On the multiaxial fatigue assessment of complex three-dimensional stress concentrators

This paper assesses and quantifies the detrimental effects of complex tri-dimensional notches subjected to uniaxial and multiaxial fatigue loading. A number of experimental results taken from the technical literature and generated by testing specimens containing complex geometrical features were reanalysed using a critical distance/plane method. The investigated notched samples were tested under uniaxial and multiaxial constant amplitude load histories, considering also the effects of non-zero mean stresses as well as non-proportional loading. The common feature of the considered notched geometries was that the position of the critical location changed as the degree of multiaxiality of the applied loading varied. The relevant linear-elastic stress fields in the vicinity of the crack initiation points were calculated by the Finite Element method and subsequently post-processed using the Modified Wöhler Curve Method in conjunction with the Theory of Critical Distances (the latter theory being applied in the form of the Point Method). This validation exercise confirms the accuracy and reliability of our multiaxial fatigue life assessment technique, which can be efficiently used in situations of practical interest by directly post-processing the relevant linear-elastic stress fields calculated with commercial Finite Element software packages.Safe Technology Limite

Heat pipes as perspective base elements of heat recovery in heat supply and ventilating systems

Thermotechnical characteristics of heat pipes are considered as high-efficient heat-transfer devices, which can provide energy-saving technologies for heat supply and ventilating systems and for different branches of industry. Thermotechnical and working (”performance capability”) characteristics of heat pipes are investigated. By ”performance capability” of heat pipes and heat-transfer devices on heat pipes we mean the system state, where it can perform set functions and keep parameter values (thermal power, conductivity, thermal resistance, heat-transfer coefficient, temperature level and differential, etc.) within the regulations of standardized specifications. The article presents theoretical and experimental methods of «gaslock» length determination on noncondensable gases during long-lasting tests of ammonia heat pipes made of aluminum shape АS – КRА 7.5 – R1 (alloy АD – 31). The paper gives results of research of thermotechnical characteristics of heat pipes in horizontal and vertical states (separate and as a set part) while using different systems of thermal insulation. The obtained results of thermotechnical and resource tests show the advantages of ammonia heat pipes as basic elements for heat exchanger design in heating and ventilation systems

Once Achieved, What is it Worth?

Once Achieved, What is it Worth? examines the contemporary social, political and physical landscape of the American West. My research for the past three years has been exploring the myths and misconceptions associated with this region and how these illusions inform, misinform, distort and taint the cultural norms of the region. My intention is to create a more factual representation of the American West relative to my own experience. The American West is a region that has been marauded for its resources, historically to the present day. There is little difference between the fracking boom that North Dakota is currently experiencing than the gold rushes of the late 1800s in South Dakota or the copper boom that made Butte, Montana, “the richest hill on earth.” The boom and bust culture of this region is part and parcel to what it means to be a Wyomingite, a South Dakotan or a Montanan…all of which are monikers that we Westerners adopt, wear and identify with. At its most basic, the American West is a cash cow for the two coasts and the inhabitants of the region will continue to be subject to benefits and detriments of boom and bust culture. My goal is to remove the romantic façade of the West in favor of a more austere interpretation built upon greed, brutality and guilt. The body of this thesis delves into a variety of aspects of my practice, touching on personal experience, the myth of the American West, mapping, art and critical theory, socio-economics and aesthetics, forming the body of a thesis. This paper may be seen as a more direct examination of my thesis exhibition. The writings should be considered in relationship to my studio practice, however, I also think of the writings as self-contained thoughts on specific subjects. The writings serve as reflections of my process and the various currents that run within it and largely represent my intellectual approach to art practice and making, and as such slightly break from the traditional format of the thesis paper. I hope for this effort to be a more insightful approach as it is a more specific representation, where ideas and concepts are paramount, continually expanding and informing one another, resulting in the visual articulation of these ideas

Clinical approach to non-resolving pneumonia: a survey of Wisconsin primary care clinicians

Background/significance: Little has been reported regarding the approach of primary care clinicians to ambulatory, non-responsive pneumonia (ANRP), variously defined as pneumonia which has not improved with 3-10 days of antibiotic therapy. Anecdotal experience suggests that changes in antibiotic prescription may occur without diagnostic testing for uncovered etiologic agents such as fungi (estimated 1-7% of pneumonia in Wisconsin). Purpose: To determine the stated approach to this clinical problem by primary care clinicians. Methods: A survey containing an algorhythmic, scenario based clinical case of ANRP was sent electronically to the 103 eligible members of the Wisconsin Research and Education Network Survey Group of Wisconsin area primary care clinicians. Respondents were presented with potential diagnostic and therapeutic responses to the case scenario which was constructed from recent consensus guidelines. Results: Surveys were returned from 53/103 members of which 44 were completed (61% male, 30% rural, mean 20 years practice, 13 counties). X-rays were “ordered” by 39 (89%) at initial presentation, and all 39 ordered antibiotics (70% azithromycin). After 4 days of no response, 25/39 (64%) did additional diagnostic testing, 26/39 (67%) changed antibiotics (5 without further testing); after 11 days of no response 3/39 (59%) ordered CT, 16 (41%) bronchoscopy and 28 (72%) either CT or bronchoscopy. Five clinicians (11%) did not order initial X-rays (3/5 started antibiotics), nor did they order further testing after 4 days of no response. Overall, 29/44 (66%) had done no sputum or antigen testing for bacteria by 4 days, and 24/44 (55%) had done no specific testing for fungi by 11 days of ANRP. Conclusion: When presented with an ANRP scenario, a majority of regional primary care clinicians both change antibiotics and do further testing after 4 days of no response, but do not test for fungi by 11 days. These findings highlight the need for practice guidelines based on research outcomes and expert experience to establish pathways for optimal treatment of ANRP. Studies are underway to determine what is done in actual practice

Developing the Theory of Critical Distances for practical integrity assessment of real-life structural components

This PhD thesis details the research conducted to answer three questions in the field of fracture and fatigue engineering. The opening chapters provide fracture and fatigue background theory as well as a more comprehensive review of the Theory of Critical Distances (TCD), a theory proven to be successful in the assessment of components containing stress concentration features. Chapter 4 details an engineering approach based on the TCD for the static assessment of engineering components containing stress concentrators made of brittle, quasi-brittle and ductile materials; and loaded by any combination of static forces. To validate the method, 1744 experimental data was taken from technical literature is provided in Annex A. Each data was modelled using FE software, the extracted stress data was then post-processed using this reformulation of the TCD. The results obtained were compared to the commonly used Hot-Spot Stress-Method, across the same set of data there was an order of magnitude improvement in accuracy, the TCD Point Method giving an average error less than 30% whilst the HSSM gave an average error greater than 300%. Chapter 5 is concerned with the use of the linear-elastic TCD to assess notched metallic components in the high-cycle fatigue regime at elevated temperatures. Full details of two experimental programmes are provided, notched samples of a low carbon steel C45 and an aluminium alloy A319 T7 was tested, the results are provided in Annex C. Additional experimental data was taken from technical literature to further validate the method. The results showed that the approach was highly accurate with errors falling within ±20%. The 6th Chapter gives account of a study into the combined use of the TCD and the Modified Wöhler Curve Method (MWCM to accurately and efficiently assess metal engineering components IV containing complex 3D stress raisers experiencing complex load histories that resulted in fatigue failures in the medium- and high-cycle fatigue regime. The method is based on critical plane theory which assumes that fatigue cracks initiate on the material plane experiencing the maximum shear stress amplitude. The method was proven to be successful independent of the stress raiser geometry and the complexity of the load history, typically returning errors of ±20%. Chapters 4-6 each have their individual conclusions and suggestions for further work, chapter 7 gives a summary of the conclusions and chapter 8 provides some suggestions for further work

The linear-elastic Theory of Critical Distances to estimate high-cycle fatigue strength of notched metallic materials at elevated temperatures

This paper investigates the accuracy of the linear-elastic Theory of Critical Distances (TCD) in estimating high-cycle fatigue streng th of notched metallic materials experienc- ing elevated temperatures during in-service operations. The TCD postulates that the fatigue damage extent can be estimated by directly post-processing the entire linear-elastic stress field acting on the material in the vicinity of the crack initiation locations. The key feature of this theory is that the high-cycle fatigue assessment is based on a scale length parameter that is assumed to be a material property. The accuracy of this design method was checked against a number of experimental results generated, under axial loading, by testing, at 250 °C, notched specimens of carbon steel C45. To further investigate the reliability of the TCD, its accuracy was also checked via several data taken from the literature, these experimental results being generated by testing notched samples of Inconel 718 at 500 °C as well as notched specimens of directionally solidified superalloy DZ125 at 850 °C. This validation exercise allowed us to prove that the linear-elastic TCD is successful in estimating high-cycle fatigue strength of notched metallic materials exposed to elevated temperature, resulting in estimates falling within an error interval of ±20%. Such a high level of accuracy suggests that, in situations of practical interest, reliable high-cycle fatigue assessment can be performed without the need for taking into account those non-linearities characterising the mechanical behaviour of metallic materials at high temperature, the used critical distance being still a material property whose value does not depend on the sharpness of the notch being designed