Mines Repository (Colorado School of Mines)
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Development of an iterative coupled MCNP and ABAQUS heat transfer analysis process for moderated low-enriched uranium kilowatt-class space nuclear reactors
No full textIncludes bibliographical references.2024 Summer.This thesis presents the development of a coupled MCNP and ABAQUS iterative heat transfer process using unstructured meshes. The reactor cores used in this process are representative of a lowly enriched uranium Kilowatt-style reactor derived from the highly enriched uranium fueled Kilowatt Reactor Using Stirring Engine TechnologY (KRUSTY). The project considered three core fuel geometries - discs, helices, and spheres. Coreform CUBIT constructs the core geometry with is meshed in ABAQUS and read into MCNP. After the MCNP neutronics analysis, ABAQUS performs a core heat transfer analysis to calculate the temperatures in the core using the nodal energy deposition tallies from MCNP. These temperatures are binned into equally spaced temperature groups to redefine the materials in MCNP based by updating the unstructured mesh input file. The process temperature binning process was successfully completed on a single part system, however failed on a multi-part system. The complete iterative process was completed on a multi-part system, but instead the average fuel temperature and average moderator temperature were updated in MCNP after each iteration
Sphalerite var. schalenblende
No full textPhotographed by Ron Wolf.Dull botryoidal mass of grey brown schalenblende (variety of sphalerite)
Association of Environmental and Engineering Geologists special publication no. 32
No full textPermission was granted by the Association of Environmental & Engineering Geologists to distribute this publication in the Mines Repository.Includes bibliographical references.Transportation corridors are frequently located in complex geologic settings where unexpected geologic hazards may exist; either because of their rarity, or because they are beyond the previous experience of the engineers involved. This guidance was developed for the identification and characterization of geologic hazards affecting transportation corridors. It is designed to be efficient and easy to use, taking the form of flowcharts, checklists and concise documentation. The aim is to identify, characterize and evaluate geologic hazards in the early stages of engineering projects, in order to facilitate better selection of alignment alternatives, expedite the design process and prevent costly change orders during construction. The problematic effects of geologic hazards are not restricted to transportation corridors. Geologic hazards pose a threat to all kinds of engineered works, and are often a danger to human life. A system of hazard identification and characterization that could be implemented in the early stages of land-use planning and feasibility studies would be widely applicable and could potentially save money and lives. Previously, no single system has been developed to identify and characterize a wide range of geologic hazards. This document presents such a system.The United States Federal Highway Administration sponsored this study. This document is published with their permission
Recall informed self-attention representation learning and generative AI for improved car accident detection in highly unbalanced datasets
No full textIncludes bibliographical references.2024 Summer.This thesis explores the application of self-attention mechanisms in conjunction with recall-informed loss functions and generative models to the domain of traffic safety analysis and car accident predictions. Utilizing a comprehensive dataset compiled from the Colorado Department of Transportation, supplemented with historical weather data, this study introduces a novel approach that leverages the dynamic and complex nature of traffic data while focusing on rare but critical events such as car accidents. We present a self-representation learning model to learn latent representations of traffic data that effectively capture the time-series sequence and periodicity nuances of vehicle traffic. This model works in conjunction with two novel loss functions that prioritize recall over accuracy. The incorporation of these recall-informed loss functions into the classification task addresses the problem of class imbalance which is prevalent in car accident detection tasks. This enables car accidents, which are uncommon but critical events to be more effectively detected when combined with self-representation learning methods. Further, this study explores the use of self-attention in generative models and its efficacy for utilization in data balancing to increase successful detection of uncommon and critical events. The experiments presented in this paper contribute to the advancement of machine learning in the field of traffic safety and demonstrate that the combination of self-representation learning and recall-informed loss functions have the potential to improve the performance of car accident and traffic anomaly models in terms of ``critical-event'' detection
Chalcopyrite
No full textPhotographed by Ron Wolf.Brown-grey clusters of chalcopyrite in mass of yellow-white opaque crystals, Liskeard district, Cornwall, England
Processing and microstructure design of medium-manganese low-density steels for automotive and transportation applications
No full textIncludes bibliographical references.2024 Summer.With the automotive industry under pressure to reduce greenhouse gas emissions, vehicle lightweighting has become a pivotal technology. In addition to sheet downgauging of advanced high-strength steels (AHSS) used in vehicle body structures, mass savings can be achieved by reducing density through alloying. Low-density steels encompass a broad class of Fe-Mn-Al-C-based alloys with decreased densities (–1.3 % per wt% Al). With medium-Mn (3–12 wt%) and Al (3.5–10 wt%) additions, they display duplex (austenite + ferrite) or multiphase (+ martensite, carbides) microstructures with an excellent balance of mechanical properties and decreased alloying costs relative to austenitic grades. A wide range of properties can be tuned through intercritical annealing (IA), enabled by numerous strengthening and strain hardening mechanisms essential for crash performance.
Despite this, reduced strengths and damage tolerances have been observed when these steels are processed using laboratory-scale methods that mimic industrial cold- or hot-stamping lines, requiring significant modifications or the development of new processing routes to enhance specific strengths. Al additions promote banded δ-ferrite and increased austenite stabilities, limiting use of as-quenched martensite and transformation-/twinning-induced plasticity (TRIP/TWIP) in metastable austenite. Looking deeper, this complex metallurgy offers interesting pathways to address these challenges. In this work, novel processing and microstructure design of steels with 7–9Mn, 4–6Al, 0.2–0.3C and 0–1Si and Cr (wt%) was explored with intent to promote strength-ductility synergies geared towards enhanced crash resistance and formability.
Initial efforts were concentrated in cold-rolling and IA, finding microstructures and deformation behaviors were sensitive to IA parameters, as elevated temperatures and shorter isothermal hold times promoted optimal properties, characterized using electron backscatter diffraction (EBSD) and quasistatic tensile testing. Additionally, the use of rapid heating rates up to 300 °C/s and omission of the hold step were investigated, observing improved tensile properties attributed to a rapid austenite growth mechanism concurrent with partially recrystallized and refined microstructures.
To further reduce the austenite stability and promote as-quenched martensite, increased IA temperatures are required (e.g., >950 °C), which can promote low yield strengths and early fracture. Cold quenching treatments (–20 or –196 °C) in conjunction with tempering at 180 °C were investigated on specimens previously IA at 950 °C to optimize martensitic microstructures. Tensile testing revealed increases to yield strength (e.g., +341 MPa) with minimal ductility losses (e.g., 4) after cold quenching treatments, attributed to the depletion of unstable austenite in favor of hard martensite.
Large fractions of soft δ-ferrite can limit strengthening pathways, and thus warm-rolling deformation was proposed as a method of dislocation-strengthening while retaining large austenite fractions. An exceptional strength-ductility combination (1380 MPa, 16.5% elongation) was achieved after warm rolling at 400 °C, attributed to the dislocation-rich, deformed martensitic and δ-ferrite. The latter specimen also displayed continuous, uncommon to warm-rolled steels, which served to shed some light on elusive mechanisms responsible for yield point elongation in steels.
Lastly, limited data on application properties such as formability is available. Taking select specimens, plastic anisotropy ratios were calculated in tensile specimens oriented 0, 45, and 90° to rolling directions, finding r-values common to AHSS, and direction-dependent tensile properties intimately tied to the microstructural banding. Notably, increased yield strengths and brittle fracture were noted at 90° to the rolling and banding directions. Overall, this work demonstrates potential in improving the crashworthiness and formability of low-density steels
Toward secure content security policy deployment
No full textIncludes bibliographical references.2024 Spring.Content Security Policy (CSP) is a standardized leading technique for protecting webpages against attacks such as Cross Site Scripting (XSS). As a powerful technique successfully adopted by all major web browsers, CSP provides web application developers with the capability to comprehensively define the policy regarding the permissible resources (e.g., scripts) and behaviors (e.g., form submissions) on each webpage. A CSP is composed of a set of directives, and each directive is typically composed of a directive name with a set of directive values. To effectively protect a webpage, a CSP should be carefully designed according to resources and behaviors on the protected webpage. However, it is often hard to properly deploy CSPs on webpages, and the deployed CSPs often contain security issues or errors. Therefore, helping developers properly deploy CSPs on their websites is important to the enhancement of web security.
This dissertation concentrates on promoting the proper deployment of CSPs by investigating the protection capability of deployed CSPs, analyzing CSP deployment issues, and exploring the feasibility of adopting secure CSP solutions on websites. We first investigated the security levels of the deployed CSPs from the directive coverage and secure use perspectives by taking an unsupervised clustering approach which can automatically categorize very diverse and complex CSPs. Next, we focused on investigating CSP deployment issues related to third-party scripts (i.e., JavaScript code or script files) among different websites by conducting a measurement study. We analyzed the usage of third-party scripts on websites based on the collected CSP violations triggered by the accesses of resources used on websites under our inserted CSP. Furthermore, we evaluated the feasibility of taking Google's secure CSP approach on websites. The evaluation is based on CSP violations that are triggered under the four inserted CSPs of the secure CSP approach. A large-scale web measurement usually relies on a crawler. We also studied two browser-based crawler implementation approaches in the context of the Google Chrome browser and further built a Google Chrome extension named WebMea as a baseline Google Chrome extension that can measure multiple types of web data
Microstructure development and weldability of inoculated 6061 processed with gas metal arc directed energy deposition
No full textIncludes bibliographical references.2024 Summer.High strength aluminum alloys have been largely inaccessible to fusion based additive manufacturing (AM) due to extensive solidification cracking. Recently, it has been shown that adding nucleation sites, also called inoculants, to high strength aluminum alloys results in grain refinement and elimination of solidification cracking during additive manufacturing. These inoculated alloys processed with various AM technologies also possess unique microstructural features such as nearly equiaxed grains and an absence of dendritic microsegregation. Although cracking is often eliminated in inoculated alloys, very little work has been done to predict the unique microstructural features or assess weldability of processes that result in crack free AM builds. In this work, the solidification microstructure and weldability of plain and inoculated 6061 aluminum produced with gas metal arc directed energy deposition (GMA-DED) was studied with a combination of models and experiments. Single bead wide walls were manufactured with GMA-DED using plain and inoculated wires, and the as-solidified microstructure was characterized using electron back-scatter diffraction (EBSD). The results showed large, columnar grains with intergranular solidification cracking in the plain 6061 build, while a crack free, fine grain, near-equiaxed microstructure was seen in the inoculated build. By combining EBSD and energy dispersive spectrometry (EDS), the inoculated build was shown to have exhibited globular growth while the non-inoculated build displayed a dendritic microstructure. A modification is proposed to the criterion marking the transition from globular to dendritic growth that better matches experimental results in this work. To evaluate weldability, plates of plain and inoculated 6061 processed with GMA-DED and wrought 6061 were autogenously gas tungsten arc welded (GTAW) with varying heat inputs while using the SigmaJig weldability test, and the degree of cracking was evaluated. It was found that the degree of cracking in the inoculated 6061 material was lower than that of plain GMA-DED and wrought 6061 materials. Microstructure characterization revealed that the autogenous weld on the inoculated 6061 material showed fine equiaxed grains whereas the plain 6061 showed coarse columnar grains, consistent with the microstructures of the GMA-DED materials themselves. A combination of heat transfer and modified grain morphology models were employed to predict the solidification morphology of the 6061 builds and welds, which closely match experimental results in all cases. The results of this work provide improved solidification modeling methods which can guide the design of inoculated alloys for printing and welding applications, as well as inform the development of printing and welding processes for inoculated wire feedstocks
