Quantitative Ultrasonic Coda Wave (Diffuse Field) NDE of Carbon-Fiber Reinforced Polymer Plates

The increasing presence and applications of composite materials in aerospace structures precipitates the need for improved Nondestructive Evaluation (NDE) techniques to move from simple damage detection to damage diagnosis and structural prognosis. Structural Health Monitoring (SHM) with advanced ultrasonic (UT) inspection methods can potentially address these issues. Ultrasonic coda wave NDE is one of the advanced methods currently under investigation. Coda wave NDE has been applied to concrete and metallic specimens to assess damage with some success, but currently the method is not fully mature or ready to be applied for SHM. Additionally, the damage diagnosis capabilities and limitations of coda wave NDE applied to fibrous composite materials have not been widely addressed in literature. The central objective of this work, therefore, is to develop a quantitative foundation for the use of coda wave NDE for the inspection and evaluation of fibrous composite materials. Coda waves are defined as the superposition of late arriving wave modes that have been scattered or reflected multiple times. This results in long, complex signals where individual wave modes cannot be discriminated. One method of interpreting the changes in such signals caused by the introduction or growth of damage is to isolate and quantify the difference between baseline and damage signals. Several differential signal features are used in this work to quantify changes in the coda waves which can then be correlated to damage size and growth. Experimental results show that coda wave differential features are effective in detecting drilled through-holes as small as 0.4 mm in a 50x100x6 mm plate and discriminating between increasing hole diameter and increasing number of holes. The differential features are also shown to have an underlying basis function that is dependent on the hole volume and can be scaled by a material dependent coefficient to estimate the feature amplitude and size holes. The fundamental capabilities of the coda wave measurements, such as error, repeatability, and reproducibility, are also examined. Damage detection was found to be repeatable, reproducible, and relatively insensitive to noise. The measurements are found to be sensitive to thermal changes and absorbing boundaries. Several propagation models are also presented and discussed along with a brief analysis of coda wave signals and spectra

Flaw detection in Multi-layer, Multi-material Composites by Resonance Imaging: utilizing Air-coupled Ultrasonics and Finite Element Modeling

Ceramic tiles are the main ingredient of a multi–material, multi–layered composite being considered for the modernization of tank armors. The high stiffness, low attenuation, and precise dimensions of these uniform tiles make them remarkable resonators when driven to vibrate. Defects in the tile, during manufacture or after usage, are expected to change the resonance frequencies and resonance images of the tile. The comparison of the resonance frequencies and resonance images of a pristine tile/lay–up to a defective tile/lay–up will thus be a quantitative damage metric. By examining the vibrational behavior of these tiles and the composite lay–up with Finite Element Modeling and analytical plate vibration equations, the development of a new Nondestructive Evaluation technique is possible. This study examines the development of the Air–Coupled Ultrasonic Resonance Imaging technique as applied to a hexagonal ceramic tile and a multi–material, multi–layered composite

DEVELOPING SPATIALLY-EXPLICIT ASSESSMENT TOOLS FOR EASTERN OYSTER IN CHESAPEAKE BAY

Decreasing abundance of the eastern oyster Crassostrea virginica in Chesapeake Bay is of concern because of its ecological, economic, and cultural importance. The objective of my study was to develop methods for conducting stock assessments of eastern oysters in Maryland waters of Chesapeake Bay that estimate abundance, recruitment, and fishing mortality at regional scales. First, I evaluated how spatial patterns in autocorrelation of recruitment and adult relativity density varied over time by fitting semivariogram models to survey data for each year. This information was then used to determine appropriate scales for my second objective which was to develop a stage-based model for the lower Potomac River using data from the Maryland Department of Natural Resources fall dredge survey and fishery data from the Potomac River Fisheries Commission. Estimated abundance declined to approximately 39% of that in 1990. The analyses will provide a platform for regional management of eastern oysters

Maternal preconception health and neighborhood factors in relation to preterm birth in Georgia, 2012-2014

BACKGROUND: Relationships between maternal preconception health and preterm birth have been demonstrated in the literature, as have relationships between neighborhood factors and maternal preconception health. Determining how maternal preconception health and neighborhood factors simultaneously contribute to preterm birth will help researchers and clinicians better understand the complex risk factors of preterm birth. METHODS: Data were collected during 2012-2014 in the Georgia Pregnancy Risk Assessment Monitoring System. Data were geocoded to American Community Survey 2011-2015 5-year estimates (n=3085). Descriptive statistics were calculated. Effects of maternal preconception health and neighborhood factors on preterm birth were analyzed using hierarchical generalized linear modeling (SAS PROC GLIMMIX). RESULTS: From 2012-2014, about 9.38% of Georgia moms gave birth to a preterm infant. Considering cross-level interactions, for women who reported recently dieting and who lived in census tracts with 1.00% more crowded households than average, the estimated odds of preterm birth were 0.83 times the estimated odds for the average interaction (95% CI 0.81-0.85). For women with a pre-pregnancy chronic disease who lived in rural counties, the estimated odds of preterm birth were 1.35 times the estimated odds for the average interaction (95% CI 1.17-1.57). CONCLUSIONS: Maternal preconception health and neighborhood factors were simultaneously significantly associated with preterm birth, demonstrating the complexity of risk factors associated with preterm birth. Programs to promote healthy weight management and exercise before pregnancy and to encourage physicians to work in rural counties could improve maternal preconception health and decrease preterm births

Determination of the most appropriate method for extrapolating overall survival data from a placebo-controlled clinical trial of lenvatinib for progressive, radioiodine-refractory differentiated thyroid cancer

Background: Cost-effectiveness models for the treatment of long-term conditions often require information on survival beyond the period of available data. Objectives: This paper aims to identify a robust and reliable method for the extrapolation of overall survival (OS) in patients with radioiodine-refractory differentiated thyroid cancer receiving lenvatinib or placebo. Methods: Data from 392 patients (lenvatinib: 261, placebo: 131) from the SELECT trial are used over a 34-month period of follow-up. A previously published criterion-based approach is employed to ascertain credible estimates of OS beyond the trial data. Parametric models with and without a treatment covariate and piecewise models are used to extrapolate OS, and a holistic approach, where a series of statistical and visual tests are considered collectively, is taken in determining the most appropriate extrapolation model. Results: A piecewise model, in which the Kaplan–Meier survivor function is used over the trial period and an extrapolated tail is based on the Exponential distribution, is identified as the optimal model. Conclusion: In the absence of long-term survival estimates from clinical trials, survival estimates often need to be extrapolated from the available data. The use of a systematic method based on a priori determined selection criteria provides a transparent approach and reduces the risk of bias. The extrapolated OS estimates will be used to investigate the potential long-term benefits of lenvatinib in the treatment of radioiodine-refractory differentiated thyroid cancer patients and populate future cost-effectiveness analyses

Detection of 4-point Bend Induced Micro-cracks in CFRP Laminates via Coda Wave NDE

Although coda wave NDE has been shown to have some sensitivity to realistic damage in concrete structures, the technique’s capability for detecting micro-cracks in fibrous composite materials has yet to be evaluated. This paper reports on the first investigation of realistic damage, specifically micro-cracks, in fibrous composite materials using coda wave differential signal features. Micro-cracks were generated in CFRP samples using the 4-point bending configuration shown in Fig. 1. The damage was monitored during loading with Acoustic Emission, and the loading was stopped after each significant damage event. The damage was then examined with coda wave NDE, immersion UT, and micrographs. This work demonstrates the capability of coda waves to detect and monitor micro-cracks in CFRP laminates. Coda wave sensitivity, repeatability, and reproducibility is presented and discussed. This material is based on work supported by the NSF Industry/University Cooperative Research Program of the Center for Nondestructive Evaluation at Iowa State University

Comparison of Two Zooplankton Sampling Gears in Shallow, Homogeneous Lakes

We compared two zooplankton collection gears, Wisconsin nets and column samplers, to evaluate the effectiveness of each gear in quantifying inshore and offshore zooplankton density and size structure in shallow, homogeneous lakes. Zooplankton densities (within gear) did not differ (P \u3e 0.05) between inshore and offshore sites in either study lake, with the exception of Wisconsin-netted Cyclops sp. in Lake Goldsmith. Wisconsin net samples produced a higher mean zooplankton density than column samplers for Bosmina sp., Cyclops sp., and Daphnia sp. in East Oakwood Lake and for Cyclops sp. (inshore), Daphnia sp., and Diaptomus sp. in Lake Goldsmith. Zooplankton densities had greater variability (coefficients of variation) in 4 of 5 taxa collected with the Wisconsin net in both study lakes. Zooplankton size structure did not differ (P\u3e 0.05) between gears in either study lake, with the exception of Diaptomus sp. in East Oakwood Lake. Our results suggest that column samplers have higher precision than Wisconsin nets when sampling common zooplankton species in shallow, homogeneous lakes

A content analysis of eighteen scholarly journals: What has been written about online family therapy?

The purpose of this study was to ascertain what has been written about online family therapy in selected scholarly journals focused on marriage and family issues. Technology is impacting the way individuals communicate and has changed the face of how therapy can be provided to clients. Online therapy has multiple definitions across a variety of disciplines including social work, psychology, family therapy, technology, and communication fields. A consistent definition for online family therapy is lacking in the literature and a call is made for family therapists to define and create standards and practices for the field. The content analysis utilized quantitative and qualitative methods to report results. A coding team was utilized to determine results and identify themes emerging in the literature. Themes were obtained from ten scholarly articles outlining practices of online family therapy and recommendations for family therapist practitioners are presented. The Family Journal yielded the most results with an article prevalence rate of 0.58%. Major themes emerging from the literature are Legal and Ethical Concerns, Benefits, and Technology as an Adjunct to Traditional Therapy. A discussion of the results was presented and conclusions were drawn. Finally, implications and recommendations were given to discuss the future of online family therapy.Brock, LindaJennings, GlenWoods, Sara

Limitations of symmetry in FE modeling: A comparison of fem and air-coupled resonance imaging

It has long been an accepted practice to use symmetry in Finite Element Modeling. Whenever modeling a large structure, we turn to symmetry in order to significantly reduce the model size and computation time. But is symmetry always the solution to long computation times, and is it always accurate? This study is aimed at modeling a whole ceramic tile and several possible symmetric models under several different loading cases and comparing them to each other and Air-Coupled Ultrasonic scans to determine if the Finite Element Models can accurately predict the vibrational resonance patterns. The reason for the accuracy or inaccuracy will also be examined. The understanding of the limitations of using symmetry to model large structures will be very useful in all future modeling

Flaw investigation in a multi-layered, multi-material composite: Using air-coupled ultrasonic resonance imaging

Ceramic tiles are the main ingredient of a multi-material, multi-layered composite being considered for the modernization of tank armors. The high stiffness, low attenuation, and precise dimensions of these uniform tiles make them remarkable resonators when driven to vibrate. Defects in the tile, during manufacture or after usage, are expected to change the resonance frequencies and resonance images of the tile. The comparison of the resonance frequencies and resonance images of a pristine tile/lay-up to a defective tile/lay-up will thus be a quantitative damage metric. By examining the vibrational behavior of these tiles and the composite lay-up with Finite Element Modeling and analytical plate vibration equations, the development of a new Nondestructive Evaluation technique is possible. This study examines the development of the Air-Coupled Ultrasonic Resonance Imaging technique as applied to a hexagonal ceramic tile and a multi-material, multi-layered composite