Modeling 3D Fiber Reinforced Foam Core Sandwich Structures Using a Multi-Scale Finite Element Approach.

An engineering challenge of composite sandwich structures is quantifying their ability to tolerate damage, particularly in launch vehicles and spacecraft, where mission assurance is critical. Recently, there has been a development of new core materials that may alter their damage tolerance through the use of a three-dimensional, truss-like network of reinforcing fibers inside a lightweight foam core. This research focuses on the testing and developing a multi-scale approach to model 3D Fiber Reinforced Foam Core (3DFRFC) sandwich composites with defects across typical operating temperatures. Details of the 3DFRFC measured directly from the microstructure were utilized to develop a parametric code for generating detailed embedded element models. These models were used for direct detailed modeling of fracture, edgewise compression, flatwise tension, flatwise compression, and three point bending test specimens. The embedded element models were also used as the cornerstone of a new method of developing effective homogenized properties for 3DFRFCs based on the details of the microstructure. Improved homogenization techniques developed by including the local interaction between the facesheet and the core are also included. The development of a new bonded double cantilever beam (BDCB) specimen for testing the Mode I fracture of a 3DFRFC sandwich structures is presented. The BDCB specimens exhibited relatively smooth crack propagation and produced GIc values similar to honeycomb sandwich structures and significantly higher than comparable foam structures. A full fabrication, testing, and evaluation of 3DFRFC specimens with differing sizes of facesheet-to-core interface debonds is also presented. The analysis methods were able to predict the failure load and modes within 5%. The 3DFRFC proved to be tolerant to facesheet-to-core debonds with only the largest debond demonstrating a statistically significant reduction of 22%. Finally, a detailed investigation of the through thickness behavior of a 3DFRFC composite under ambient and cold conditions is included demonstrating better through thickness ambient performance than unreinforced cores and relatively small reductions in strength at cold temperatures. The investigation into the performance of 3DFRFC composite structures highlights the robust behavior of the structure to cold environments while underscoring the importance of loading direction on the structural response of these highly orthotropic composites.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111577/1/ztkier_1.pd

Determining Effective Interface Fracture Properties of 3D Fiber Reinforced Foam Core Sandwich Structures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106494/1/AIAA2013-1547.pd

Effects of Ply Stacking Sequence in 3D Fiber Reinforced Foam Core Sandwich Structures with Defects

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140407/1/6.2014-0504.pd

Determining Effective Interface Fracture Properties of 3D Fiber Reinforced Foam Core Sandwich Structures

The aim of this study is to describe several important trends from the Valley of Yaqui's agricultural expansion, in the northeast Mexico, showed from 1925. At the same time, the construction of a production/enterprise web fed with the rural activity, and coming from an internal linkage is also analyzed. It is included a review of the water system development in the Valley, a description of the historical importance of certain cultivations, specially corn, and the birth of a business force which if certainly included several activities, but it was focused mainly on agriculture.La finalidad de este estudio es mostrar algunos rasgos básicos de la expansión de la frontera agrícola en el valle del Yaqui, en el noroeste de México, a partir de 1925. De manera paralela se analiza la construcción de un tejido productivo-empresarial alimentado por la actividad rural y derivado, sobre todo, de un conjunto de multiplicadores internos. El texto incluye una reseña sobre el desarrollo del sistema de riego en el valle, describe la preponderancia histórica de ciertos cultivos, en especial del trigo, y la correspondiente aparición de un entramado empresarial que si bien abarcó actividades diversas operó sobre todo desde la agricultura

The Clinical Impact of the Covid-19 Pandemic First Wave on Patients With Cystic Fibrosis in New York

BACKGROUND: People with cystic fibrosis (pwCF) may be at risk of complications from COVID-19 but the impact of COVID-19 on pwCF remains unknown. METHODS: We conducted a multicenter retrospective cohort study to assess the impact of the COVID-19 pandemic first wave on pwCF in the New York metropolitan area (NY) from March 1, 2020 to August 31, 2020. Objectives were to determine (1) the prevalence of COVID-19 by PCR and IgG antibody testing, (2) the clinical characteristics of COVID-19, (3) delay in routine outpatient care, and (4) the effect on anxiety and depression in pwCF. RESULTS: There were 26 COVID-19 cases diagnosed by PCR or antibody testing among the study cohort of 810 pwCF. The prevalence of COVID-19 by PCR (1.6%) and IgG antibody (12.2%) testing was low. 58% of cases were asymptomatic and 82% were managed at home. 8% were hospitalized and 1 person died. 89% of pwCF experienced delay in care. The prevalence of anxiety increased from 43% baseline to 58% during the pandemic (P\u3c0.01). In post-hoc analysis, the proportion of patients with diabetes (38% versus 16%, P\u3c0.01) and pancreatic insufficiency (96% versus 66%, P\u3c0.01) were higher while CFTR modulator use was lower (46% versus 65%, P = 0.05) in pwCF who tested positive for COVID-19. CONCLUSIONS: The prevalence of COVID-19 among pwCF in NY during the pandemic first wave was low and most cases were managed at home. CFTR modulators may be protective. PwCF experienced delay in routine care and increased anxiety