Evaluation Of The Effect Of Tack Coat Type, Application Rate, And Surface Type On Interlayer Shear Strength, 2018 South Dakota State University
Evaluation Of The Effect Of Tack Coat Type, Application Rate, And Surface Type On Interlayer Shear Strength, Chamika Prashan Dharmarathna
Electronic Theses and Dissertations
Tack coat is an asphaltic material applied between asphalt pavement layers. Since pavement is a multilayered structure, it is highly important to make proper bond between the layers to achieve a monolithic behavior. Hence, inadequate bond due to application of inadequate amount of tack coat may lead to poor structural behavior and premature failure. Also, applying excessive amount of tack coat may lead to layer slippage and binder migration. Therefore, it is highly important to apply an optimum amount of tack coat between layers. Over the past decades several studies have been conducted to determine the optimum tack coat application ...
The Formation Mechanism Of Α-Phase Dispersoids And Quantification Of Fatigue Crack Initiation By Experiments And Theoretical Modeling In Modified Aa6061 (Al-Mg-Si-Cu) Alloys, 2018 University of Kentucky
The Formation Mechanism Of Α-Phase Dispersoids And Quantification Of Fatigue Crack Initiation By Experiments And Theoretical Modeling In Modified Aa6061 (Al-Mg-Si-Cu) Alloys, Gongwang Zhang
Theses and Dissertations--Chemical and Materials Engineering
AA6061 Al alloys modified with addition of Mn, Cr and Cu were homogenized at temperatures between 350 ºC and 550 ºC after casting. STEM experiments revealed that the formation of α-Al(MnFeCr)Si dispersoids during homogenization were strongly affected by various factors such as heating rate, concentration of Mn, low temperature pre-nucleation treatment and homogenization temperature. Through analysis of the STEM results using an image software Image-Pro, the size distributions and number densities of the dispersoids formed during different annealing treatments were quantitatively measured. It was revealed that increasing the heating rate or homogenization temperature led to a ...
High Pressure Phase Transformations Revisited, 2018 Iowa State University
High Pressure Phase Transformations Revisited, Valery I. Levitas
Aerospace Engineering Publications
High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The ...
Phase Transitions And Their Interaction With Dislocations In Silicon, 2018 Iowa State University
Phase Transitions And Their Interaction With Dislocations In Silicon, Valery I. Levitas, Hao Chen, Liming Xiong
Aerospace Engineering Publications
In this paper, phase transformations (PTs) in silicon were investigated through molecular dynamics (MD) using Tersoff potential. In the first step, simulations of PTs in single crystal silicon under various stress-controlled loading were carried out. Results shows that all instability points under various stress states are described by criteria, which are linear in the space of normal stresses. There is a region in the stress space in which conditions for direct and reverse PTs coincide and a unique homogeneous phase transition (without nucleation) can be realized. Finally, phase transition in bi-crystalline silicon with a dislocation pileup along the grain boundary ...
Microscale Phase Field Modeling Of The Martensitic Transformation During Cyclic Loading Of Niti Single Crystal, 2018 Iowa State University
Microscale Phase Field Modeling Of The Martensitic Transformation During Cyclic Loading Of Niti Single Crystal, S. Ehsan Esfahani, Iman Ghamarian, Valery I. Levitas, Peter Collins
Aerospace Engineering Publications
A microscale phase field model developed in Levitas et al. (2004) and Idesman et al. (2005) is slightly advanced for different and anisotropic elastic moduli of phases and is employed for the study of the stress-induced cubic-monoclinic phase transition in NiTi single crystal involving all 12 martensitic variants. The model is scale-independent, without the gradient term, and it is applicable for any scale greater than 100 nm. This model includes strain softening and the corresponding transformation strain localization, and it reproduces a discrete martensitic microstructure. The model only tracks finite-width interfaces between austenite and the mixture of martensitic variants, and ...
Phase-Field Approach For Stress- And Temperature-Induced Phase Transformations That Satisfies Lattice Instability Conditions. Part 2. Simulations Of Phase Transformations Si I↔↔ Si Ii, 2018 Iowa State University
Phase-Field Approach For Stress- And Temperature-Induced Phase Transformations That Satisfies Lattice Instability Conditions. Part 2. Simulations Of Phase Transformations Si I↔↔ Si Ii, Hamed Babaei, Valery I. Levitas
Aerospace Engineering Publications
A complete system of equations of the advanced phase-field theory for martensitic phase transformations (PTs) under a general stress tensor is presented. Theory includes a fully geometrically nonlinear formulation for the general case of finite elastic and transformational strains as well as anisotropic and different elastic properties of phases. Material parameters are calibrated, in particular, based on the crystal lattice instability conditions from atomistic simulations for martensitic PTs between cubic Si I and tetragonal Si II phases under complex triaxial compression-tension loading. A finite element algorithm and numerical procedure is developed and implemented in the code deal.II. Various 3D ...
Detection Of Buried Non-Metallic (Plastic And Frp Composite) Pipes Using Gpr And Irt, 2018 West Virginia University
Detection Of Buried Non-Metallic (Plastic And Frp Composite) Pipes Using Gpr And Irt, Jonas Kavi
Graduate Theses, Dissertations, and Problem Reports
This research investigated alternative strategies for making buried non-metallic pipes (CFRP, GFRP, and PVC) easily locatable using Ground Penetrating Radar (GPR). Pipe diameters up to 12" and buried with up to 4 ft. of soil cover were investigated. The findings of this study will help address the detection problem of non-metallic pipelines and speed the adoption of composite pipes by the petroleum and natural gas industry. The research also investigated the possibility of locating buried pipes transporting hot fluids using Infrared Thermography (IRT).
Results from the study have shown that, using carbon fabric and aluminum tape overlay on non‑metallic ...
Physics-Aware Deep Generative Models For Creating Synthetic Microstructures, 2018 Iowa State University
Physics-Aware Deep Generative Models For Creating Synthetic Microstructures, Rahul Singh, Viraj Shah, Balaji Pokuri, Soumik Sarkar, Baskar Ganapathysubramanian, Chinmay Hegde
Mechanical Engineering Publications
A key problem in computational material science deals with understanding the effect of material distribution (i.e., microstructure) on material performance. The challenge is to synthesize microstructures, given a finite number of microstructure images, and/or some physical invariances that the microstructure exhibits. Conventional approaches are based on stochastic optimization and are computationally intensive. We introduce three generative models for the fast synthesis of binary microstructure images. The first model is a WGAN model that uses a finite number of training images to synthesize new microstructures that weakly satisfy the physical invariances respected by the original data. The second model ...
Deformation, Lattice Instability, And Metallization During Solid-Solid Structural Transformations Under General Applied Stress Tensor: Example Of Si I -> Si Ii, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson
Materials Science and Engineering Publications
Density functional theory (DFT) was employed to study the stress-strain behavior, elastic instabilities, and metallization during a solid-solid phase transformation (PT) between semiconducting Si I (cubic A4) and metallic Si II (tetragonal A5 structure) when subjected to a general stress tensor. With normal stresses (σ1, σ2, σ3) acting along ⟨110⟩, ⟨11¯0⟩, and ⟨001⟩, respectively, dictating the simulation cell, we determine combinations of 6 independent stresses that drive a lattice instability for the Si I→Si II PT, and a semiconductor-metal electronic transition. Metallization precedes the structural PT, hence, a stressed Si I can be a metal. Surprisingly, a stress-free ...
Tunable Mechanical Metamaterials Through Hybrid Kirigami Structures, 2018 Iowa State University
Tunable Mechanical Metamaterials Through Hybrid Kirigami Structures, Doh-Gyu Hwang, Michael Bartlett
Materials Science and Engineering Publications
Inspired by the art of paper cutting, kirigami provides intriguing tools to create materials with unconventional mechanical and morphological responses. This behavior is appealing in multiple applications such as stretchable electronics and soft robotics and presents a tractable platform to study structure-property relationships in material systems. However, mechanical response is typically controlled through a single or fractal cut type patterned across an entire kirigami sheet, limiting deformation modes and tunability. Here we show how hybrid patterns of major and minor cuts creates new opportunities to introduce boundary conditions and non-prismatic beams to enable highly tunable mechanical responses. This hybrid approach ...
3d Printing – An Insider’S Perspective, 2017 Make Whale
3d Printing – An Insider’S Perspective, Siddharth Sah
The STEAM Journal
The 3D printing market globally is still at its infancy, - or some might argue that there isn’t really a market yet. The knowledge of 3D printing design is still largely limited to engineering design – not product design. At MakeWhale, we are constantly pushing the boundaries of the application of 3D printing technology to consumer products resulting in a beautiful mix of technology and art.
A Comparison Study Of Composite Laminated Plates With Holes Under Tension, 2017 California Polytechnic State University, San Luis Obispo
A Comparison Study Of Composite Laminated Plates With Holes Under Tension, Joun S. Kim
Master's Theses and Project Reports
A Comparison Study of Composite Laminated Plates with Holes under Tension
A study was conducted to quantify the accuracy of numerical approximations to deem sufficiency in validating structural composite design, thus minimizing, or even eliminating the need for experimental test. Error values for stress and strain were compared between Finite Element Analysis (FEA) and analytical (Classical Laminated Plate Theory), and FEA and experimental tensile test for two composite plate designs under tension: a cross-ply composite plate design of [(0/90)4]s, and a quasi-isotropic layup design of [02/+45/-45/902]s, each with a single, centered hole of ...
Modeling Of Dislocation Channel Formation And Evolution In Irradiated Metals, 2017 University of Tennessee, Knoxville
Modeling Of Dislocation Channel Formation And Evolution In Irradiated Metals, Peter James Doyle
Defect-free dislocation channel formation has been reported to promote plastic instability during tensile testing via localized plastic flow, leading to a distinct loss of ductility and strain hardening in many low-temperature irradiated materials. In order to study the underlying mechanisms governing dislocation channel width and formation, the channel formation process is modeled via a simple stochastic dislocation-jog process dependent upon grain size, defect cluster density, and defect size. Dislocations traverse a field of defect clusters and jog stochastically upon defect interaction, forming channels of low defect-density. Based upon prior molecular dynamics (MD) simulations and in-situ experimental transmission electron microscopy (TEM ...
Smart Bricks For Strain Sensing And Crack Detection In Masonry Structures, 2017 Iowa State University
Smart Bricks For Strain Sensing And Crack Detection In Masonry Structures, Austin Downey, Antonella D'Alessandro, Simon Laflamme, Filippo Ubertini
Civil, Construction and Environmental Engineering Publications
The paper proposes the novel concept of smart bricks as a durable sensing solution for structural health monitoring of masonry structures. The term smart bricks denotes piezoresistive clay bricks with suitable electronics capable of outputting measurable changes in their electrical properties under changes in their state of strain. This feature can be exploited to evaluate stress at critical locations inside a masonry wall and to detect changes in loading paths associated with structural damage, for instance following an earthquake. Results from an experimental campaign show that normal clay bricks, fabricated in the laboratory with embedded electrodes made of a special ...
Control Of Columnar To Equiaxed Transition In Solidification Macrostructure Of Austenitic Stainless Steel Castings, 2017 Missouri University of Science and Technology
Control Of Columnar To Equiaxed Transition In Solidification Macrostructure Of Austenitic Stainless Steel Castings, Semen Naumovich Lekakh, Ronald J. O'Malley, Mark Emmendorfer, Brenton Hrebec
Ronald J. O'Malley
Solidification macrostructure is of great importance for the properties and the quality of castings made from austenitic grade stainless steels (ASS) because there are limited options to change as-cast macrostructure in the solid condition. A typical cast macrostructure of ASS has a fine surface chilled zone followed by an elongated dendrite zone, columnar to equiaxed transition (CET) zone, and centrally located equiaxed crystals. Several castings from ASS were produced to determine the effects of casting geometry, chilling, and grain refinement on CET. The transient thermal field in solidified heavy castings was simulated and used to determine an isotherm velocity (V ...
Evolution Of Non-Metallic Inclusions In Foundry Steel Casting Processes, 2017 Missouri University of Science and Technology
Evolution Of Non-Metallic Inclusions In Foundry Steel Casting Processes, Marc Harris, Von Richards, Ronald J. O'Malley, Semen Naumovich Lekakh
Ronald J. O'Malley
The evolution of nonmetallic inclusions was examined for 4320 steel at an industrial steel foundry. The steel was followed from electric arc furnace melting through ladle refining to final casting. Timed sampling was performed at all stages of the process. Samples were analyzed using an automated SEM/EDS system. The overall evolution of oxide inclusions in terms of nucleation, growth, and flotation during liquid processing was studied using area fraction and average diameter. Chemical composition evolution was observed using a joint ternary plotting tool developed under this program. It was found that the use of zirconium as an addition for ...
Effect Of Zinc Galvanization On The Microstructure And Fracture Behavior Of Low And Medium Carbon Structural Steels, 2017 Missouri University of Science and Technology
Effect Of Zinc Galvanization On The Microstructure And Fracture Behavior Of Low And Medium Carbon Structural Steels, Ignatius C. Okafor, Ronald J. O'Malley, Kaushal R. Prayakarao, Heshmat A. Aglan
Ronald J. O'Malley
Microstructure and fracture behavior of ASTM 572 Grade 65 steels used for wind tower applications have been studied. Steels of two carbon level chemistries designed for this grade were used in the study. Fracture toughness of the steels was studied using 3-point bend test on samples coated with zinc and not coated with zinc. Lower carbon steel showed higher resistance to fracture than medium carbon steel after zinc galvanization. SEM study suggests that zinc and zinc bath additives that migrated to crack tips are responsible for the loss in ductility. The phenomenon of Liquid Metal Embrittlement (LME) is suggested to ...
Rigid Pavement Backcalculation Using Differential Evolution, 2017 Iowa State University
Rigid Pavement Backcalculation Using Differential Evolution, Kasthurirangan Gopalakrishnan, Halil Ceylan
The backcalculation of pavement layer moduli from Falling Weight Deflectometer (FWD) measured surface deflections is a challenging task. It can also be formulated as a global optimization problem with the objective of finding the optimal pavement layer moduli values that minimize the error between measured and computed surface deflections. Over the years, several backcalculation methodologies have been developed including the use of soft computing techniques such as Neural Networks (NNs), Genetic Algorithms (GAs), etc. In this paper, Differential Evolution (DE), a stochastic parallel direct search evolution strategy optimization method is integrated with rapid surrogate mapping of Finite Element (FE) solutions ...
Effect Of Pcc Material Properties On Mepdg Jointed Plain Concrete Pavement (Jpcp) Performance Prediction, 2017 Iowa State University
Effect Of Pcc Material Properties On Mepdg Jointed Plain Concrete Pavement (Jpcp) Performance Prediction, Halil Ceylan, Sunghwan Kim, Charles W. Schwartz, Rui Li, Kasthurirangan Gopalakrishnan
This paper focuses on comprehensive sensitivity analyses of various rigid pavement scenarios. Jointed Plain Concrete Pavement (JPCP) sections designed for three traffic levels in each of five climate zones are evaluated in the sensitivity analyses. One-at-a-time (OAT) local sensitivity analysis was implemented using a design limit normalized sensitivity index (NSI) to provide both quantitative and qualitative sensitivity information. All portland cement concrete (PCC) material properties examined showed sensitivity to at least one rigid pavement performance measure. The highest ranked sensitive inputs for JPCP analysis include the PCC strength and stiffness properties and the curling and warping related properties. The findings ...
Smart Concrete For Enhanced Nondestructive Evaluation, 2017 Iowa State University
Smart Concrete For Enhanced Nondestructive Evaluation, Simon Laflamme, David J. Eisenmann, Kejin Wang, Filippo Ubertini, Irvin Pinto, Akira Demoss
Civil, Construction and Environmental Engineering Conference Presentations and Proceedings
The authors recently investigated the use of conductive concrete to enhance nondestructive evaluation (NDE) capa- bilities. Preliminary results have shown that a conductive concrete can facilitate the utilization of an eddy current technique, where damages in a conductive specimen were easier to detect compared with a non-conductive substrate. While such results demonstrated the promise of using conductive concrete to facilitate and potentially accelerate the NDE process, the fabrication of an homogeneous conductive concrete is technically or economically challenging, depending on the conductive filler used in the process. In this paper, we propose a new cementitious composite to accelerate NDE. The ...