Stress intensity factors for deep cracks emanating from the corner formed by a hole intersecting a plate surface

A technique consisting of freezing photo-elasticity and a numerical method was used to obtain stress intensity factors for natural cracks emanating from the corner at which a hole intersects a plate surface. Geometries studied were: (1) crack depth to thickness ratios of approximately 0.2, (2) 0.5 and 0.75; (3) crack depth to crack length ratios of approximately 1.0 to 2.0; and (4) crack length to hole radius ratios of about 0.5 to 2.0. All final crack geometries were grown under monotonic loading and growth was not self similar, with most of the growth occuring through the thickness under remote extension. Stress intensity factors were determined at the intersection of the flaw border

Stress intensity factors for deep cracks emanating from the corner formed by a hole intersecting a plate surface

A technique consisting of a marriage between stress freezing photoelasticity and a numerical method was used to obtain stress intensity factors for natural cracks emanating from the corner at which a hole intersects a plate surface. Geometrics studied were: crack depth to thickness ratios of approximately 0.2, 0.5, and 0.75; crack depth to crack length ratios of approximately 1.0 to 2.0. All final crack geometries were grown under monotonic loading and growth was not self similar with most of the growth occurring through the thickness under remote extension. Stress intensity plate surface K sub s factors were determined at the intersection of the flaw border with the plate surface K sub s and with the edge of the hole K sub h. Results showed that for the relatively shallow flaws K sub h approximately equal to 1.5 K sub s, for the moderately deep flaws K sub h approximately equal to K sub s, and for the deep flaws K sub h approximately equal to 0.5 K sub s, revealing a severe sensitivity of K to flaw geometry

A plane strain analysis of the blunted crack tip using small strain deformation plasticity theory

A deformation plasticity analysis of the tip region of a blunted crack in plane strain is presented. The power hardening material is incompressible both elastically and plastically, in order to simulate behavior of a stress freezing material above critical temperature. Stress and displacement fields surrounding the crack tip are presented. The results indicate that the maximum stress seen at the crack tip is indeed limited and is determined by the tensile properties; however, the scale over which the stresses act is dependent on the loading. Comparisons are good between the forward crack tip displacement and micro-fractographic measurments of stretch zones observed in plane strain fracture toughness tests

Leading-edge slat optimization for maximum airfoil lift

A numerical procedure for determining the position (horizontal location, vertical location, and deflection) of a leading edge slat that maximizes the lift of multielement airfoils is presented. The structure of the flow field is calculated by iteratively coupling potential flow and boundary layer analysis. This aerodynamic calculation is combined with a constrained function minimization analysis to determine the position of a leading edge slat so that the suction peak on the nose of the main airfoil is minized. The slat position is constrained by the numerical procedure to ensure an attached boundary layer on the upper surface of the slat and to ensure negligible interaction between the slat wake and the boundary layer on the upper surface of the main airfoil. The highest angle attack at which this optimized slat position can maintain attached flow on the main airfoil defines the optimum slat position for maximum lift. The design method is demonstrated for an airfoil equipped with a leading-edge slat and a trailing edge, single-slotted flap. The theoretical results are compared with experimental data, obtained in the Ames 40 by 80 Foot Wind Tunnel, to verify experimentally the predicted slat position for maximum lift. The experimentally optimized slat position is in good agreement with the theoretical prediction, indicating that the theoretical procedure is a feasible design method

Utilization of the Building-Block Approach in Structural Mechanics Research

In the last 20 years NASA has worked in collaboration with industry to develop enabling technologies needed to make aircraft safer and more affordable, extend their lifetime, improve their reliability, better understand their behavior, and reduce their weight. To support these efforts, research programs starting with ideas and culminating in full-scale structural testing were conducted at the NASA Langley Research Center. Each program contained development efforts that (a) started with selecting the material system and manufacturing approach; (b) moved on to experimentation and analysis of small samples to characterize the system and quantify behavior in the presence of defects like damage and imperfections; (c) progressed on to examining larger structures to examine buckling behavior, combined loadings, and built-up structures; and (d) finally moved to complicated subcomponents and full-scale components. Each step along the way was supported by detailed analysis, including tool development, to prove that the behavior of these structures was well-understood and predictable. This approach for developing technology became known as the "building-block" approach. In the Advanced Composites Technology Program and the High Speed Research Program the building-block approach was used to develop a true understanding of the response of the structures involved through experimentation and analysis. The philosophy that if the structural response couldn't be accurately predicted, it wasn't really understood, was critical to the progression of these programs. To this end, analytical techniques including closed-form and finite elements were employed and experimentation used to verify assumptions at each step along the way. This paper presents a discussion of the utilization of the building-block approach described previously in structural mechanics research and development programs at NASA Langley Research Center. Specific examples that illustrate the use of this approach are included from recent research and development programs for both subsonic and supersonic transports

Linking Health Information Technology to Patient Safety and Quality Outcomes: A Bibliometric Analysis and Review

Informatics for Health and Social Care is published by Informa Healthcare. Publisher's version can be found at: http://informahealthcare.com/doi/abs/10.3109/17538157.2012.678451OBJECTIVE: To assess the scholarly output of grants funded by the Agency for Healthcare Research and Quality (AHRQ) that published knowledge relevant to the impact of health information technologies on patient safety and quality of care outcomes. STUDY DESIGN: We performed a bibliometric analysis of the identified scholarly articles, their journals, and citations. In addition, we performed a qualitative review of the full-text articles and grant documents. DATA COLLECTION/EXTRACTION METHODS: Papers published by AHRQ-funded investigators were retrieved from MEDLINE, journal impact factors were extracted from the 2010 Thompson Reuters Journal Citation Report, citations were retrieved from ISI's Web of Knowledge and Google Scholar. PRINCIPAL FINDINGS: Seventy-two articles met the criteria for review. Most articles addressed one or more of AHRQ's outcome goals and focus priorities. The average impact factor for the journals was 4.005 (range: 0.654-28.899). The articles, and their respective grants, represented a broad range of health information technologies. CONCLUSIONS: This set of AHRQ-funded research projects addressed the goals and priorities of AHRQ, indicating notable contributions to the scientific knowledge base on the impact of information system use in healthcare.This work was supported, in part, by the National Resource Center of the Agency for Healthcare Research and Quality, contract number 290-04-0016

Late Quaternary vegetation history of North Stradbroke Island, Queensland, eastern Australia

Currently there is a paucity of records of late Quaternary palaeoenvironmental variability available from the subtropics of Australia. The three continuous palaeoecological records presented here, from North Stradbroke Island, subtropical Queensland, assist in bridging this large spatial gap in the current state of knowledge. The dominance of arboreal taxa in the pollen records throughout the past >40,000 years is in contrast with the majority of records from temperate Australia, and indicates a positive moisture balance for North Stradbroke Island. The charcoal records show considerable inter-site variability indicating the importance of local-scale events on individual records, and highlighting the caution that needs to be applied when interpreting a single site as a regional record. The variability in the burning regimes is interpreted as being influenced by both climatic and human factors. Despite this inter-site variability, broad environmental trends are identifiable, with changes in the three records comparable with the OZ-INTIMATE climate synthesis for the last 35,000 years. © 2013 Elsevier Ltd.Patrick T. Moss, John Tibby, Lynda Petherick, Hamish McGowan, Cameron Bar

Weak Disorder in Fibonacci Sequences

We study how weak disorder affects the growth of the Fibonacci series. We introduce a family of stochastic sequences that grow by the normal Fibonacci recursion with probability 1-epsilon, but follow a different recursion rule with a small probability epsilon. We focus on the weak disorder limit and obtain the Lyapunov exponent, that characterizes the typical growth of the sequence elements, using perturbation theory. The limiting distribution for the ratio of consecutive sequence elements is obtained as well. A number of variations to the basic Fibonacci recursion including shift, doubling, and copying are considered.Comment: 4 pages, 2 figure

The effect of manually facilitated flexion of the thoracic spine on the interspinous space among horses with impinging dorsal spinous processes of the thoracic vertebrae

Impinging dorsal spinous processes (IDSP) are typically diagnosed and graded using radiography, during which the effect of the horses' thoracolumbar posture on the interspinous spaces is not commonly considered. Posture can be altered from a spontaneous, relatively extended, or lordotic, position by manual facilitation of thoracic flexion ('thoracic lift'). This study aimed to ascertain if the thoracic vertebral interspinous space distances were increased by using facilitated thoracic flexion to alter the posture in horses diagnosed with IDSP. Seven horses of mixed breed and sex, median age 9.1 years (interquartile range, 7.2-12.4 years), with a diagnosis of thoracic IDSP with no history of spinal surgery, were included in the study. Two sets of radiographs were obtained. The initial set was taken in the horses' spontaneous posture and the second in the manually facilitated flexed posture. Each image was anonymised allowing blinded measurement of the interspinous spaces. Analysis was performed using Hodges-Lehmann median differences estimates. An increase in the median interspinous space distance was achieved after manual facilitation of thoracic flexion at every thoracic intervertebral space (5th-18th thoracic [T] vertebra). The greatest median increase was seen between T7-T8 and T12-T13 (3.1 mm and 3.0 mm, respec-tively) whereas the lowest median increase was seen between T17-T18 (0.7 mm). In this study, thoracic inter-spinous space distances could be increased by using manual facilitation to alter the thoracic posture in horses with IDSP, which could affect grading and decision making.Peer reviewe