Fracture toughness and fatigue-crack propagation in a Zr–Ti–Ni–Cu–Be bulk metallic glass

The recent development of metallic alloy systems which can be processed with an amorphous structure over large dimensions, specifically to form metallic glasses at low cooling rates (similar to 10 K/s), has permitted novel measurements of important mechanical properties. These include, for example, fatigue-crack growth and fracture toughness behavior, representing the conditions governing the subcritical and critical propagation of cracks in these structures. In the present study, bulk plates of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy, machined into 7 mm wide, 38 mm thick compact-tension specimens and fatigue precracked following standard procedures, revealed fracture toughnesses in the fully amorphous structure of K(lc)similar to 55 MPa root m, i.e., comparable with that of a high-strength steel or aluminum ahoy. However, partial and full crystallization, e.g., following thermal exposure at 633 K or more, was found to result in a drastic reduction in fracture toughness to similar to 1 MPa root m, i.e., comparable with silica glass. The fully amorphous alloy was also found to be susceptible to fatigue-crack growth under cyclic loading, with growth-rate properties comparable to that of ductile crystalline metallic alloys, such as high-strength steels or aluminum alloys; no such fatigue was seen in the partially or fully crystallized alloys which behaved like very brittle ceramics. Possible micromechanical mechanisms for such behavior are discussed

Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of ≈2 μm, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these “designed” composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems

Fracture toughness and crack-resistance curve behavior in metallic glass-matrix composites

Nonlinear-elastic fracture mechanics methods are used to assess the fracture toughness of bulk metallic glass (BMG) composites; results are compared with similar measurements for other monolithic and composite BMG alloys. Mechanistically, plastic shielding gives rise to characteristic resistance-curve behavior where the fracture resistance increases with crack extension. Specifically, confinement of damage by second-phase dendrites is shown to result in enhancement of the toughness by nearly an order of magnitude relative to unreinforced glass

On the tear resistance of skin.

Tear resistance is of vital importance in the various functions of skin, especially protection from predatorial attack. Here, we mechanistically quantify the extreme tear resistance of skin and identify the underlying structural features, which lead to its sophisticated failure mechanisms. We explain why it is virtually impossible to propagate a tear in rabbit skin, chosen as a model material for the dermis of vertebrates. We express the deformation in terms of four mechanisms of collagen fibril activity in skin under tensile loading that virtually eliminate the possibility of tearing in pre-notched samples: fibril straightening, fibril reorientation towards the tensile direction, elastic stretching and interfibrillar sliding, all of which contribute to the redistribution of the stresses at the notch tip

Key to the Past: Community Perceptions of Yup’ik Youth Interaction with Culturally Relevant Education Inspired by the Nunalleq Archaeology Project

This study qualitatively describes a) the implementation of culturally relevant education (CRE) programs for Yup’ik youth in Quinhagak, Alaska that developed from the Nunalleq Project—a nearby archaeological excavation—and b) community members’ and program facilitators’ perceptions of associated youth social and psychological outcomes. Ten semi-structured interviews (seven community members, three program facilitators) were undertaken and analyzed using constant comparative analysis. Community members and program facilitators attributed numerous outcomes to the Nunalleq-related CRE, such as imparting practical skills (e.g., wilderness survival, artistic and technological skills), teaching young people to value their heritage (e.g., educating them about the struggles their ancestors overcame), and psychological outcomes (e.g., improving self-esteem). Interviewees also offered specific recommendations for planning future local CRE programs. These results provide guidance for local program planners and a framework for researchers to directly assess CRE outcomes in Quinhagak. This project is a step towards the development of a systematic approach to CRE outcome evaluation rooted in community members’ perspectives. Educators developing archaeology-inspired CRE programs in other Indigenous communities may also draw from this study’s results

Some Empirical Criteria for Attributing Creativity to a Computer Program

Peer reviewedPostprin

Anesthetic Management of Renal Cell Carcinoma With Level 3 Inferior Vena Cava Extension in a Patient With Severe Coronary Artery Disease

A 49-year-old male with untreated type 2 diabetes and a family history of coronary artery disease (CAD) presented with right flank pain and profound progressive dyspnea on exertion to the emergency department of Ben Taub Hospital, a tertiary county hospital. Workup revealed right renal cell carcinoma with metastatic extension into the inferior vena cava (IVC). In addition, the patient had significant CAD with 95% occlusion of the proximal left anterior descending coronary artery amenable to percutaneous coronary intervention (PCI). After multidisciplinary discussions involving cardiovascular anesthesiology, cardiology, urology, and cardiothoracic surgery, it was estimated that the mortality benefit of immediate tumor resection outweighed the patient\u27s need for PCI and further cardiac optimization. The patient underwent curative resection and thrombectomy under transesophageal echocardiography (TEE) guidance without complication, made an expedient recovery, and was discharged home on postoperative day seven

The effect of screening long-range Coulomb interactions on the metallic behavior in two-dimensional hole systems

We have developed a technique utilizing a double quantum well heterostructure that allows us to study the effect of a nearby ground-plane on the metallic behavior in a GaAs two-dimensional hole system (2DHS) in a single sample and measurement cool-down, thereby maintaining a constant disorder potential. In contrast to recent measurements of the effect of ground-plane screening of the long-range Coulomb interaction in the insulating regime, we find surprisingly little effect on the metallic behavior when we change the distance between the 2DHS and the nearby ground-plane.Comment: 5 pages, 4 figures, accepted for publication in PR