Investigation on Plastic Flow Behaviors of FCC Polycrystalline Aluminum under Pre-Cyclic Tension-Compression Loading: Experiments and Crystal Plasticity Modeling.

The plastic flow behaviors of FCC polycrystalline aluminum after pre-cyclic tension-compression deformation are mainly investigated in tension-torsion stress space by the physically based crystal plasticity model introducing a back-stress. A global finite element model (GFEM) constructed of sufficient grains was established to simulate the same-size thin-walled tube specimen constrained and loaded as the experiments of yield surfaces. The computational results showed that the shape of subsequent yield surfaces and the plastic flow directions directly depended on the given offset strain levels and the applied re-loading paths under different pre-cyclic deformations. The angle deviation between the plastic flow direction and the theoretical orthogonal direction further indicated that there was a large difference between them in the inverse pre-straining direction, but the difference was negligible in the pre-straining direction. From the influence of the anisotropic evolution of the subsequent yield surfaces on plastic flow, we found that the plastic normality rule followed the smooth yield locus; conversely, the significant non-associated flow was attributed to the distorted yield locus. Furthermore, it was also demonstrated that the anisotropic evolution and the plastic flow trend of the subsequent yield surfaces obtained by experiments can be better reproduced by the crystal plasticity model.

Investigation of Yield Surfaces Evolution for Polycrystalline Aluminum after Pre-Cyclic Loading by Experiment and Crystal Plasticity Simulation.

This study aims at introducing the back stress of anisotropic strain-hardening into the crystal plasticity theory and demonstrating the rationality of this crystal plasticity model to describe the evolution of the subsequent yield surface of polycrystalline aluminum at the mesoscopic scale under complex pre-cyclic loading paths. By using two different scale finite element models, namely a global finite element model (GFEM) as the same size of the thin-walled tube specimen used in the experiments and a 3D cubic polycrystalline aggregate representative volume element (RVE) model, the evolution of the subsequent yield surface for different unloading cases after 30 pre-cycles is further performed by experiments and numerical simulations within a crystal plasticity finite element (CPFE) frame. Results show that the size and shape of the subsequent yield surfaces are extremely sensitive to the chosen offset strain and the pre-cyclic loading direction, which present pronounced anisotropic hardening through a translation and a distortion of the yield surface characterized by the obvious "sharp corner" in the pre-deformation direction and "flat" in the reverse direction by the definition of small offset strain, while the subsequent yield surface exhibits isotropic hardening reflected by the von Mises circle to be distorted into an ellipse by the definition of large offset strain. In addition, the heterogeneous properties of equivalent plastic strain increment are further discussed under different offset strain conditions. Modeling results from this study show that the heterogeneity of plastic deformation decreases as a law of fraction exponential function with the increasing offset strain. The above analysis indicates that anisotropic hardening of the yield surface is correlated with heterogeneous deformation caused by crystal microstructure and crystal slip. The crystal plasticity model based on the above microscopic mechanism can accurately capture the directional hardening features of the yield surface.

The Anisotropic Distortional Yield Surface Constitutive Model Based on the Chaboche Cyclic Plastic Model.

Considering the cross effect in the evolution of subsequent yield surfaces for metals, an anisotropic distortional yield surface constitutive model is developed. By introducing an anisotropic distortional hardening function into the isotropic hardening part of the classical Chaboche rate-dependent constitutive model, the plastic-deformation-induced distortional and anisotropic hardening behaviors of subsequent yield surfaces are characterized. The experimental data of distortional yield surfaces for T2 pure copper under three different loading paths, including pre-tension, pre-torsion, and pre-tension-torsion proportional loading of 45-degree, are simulated by implementing the models into a numerical user defined material (UMAT) procedure based on the ABAQUS finite element package. To validate the anisotropic plastic model, the simulated yield surfaces are compared with experimental observations and predicted results for a crystal plasticity model and good agreement are noted. The simulations demonstrate that the proposed model can accurately capture the characteristics of the distortional yield surface and the anisotropic hardening process of the yield surface. Moreover, the distortional shapes of experimental subsequent yield surfaces in loading direction and opposite direction can be better revealed by the anisotropic plastic constitutive model than the crystal plastic constitutive model.

Acupuncture for fecal incontinence: Protocol for a systematic review and data mining.

BACKGROUND: Fecal incontinence is a socially and emotionally destructive condition that has a negative impact on personal image, self-confidence, and quality of life. Acupuncture is commonly used to treat chronic conditions, including fecal incontinence. However, no relevant systematic review or meta-analysis has been designed to evaluate the effects of acupuncture on fecal incontinence. METHODS: We will identify relevant randomized controlled trials (RCTs) from the Cochrane Library, Medline, Embase, PubMed, Springer, Web of Science, China National Knowledge Infrastructure, VIP Chinese Science and Technology Journals Database, Wanfang database, and clinical trial registration center from their inception to February 28, 2019. The primary outcome measures will be clinical effective rate, functional outcomes, and quality of life. Data that meets the inclusion criteria will be extracted and analyzed using RevMan V.5.3 software. Two reviewers will evaluate the studies using the Cochrane Collaboration risk of bias tool. Publication bias will be assessed by funnel plots, Egger test, and Begg test using the Stata software. Acupoints characteristics will be analyzed by Traditional Chinese Medicine inheritance support system. RESULTS: This study will analyze the clinical effective rate, functional outcomes, quality of life, daily average number of fecal incontinence, and effective prescriptions of acupuncture for patients with fecal incontinence. CONCLUSION: Our findings will provide evidence for the effectiveness and potential treatment prescriptions of acupuncture for patients with fecal incontinence. PROSPERO REGISTRATION NUMBER: PROSPERO CRD42019119680.

Enhanced catalytic activity of the nanostructured Co-W-B film catalysts for hydrogen evolution from the hydrolysis of ammonia borane.

In this work, nanostructured Co-W-B films are successfully synthesized on the foam sponge by electroless plating method and employed as the catalysts with enhanced catalytic activity towards hydrogen evolution from the hydrolysis of ammonia borane (NH3BH3, AB) at room temperature. The particle size of the as-prepared Co-W-B film catalysts is varied by adjusting the depositional pH value to identify the most suitable particle size for hydrogen evolution of AB hydrolysis. The Co-W-B film catalyst with the particle size of about 67.3 nm shows the highest catalytic activity and can reach a hydrogen generation rate of 3327.7 mL min-1 gcat-1 at 298 K. The activation energy of the hydrolysis reaction of AB is determined to be 32.2 kJ mol-1. Remarkably, the as-obtained Co-W-B film is also a reusable catalyst preserving 78.4% of their initial catalytic activity even after 5 cycles in hydrolysis of AB at room temperature. Thus, the enhanced catalytic activity illustrates that the Co-W-B film is a promising catalyst for AB hydrolytic dehydrogenation in fuel cells and the related fields.

Functional properties of Chinese yam (Dioscorea opposita Thunb. cv. Baiyu) soluble protein.

In this study, yam soluble protein (YSP) was extracted from Chinese yam (Dioscorea opposita Thunb. cv. Baiyu) and the functional properties were investigated under the influence of pH and ionic strength. As results, YSP was highly soluble and had better emulsifying activity over a wide range of pH. The solubility of YSP decreased in 0.5 and 1.0 M NaCl solution. An increment in NaCl concentration reduced the emulsion activity index and emulsion stability index of YSP. The oil absorption capacity of YSP was 3.2 ml/g protein. With the increase of pH, the foam capacity (FC) and stability (FS) decreased and then increased. FS of YSP increased as the salt concentration increased from 0 to 0.5 M, and then decreased. The minimal gelation concentration of YSP was 8% (w/v) and 10% YSP gel (w/v) had maximum gel strength in 0.1 M NaCl. These results suggested that YSP produced by acid precipitation may be used as a protein source with remarkable functional properties.