A review of the changes of internal state related to high temperature creep of polycrystalline metals and alloys

When polycrystalline metals and their alloys are used at high temperature, creep deformation leads to changes in their internal state. The change in internal state manifests itself in many ways, but the two ways that concern us in this review are (i) the creation of internal stress arising from the strain incompatibility between grains and/or the formation of cell/sub-grain structures and (ii) a change in the material resistance. This review aims to provide a clear separation of these two concepts by exploring the origin of each term and how it is associated with the creep deformation mechanism. Experimental techniques used to measure the internal stress and internal resistance over different length-scales are critically reviewed. It is demonstrated that the interpretation of the measured values requires knowledge of the dominant creep deformation mechanism. Finally, the concluding comments provide a summary of the key messages delivered in this review and highlight the challenges that remain to be addressed

Navigating Challenges Presented by State CCR Regulations

Navigating Challenges Presented by State CCR Regulations Authors Mr. Brian Hennings - United States - Ramboll Mr. Eric Tlachac - United States - Ramboll Mr. Victor Modeer - United States - Luminant Abstract State regulation of coal combustion residuals (CCRs) continues to evolve following the United States Environmental Protection Agency’s (USEPA’s) 2015 final rule, Disposal of Coal Combustion Residuals from Electric Utilities (CCR Rule). The 2016 Water Infrastructure Improvements for the Nation (WIIN) Act amended Section 4005 of the Resource Conservation and Recovery Act (RCRA) to provide a framework for the establishment of state CCR permit programs with review and approval by USEPA, and multiple states have either already used this framework to establish a permit program or are in the process of doing so. This abstract expands upon content presented at the 2022 WOCA Conference incorporating activities that have occurred since that time. While state permit programs, if implemented, are required to comply with the 2015 rule and subsequent revisions, they may also be more stringent. Because USEPA is required to review and approve these programs, associated state regulations are often promulgated and become effective before USEPA is able to complete review and approval. This discrepancy in timing presents owners and operators with the complexity of simultaneously complying with both federal and state requirements that do not align exactly. An updated summary of state CCR regulatory activity at the time of publication is presented, along with example case studies involving implementation of Illinois’ related Part 845 regulations promulgated in 2021 and Wisconsin’s incorporation of the CCR Rule into their Chapter NR 500 solid waste management regulations in 2022

Implementing the Final CCR Legacy Rule

Implementing the Final CCR Legacy Rule Authors Mr. Robert Glazier - United States - Geosyntec Consultants, Inc. Mrs. Martha Thomsen - United States - Baker Botts LLP Mr. John Seymour - United States - Geosyntec Consultants, Inc. Mr. Victor Modeer - United States - Vistra Abstract Inactive surface impoundments at inactive power stations (legacy units) were exempt from the 2015 Federal Coal Combustion Residuals (CCR) Rule. In August 2018, the U.S. Court of Appeals for the D.C. District vacated and remanded that exemption back to the U.S. Environmental Protection Agency (USEPA). On October 14, 2020, USEPA published an Advance Notice of Proposed Rulemaking (ANPR) and subsequently received 15,170 comments. On May 18, 2023, USEPA published the draft rule for public comment and received over 120 sets of comments. For the first time in the proposed rule, EPA proposed expanding the CCR Rule to include coal combustion management units (CCRMUs). The Final Legacy Rule is targeted for publication in May 2024. In addition, EPA sent a NODA related to this rulemaking for OMB review in October 2023. There are several common themes among industry’s concerns with the proposed rule, including unrealistic deadlines, closure constraints and operational impacts, and substantial retroactive requirements applied to long-closed units. These legal and technical themes will be reviewed by the panel with the benefit of additional deliberation after the short 30-day public comment deadline. Strategies for compliance in the short term while industry potentially litigates the final rule will also be discussed

Potential Failure Mode Analysis for Groundwater Collection Trench Between a CCR Landfill Dike and a River

Potential Failure Mode Analysis for Groundwater Collection Trench Between a CCR Landfill Berm and a River Authors Mr. John Seymour - United States - Geosyntec Consultants, Inc. Dr. Onur Tastan - United States - Geosyntec Consultants, Inc. Dr. Paul Sabatini - United States - Geosyntec Consultants, Inc. Mr. Victor Modeer - United States - Vistra Mr. Isaiah Vaught - United States - Geosyntec Consultants, Inc. Abstract A potential failure mode analysis (PFMA) was conducted to assess the risks of failure for the construction of a groundwater collection trench located between the containment berm of a CCR landfill and a river. The trench is to be 20-ft deep and over 1,000 ft long. A one-pass trenching method was proposed. The PFMA process is typically used under dam safety programs. The PFMA was adopted for this condition due to the high risk of failure of the trench by collapse that could affect the containment berm. Risks included containment dike failure, human safety, and loss of CCR into the river. Five PFMs were identified during the PFMA workshop. Subsequently, potential risk reduction measures were developed and implemented into the design. The risk assessment included completing a seepage analysis at the base of the trench, conducting a FLAC analysis to assess the impacts of stress relief on the trench excavation, and conducting slope stability analyses of the trench and containment berm and riverbank. The risk reduction was incorporated into the construction technique by including contractor responsibilities for sequencing, limiting the timing of construction to dry/low river flow seasons, construction inspections and monitoring, requirements to avoid having an open trench for an excessive time, and to place backfill quickly

Foundation Selection and Construction Performance - Clark Bridge Replacement

The paper describes the foundation investigation for the Clark Bridge Replacement, which spans the Mississippi River at Alton, Illinois. The subsurface investigation and the design considerations leading to the foundation piling selection are detailed. The construction performances of the selected H-piles and composite piles are described, including the use of pre-construction wave equation analyses to predict the performance of proposed pile hammers, and the use of the dynamic pile driving analyzer during construction to limit driving stresses and prevent pile damage

Modeling and control of a tapped-inductor buck converter with pulse frequency modulation

The tapped-inductor buck (TI-buck) converter has shown to be a suitable solution for auxiliary power supply for modular multilevel converter submodules. Such application features a large step-down voltage conversion, made at relatively low output power. This converter operates in discontinuous conduction mode with zero voltage switching of the high-voltage valve. This paper treats the dynamic behaviour of the aforementioned converter. First, an average output current model of the converter is developed and a small signal model is obtained. Then, a closed-loop output voltage control, which uses the switching frequency as control variable, is designed and implemented using a microcontroller. Measurements on a down-scaled prototype shows that the control system provides a well-controlled average output voltage, which is stable under significant load variation. Finally, a solution for implementing the start-up of the converter is presented and tested.</p

Obesity and caries in four-to-six year old English children: a cross-sectional study.

BACKGROUND: Obesity and caries are common conditions in childhood and can have significant implications on children's wellbeing. Evidence into their association remains conflicting. Furthermore, studies examining the ssociation between obesity and caries commonly focus on individual-level determinants. The present study aimed to examine the association between obesity and caries in young English children and to determine the impact of deprivation and area-level characteristics on the distribution of the two conditions. METHODS: This was a cross-sectional study among children in Plymouth city aged four-to-six years. Anthropometric measurements included weight and height (converted to Body Mass Index centiles and z-scores), and waist circumference. Caries was assessed by using the sum of the number of teeth that were decayed, missing or filled. A questionnaire was used to obtain information on children's demographic characteristics, oral hygiene, and dietary habits. The impact of deprivation on anthropometric variables and caries was determined using Linear and Poisson regression models, respectively. Multiple logistic regression was used to assess the association between different anthropometric measures and caries. Logistic regression models were also used to examine the impact of several demographic characteristics and health behaviours on the presence of obesity and caries. RESULTS: The total sample included 347 children aged 5.10 ± 0.31 (mean ± SD). Deprivation had a significant impact on caries and BMI z-scores (p < 0.05). Neither BMI- nor waist circumference z-scores were shown to be significantly associated with dental caries. Among the neighbourhood characteristics examined, the percentage of people dependent on benefits was found to have a significant impact on caries rates (p < 0.05). Household's total annual income was inversely related to caries risk and parental educational level affected children's tooth brushing frequency. CONCLUSIONS: No associations between any measure of obesity and caries were found. However, deprivation affected both obesity and caries, thus highlighting the need to prioritise disadvantaged children in future prevention programmes