Tasnim Hassan

The project team will perform several closely-knit tasks to probe the microstructural behavior and to evaluate their effects on the mechanical properties of two candidate cladding alloys ??? FeCrAl and ODS-14YWT. These alloys have been investigated for reactor use for a number of years and are widely considered to be radiation-tolerant materials that can withstand the extreme environment of a nuclear reactor. As mentioned previously, the behavior at extremely large doses and high temperatures is largely unknown. The project team, therefore, proposes ion irradiation with doses reaching to 400 dpa for temperatures ranging from 300 to 700??C on two alloys FeCrAl and ODS-14YWT. At the University of Tennessee-Knoxville (UTK) ??? Ion Beam Materials Laboratory, co-PI Weber will conduct the irradiation tests with several types of ions. These experiments will generate a database on microstructure evolution and material degradation, with irradiation temperature and high dose as key variables. Separate gas implantation effects will be probed to investigate the effects of He concentration at high irradiation doses. Thus, the effects of void interactions and void swelling, which are critical to the technical readiness of these alloys, will be evaluated at high dpas and temperatures. Leveraging the ongoing NEUP projects on miniature specimen testing, the project team will then perform in-situ thermo-mechanical experiments (tension, torsion, creep, and creep-fatigue) on the ion-irradiated samples up to a temperature of 700??C. The primary objective is to probe and characterize the microstructural changes in-situ using a scanning electron microscope (SEM). The test rig is currently being installed as a user facility by PI/PD, and co-PIs Hassan and Eapen.

Fast and accurate measurements of creep are needed for qualifying new alloys for current and next generation reactors. For recently developed ferritic alloys such as FeCrAl, the lack of creep/fatigue data is more acute. To address this concern, this project will design and develop a novel miniature creep testing system for performing creep and load relaxation tests at multiple scales inside a scanning electron microscope (SEM). The primary objectives of the proposal are: (i) Collect rapid thermal creep and load relaxation data for two selected ferritic alloys: FeCrAl and oxide dispersed strengthened (ODS-14YWT) alloy at accelerated test conditions using solid, thin-walled and flat specimens under biaxial and uniaxial loading conditions across a temperature range of 500 ?????????C to 1000 ?????????C, (ii) Benchmark select data from miniature specimens against data from conventional creep tests with larger samples, (iii) Extract deformation mechanisms using in-situ SEM for virgin and neutron irradiated samples using the miniature tester, which otherwise is onerous with macroscopic creep equipment, and (iv) Perform mesoscale discrete dislocation dynamics (DD) simulations using information derived from SEM, and macroscopic constitutive modeling for predicting long-time behavior.

A novel thermo-mechanical fatigue (TMF) testing system, referred by miniature TMF (MTMF) system has been developed at NCSU for in-situ testing of miniature specimens within Scanning Electron Microscopes (SEM). The MTMF is capable of prescribing axial-torsional loading to solid specimen and axial-torsional-internal pressure loading to tubular specimen of 1 mm diameter at elevated temperatures (up to 1000oC) to investigate deformation of microstructure and failure mechanism in real time. Currently, in-situ SEM testing with the MTMF is performed at the Analytical Instrumentation Facility (AIF) at NCSU. This poses a serious restriction to investigate failure mechanisms of very high temperature reactor (VHTRs) materials primarily because with a user facility, such as AIF, we can only perform short-term tests that span over few days. However, fatigue, creep and creep-fatigue tests for VHTR materials may span from few days to several weeks. Hence, existing SEMs on campus are not available for long-term in-situ testing of VHTR materials. Currently, fatigue, creep and creep-fatigue failure mechanisms of new and existing alloys are mostly investigated through ex-situ testing or short duration in-situ uniaxial testing within SEM. Consequently, initiation and propagation of many failure mechanisms, especially interactions between creep and fatigue mechanisms in reducing high temperature component lives remain unknown. Hence, developing a shared in-situ testing laboratory (ISTL) is essential to allow NCSU researchers to perform novel research on nuclear materials addressing issues of fatigue, creep and creep-fatigue failure mechanisms. The proposed ISTL dedicated to performing long-term fatigue, creep and creep-fatigue tests is in critical need to develop design criteria of VHTR materials for ASME Code Sec III Div 5. However, existing facilities at NCSU or any other universities or national labs in the nation do not have a facility dedicated to perform long term tests representing realistic loading conditions of VHTR. Therefore, a suitable SEM compatible with the MTMF system at NCSU is proposed to be acquired to develop an ISTL to address high temperature nuclear materials and ASME Code issues. With the availability of such a ISTL, uniaxial and multiaxial cyclic experiments prescribing realistic thermo-mechanical fatigue (TMF), creep and creep-fatigue loading can be performed on specimens of VHTR materials, such as Alloy 617, 316H, 800H, Grade 91 steel, for addressing the high temperature component design and development issues. Finally, because of the size of commercially available TMF systems, these cannot be used for in-situ SEM testing, which is essential for investigating existing alloys and developing new alloy for VHTRs. Hence, acquisition of a SEM will give the NCSU research community unprecedented capability to perform fundamental research and educate next generation scientists in studying real-time long-term microstructure evolution of nuclear materials under uniaxial and multiaxial loading. In addition, the proposed equipment will allow training undergraduate and graduate students and postdocs in performing material characterization using advanced techniques and provide hands on experiences to students in various undergraduate and graduate courses.

The proposed project will implement the recently developed elastic-perfectly plastic (EPP) analysis methodologies in accordance with the ASME Code, Section III, Division 5 for diffusion welded compact heat exchangers (CHXs) in high temperature nuclear service. Burst, and cyclic pressure and thermal experiments on diffusion bonded CHX specimens of SS316L and Alloy 617 will be performed for investigating stress concentrations at sharp channel corners and determining possible failure modes. Hybrid and printed circuit heat exchangers (H2X and PCHE) meet the requirements of space and weight savings, high thermal effectiveness, low pressure drop and high design pressure capability. These attributes improve cost and efficiency of advanced reactors and thereby advances DOE??????????????????s goal of carbon-free energy production. Currently, CHXs are covered by design rules in the ASME Code, Section VIII, Division 1 along with Section IX procedures for diffusion welding. But the Section VIII rules are limited to the maximum temperature of 427oC, hence cannot be applied to the intermediate and secondary heat exchangers (IHXs and SHXs) in Sodium Fast Reactors (SFRs) at 550oC and in high temperature gas-cooled reactors (HTGRs) at 950oC). No detailed design strategies for the CHX at the temperature range (550-950oC) have been published. For the IHXs in SFR and HTGR, thermal stresses, fatigue and creep deformation and rupture life limits must be considered for Section III, Division 5, Class A applications, and these are not covered in the Section VIII design methodology. Some IHX and SHX applications are anticipated to operate at significant pressure differentials in addition to cyclic thermal conditions. Hence, determination of thermal stresses in addition to primary stresses is essential for the calculation of creep strains, thermal deformations and peak stresses for fatigue and creep/fatigue usage estimates. It is anticipated that the thermal stresses in the diffusion bonded core will be large, especially during transients. Also high thermal strain concentrations are expected in the core near sidewalls, as well as at header attachment welds. On some scales, these concerns may be best addressed by the recently introduced EPP analysis methodology proposed for the evaluation of primary loads, strain limits and creep-fatigue in Division 5 of the ASME Code. Current Division 5 rules using simplified elastic, and decoupled creep and plasticity analyses have been deemed inappropriate for elevated temperature applications. Hence, EPP methodologies which considers creep-plasticity interactions will allow limit to various stress measures and strain limits. This project will perform a systematic set experiments on stainless 316L and Alloy 617 ASTM coupons and CHX specimens to develop structural design methodology based on EPP analysis in order to provide assessment of the elevated temperature failure modes of two types of CHXs under sustained and cyclic thermal and pressure loads. The research will be performed in consultation with the industry and ASME Code experts such that the outcomes can be used as technical basis for Section III, Division 5 ASME Code Case for CHXs in high temperature nuclear service.

A group of investigators from several universities and industrial organizations (with University of Wisconsin as the lead) proposes to advance the state of the ASME section III code (nuclear service) for compact heat exchangers (CHXs). This proposed project will advance the technical knowledge of CHXs and lay the foundation necessary for of CHXs to be certified for use in nuclear service. During the course of this project the investigators will advance the understanding of the performance, integrity and lifetime of the CHXs for use in any industrial application making their use more attractive and accessible to industry. This will be achieved by developing qualification and inspection procedures that utilize non-destructive evaluation (NDE) and advanced in service inspection techniques, with insight from an industrial utility leader, EPRI. ASME Code experts on section III from MPR associates will direct the testing and help to develop a series of documents that define the rules and regulations for use of the CHX with input from members of the ASME section III committee. Currently, CHXs are covered by design rules in the ASME Code, Section VIII, Division 1, which is limited to the maximum temperature of 427oC, hence cannot be applied to the intermediate and secondary heat exchangers in Sodium Fast Reactors (SFRs) and High Temperature Gas-Cooled Reactors (HTGRs) with maximum outlet temperatures 550oC and 950oC, respectively. No detailed design strategies for the CHXs in the temperature range 550-950oC have been published. Through this IRP and earlier CHX projects sponsored by the US DOE, the investigators at NC State University (NCSU) will develop high temperature material properties of diffusion welded laminated structures for Alloys 617 and 800H, and Stainless Steel (SS) 316H. A set of isothermal tension, creep, fatigue and creep-fatigue tests on diffusion welded Alloy 800H will be performed and combined with the diffusion welded Alloy 617 and SS316H data from earlier CHX projects to determine the elevated temperature material properties of these ASME Code approved materials. NCSU will perform isothermal burst, and steady and cyclic pressure experiments on diffusion bonded small CHX cores of Alloy 800H, and again will combine with the earlier CHX test results on Alloy 617 and SS316H to explore the influence of sharp channel corners and thermal stresses on the failure modes. NCSU will implement a recently developed advanced unified constitutive model (UCM) in performing full inelastic analyses of CHX to provide insight on the failure responses observed in the CHX experiments to be performed through this proposed IRP. The primary outcomes of the NCSU tasks will include, i) a set of high temperature fatigue, creep, and fatigue-creep properties of three ASME Code approved materials, ii) a set of fatigue, creep and fatigue-creep test data of diffusion welded CHX cores of these materials, iii) experimentally validated UCMs and corresponding model parameters of the ASME Code approved materials, and finally iv) insight on the influence of sharp channel corners and thermal stresses on the failure modes of CHXx. These outcomes will facilitate the development of an elastic perfectly plastic (EPP) analysis based design methodologies for CHXs, background document for incorporating the EPP based structural design methodologies as an ASME Code case in Section III, Division 5, and NDE and service inspection methodologies. The project tasks will be accomplished through integrated efforts of one PhD and one undergraduate students, and two NCSU faculty members. The PhD and undergraduate students will perform the analysis and experimental tasks under the supervision of the faculty members. Through performing the research tasks and interacting with other university researchers and industry experts, graduate and undergraduate students will be trained for the future work force of the nuclear power industry.

Honeywell Aerospace is interested to develop a USERMAT subroutine in ANSYS to analyze the deformation behavior of wrought Haynes 282 (HA-282) combustor liners. The commercially available nonlinear finite element codes such as ABAQUS and ANSYS, which are used for the analysis of such components, do not have the proper constitutive model in their material libraries. Hence, it will be necessary to develop an experimentally validated advanced constitutive model and develop necessary numerical scheme to incorporate the model into the ANSYS USERMAT subroutine in order to perform combustor liner and other high temperature structural analyses. Honeywell Aerospace will develop the needed set of high temperature experimental data through consultation with the NCSU investigators.

A novel testing system will be designed and developed for mechanical testing of miniature tubular specimens under any combination of axial, torsional, and internal pressure monotonic and cyclic loading in the room to 1000oC temperature. The proposed test system size and orientation will be designed such that it can be set under an optical microscope (OM) and scanning electron microscope (SEM) for in-situ microstructural studies. With the emerging research in materials genome and integrated computational materials engineering, importance and significance in performing materials testing under realistic multiaxial loading and environmental (temperature, chemical and gas) conditions are in urgent need. For enhancing resilience of manufactured components, design of new materials should consider failure mechanisms at critical points (weld toe, stress concentration and hot spot) through testing miniature specimen under multiaxial loading. Such tests need to be performed at high temperatures for understanding premature failures of components in energy and aerospace industries. Manufacturing processes, welding, cold drawing, quenching, surface finishing etc. induce localized material heterogeneity whose influence on failure mechanism can only be studied through testing miniature coupons. Extreme service loading and environmental conditions alter local material properties, which can only be studied through miniature specimens in determining remaining life of critical components. Development of micro-fabrication techniques requires material properties and their evolutions which can only be determined accurately through miniature specimen testing under realistic loading. According to the investigators? knowledge, the proposed testing system currently is not commercially available anywhere in the world. Moreover, even a standard size axial-torsion mechanical testing machine with or without high temperature capability is not available at any universities in North Carolina or its neighboring states. The proposed miniature testing system will be shared by a large group of inter and intra university researchers in performing fundamental research on advanced material design and characterization, micro-forming, constitutive modeling, computational modeling, and failure-life prediction for the energy, aerospace, automobile, electronics, communication, biomedical, sensor and infrastructure industries. The proposed testing system will create research opportunities in material design and component manufacturing, integrated through constitutive and computational modeling research, as well as, meeting the research needs of material characterization usually obtained through standard testing systems. Development of the proposed testing system will performed by detailed thermo-mechanical analysis. Technologies of actuators, sensors, heating and pressurization, digital image correlation, water cooled grips and their controls will be critically evaluated in developing and integrating technologies needed for developing the proposed material testing system. Cooperation with the U.S. commercial partners will facilitate this process. The proposed system will impact design and development of new materials, high performance components, and micro-forming processes. Other important outcomes will be eliminating the long (10-20 years) trial & error methods of designing new materials for enhancing component life, and predicting failure life of components with much less uncertainty than today. Two Graduate and one undergraduate student will be trained on the novel testing system through designing and developing the proposed testing system. Many other students will be trained for use of the testing system in performing their research towards MS and PhD degrees. Undergraduate students through their research projects and K-12 teachers through The Engineering Place and Women in Engineering will perform experiments with the proposed system. Partnership with an US commercial testing system manufacturer will allow quick commercialization of the new system to other r

Grade 91 (modified 9Cr-1Mo, or 9Cr-1Mo-V) martensitic steel is an important material in the domestic and international power generation industries. It is the default material for high temperature steam outlet headers and main steam piping around the world. The material relies on a specific state of microstructure to ensure its excellent high temperature strength, but changes to this microstructure, and a subsequent loss of strength, often occur in operation due to strain cycling and aging. There is a very large class of pressure equipment that sees only a few hundred cycles over its lifetime, although of typically significant strain amplitude. This equipment usually sees creep and plasticity occurring independently (time-independent plastic straining followed by high temperature relaxation, or vice-versa). For this class of problem, creep damage is the focus and fatigue (or plastic strain) is the quantity lumped into the damage properties, margin or calculation procedure. This is the type of equipment and the operation that is of concern in this project. Hence, for feasible design development for components of such pressure equipment, it is essential to develop advanced constitutive models to simulate the tertiary creep, low-cycle fatigue and creep-fatigue responses of Grade 91 steels. As such, meaningful predictions of time-independent strain, short term relaxation and long term creep and failure can be predicted with a single model. Emphasis will be given on the actual damage and failure prediction rather than extremely exact strain responses. Hence, the project is envisioned to be executed in two phases, with the first phase dedicated to the development of a one-way coupled viscoplasticity-Omega model, and the second phase dedicated to the development of a two-way coupled viscoplasticity-Omega model, and subsequently a robust unified viscoplasticty model. All models to be developed will be validated against a set of uniaxial experimental responses to be acquired from published literature.

The objectives of this Grant Opportunity for Academic Liaison with Industry (GOALI) research project are to, a) create a fundamental understanding of the mechanism which enhances formability during continuous-bending-under-tension (CBT) and b) to exploit this behavior through innovative manufacturing processes. If less formable materials such as advanced high strength steels (AHSS) and Aluminum alloys are able to be processed more easily using this concept, significant improvements in product performance, environmental friendliness, and productivity of sheet metal components will be achieved. The PIs and senior personnel have significant and relevant expertise in experimental mechanics; material characterization; microstructural and continuum modeling; numerical simulations; and sheet metal forming processes, to assure the success of this research. Background: A ubiquitous experiment to characterize the formability of sheet metal is the standard uniaxial tension test. Past research has shown that if the material is repeatedly bent and unbent during this test (i.e., CBT), the percent elongation at failure increases significantly (e.g., from 22% to 290% for an AISI 1006 steel). This phenomenon has also been empirically observed in industry; the failure strains of a sheet which is passed through a drawbead (i.e., has been bent and unbent three times before entering the die) are considerably higher than those of the original sheet. The phenomenological rationale for this behavior is that the compressive stresses due to bending lower the net axial force on a cross-section, thus delaying necking. However, the exact microstructural cause of this ductility enhancement and the effect of precipitants, alloying elements, grain size, loading paths, specimen geometry, etc., are not known. Because of this lack of fundamental understanding, failure cannot be accurately predicted, restricting applications. Intellectual merit: In order for the industry to take advantage of CBT to achieve formability improvements, fundamental knowledge of the underlying phenomena, accurate models to characterize the effect, and innovative processes to exploit this behavior are required. The tasks proposed here, which will all benefit from the industrial collaboration, are, a) conducting strip- and sheet-CBT tests with real-time variation of process parameters to determine the material behavior during CBT, b) assessing the remaining formability after a specified number of CBT cycles, c) characterizing the material microstructure after CBT processing, d) developing material and numerical models (including experiments to assess the kinematic hardening behavior of the material) to accurately capture the observed CBT effects, e) devising and implementing process innovations to exploit this behavior, and f) disseminating the results to industry through workshops, presentations, and publications. Two specific materials, DP780 and AA6022, will be investigated in this research. Both of these are of interest for various weight-sensitive applications, but have very different microstructures and are expected to behave differently during CBT. In addition to enlarging and enhancing the scientific understanding of the CBT process, the knowledge gained from this research will also benefit other non-conventional forming processes, e.g., incremental sheet forming, and will provide insight into the failure modes during bending of AHSS over small radii. Broader impacts: The CBT process and models developed in this research will benefit society at large by reducing the environmental impact of products such as automobiles and by enabling more aggressive product designs, which will further decrease the weight and cost of components. Graduate and undergraduate students will benefit from the industrial focus of this project and the fact that the results will be directly integrated into the curriculum. In addition, the PIs will build on their past success in recruiting students from underrepresented groups in engineering to participate in the research. Research Experience for

Feasibility and sustainability of the Gen IV nuclear power plants (NPPs) require operation at high temperature around 900oC for a design life of 60 years. For design code development and structural integrity evaluation of the Gen IV NPP components, such as, reactor pressure vessels (RPVs), heat exchanger and steam generator, one of the major missions of the DOE is to develop mechanistic understanding of creep, creep-fatigue and creep-ratcheting failures of their candidate steels. Towards reaching the goals of the DOE mission, this proposed project will conduct a systematic set of experiments to understand multiaxial, low-cycle, creep-fatigue and creep-ratcheting failures of Grade 91 steel. The experimental loading parameters will represent the Gen IV RPV stress and temperature histories at critical locations. Detailed finite element analysis of the Gen IV RPV will be performed to determine these experimental loading histories. The multiaxial cyclic loading to be prescribed to the Grade 91 steel tubular coupons will involve axial, torsion and internal pressure cycles. Various temperature levels, and stress and strain rates will be prescribed to quantify the influence of ?dynamic strain ageing? on the creep-fatigue and creep-ratcheting failure responses. TEM study will be conducted to understand the dislocation substructure evolution and failure mechanisms of Grade 91 steel at various stages of the fatigue loading. An experimentally validated thermo-mechanical constitutive model will be developed for simulating the elevated temperature, multiaxial failure responses of Grade 91 RPV steel and its weld joints. A unified, non-linear kinematic hardening model involving various internal state variables to simulate rate and temperature dependent material responses will be developed. This advanced constitutive model will be implemented into the widely used finite element software package ANSYS so that realistic simulations of Gen IV RPV can be performed for developing ASME code (ASME-NH) design methodologies and addressing licensing issues.

The proposed research will build upon a current investigation to develop a unified constitutive model intended for design-by-analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-fatigue and creep-ratcheting are being conducted on the nickel-base Alloy 617 at temperatures of 850 and 950 ??A?C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load control cycling, are major concerns for NGNP design. The proposed research is aimed at characterizing the microstructure mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method will be researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter will be correlated to microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-fatigue and creep-ratcheting deformation. Limited mechanical testing is proposed to supplement the current investigation and provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-ratcheting. Thorough microscopy, including High Resolution Transmission Electron Microscopy (HR-TEM), Scanning Transmission Electron Microscopy (STEM), Energy Dispersive Spectroscopy (EDS), and Scanning Electron Microscopy (SEM), is required and will be conducted to correlate the beta parameter with individual microstructure mechanisms. The acoustic harmonic generation method is well developed for longitudinal waves in large specimens. Higher harmonic generation in thin plates is becoming better understood and some success has been achieved. We propose to research applying the method to tubular mechanical test specimens, and eventually pipes for nondestructive evaluation. Tubular specimens, samples sectioned from these specimens, and pipes will all act as waveguides, thus we will apply the acoustic harmonic generation method to guided waves in shells. Coupling ultrasonic transducers to the shell sample will be achieved to generate a pure mode and receive low amplitude harmonics. The diverse project team, which includes a minority institution, enables the results of the microstructural evolution characterization to be employed for remaining useful life prediction. The unified constitutive model currently being developed for design purposes will be adapted for life prediction by correlating the beta parameter evolution obtained from nondestructive evaluation (or eventually online monitoring) to the model?s internal state variables. Such a microstructure based constitutive model will enable improving the ASME-NH code for Alloy 617.

An innovative technique for improving seismic performance of steel beam-column connection with the advantages of the reduced beam section (RBS) connection, but with improved energy dissipation. Through a pilot study the concept is validated numerically at NC State University. This proposed research will conduct a systematic set of beam-column connection experiments for evaluating the novel seismic performance enhancement concept. The novel concept involves heat treating sections of beam flanges by exposing these sections to very high temperatures for certain amount of time before slow air cooling. Such heat treatment reduces the strength of steel in the heat treated areas of the flange. Consequently, under seismic loading plastic hinge develops at the heat treated beam section (HBS). Among the three moment resisting connections prequalified for special and intermediate moment frames by the 2005 AISC 358 standards, the reduced beam section (RBS) is the most popular because of its seismic performance and cost effectiveness. In the RBS connections, ?weakening? of the beam flanges induces plastic hinge away from the welds. In case of the HBS connections, plastic hinge develops at the heat treated beam section where steel strength is reduced by the heat treatment. As the beam flange dimensions, and the elastic and plastic moduli of steel are not altered in the HBS connection, the lateral and torsional buckling resistance of the HBS connection is higher than the RBS connection. Consequently, the HBS connections will dissipate a larger amount of energy with a minimum loss of strength or stiffness than the RBS connections. The proposed research will experimentally validate this novel seismic performance enhancement concept, and develop the design methodology for implementing the concept. The proposed research will conduct seven seismic experiments on the HBS beam-column connections to evaluate their seismic performance. The novel seismic performance enhancement technique will be validated on the welded unreinforced flange-bolted web (WUF-B) connection and hence an additional experiment on WUF-B connection (without heat treatment) will be conducted for reference. Strains, displacements and rotations at various locations will be recorded for investigating both the local and global failure mechanisms of the HBS connections. In the first step, a set of monotonic and cyclic material experiments on heat treated coupons will be conducted. The material coupons will be heat treated by exposing to various peak temperatures in the range of 800-1150oC and two hold times at peak temperatures. This set of material data will be analyzed to quantify the influence of heat treatment on material responses and used to determine the constitutive model parameters of the Chaboche model in ANSYS. A series of finite element analyses of the HBS connection using the Chaboche nonlinear kinematic hardening model will be performed to determine the optimum heat treatment parameters: i) maximum temperature and hold time, and ii) length of the heat treated flange section and, and iii) offset of the heat treated section from the column flange. The seismic performance of the HBS connection with i) both the top and bottom flanges are heat treated (new construction), and ii) only the bottom flange is heat treated (existing building) will be evaluated experimentally. Finally, based on the experimental and finite element analysis data a design methodology for the novel HBS connection will be developed.

Honeywell Aerospace is seeking the development of time independent and time dependent plasticity models for analyzing the constitutive response of metallic alloys which are employed in gas turbine engines. The alloys range from low strength materials such as HA-230 and Hast-X to intermediate strength alloys such as Ti-6-4 and Ti-6-2-4-2 to high strength alloys such as U720LI, DP718. This study will develop constitutive model for simulating thermo-mechanical responses of HA-230. The temperatures range will vary from room temperature to as high as 1800F. At elevated temperatures, time dependence of deformation is expected to play a significant part. The phenomena that have to be included in an all encompassing constitutive model are (i) the hysteresis and Bauschinger effect, and strain hardening and softening and (ii) stress relaxation and time dependent creep at peak stresses. Development of advanced constitutive models helps in improving accuracy and fidelity in prediction of stress and strain redistribution in engine components during service. The redistributed stresses and strains are parameters that are used to assess the useful life of a component. Models for predicting component lives are developed from specimen coupon tests, the results of which embody stress redistribution according to at least one of the phenomena mentioned above.

Past performance of spirally welded pipe piles has been questionable, however, advantages related to quick delivery and cost make their use attractive. As a result, the project described in this proposal has been developed to identify the required information needed by structural engineers to make a proper judgment on the use of these piles in coastal applications subjected to storm surge and wave action. Spirally welded pipe piles are manufactured in a manner that may result in various categories of welded joints (examples of three are shown in Fig. 1), any of which at or near the plastic hinge zone of a pile may impact its performance. The location of the plastic hinge zone in the ground will depend on the stiffness of the soil and pile diameter. The three scenarios of weld categories shown in Fig, 1 represent the simplest, which is spiral only (Fig. 1a) to most complex, which includes a spiral, skelp and splice weld (Fig. 1c) . This project will conduct experiments to determine the load-displacement responses under a load history that would mimic the effects of surge loading as well as to determine failure mechanisms for these three welds located at the plastic hinge of the pile.

The main objective of this proposed visit is to discuss and finalize research cooperation between Profs. Hassan and Sai?s group on developing material models for simulating a broad set of low-cycle fatigue (LCF) failure responses of stainless steel (SS) 304. Using the proposed travel grant, Hassan from North Carolina State University will visit Sai at Ecole Nationale d?Ing??A?nieurs de Sfax, Tunisia (National Engineering School of Sfax, Tunisia). Their past two years of research cooperation over email communications have evaluated two advanced constitutive models against a set of LCF failure responses of stainless steel (SS) 304. One of the constitutive models is the nonlinear kinematic hardening rule (macroscopic) model, developed by Hassan?s group over the last eight years that demonstrated a reasonable success in simulating the SS304 responses. The limitation identified for this model was that it can only simulate the class of material responses which were used in the parameter determination. The other constitutive model evaluated was the multiscale model developed by Sai?s group for simulating the same set of fatigue responses. This model was deficient in simulating the fatigue responses. Further improvement of these models is warranted to meet the need of a robust material model for designing economical and sustainable power generation and chemical plants, offshore structures, buildings and bridges. Towards that direction, Hassan and Sai?s forty years of material modeling experience will be combined and their modeling ideas will be exchanged for developing the next generation material models. Hassan?s group will provide the material responses for model development and validation.

Provide Honeywell Aerospace personnel with uniaxial, cyclic loading histories to be prescribed in the material experiments for parameter determination. Honeywell will conduct the experiments and send the recorded stress-strain data files from the experiements to our P.I., Dr. Hassan, for determining the model parameters of the Chaboche model. In addition to the stress-strain responses, peak data from each experiment will also be needed for the model parameter determination.

The research described here aims to assess the influence of low temperatures on the ductility of reinforced concrete structures in seismically active regions such as those found in Alaska. The final goal of the research project is to develop recommendations for: (1) Temperature dependent ductility factors for Alaska DOT bridge structures, and (2) Temperature dependent overstrength factors for Alaska DOT bridge structures. This will be accomplished through a series of 10 large scale tests (see Table 1), and analysis of typical Alaska DOT structures accounting for the effects of temperature on strength and ductility. Recommendations will be provided for both current force-based design utilized by Alaska DOT as well as for displacement-based design. These recommendations will be provided in a final report and will also be presented to Alaska DOT engineers at a workshop at the conclusion of the research program.

The original budget is revised as per the communication from NSF. The revised budget is entered in the NSF-FastLane.

The research described in the original proposal aims to investigate the use of polymer fiber and waveguide sensors for the performance-based assessment and health monitoring of civil infrastructure systems. Although the sensors to be developed as part of the proposal can be utilized to measure strains under a variety of load conditions and structural materials, this research program will focus on application of the sensors to concrete and steel structures subjected to dynamic load conditions, such as those imposed due to earthquakes loads

This proposed project will perform, (i) finite element analysis of bottom tendon connector, and (ii) microstructural examination of the recovered Typhoon bottom connector slivers. Microstructural examinations on initially recovered load shoulder slivers indicated ratcheting failure mechanisms, however, finite element analysis with bilinear kinematic hardening model indicated no potential of strain ratcheting. One of the objectives of the proposed work is to investigate if finite element analyses with an advanced cyclic plasticity model predict any occurrence of ratcheting strain or deformation in the Typhoon bottom connector under cyclic loads. The second objective of the proposal is to perform microstructural examination on the recovered slivers of load shoulders and lock rings for detecting similar signs of ratcheting mechanisms as detected earlier. Ratcheting is defined as the accumulation of deformation or strain with load cycles. The failure induced by ratcheting could be either initiated by local crack initiation (fatigue failure) or by collapse due to large deformation accumulations. It is worthwhile to mention here that understanding or knowledge on these two failure mechanisms is extremely limited. However, few constitutive models proposed recently showed some success in simulating ratcheting. This proposed work will use the Chaboche?s constitutive model available in ANSYS and microstructural examinations for investigating the potential of ratcheting in the Typhoon bottom connectors through the following two tasks: