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Adhesively bonded doublers and adhesively bonded repairs are extensively used to extend the operational life of metallic aircraft structures. Consequently, this paper focuses on the tools needed to address sustainment issues associated with both adhesively bonded doublers and adhesively bonded repairs to (metallic) aircraft structures, in a fashion that is consistent with the building-block approach mandated in the United States Air Force (USAF) airworthiness certification standard MIL-STD-1530D and also in the United States (US) Joint Services Structural Guidelines JSSG-2006. In this context, it is shown that the effect of biaxial loads on cohesive crack growth in a bonded doubler under both constant amplitude fatigue loads and operational flight loads can be significant. It is also suggested that as a result, for uniaxial tests to replicate the cohesive crack growth seen in adhesively bonded doublers and adhesively bonded repairs under operational flight loads, the magnitude of the applied load spectrum may need to be continuously modified so as to ensure that the crack tip similitude parameter in the laboratory tests reflects that seen in the full-scale aircraft. [ABSTRACT FROM AUTHOR]

Buckling-restrained braces (BRBs) have recently become popular in the United States for use as primary members of seismic lateral-force-resisting systems. A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression. Although design guidelines for BRB applications have been developed, systematic procedures for assessing performance and quantifying reliability are still needed. This paper presents an analytical framework for assessing buckling-restrained braced frame (BRBF) reliability when subjected to seismic loads. This framework efficiently quantifies the risk of BRB failure due to low-cycle fatigue fracture of the BRB core. The procedure includes a series of components that: (1) quantify BRB demand in terms of BRB core deformation histories generated through stochastic dynamic analyses; (2) quantify the limit-state of a BRB in terms of its remaining cumulative plastic ductility capacity based on an experimental database; and (3) evaluate the probability of BRB failure, given the quantified demand and capacity, through structural reliability analyses. Parametric studies were conducted to investigate the effects of the seismic load, and characteristics of the BRB and BRBF on the probability of brace failure. In addition, fragility curves (i.e., conditional probabilities of brace failure given ground shaking intensity parameters) were created by the proposed framework. While the framework presented in this paper is applied to the assessment of BRBFs, the modular nature of the framework components allows for application to other structural components and systems. [ABSTRACT FROM AUTHOR]

The purpose of the research presented in this paper is to reexamine the current Charpy V-notch (CVN) requirements for steel bridges in the United States using state-of-the-art applied fracture mechanics analysis. Proposed revisions to the current CVN requirements are introduced. It is shown that, in general, the typical fracture toughness implied by current minimum CVN requirements results in a trend of decreasing resistance to brittle fracture as the minimum specified yield strength grade increases. The results also show that fracture resistance for the current minimum CVN requirements for the three AASHTO temperature zones is inconsistent for different high-performance steel (HPS) grades. A realignment of the current CVN test temperatures and required notch energy is proposed by normalizing all grades to the crack tolerance associated with the AASHTO yield strength grade 36 ksi steel CVN requirements. [ABSTRACT FROM AUTHOR]

Lock gates are an important part of the transportation infrastructure within the United States (US). Unfortunately, many existing lock gates have reached or exceeded their initial design lives and require frequent repairs to remain in service. Unscheduled repairs often increase as gates age, having a local economic impact on freight transport, which can create economic ripples throughout the nation. Metal fatigue is a key cause of unscheduled service interruptions, degrading lock gate components over time. Additionally, because lock gates are submerged during operation, crack detection prior to component failure can be difficult, and repair costs can be high. This paper presents an analytical and experimental investigation into fatigue damage within common lock gate geometries, as well as fatigue mitigation strategies with a focus on extending gate service lives. Detailed finite element analyses are combined with fatigue and fracture mechanics theories to predict critical fatigue regions within common gate details and develop retrofit strategies for mitigating fatigue cracking. Full-scale experimental fatigue testing of a critical lock gate component is conducted to provide a baseline for the evaluation of retrofit strategies. Retrofit strategies and issues in using carbon fiber reinforced polymer (CFRP) plates having optimized pre-stress levels are discussed. [ABSTRACT FROM AUTHOR]

Vast governmental budgets are spent annually to face corrosion problems of steel reinforcement in concrete bridges attributable to the extensive use of deicing salts. Corrosion controls the lifetime of a bridge, which has two distinct periods. During the first period, chlorides diffuse through the cover. When sufficient chlorides are formed at the rebars, corrosion initiates. This marks the start of the second period, during which rust with higher volume to bare steel is produced. The rust puts pressure on the cover, which finally leads to cover spalling. In this paper, a model is developed to determine the time span of the second period. The model includes a volume compatibility condition that allows for the proper introduction of compaction of all materials that contribute to cover spalling, including the rust. A new condition for marking failure of the cover is also established, based on fracture mechanics and strain energies. Finally, a new formula is proposed for the rate of rust production, which allows for the constant rust production at early and nonlinear diffusion dependant rates at latter stages of corrosion. [ABSTRACT FROM AUTHOR]

The proposed assessment procedure presented in this paper may be used to establish inspection intervals for steel bridges with fracture critical members (FCMs) (if adopted by the Federal Highway Administration). The procedure proposed herein only applies to FCM inspections which are defined as follows: a hands-on inspection of a FCM or member components that may include visual and other nondestructive evaluations. The method is rather simple and provides an alternative procedure to the pure calendar based inspection methodology currently specified in the Code of Federal Regulations for all FCMs. There are only two requirements which must first be satisfied in order to use the assessment. The first is that the routine 24-month inspection must continue to be performed on the bridge under evaluation. The second is that a FCM inspection must be performed on the bridge or the FCM under evaluation prior to the implementation of the resulting inspection intervals given from this assessment. The “initial inspection” should be performed as a typical FCM inspection. The assessment procedure is intended to be applied to individual FCMs and not the entire bridge itself. However, on bridges with multiple FCMs, the “worst case” FCM may be evaluated using the assessment and the resulting inspection interval may be applied to all FCMs on the bridge (for simplicity and bookkeeping purposes). The decision of whether to apply the assessment to all FCMs or the bridge’s worst case FCM is left up to the owner or engineer. The approach is not based on more rigorous damage tolerant design concepts or other fracture mechanics based methods. Nevertheless, the method is a first step in providing a more rational alternative to calendar based inspection and allows owners to prioritize structures and resource allocation. Using engineering experience and judgment, the interval for the hands-on inspection of steel bridges with FCMs can then be selected based on upper limits established through a consensus. Although the focus is on fracture critical bridges and members, the writers believe that the concept could be extended to a variety of structure types and configurations. [ABSTRACT FROM AUTHOR]

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This paper proposes a methodology for the rational assessment of lifetime costs on tall buildings due to hurricane-induced damage along the US Atlantic coastline accounting for plausible future warming climate scenarios. The hurricane simulation is based on Vickery’s empirical model. Initially, regression errors in Vickery’s model are discussed; some adjustments are proposed to enable hurricane simulation in future climates. After verification of the hurricane model’s ability to simulate the results of the United States historical hurricane database, simulation of hurricane activity in future climates is examined. The warming climate scenarios are reproduced from the results of the community earth system model, maintained by the National Center for Atmospheric Research (NCAR). Three different future climate scenarios, RCP2.6, RCP4.5 and RCP8.5, are considered. The influence of warming climate on two quantities, relevant to wind engineering, is examined: hurricane frequency and hurricane intensity. It is found that, in a warming climate environment, the hurricane frequency and hurricane intensity may vary depending on the RCP scenario. Therefore, the probability distribution of the wind speed in hurricane-prone areas of the United States, both coastal and interior areas, will also be influenced by the RCPs. The numerical methodology for computing wind speed probability distribution in a future warming climate, influenced by the various RCP scenarios, is subsequently coupled with an existing approach for structural performance analysis against wind hazards to predict the indirect effect of future warming climate on the structural intervention costs (i.e. repair costs), induced by the damaging winds. A 180-m tall benchmark building, located in Miami (Florida, USA), is used as one example of application in conjunction with a series of structural fragility curves, derived from a recent study for the same structure. The evaluation of lifetime intervention costs is later expanded to demonstrate the ability of the proposed methodology to predict hurricane wind damage, if the location of the structure is moved to several other cities along the Atlantic coast of the United States. [ABSTRACT FROM AUTHOR]

Purpose: Outcome research has become an increasingly important form of clinical evidence for making health care decisions, including oral health considerations in the field of dentistry. In oral reconstruction involving dental implants, the risk of implant failure may be influenced by a patient's underlying medical condition. To identify associations, implant failure and systemic conditions or diseases were studied in a consecutive series of patients who received dental implants from October 1, 1983, to December 31, 2014, in the Department of Dental Specialties at Mayo Clinic in Rochester, Minnesota. Materials and Methods: Data were abstracted from a prospective clinical database and electronic health records for patients' demographic, implant-specific, and medical profiles to determine time to first implant failure. Survival free of implant failure at the patient level was estimated by using the Kaplan-Meier method. Associations of demographic and systemic characteristics with implant failure were evaluated by using Cox proportional hazards regression models and summarized with hazard ratios and 95% confidence intervals. Results: The patient cohort consisted of 6,358 patients with a median age of 53 years at placement of the first implant. A total of 713 patients experienced implant failure at a median of 0.6 years. Among the 5,645 patients who did not experience implant failure, the median duration of follow-up was 5.8 years. More than 20 systemic diseases or conditions were identified for assessment, of which 15 comprised more than 50 patients and five comprised more than 500 patients. All associations were adjusted for age, sex, and era of implant, given the strong influence of these features on implant failure. After adjustment, no systemic disease or condition was shown to increase the risk for implant failure in the population and setting studied. Conclusion: Patients considering oral reconstruction involving implants in the medical setting studied do not appear to risk implant loss because of systemic conditions or diseases. [ABSTRACT FROM AUTHOR]

The article reports on the release of a practice guide titled "Fractography of Ceramics and Glasses" by the U.S. Department of Commerce's National Institute of Standards and Technology (NIST), which aims to promote the use of fractography for the analysis of brittle materials. It notes that the page guide explores practical aproaches for fracture analysis and emphasizes the importance of fractography to other applications. The publication also contains 725 images and drawings to help fractographers in identifying patterns.

Abstract: Despite how common folds are as structural features, along-strike fold propagation has proven elusive to document. However, if a fold grows laterally along its axis, early-formed fold-related joints may differ significantly in orientation from joints that form later. In this paper, we integrate mechanical stratigraphy with joint pattern analysis to determine relative timing of jointing. Additionally, we demonstrate that joint patterns can be related to stresses on both the top and bottom of the bed during flexure. We present joint data from eight sedimentary beds on the fold terminus at Sheep Mountain Anticline, Wyoming, USA. The joint patterns around the terminus show two distinct patterns: joints in six of the beds show a radial pattern around the terminus whereas joint patterns in the two remaining beds differ from proximal units, despite being in the same structural position. Fracture resistance calculations confirm that the beds with mis-oriented fractures are less resistant to fracturing than other units in the study, and therefore would have fractured earlier in fold growth history. We present a plate bending model that illustrates potential joint patterns around a plunging fold nose from stresses along both the top and bottom of the bed. The joint strike predictions for the area in front of the inflection line on the fold nose match the orientations in our less resistant beds, which are now positioned behind the inflection line, suggesting that the fold grew laterally. The combined analysis of fracture pattern and mechanical stratigraphy provides a new way to investigate fold evolution. [ABSTRACT FROM AUTHOR]

Fracture intensity indicators from well data are highly uncertain when applied or extrapolated to the whole field. Statistical techniques offer some useful tools for dealing with such problems in reservoir modeling. The recent research and development of effort focuses strongly on the development of hybrid techniques that aim at overcoming the inherent assumptions and limitations of individual techniques and taking into consideration uncertain data for estimating error bars (or confidence bounds) on the calculated outputs. This paper presents a recently developed hybrid technique based on soft computing methods and shows how this technique can be used to improve the workflow of fracture characterization and sweet-spots identification. It uses a set of rock matrix properties and a fracture-related seismic attribute to simulate a three-dimensional fracture intensity model at the Pinedale anticline in Wyoming. The estimated fracture intensity results agree very well with the data at four virtual wells. It also shows that use of the fracture intensity estimations, together with their error bars, is a valuable tool for the identification of potential sweet spots with reduced risks. [ABSTRACT FROM AUTHOR]

Possible changes in the United States product liability laws have been identified as having an increasing negative influence on the engineering design process. This paper considers a specific case of a materials failure which has recently been argued through the English courts under the 1987 Consumer Protection Act. This act, and its interpretation, is discussed with regard to its possible future impact on the design rationale. [Copyright &y& Elsevier]

Calls for papers for the Third International American Society of Testing Materials Symposium on Fatigue and Fracture Mechanics on May 16-19, 2005, in the U.S. Aim of the symposium to promote discussion and dissemination of the state-of-the-art advances in the multiscale modeling and characterization of the creep and fatigue and fracture response of materials and structures; Instructions for publication of symposium papers; Contact information.

Health monitoring is highly dependent on sensor systems that are capable of performing in various engine environmental conditions and able to transmit a signal upon a predetermined crack length, while acting in a neutral form upon the overall performance of the engine system. Efforts are under way at NASA Glenn Research Center through support of the Intelligent Vehicle Health Management Project (IVHM) to develop and implement such sensor technology for a wide variety of applications. These efforts are focused on developing high temperature, wireless, low cost, and durable products. In an effort to address technical issues concerning health monitoring, this article considers data collected from an experimental study using high frequency capacitive sensor technology to capture blade tip clearance and tip timing measurements in a rotating turbine engine-like-disk to detect the disk faults and assess its structural integrity. The experimental results composed at a range of rotational speeds from tests conducted at the NASA Glenn Research Center’s Rotordynamics Laboratory are evaluated and integrated into multiple data-driven anomaly detection techniques to identify faults and anomalies in the disk. In summary, this study presents a select evaluation of online health monitoring of a rotating disk using high caliber capacitive sensors and demonstrates the capability of the in-house spin system. [ABSTRACT FROM AUTHOR]