Heterogeneous deformation in H-Ti alloys at the microscale

Detailed characterization of full field deformation at the microstructural length scale is important for understanding local damage nucleation and failure mechanisms during heterogeneous deformation, and their impact on macroscopic mechanical properties. In the current study, an experimental method combining in-situ mechanical testing, electron backscatter diffraction (EBSD), and scanning electron microscopy with digital image correlation (SEM-DIC) was applied to study the multiscale deformation behavior of forged and annealed polycrystalline -Ti alloys with various Al content. Microstructural information (EBSD) and its evolution during loading was compared with continuous tracking of full-field deformation (SEM-DIC) during thermomechanical loading to examine the effect of microstructure heterogeneity such as microtexture, grain size and orientation, and alloying concentration on deformation and damage mechanisms during tensile deformation. Post-test processing for drift and spatial distortion correction allowed for accurate measurement of the displacement field

A New Experimental Approach for In Situ Damage Assessment in Fibrous Ceramic Matrix Composites at High Temperature

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112011/1/jace13538.pd

Characterization of microstructural effects on small fatigue crack growth mechanisms in Ti-6242S

Design and life management of fracture critical components are made difficult by small scale deformation responses to low applied stresses in the very high cycle fatigue (VHCF) regime, where the number of cycles exceeds 107 and fatigue life is dominated by crack initiation and the growth of microstructurally small cracks. Furthermore, fatigue crack formation is extremely sensitive to microstructural features. Existing models do not fully capture small scale microstructural influences on early fatigue deformation behavior. An understanding of the interactions between the local microstructure and the plastic zone present at the crack tip of a microstructurally small fatigue crack is critical to modeling fatigue crack growth mechanisms. Plastic zone sizes at this scale are highly influenced by local microstructural characteristics such as grain boundary misorientation, phase boundaries, and the presence of precipitates. The use of multiple experimental techniques that enable study of the interactions between the crack-tip plastic zone and local microstructural features in-situ will help develop a quantitative understanding of the underlying small crack growth mechanisms. The role of microstructure on small fatigue crack growth mechanics in the near a titanium alloy Ti6242S has been investigated in the VHCF regime. An experimental methodology for in-situ ultrasonic fatigue (20 kHz) in a scanning electron microscope (SEM) has been developed to investigate mechanisms of fatigue crack formation and the growth of microstructurally small cracks in vacuum and in varying partial pressures of water vapor. In-situ observations of small crack growth behavior from focused ion beam machined micronotches located at key microstructural sites indicated a significant microstructural dependence on crack growth rates. Fatigue crack propagation behavior is also correlated with crack opening displacement and cyclic strain accumulation as measured by advanced in-situ scanning electron microscopy digital image correlation techniques. The evolution of small-scale strain fields at crack tips and in the microstructural neighborhood of the advancing crack is also examined. The specifics of the ultrasonic fatigue SEM instrumentation and the influence of microstructure on small fatigue crack propagation, crack-tip plasticity, and strain localization in the VHCF regime will be described

Deformation Behavior of a Shape Memory Alloy, Nitinol

Nickel-Titanium, commonly referred to as Nitinol, is a shape-memory alloy with numerous applications due to its superelastic nature and its ability to revert to a previously defined shape when deformed and then heated past a set transformation temperature. While the crystallography and the overall phenomenology are reasonably well understood, much remains unknown about the deformation and failure mechanisms of these materials. These latter issues are becoming critically important as Nitinol is being increasingly used in medical devices and space applications. The talk will describe the investigation of the deformation and failure of Nitinol using an in-situ optical technique called Digital Image Correlation (DIC). With this technique, full-field quantitative maps of strain localization are obtained for the first time in thin sheets of Nitinol under tension. These experiments provide new information connecting previous observations on the micro- and macro- scale. They show that martensitic transformation initiates before the formation of localized bands, and that the strain inside the bands does not saturate when the bands nucleate. The effect of rolling texture, the validity of the widely used resolved stress transformation criterion, and the role of geometric defects are examined

Crack opening behavior in ceramic matrix composites

The evolution of matrix cracks in a melt‐infiltrated SiC/SiC ceramic matrix composite (CMC) under uniaxial tension was examined using scanning electron microscopy (SEM) combined with digital image correlation (DIC) and manual crack opening displacement (COD) measurements. CMC modeling and life prediction strongly depend a thorough understanding of when matrix cracks occur, the extent of cracking for given conditions (time‐temperature‐environment‐stress), and the interactions of matrix cracks with fibers and interfaces. In this work, strain relaxation due to matrix cracking, the relationship between CODs and applied stress, and damage evolution at stresses below the proportional limit were assessed. Direct experimental observation of strain relaxation adjacent to regions of matrix cracking is presented and discussed. Additionally, crack openings were found to increase linearly with increasing applied stress, and no crack was found to pass fully through the gage cross‐section. This calls into question the modeling assumption of through‐cracks for all loading conditions and fiber architectures, which can obscure oxidation mechanisms that are active in realistic cracking conditions. Finally, the combination of SEM with DIC is demonstrated throughout to be a powerful means for damage identification and quantification in CMCs at stresses well below the proportional limit.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138389/1/jace14976_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138389/2/jace14976.pd

Transmission of Equine Influenza Virus to English Foxhounds

We retrospectively demonstrated that an outbreak of severe respiratory disease in a pack of English foxhounds in the United Kingdom in September 2002 was caused by an equine influenza A virus (H3N8). We also demonstrated that canine respiratory tissue possesses the relevant receptors for infection with equine influenza virus

Competition from Within: Ethnicity, Power, and Militant Group Rivalry

Why do militant groups turn on each other? This behavior is somewhat puzzling, since such groups are often on the same side of a conflict. A growing body of literature seeks to understand political violence by looking at cooperative and competitive relationships among non-state actors. Debates continue about the sources of militant group rivalry. We argue that shared motivations, especially ethnic motivations, along with power differences among groups should help explain inter-group fighting. Our analysis uses new dyadic data on rivalry among the militant groups of Africa and Asia since 1990. Unlike some previous studies, we analyze both terrorist and insurgent organizations. Results suggest that pairs of groups with a shared ethnic identity are more likely than others to have rivalrous relationships. Power asymmetry is also somewhat associated with rivalry, but interaction models indicate that the association is only statistically significant in the presence of shared ethnic motivations

Computed tomography diagnosed cachexia and sarcopenia in 725 oncology patients: is nutritional screening capturing hidden malnutrition?

Background: Nutrition screening on admission to hospital is mandated in many countries, but to date, there is no consensus on which tool is optimal in the oncology setting. Wasting conditions such as cancer cachexia (CC) and sarcopenia are common in cancer patients and negatively impact on outcomes; however, they are often masked by excessive adiposity. This study aimed to inform the application of screening in cancer populations by investigating whether commonly used nutritional screening tools are adequately capturing nutritionally vulnerable patients, including those with abnormal body composition phenotypes (CC, sarcopenia, and myosteatosis). Methods: A prospective study of ambulatory oncology outpatients presenting for chemotherapy was performed. A detailed survey incorporating clinical, nutritional, biochemical, and quality of life data was administered. Participants were screened for malnutrition using the Malnutrition Universal Screening Tool (MUST), Malnutrition Screening Tool (MST), and the Nutritional Risk Index (NRI). Computed tomography (CT) assessment of body composition was performed to diagnose CC, sarcopenia, and myosteatosis according to consensus criteria. Results: A total of 725 patients (60% male, median age 64 years) with solid tumours participated (45% metastatic disease). The majority were overweight/obese (57%). However, 67% were losing weight, and CT analysis revealed CC in 42%, sarcopenia in 41%, and myosteatosis in 46%. Among patients with CT-identified CC, the MUST, MST, and NRI tools categorized 27%, 35%, and 7% of them as ‘low nutritional risk’, respectively. The percentage of patients with CT-identified sarcopenia and myosteatosis that were categorised as ‘low nutritional risk’ by MUST, MST and NRI were 55%, 61%, and 14% and 52%, 50%, and 11%, respectively. Among these tools, the NRI was most sensitive, with scores <97.5 detecting 85.8%, 88.6%, and 92.9% of sarcopenia, myosteatosis, and CC cases, respectively. Using multivariate Cox proportional hazards models, NRI score < 97.5 predicted greater mortality risk (hazard ratio 1.8, confidence interval: 1.2–2.8, P = 0.007). Conclusions: High numbers of nutritionally vulnerable patients, with demonstrated abnormal body composition phenotypes on CT analysis, were misclassified by MUST and MST. Caution should be exercised when categorizing the nutritional risk of oncology patients using these tools. NRI detected the majority of abnormal body composition phenotypes and independently predicted survival. Of the tools examined, the NRI yielded the most valuable information from screening and demonstrated usefulness as an initial nutritional risk grading system in ambulatory oncology patients

New resources for the Drosophila 4th chromosome : FRT101F enabled mitotic clones and Bloom syndrome helicase enabled meiotic recombination

Genes on the long arm of the Drosophila melanogaster 4th chromosome are difficult to study because the chromosome lacks mitotic and meiotic recombination. Without recombination numerous standard methods of genetic analysis are impossible. Here, we report new resources for the 4th. For mitotic recombination, we generated a chromosome with an FRT very near the centromere in 101F and a derivative that carries FRT101F with a distal ubiquitously expressed GAL80 transgene. This pair of chromosomes enables both unmarked and MARCM clones. For meiotic recombination, we demonstrate that a Bloom syndrome helicase and recombination defective double mutant genotype can create recombinant 4th chromosomes via female meiosis. All strains will be available to the community via the Bloomington Drosophila Stock Center. Additional resources for studies of the 4th are in preparation and will also be made available. The goal of the 4th Chromosome Resource Project is to accelerate the genetic analysis of protein-coding genes on the 4th, including the 44 genes with no demonstrated function. Studies of these previously inaccessible but largely conserved genes will close longstanding gaps in our knowledge of metazoan development and physiology.Peer reviewe