Mechanical response of self-ion irradiated, single crystal, FCC micropillars

Increasing energy demands and regulations on cleaner and more efficient energy sources has reinvigorated research into next generation nuclear reactors. The safe and optimal operation of the various proposed reactors requires the cladding and structural metals to perform under a combination of extreme environments including radiation damage levels \u3e100 dpa. This presentation will highlight a rapid screening technique developed at Sandia National Laboratories to determine the relative merit of implementing various advanced structural alloys and composites in high radiation environments. In addition to an overview of the technique and the wealth of alloy systems it has been applied to, this presentation will focus on the detailed mechanisms that can be elucidated from the micropillar compression of ion irradiated single crystal copper and nickel. Single crystal Cu micropillars self-ion irradiated up to 190 dpa at the end of range were compressed along the \u3c110\u3e to 10% strain. To elucidate the interaction of different length scales on the mechanical response, three specimen configurations were explored: large 10 μm tall, intermediate 5 μm tall, and small 4 μm tall pillars. In a similar manner, pristine and self-ion irradiated \u3c111\u3e Ni pillars were subject to in-situ microcompression in a scanning electron microscope (SEM). By performing these experiments during real time SEM observation a direct correlation between the mechanical responses and the pillars’ structural evolution can be obtained. Specifically, the dynamics resulting from the defect free channel formation and subsequent localization can be associated with heterogeneous plastic flow. This presentation will highlight the multiple length scale effects that are active during the micropillar compression of self-ion irradiated, single crystal, FCC micropillars. These results will be discussed in the context of an end of range effect, a damage gradient effect, and size effects, as well as compared to other small scale mechanical testing methods of ion and neutron irradiated materials. Finally, the benefits and limitations of applying these methods to rapidly screen advanced materials for potential future nuclear reactor applications will be discussed. This study is supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000

The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set

Background Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables. Methods Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set. Results Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15–0.23), higher ASA scores (OR 0.19, 95% CI 0.15–0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58–0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48–0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34–0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of ≤5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (p < 0.001). Conclusions The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy

Mechanical relaxation of localized residual stresses associated with foreign object damage

Foreign-object damage associated with the ingestion of debris into aircraft turbine engines can lead to a marked degradation in the high-cycle fatigue life of turbine components. This degradation is generally considered to be associated with the premature initiation of fatigue cracks at or near the damage sites; this is suspected to be due to, at least in part, the impact-induced residual stress state, which can be strongly tensile in these locations

Mechanical relaxation of localized residual stresses associated with foreign object damage

Foreign-object damage associated with the ingestion of debris into aircraft turbine engines can lead to a marked degradation in the high-cycle fatigue life of turbine components. This degradation is generally considered to be associated with the premature initiation of fatigue cracks at or near the damage sites; this is suspected to be due to, at least in part, the impact-induced residual stress state, which can be strongly tensile in these locations

Thresholds for high-cycle fatigue in a turbine engine Ti-6Al-4V alloy

The characterization of critical levels of microstructural damage that can lead to fatigue-crack propagation under high-cycle fatigue loading conditions is a major concern for the aircraft industry with respect to the structural integrity of turbine engine components. The extremely high cyclic frequencies characteristic of in-flight loading spectra necessitate that a damage-tolerant design approach be based on a crack-propagation threshold, #K TH . The present study identifies a practical lower-bound large-crack threshold under high-cycle fatigue conditions in a Ti--6Al--4V blade alloy (with #60% primary a in a matrix of lamellar a+b). Lower-bound thresholds are measured by modifying standard large-crack propagation tests to simulate small-crack behavior. These techniques include high load-ratio testing under both constant-R and constant-K max conditions, performed at cyclic loading frequencies up to 1 kHz and R-ratios up to 0.92. The results of these tests are compared to the near-thr..

Rare Bone Diseases and Their Dental, Oral, and Craniofacial Manifestations

Hereditary diseases affecting the skeleton are heterogeneous in etiology and severity. Though many of these conditions are individually rare, the total number of people affected is great. These disorders often include dental-oral-craniofacial (DOC) manifestations, but the combination of the rarity and lack of in-depth reporting often limit our understanding and ability to diagnose and treat affected individuals. In this review, we focus on dental, oral, and craniofacial manifestations of rare bone diseases. Discussed are defects in 4 key physiologic processes in bone/tooth formation that serve as models for the understanding of other diseases in the skeleton and DOC complex: progenitor cell differentiation (fibrous dysplasia), extracellular matrix production (osteogenesis imperfecta), mineralization (familial tumoral calcinosis/hyperostosis hyperphosphatemia syndrome, hypophosphatemic rickets, and hypophosphatasia), and bone resorption (Gorham-Stout disease). For each condition, we highlight causative mutations (when known), etiopathology in the skeleton and DOC complex, and treatments. By understanding how these 4 foci are subverted to cause disease, we aim to improve the identification of genetic, molecular, and/or biologic causes, diagnoses, and treatment of these and other rare bone conditions that may share underlying mechanisms of disease

Using Additive Manufacturing as a Pathway to Change the Qualification Paradigm

Additive Manufacturing (AM) offers the opportunity to transform design, manufacturing, and qualification with its unique capabilities. AM is a disruptive technology, allowing the capability to simultaneously create part and material while tightly controlling and monitoring the manufacturing process at the voxel level, with the inherent flexibility and agility in printing layer-by-layer. AM enables the possibility of measuring critical material and part parameters during manufacturing, thus changing the way we collect data, assess performance, and accept or qualify parts. It provides an opportunity to shift from the current iterative design-build-test qualification paradigm using traditional manufacturing processes to design-by-predictivity where requirements are addressed concurrently and rapidly. The new qualification paradigm driven by AM provides the opportunity to predict performance probabilistically, to optimally control the manufacturing process, and to implement accelerated cycles of learning. Exploiting these capabilities to realize a new uncertainty quantification-driven qualification that is rapid, flexible, and practical is the focus of this paper.Mechanical Engineerin