Macroscopic modeling of distortional hardening in polycrystals: application to magnesium alloys

Texture evolution in metals due to rotation of the atomic lattice results in a complex macroscopic mechanical behaviour which cannot in general be reasonably captured by only classical isotropic or kinematic hardening. Focusing on standard rate-independent plasticity, the evolution of microstructure leads to an evolving macroscopic anisotropy of the yield surface, also known as distortional or differential hardening. This effect is very important, particularly if non-radial loading paths such as those associated with forming processes are to be numerically analyzed. In the present work, different existing distortional hardening models are critically reviewed. They are reformulated into the modern framework of hyperelastoplasticity and the same objective time derivative is applied to all evolution equations for a better comparison. Furthermore, since the original models are based on a yield function not accounting for the different mechanical responses between tension and compression as observed in metals showing a close-packed atomic structure, respective generalizations are also discussed. It is shown that only one of the extended models can fulfill the second law of thermodynamics. That model predicts a high curvature of the yield surface in the loading direction, while the opposite region of the yield surface is rather at. Such a response can indeed be observed for some materials. In the case of magnesium alloys, however, that does not seem to be true. Therefore, a new constitutive model is presented. Its underlying structure is surprisingly simple and the model is not only thermodynamically consistent but also variationally consistent. Conceptually, distortional hardening is described by an Armstrong-Frederick-type evolution equation. The calibrated new model is implemented in a finite element framework and its predictive capabilities are demonstrated.Texturentwicklung in Metallen aufgrund der Rotation des atomaren Gitters führt zu einem komplexem mechanischen Verhalten, welches nicht hinreichend durch klassische Plastizitätsmodelle mit isotroper und/oder kinematischer Verfestigung beschrieben werden kann. Im Rahmen der ratenunabhängigen Plastizität führt die Entwicklung der Mikrostruktur zu einer Anisotropie der Fließ äche, auch bekannt unter dem Namen distortional hardening (Formänderungsverfestigung). Die Berücksichtigung dieses Effekts ist insbesondere bei nicht-radialen Lastpfaden bedeutend, welche z.B. bei Umformprozessen auftreten. In der vorliegenden Arbeit werden zunächst verschiedene existierende Plastizitätsmodelle mit Formänderungsverfestigung untersucht. Diese Modelle werden in einen einheitlichen hyperelastisch{plastischen Rahmen überführt. Zum Beispiel wird für eine bessere Vergleichbarkeit die selbe Zeitableitung für alle Evolutionsgleichungen verwendet. Da die bereits existierenden Modelle keine Zug-Druck-Asymmetrie berücksichtigen, welche aber in Magnesium-Legierungen zu beobachten ist, werden auch Erweiterungen der zugrunde liegenden Fließfunktionen diskutiert. Es wird gezeigt, dass nur eines der erweiterten Modelle den Zweiten Hauptsatz der Thermodynamik erfüllt. Charakteristisches Merkmal dieses Modells ist eine starke Krümmung der Fließ äche in Belastungsrichtung. Solches Verhalten kann bei verschiedenen Materialien beobachtet werden; allerdings trifft dies nicht für Magnesium zu. Aus diesem Grund wird ein neues Materialmodell vorgestellt. Die resultierende physikalische Beschreibung ist nicht nur thermodynamisch sondern auch variationell konsistent. Die Formänderungsverfestigung wird auf der Grundlage einer Entwicklungsgleichung vom Armstrong-Frederick-Typ berücksichtigt. Das Materialmodell wird im Rahmen der Finite-Elemente-Methode implementiert, und die Materialparameter werden an Experimente mit einer Magnesium-Legierung angepasst

Ultrasound-triggered with ROS-responsive SN38 nanoparticle for enhanced combination cancer immunotherapy

Controlled generation of cytotoxic reactive oxygen species (ROS) is essential in cancer therapy. Ultrasound (US)-triggered sonodynamic therapy (SDT) has shown considerable ability to trigger in situ ROS generation. Unfortunately, US therapy alone is insufficient to trigger an efficient anticancer response, owing to the induction of multiple immunosuppressive factors. It was identified that 7-ethyl-10-hydroxycamptothecin (SN38) could notably inhibit DNA topoisomerase I, induce DNA damage and boost robust anticancer immunity. However, limited by the low metabolic stability, poor bioavailability, and dose-limiting toxicity, the direct usage of SN38 is inadequate in immune motivation, which limits its clinical application. Hence, new strategies are needed to improve drug delivery efficiency to enhance DNA topoisomerase I inhibition and DNA damage and elicit a vigorous anticancer cancer immunity response. Considering US irradiation can efficiently generate large amounts of ROS under low-intensity irradiation, in this study, we aimed to design a polymeric, ROS-responsive SN38 nanoformulation for in vivo drug delivery. Upon the in-situ generation of ROS by US therapy, controlled on-demand release of SN38 occurred in tumor sites, which enhanced DNA damage, induced DC cell maturation, and boosted anticancer immunity. Our results demonstrated that a new strategy of involving the combination of a SN38 nanoformulation and US therapy could be used for cancer immunotherapy

Influences of Canopy Nitrogen and Water Addition on AM Fungal Biodiversity and Community Composition in a Mixed Deciduous Forest of China

Nitrogen (N) deposition and precipitation could profoundly influence the structure and function of forest ecosystems. However, conventional studies with understory additions of nitrogen and water largely ignored canopy-associated ecological processes and may have not accurately reflected the natural situations. Additionally, most studies only made sampling at one time point, overlooked temporal dynamics of ecosystem response to environmental changes. Here we carried out a field trial in a mixed deciduous forest of China with canopy addition of N and water for 4 years to investigate the effects of increased N deposition and precipitation on the diversity and community composition of arbuscular mycorrhizal (AM) fungi, the ubiquitous symbiotic fungi for the majority of terrestrial plants. We found that (1) in the 1st year, N addition, water addition and their interactions all exhibited significant influences on AM fungal community composition; (2) in the 2nd year, only water addition significantly reduced AM fungal alpha-diversity (richness and Shannon index); (3) in the next 2 years, both N addition and water addition showed no significant effect on AM fungal community composition or alpha-diversity, with an exception that water addition significantly changed AM fungal community composition in the 4th year; (4) the increment of N or water tended to decrease the abundance and richness of the dominant genus Glomus and favored other AM fungi. (5) soil pH was marginally positively related with AM fungal community composition dissimilarity, soil NH4+-N and N/P showed significant/marginal positive correlation with AM fungal alpha-diversity. We concluded that the effect of increased N deposition and precipitation on AM fungal community composition was time-dependent, mediated by soil factors, and possibly related to the sensitivity and resilience of forest ecosystem to environmental changes

Real-time and online lubricating oil condition monitoring enabled by triboelectric nanogenerator

An intelligent monitoring lubricant is essential for the development of smart machines because unexpected and fatal failures of critical dynamic components in the machines happen every day, threatening the life and health of humans. Inspired by the triboelectric nanogenerators (TENGs) work on water, we present a feasible way to prepare a self-powered triboelectric sensor for real-time monitoring of lubricating oils via the contact electrification process of oil-solid contact (O-S TENG). Typical intruding contaminants in pure base oils can be successfully monitored. The O-S TENG has very good sensitivity, which even can respectively detect at least 1 mg mL-1 debris and 0.01 wt % water contaminants. Furthermore, the real-time monitoring of formulated engine lubricating oil in a real engine oil tank is achieved. Our results show that electron transfer is possible from an oil to solid surface during contact electrification. The electrical output characteristic depends on the screen effect from such as wear debris, deposited carbons, and age-induced organic molecules in oils. Previous work only qualitatively identified that the output ability of liquid can be improved by leaving less liquid adsorbed on the TENG surface, but the adsorption mass and adsorption speed of liquid and its consequences for the output performance were not studied. We quantitatively study the internal relationship between output ability and adsorbing behavior of lubricating oils by quartz crystal microbalance with dissipation (QCM-D) for liquid-solid contact interfaces. This study provides a real-time, online, self-powered strategy for intelligent diagnosis of lubricating oils

A Fine Grain, High Mn Steel with Excellent Cryogenic Temperature Properties and Corresponding Constitutive Behaviour

A Fe-34.5 wt % Mn-0.04 wt % C ultra-high Mn steel with a fully recrystallised fine-grained structure was produced by cold rolling and subsequent annealing. The steel exhibited excellent cryogenic temperature properties with enhanced work hardening rate, high tensile strength, and high uniform elongation. In order to capture the unique mechanical behaviour, a constitutive model within finite strain plasticity framework based on Hill-type yield function was established with standard Armstrong-Frederick type isotropic hardening. In particular, the evolution of isotropic hardening was determined by the content of martensite; thus, a relationship between model parameters and martensite content is built explicitly

Integrated optical waveguide-based fluorescent immunosensor for fast and sensitive detection of microcystin-LR in lakes: optimization and analysis

Nowadays, biosensor technologies which can detect various contaminants in water quickly and cost-effectively are in great demand.Herein, we report an integrated channel waveguide-based fluorescent immunosensor with the ability to detect a maximum of 32 contaminants rapidly and simultaneously. In particular, we use waveguide tapers to improve the efficiency of excitation and collection of fluorescent signals in the presence of fluorophore photobleaching in a solid surface bioassay. Under the optimized waveguide geometry, this is the first demonstration of using such a type of waveguide immunosensor for the detection of microcystin-LR (MC-LR) in lake water. The waveguide chip was22 activated by (3-Mercaptopropyl)23 trimethoxysilane/N-(4-maleimidobutyryloxy) succinimide (MTS/GMBS) for immobilization of BSA-MC-LR conjugate, which was confirmed to have uniform monolayer distribution by atomic force microscopy. All real lake samples, even those containing MC-LR in the sub-microgram per liter range (e.g. 0.5 μg/L), could be determined by the immunosensor with recovery rates between 84% and 108%, confirming its application potential in the measurement of MC-LR in real water samples

The complete mitochondrial genome of the Riparia riparia (Passeriformes: Hirundinidae)

The Sand Martin (Riparia riparia) belongs to Hirundinidae. In this study, the complete mitochondrial genome of R. riparia was sequenced and characterized. The genome was 17,963 bases in length (GenBank accession no. OK537984) including 13 protein-coding genes, two ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and two control regions. The overall base composition of R. riparia mitogenome was 30.5% for A, 31.8% for C, 14.5% for G, and 23.2% for T. Phylogenetic analysis revealed that R. riparia was genetically closest to the species of genus Tachycineta. R. riparia mitogenome could contribute to our understanding of the phylogeny and evolution of this species