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Studies On Stable Crack Growth, Mohammed Juma Humaid Al-Ghafri 2017 United Arab Emirates University

Studies On Stable Crack Growth, Mohammed Juma Humaid Al-Ghafri

Theses

The goal of this work is to experimentally investigate the stable crack growth (SCG) fracture behavior of AISI 4340 alloy steel. A series of mode I and mixed mode SCG fracture tests were carried out on 8 mm thick compact tension (CT) specimens subjected to quasistatic loading. The wire cutting technique was used to introduce a pre-notch/ pre-crack of 0.05 mm root radius to the specimen. Five different loading angles Ψ between the loading axis and the crack surface were employed; 90° (mode I), 75°, 65°, 60° and 50°. Five different ratios of original crack length to specimen width ...


An Evaluation Of The Efficiency Of Compartmented Alginate Fibres Encapsulating Rejuvenator As Asphalt Pavement Healing System, Amir Tabakovic, Luke Schuyffel, Aleksandar Karac, Erik Schlangen 2017 Dublin Institute of Technology

An Evaluation Of The Efficiency Of Compartmented Alginate Fibres Encapsulating Rejuvenator As Asphalt Pavement Healing System, Amir Tabakovic, Luke Schuyffel, Aleksandar Karac, Erik Schlangen

Articles

This paper explores the potential methods for evaluating a healing system for asphalt pavements. The healing system under investigation involves compartmented calcium-alginate fibres encapsulating an asphalt binder healing agent (rejuvenator). This system presents a novel method of incorporating rejuvenators into asphalt pavement mixtures. The compartmented fibres are used to distribute the rejuvenator throughout the pavement mixture, thereby overcoming some of the problems associated with alternate asphalt pavement healing methods, i.e., spherical capsules and hollow fibres. The asphalt healing efficiency methods to be evaluated in this paper include: (i) standard test methods for asphalt pavements, such as the Indirect Tensile ...


Engineered, Spatially Varying Isothermal Holds: Enabling Combinatorial Studies Of Temperature Effects, As Applied To Metastable Titanium Alloy Β-21s, Brian Martin, Peyman Samimi, Peter C. Collins 2017 Iowa State University

Engineered, Spatially Varying Isothermal Holds: Enabling Combinatorial Studies Of Temperature Effects, As Applied To Metastable Titanium Alloy Β-21s, Brian Martin, Peyman Samimi, Peter C. Collins

Peter Collins

A novel method to systematically vary temperature and thus study the resulting microstructure of a material is presented. This new method has the potential to be used in a combinatorial fashion, allowing the rapid study of thermal holds on microstructures to be conducted. This is demonstrated on a beta titanium alloy, where the thermal history has a strong effect on microstructure. It is informed by simulation and executed using the resistive heating capabilities of a Gleeble 3800 thermomechanical simulator. Spatially varying isothermal holds of 4 h were affected, where the temperature range of the multiple isothermal holds varied by ~175 ...


Function And Biodegradation In Soil Of Bioplastic Horticultural Containers Made Of Pla-Biorestm Composites, James Schrader, Kenneth McCabe, William Graves, David Grewell 2017 Iowa State University

Function And Biodegradation In Soil Of Bioplastic Horticultural Containers Made Of Pla-Biorestm Composites, James Schrader, Kenneth Mccabe, William Graves, David Grewell

William R Graves

Container-crops horticultural industries rely almost exclusively on petroleum-based plastic containers for modern production systems. Containers made of these materials fulfill all of the functions required during crop production, and perform better than containers made of clay, peat, and other natural materials, but the source of the plastic materials (fossil carbon), their lack of biodegradability, and their end-of-life disposal (97% end up in landfills) are major obstacles to sustainability. Although function and efficiency are among the most important aspects in determining the best materials for horticultural containers, there is no need for containers to persist in the environment for decades when ...


Probability Of Detection In Structural Health Monitoring, William Q. Meeker 2017 Iowa State University

Probability Of Detection In Structural Health Monitoring, William Q. Meeker

William Q Meeker

Structural Health Monitoring (SHM) is being proposed to replace traditional scheduled NDE inspections. This is raising questions about how to quantify Probability of Detection (POD) and whether the POD statistical methods of MIL-HDBK 1823 can still be used. The answer depends on the application, the nature of the SHM information, and how that information is mapped into a detect/not-detect decision. This talk will outline some of the issues involved in characterizing POD for different kinds of SHM applications.


Anisotropic Compositional Expansion And Chemical Potential For Amorphous Lithiated Silicon Under Stress Tensor, Valery I. Levitas, Hamed Attariani 2017 Wright State University - Lake Campus

Anisotropic Compositional Expansion And Chemical Potential For Amorphous Lithiated Silicon Under Stress Tensor, Valery I. Levitas, Hamed Attariani

Valery I. Levitas

Si is a promising anode material for Li-ion batteries, since it absorbs large amounts of Li. However, insertion of Li leads to 334% of volumetric expansion, huge stresses, and fracture; it can be suppressed by utilizing nanoscale anode structures. Continuum approaches to stress relaxation in LixSi, based on plasticity theory, are unrealistic, because the yield strength of LixSi is much higher than the generated stresses. Here, we suggest that stress relaxation is due to anisotropic (tensorial) compositional straining that occurs during insertion-extraction at any deviatoric stresses. Developed theory describes known experimental and atomistic simulation data. A ...


Coupled Phase Transformations And Plastic Flows Under Torsion At High Pressure In Rotational Diamond Anvil Cell: Effect Of Contact Sliding, Biao Feng, Valery I. Levitas 2017 Iowa State University

Coupled Phase Transformations And Plastic Flows Under Torsion At High Pressure In Rotational Diamond Anvil Cell: Effect Of Contact Sliding, Biao Feng, Valery I. Levitas

Valery I. Levitas

A three-dimensional large-sliding contact model coupled with strain-induced phase transformations (PTs) and plastic flow in a disk-like sample under torsion at high pressure in rotational diamond anvil cell (RDAC) is formulated and studied. Coulomb and plastic friction are combined and take into account variable parameters due to PT. Results are obtained for weaker, equal-strength, and stronger high pressure phases, and for three values of the kinetic coefficient in a strain-controlled kinetic equation and friction coefficient. All drawbacks typical of problem with cohesion are overcome, including eliminating mesh-dependent shear band and artificial plastic zones. Contact sliding intensifies radial plastic flow, which ...


Sublimation Via Virtual Melting Inside An Elastoplastic Material, Valery I. Levitas, Nataliya Altukhova 2017 Iowa State University

Sublimation Via Virtual Melting Inside An Elastoplastic Material, Valery I. Levitas, Nataliya Altukhova

Valery I. Levitas

Thermodynamic, kinetic, and mechanical approaches for sublimation inside elastoplastic material via intermediate (virtual) melting under tensile pressure are developed for a spherical nucleus. Virtual melting represents the appearance of subcritical liquid drop that immediately transforms to gas bubble. The variety of mechanisms and transformation paths are revealed in different pressure ranges. The radius of the critical gas nucleus differs from the classical one because elastic energy of melt is size dependent due to surface tension. Our developed approach can be extended for various structural changes in nanoparticles within a void inside elastoplastic material and two-stage and multistage nucleation processes. Universal ...


Influence Of Aluminum Passivation On The Reaction Mechanism: Flame Propagation Studies, Birce Dikici, Steven W. Dean, Michelle L. Pantoya, Valery I. Levitas, R. Jason Jouet 2017 Texas Tech University

Influence Of Aluminum Passivation On The Reaction Mechanism: Flame Propagation Studies, Birce Dikici, Steven W. Dean, Michelle L. Pantoya, Valery I. Levitas, R. Jason Jouet

Valery I. Levitas

Currently, two main known mechanisms of aluminum (Al) nanoparticle reaction are discussed in the literature, namely those based on diffusion through an oxide shell and melt-dispersion. The two mechanisms lead to opposite predictions in nanoparticle design. The diffusion mechanism suggests that the reduction or complete elimination of the oxide shell will increase Al reactivity, whereas the meltdispersion mechanism suggests an increase in initial oxide thickness up to an optimal value. The goal of this study is to perform critical experiments in a confined flame tube apparatus to compare these two predictions. Specifically, the flame propagation rates of perfluoroalkyl carboxylic acid ...


Size And Mechanics Effects In Surface-Induced Melting Of Nanoparticles, Valery I. Levitas, Kamran Samani 2017 Iowa State University

Size And Mechanics Effects In Surface-Induced Melting Of Nanoparticles, Valery I. Levitas, Kamran Samani

Valery I. Levitas

Various melting-related phenomena (like surface melting, size dependence of melting temperature, melting of few nm-size particles and overheating at a very fast heating rate) are of great fundamental and applied interest, although the corresponding theory is still lacking. Here we develop an advanced phase-field theory of melting coupled to mechanics, which resolves numerous existing contradictions and allowed us to reveal exciting features of melting problems. The necessity of introducing an unexpected concept, namely, coherent solid-melt interface with uniaxial transformation strain, is demonstrated. A crossover in temperature dependence of interface energy for radii below 20 nm is found. Surface-induced premelting and ...


Effects Of Zn Additions To Highly Magnetoelastic Fega Alloys, Thomas A. Lograsso, Nicholas J. Jones, Deborah L. Schlagel, Gabriela Petculescu, Marilyn Wun-Fogle, James B. Restorff, Arthur E. Clark, Kristi B. Hathaway 2017 Iowa State University

Effects Of Zn Additions To Highly Magnetoelastic Fega Alloys, Thomas A. Lograsso, Nicholas J. Jones, Deborah L. Schlagel, Gabriela Petculescu, Marilyn Wun-Fogle, James B. Restorff, Arthur E. Clark, Kristi B. Hathaway

Thomas A. Lograsso

Fe1−xMx (M = Ga, Ge, Si, Al, Mo and x ∼ 0.18) alloys offer an extraordinary combination ofmagnetoelasticity and mechanical properties. They are rare-earth-free, can be processed using conventional deformation techniques, have high magnetic permeability, low hysteresis, and low magnetic saturation fields, making them attractive for device applications such as actuators and energy harvesters. Starting with Fe-Ga as a reference and using a rigid-band-filling argument, Zhang et al. predicted that lowering the Fermi level by reducing the total number of electrons could enhance magnetoelasticity. To provide a direct experimental validation for Zhang's hypothesis, elemental additions with lower-than-Ga valence are ...


Elastic Properties Of Mnsi, Fesi And Cosi, Alla E. Petrova, Vladimir N. Krasnorussky, William M. Yuhasz, Thomas A. Lograsso, Sergei M. Stishov 2017 Russian Academy of Sciences

Elastic Properties Of Mnsi, Fesi And Cosi, Alla E. Petrova, Vladimir N. Krasnorussky, William M. Yuhasz, Thomas A. Lograsso, Sergei M. Stishov

Thomas A. Lograsso

Measurements of sound velocities in single crystals of MnSi, FeSi, and CoSi were performed in the temperature range 2.5-300 K and elastic constants were calculated. The temperature dependence of the elastic constants reveal nontrivial features, reflecting specifics of the magnetic and electronic subsystems in these materials.


Crossover In The Magnetic Response Of Single-Crystalline Ba1−Xkxfe2as2 And Lifshitz Critical Point Evidenced By Hall Effect Measurements, Yong Liu, Thomas A. Lograsso 2017 Iowa State University

Crossover In The Magnetic Response Of Single-Crystalline Ba1−Xkxfe2as2 And Lifshitz Critical Point Evidenced By Hall Effect Measurements, Yong Liu, Thomas A. Lograsso

Thomas A. Lograsso

We report on the doping evolution of magnetic susceptibility χ(T) and Hall coefficient RH in high-quality Ba1−xKxFe2As2 (0.13≤x≤1) single crystals. It is found that the normal-state magnetic susceptibility of Ba1−xKxFe2As2 compounds undergoes a crossover from linear-T dependence in the undoped and underdoped samples into KFe2As2-type magnetic response in the overdoped samples with increasing K content. Although magnetic susceptibility χ(T) of optimally doped samples (0.34≤x≤0.47) still follows a monotonic increase with increasing temperature, a big hump around 300 K emerges. As x exceeds 0.53, a broad peak forms in ...


Magnetic And Structural Transitions In La0.4na0.6fe2as2 Single Crystals, J.-Q. Yan, S. Nandi, B. Saparov, P. Čermák, Y. Xiao, Y. Su, W. T. Jin, A. Schneidewind, Th. Brückel, R. W. McCallum, T. A. Lograsso, B. C. Sales, D. G. Mandrus 2017 Oak Ridge National Laboratory

Magnetic And Structural Transitions In La0.4na0.6fe2as2 Single Crystals, J.-Q. Yan, S. Nandi, B. Saparov, P. Čermák, Y. Xiao, Y. Su, W. T. Jin, A. Schneidewind, Th. Brückel, R. W. Mccallum, T. A. Lograsso, B. C. Sales, D. G. Mandrus

Thomas A. Lograsso

La0.4Na0.6Fe2As2 single crystals have been grown out of an NaAs flux in an alumina crucible and characterized by measuring magnetic susceptibility, electrical resistivity, specific heat, as well as single-crystal x-ray and neutron diffraction. La0.4Na0.6Fe2As2 single crystals show a structural phase transition from a high-temperature tetragonal phase to a low-temperature orthorhombic phase at Ts=125 K. This structural transition is accompanied by an anomaly in the temperature dependence of electrical resistivity, anisotropic magnetic susceptibility, and specific heat. Concomitant with the structural phase transition, the Fe moments order along the a direction with an ordered moment of 0 ...


Experimental Study On Viscosity And Phase Segregation Of Al–Si Powders In Microsemisolid Powder Forming, Yufeng Wu, Iver E. Anderson, Thomas A. Lograsso, Gap-Yong Kim 2017 Iowa State University

Experimental Study On Viscosity And Phase Segregation Of Al–Si Powders In Microsemisolid Powder Forming, Yufeng Wu, Iver E. Anderson, Thomas A. Lograsso, Gap-Yong Kim

Thomas A. Lograsso

Semisolid powder forming is a promising approach for near-net shape forming of features in macro-/microscale. In this paper, viscosity and phase segregation behavior of Al–Si powders in the semisolid state were studied with back extrusion experiments. The effects of process parameters including shear rate, extrusion ratio, heating time, and precompaction pressure were analyzed using the design of experiments method. The results showed that the effects of shear rate, extrusion, ratio and heating time were statistically significant factors influencing the viscosity. The semisolid state powders showed a shear thinning behavior. Moreover, microstructure analysis of extruded parts indicated severe phase ...


Comparative Study Of The Tribological And Oxidative Properties Of Alpdmn Quasicrystals And Their Cubic Approximants, Chris Mancinelli, Jeff S. Ko, Cynthia J. Jenks, Patricia A. Thiel, Amy R. Ross, Thomas A. Lograsso, Andrew J. Gellman 2017 Carnegie Mellon University

Comparative Study Of The Tribological And Oxidative Properties Of Alpdmn Quasicrystals And Their Cubic Approximants, Chris Mancinelli, Jeff S. Ko, Cynthia J. Jenks, Patricia A. Thiel, Amy R. Ross, Thomas A. Lograsso, Andrew J. Gellman

Thomas A. Lograsso

An experimental comparison has been made between the properties of the surfaces of an Al70Pd21Mn9quasicrystal and its Al48Pd42Mn10 approximant. The Al70Pd21Mn9 sample was a single grain icosahedral quasicrystal cut to expose its five-fold symmetric (000001) surface. The approximant was polycrystalline β-phase Al48Pd42Mn10, which has a CsCl-type cubic structure. Surfaces of both were prepared under ultra-high vacuum (UHV) conditions and then used for comparative measurements of their frictional properties and oxidation rates. Both materials are oxidized by reaction with O ...


Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield 2017 Iowa State University

Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield

Thomas A. Lograsso

We report in-plane thermoelectric power measurements on single crystals of (Ba1−xKx)Fe2As2(0.44≤x≤1). We observe a minimum in the S|T=const versus x at x∼0.55 that can be associated with the change in the topology of the Fermi surface, a Lifshitz transition, related to the electron pockets at the center of M point crossing the Fermi level. This feature is clearly observable below ∼75 K. Thermoelectric power also shows a change in the x∼0.8–0.9 range, where the maximum in the thermoelectric power collapses into a plateau. This Lifshitz transition ...


Gd5(Si,Ge)4 Thin Film Displaying Large Magnetocaloric And Strain Effects Due To Magnetostructural Transition, Ravi L. Hadimani, Joao H. B. Silva, Andre M. Pereira, Devo L. Schlagel, Thomas A. Lograsso, Yang Ren, David C. Jiles, Joao P. Araújo 2017 Iowa State University

Gd5(Si,Ge)4 Thin Film Displaying Large Magnetocaloric And Strain Effects Due To Magnetostructural Transition, Ravi L. Hadimani, Joao H. B. Silva, Andre M. Pereira, Devo L. Schlagel, Thomas A. Lograsso, Yang Ren, David C. Jiles, Joao P. Araújo

Thomas A. Lograsso

Magnetic refrigeration based on the magnetocaloric effect is one of the best alternatives to compete with vapor-compression technology. Despite being already in its technology transfer stage, there is still room for optimization, namely, on the magnetic responses of the magnetocaloric material. In parallel, the demand for different magnetostrictive materials has been greatly enhanced due to the wide and innovative range of technologies that emerged in the last years (from structural evaluation to straintronics fields). In particular, the Gd5(Six Ge1−x)4 compounds are a family of well-known alloys that present both giant magnetocaloric and colossal magnetostriction effects. Despite their ...


Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin 2017 Iowa State University

Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin

Thomas A. Lograsso

We report on the different roles of two orbital-active Fe2+ at the A site and V3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV2O4. FeV2O4 exhibits three structural transitions and successive paramagnetic (PM)–collinear ferrimagnetic (CFI)–noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM–orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbit-coupling-induced anisotropy at the Fe2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V3+ at the orthorhombic/CFI–tetragonal ...


Formation Mechanism Of Superconducting Phase And Its Three-Dimensional Architecture In Pseudo-Single-Crystal Kxfe2−Yse2, Yong Liu, Qingfeng Xing, Warren E. Straszheim, Jeff Marshman, Pai Pedersen, Richard McLaughlin, Thomas A. Lograsso 2017 Ames Laboratory

Formation Mechanism Of Superconducting Phase And Its Three-Dimensional Architecture In Pseudo-Single-Crystal Kxfe2−Yse2, Yong Liu, Qingfeng Xing, Warren E. Straszheim, Jeff Marshman, Pai Pedersen, Richard Mclaughlin, Thomas A. Lograsso

Thomas A. Lograsso

We report how the superconducting phase forms in pseudo-single-crystal KxFe2−ySe2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase, whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition. It should be ...


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