Face Sheet/Core Disbond Growth in Honeycomb Sandwich Panels Subjected to Ground-Air-Ground Pressurization and In-Plane Loading

Typical damage modes in light honeycomb sandwich structures include face sheet/core disbonding and core fracture, both of which can pose a threat to the structural integrity of a component. These damage modes are of particular interest to aviation certification authorities since several in-service occurrences, such as rudder structural failure and other control surface malfunctions, have been attributed to face sheet/core disbonding. Extensive studies have shown that face sheet/core disbonding and core fracture can lead to damage propagation caused by internal pressure changes in the core. The increasing use of composite sandwich construction in aircraft applications makes it vitally important to understand the effect of ground-air-ground (GAG) cycles and conditions such as maneuver and gust loads on face sheet/core disbonding. The objective of the present study was to use a fracture mechanics based approach developed earlier to evaluate the loading at the disbond front caused by ground-air-ground pressurization and in-plane loading. A honeycomb sandwich panel containing a circular disbond at one face sheet/core interface was modeled with three-dimensional (3D) solid finite elements. The disbond was modeled as a discrete discontinuity and the strain energy release rate along the disbond front was computed using the Virtual Crack Closure Technique (VCCT). Special attention was paid to the pressure-deformation coupling which can decrease the pressure load within the disbonded sandwich section significantly when the structure is highly deformed. The commercial finite element analysis software, Abaqus/Standard, was used for the analyses. The recursive pressure-deformation coupling problem was solved by representing the entrapped air in the honeycomb cells as filled cavities in Abaqus/Standard. The results show that disbond size, face sheet thickness and core thickness are important parameters that determine crack tip loading at the disbond front. Further, the pressure-deformation coupling was found to have an important load decreasing effect [6]. In this paper, a detailed problem description is provided first. Second, the analysis methodology is presented. The fracture mechanics approach used is described and the specifics of the finite element model, including the fluid-filled cavities, are introduced. Third, the initial model verification and validation are discussed. Fourth, the findings from a closely related earlier study [6] are summarized. These findings provided the basis for the current investigation. Fifth, an aircraft ascent scenario from 0 to 12192 m (0 to 40000 ft) is considered and the resulting crack tip loading at the disbond front is determined. In-plane loading to simulate maneuvers and gust conditions are also considered. Sixth, the results are shown for a curved panel, which was used to simulate potential fuselage applications. Finally, a brief summary of observations is presented and recommendations for improvement are provided

Reactive Oxygen Species: The Good and the Bad

This chapter summarizes recent research on the biology of reactive oxygen species (ROS). The chapter is focused on the bimodal actions of ROS, which can be summarized as both beneficial and negative. The beneficial aspects of ROS are related to their effects on the redox state of cells and the important role that some ROS play in signaling cascade. The detrimental effects of ROS are related excess amounts of these chemical moieties, which are caused by excessive production and/or insufficient actions of endogenous antioxidants. The generation of these species is also discussed

A Decade of Building the Community-Engaged School of Health and Human Sciences at The University of North Carolina Greensboro

This case example illustrates key opportunities, processes, and outcomes of nearly a decade of intentional efforts to build and support community-engaged faculty culture and institutionalization in the School of Health and Human Sciences at the University of North Carolina Greensboro. Situated within a university-wide, faculty-led movement to institutionalize support for community engagement through policy and practice, we describe the motivation of faculty and administrative leadership to integrate support for community engagement across teaching, research and service roles in the Health and Human Sciences unit at UNCG. We present critical moments of opportunity that were leveraged by faculty and administrative leadership to integrate community engagement into visioning and planning documents, faculty rewards and awards, curricular programming, and trans-disciplinary scholarly work through community-engaged partnerships. Using information collected through faculty focus groups and document analysis, and as part of a multi-institutional research program sponsored by the American Association of State Colleges and Universities and the New England Resource Center for Higher Education, we describe key outcomes of efforts to institutionalize community engagement at the school level and areas in which community engagement is integrated into the School’s strategic plan. Of special importance are areas related to tenure and non-tenure track faculty recruitment, faculty promotion and tenure policies, faculty grants and awards programs, and school-level strategic planning. Finally, we describe various choices made about where to locate various activities, efforts, and resources, whether at the department, school, or university-wide level

Determining the physical limits on semi‐active control performance: a tutorial

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106822/1/stc1602.pd

Examining Students’ Experiences and Perceived Skill Attainment in an Agricultural Capstone Course

Utilizing a context-based model for teaching agriculture and qualitative research methodology, a survey of Iowa State University’s Ag 450 students was conducted over the course of two semesters regarding their competence and confidence of certain technical and professional skills expected by agricultural industry experts before and after completion of the Ag 450 capstone course. It was concluded the Ag 450 capstone course is improving student competence of technical skills and on average, students somewhat agreed they were confident regarding professional skills needed for the workplace. It is recommended that this study be replicated for more in-depth analysis and that a longitudinal study regarding how skills learned in the capstone course are being applied in the workforce be utilized as a way to further this research. Furthermore, this study may be replicated utilizing a broader range of skills or focused on the core competencies and outcomes of the course itself. Recommendations for further research and future practice were provided.This article is published as Rinker, S. P., M. S. Hainline, and S. W. Smalley. "Examining Students' Experiences and Perceived Skill Attainment in an Agricultural Capstone Course." NACTA Journal 64 (2019): 254-261. © 2019 North American Colleges and Teachers of Agriculture. Posted with permission

Methicillin resistant Staphylococcus aureus adhesion to human umbilical vein endothelial cells demonstrates wall shear stress dependent behaviour

<p>Abstract</p> <p>Background</p> <p>Methicillin-resistant <it>Staphylococcus aureus </it>(MRSA) is an increasingly prevalent pathogen capable of causing severe vascular infections. The goal of this work was to investigate the role of shear stress in early adhesion events.</p> <p>Methods</p> <p>Human umbilical vein endothelial cells (HUVEC) were exposed to MRSA for 15-60 minutes and shear stresses of 0-1.2 Pa in a parallel plate flow chamber system. Confocal microscopy stacks were captured and analyzed to assess the number of MRSA. Flow chamber parameters were validated using micro-particle image velocimetry (PIV) and computational fluid dynamics modelling (CFD).</p> <p>Results</p> <p>Under static conditions, MRSA adhered to, and were internalized by, more than 80% of HUVEC at 15 minutes, and almost 100% of the cells at 1 hour. At 30 minutes, there was no change in the percent HUVEC infected between static and low flow (0.24 Pa), but a 15% decrease was seen at 1.2 Pa. The average number of MRSA per HUVEC decreased 22% between static and 0.24 Pa, and 37% between 0.24 Pa and 1.2 Pa. However, when corrected for changes in bacterial concentration near the surface due to flow, bacteria per area was shown to increase at 0.24 Pa compared to static, with a subsequent decline at 1.2 Pa.</p> <p>Conclusions</p> <p>This study demonstrates that MRSA adhesion to endothelial cells is strongly influenced by flow conditions and time, and that MSRA adhere in greater numbers to regions of low shear stress. These areas are common in arterial bifurcations, locations also susceptible to generation of atherosclerosis.</p

Identifying the Professional and Technical Skills Agricultural Industry Employers Expect Agricultural Graduates to Possess

Through the lens of human capital theory, the Delphi technique was used to identify the most important professional and technical skills that agricultural industry employers expect graduates to possess upon entering the workforce. A panel of 23 agricultural industry experts provided the data for the Delphi study. At the conclusion of three rounds, a total of 52 items reached consensus, which included 18 technical skills (i.e. verbal communication skills, general knowledge of the agricultural industry, etc.) and 34 professional skills (i.e. flexible, accountable, relatable, etc.). It was concluded agricultural employers place a high value on many technical and professional skills that graduates should possess and this list should be used as a guide to evaluate current agricultural curriculum. It was recommended further research address how graduates are transferring these skills into the workplace.This article is published as Rinker, S. P., S. W. Smalley, and M. S. Hainline. "Identifying the professional and technical skills agricultural industry employers expect agricultural graduates to possess." NACTA Journal 65 (2020): 102-114. © 2020 North American Colleges and Teachers of Agriculture. Posted with permission