful achievement of this project will provide a platform to validate and assess new concepts and technologies that are beneficial for improving engineering fidelity of early systems integration testing based on pilots feedback and their interaction with on-board flight controls systems.

    Categories: Faculty-Staff

  • Shielded UAS Operations Detect and Avoid

    PI Hever Moncayo

    ​This effort is intended to identify risks and recommend solutions to the FAA that enable shielded UAS operations

    ​This project is funded under the FAA ASSURE program. Certain small UAS (sUAS) Beyond Visual Line of Sight (BVLOS) operations, such as structural inspection, may be in close proximity to structures that are collision hazards for manned aircraft. These types of operations that are in close proximity to manned aviation flight obstacles such that they provide significant protection from conflicts and collisions with manned aircraft are termed “shielded” operations. This effort is intended to identify risks and recommend solutions to the FAA that enable shielded UAS operations. Several topics related to this project include simulation of dynamic systems, simulation environment programming, guidance, control and dynamics, and hardware implementation.

    Categories: Faculty-Staff

  • Vision and Wireless-Based Surveying for Intelligent OSAM Navigation (VISION)

    PI Hever Moncayo

    CO-I Kadriye Merve Dogan

    ​In this project, which is a SpaceWERX Phase I STTR program with Orbital Prime, we are developing algorithms to increase autonomy of OSAM applications. 

    ​In this project, which is a SpaceWERX Phase I STTR program with Orbital Prime, we are developing algorithms to increase autonomy of OSAM applications. This includes the application of machine learning techniques to improve accuracy of position and orientation estimation for proximity operations in space. Machine learning include deep learning combined with vision-based navigation designed and tested in both, virtual simulation environment and actual thrust-based spacecraft system.

    Categories: Faculty-Staff

  • Mitigating GPS and ADS-B Risks for UAS

    PI Hever Moncayo

    ​In this project, the research team is investigating different strategies to mitigate such risks and proposing methodologies to increase safety of UAS operations within the National Airspace.

    This project is funded under the FAA ASSURE program. Unvalidated or unavailable GPS and “ADS-B In” data poses security and safety risks to automated UAS navigation and to Detect and Avoid operations. Erroneous, spoofed, jammed or dropouts of GPS data may result in unmanned aircraft position and navigation being incorrect. This may result in a fly away beyond radio control, flight into infrastructure or flight into controlled airspace. Erroneous, spoofed, jammed or dropouts of “ADSB-In” data may result in automated unmanned aircraft being unable to detect and avoid other aircraft or result in detecting and avoiding illusionary aircraft.

    In this project, the research team is investigating different strategies to mitigate such risks and proposing methodologies to increase safety of UAS operations within the National Airspace. Several topics related to this project include simulation of dynamic systems, artificial intelligence, flight testing of UAS and hardware implementation.

    Categories: Faculty-Staff

  • Nanoscale Design of Interfacial Kinematics in Composite Manufacturing

    PI Sirish Namilae

    CO-I Marwan Al-Haik

    This NSF-funded research will elucidate the role of interfacial kinematics and energetics in the evolution of inter-ply interfaces in composite structures during manufacturing. The research team will develop a novel experimental method for in-situ characterization of surface and interface deformations during composite processing, utilizing a customized commercial composite autoclave with a digital image correlation system. The surface strain and displacement measurements will be combined with ex-situ X-ray tomography and thermal characterization to map the interfacial thermomechanical response as a function of design and processing parameters. Additionally, the interfacial behavior will be engineered through the rapid and controlled growth of ZnO nanowires on carbon fibers to create a nanoscale interfacial component that increases the fiber bending resistance and creates an interlocking effect at the interfaces to mitigate defects propagation. The experimental research will be complemented by molecular dynamics simulations of the sliding of amorphous polymer interfaces and mesoscale simulation of flow in porous media. This comprehensive approach of in-situ characterization, interface design, and modeling will lead to a fundamental understanding of the ply movement during composite manufacturing and development of methods to reduce the occurrence of processing-induced defects.



    Categories: Faculty-Staff

  • Software Infrastructure For Analysis of Infection Propagation Through Air Travel

    PI Sirish Namilae

    This NSF funded  project seeks to develop a novel software that will provide a variety of pedestrian dynamics models, infection spread models, as well as data so that scientists can analyze the effect of different mechanisms on the spread of directly transmitted diseases in crowded areas. The initial focus of this project is on air travel. However, the software can be extended to a broader scope of applications in movement analysis and epidemiology, such as in theme parks and sports venues. Development of the proposed software will involve several innovations. It will include a novel phylogeography model that links fine-scale human movement data with virus genetic information to more accurately model geographic diffusion of viruses. New models for pedestrian movement will enable modeling of complex human movement patterns. A recommendation system for the choice of pedestrian dynamics models and a domain specific language for the input of policies and human behaviors will enhance usability by researchers in diverse fields. Community building initiatives will catalyze inter-disciplinary research to ensures the long-term sustainability of the project through a critical mass of contributors and users.



    Categories: Faculty-Staff

31-40 of 63 results