Grain Size Effect on Mechanical Properties Under Biaxial Stretching in Pure Tantalum

This paper reports the mechanical properties and formability under biaxial stretching in pure tantalum as a function of average grain size. The grain size of pure tantalum was adjusted from submicron to tens of micron using the high-pressure torsion process and subsequent annealing. The stretch formability was evaluated using a miniaturized Erichsen tester. Under uniaxial tension, the mechanical properties of pure tantalum followed the typical strength-ductility trade-off behavior according to the average grain size. Nevertheless, the stretch formability became rather significantly inferior in the coarse-grain tantalum, which was primarily attributed to the poor resistance to strain localization and limited work hardening capacity. This deterioration was supposed to be due to the intensified strain localization with increasing the average grain size, based on the in-grain deformation heterogeneity within individual grains and the surface roughening after the Erichsen test. Consequently, this study suggests that the excellent stretch formability and work hardening capacity under biaxial loading can be achieved at a certain range of the average grain size (8.25-19.3 mu m in this work).11Nsciescopuskc

Modelling feasibility constraints for materials design: Application to inverse crystallographic texture problem

The cornerstone of materials design is solving materials-related optimization problems to obtain microstructural or processing variables that lead to the most desirable material properties. Because the objective of materials design is to maximize their performance, the related optimization problems often require a global solution. This type of unconstrained optimization overlooks the feasibility of the solution, which is a key engineering issue. For any practical application, feasibility should be reflected in the constraints included in the optimization problems. Nevertheless, the constraints related to feasibility are considerably complex due to the high dimensionality of the design space and non-physical aspects of the constraints, such as machine specifications, material dimensions, and available initial microstructure. In this work, we propose the use of a simple support vector machine (SVM) trained with information in an existing database to model complex feasibility constraints for material optimization. We present a problem involving optimization of the initial texture of a body-centered cubic (BCC) polycrystalline material to obtain specific target textures after cold-rolling. Both unconstrained and constrained optimizations are conducted for comparison, and the results demonstrate that constrained optimizations yield viable solutions while unconstrained optimizations do not.11Nsciescopu

Diagnostic Yield and Clinical Impact of Video Capsule Endoscopy in Patients with Chronic Diarrhea: A Korean Multicenter CAPENTRY Study

BACKGROUND/AIMS: In some cases, chronic diarrhea is unexplained, and small bowel disorders may be one of the causes. The aim of this study was to assess the diagnostic yield and clinical impact of video capsule endoscopy (VCE) in patients with chronic diarrhea. METHODS: We retrospectively analyzed records from October 2002 to August 2013 in the VCE nationwide database registry (n=2,964). Ninety-one patients from 15 medical centers (60 males and 31 females; mean age, 47±19 years) were evaluated for VCE as a result of chronic diarrhea. RESULTS: The duration of chronic diarrhea was 8.3±14.7 months. The positive diagnostic yield of VCE was 42.9% (39/91). However, 15.4% (14/91) exhibited an inconsistent result, and 41.8% (38/91) were negative. Abnormal findings consistent with chronic diarrhea included erosions/aphthous ulcers (19.8%), ulcers (17.6%), mucosal erythema (3.3%), edema (1.1%), and luminal narrowing (1.1%). The most common diagnoses were functional diarrhea associated with irritable bowel syndrome in 37 patients (40.7%) and Crohn’s disease in 18 patients (19.8%). After VCE examination, the diagnosis was changed in 34.1% of the patients (31/91). Hematochezia (odds ratio [OR], 8.802; 95% confidence interval [CI], 2.126 to 36.441) and hypoalbuminemia (OR, 4.811; 95% CI, 1.241 to 18.655) are predictive factors of a positive diagnostic yield. CONCLUSIONS: VCE had a favorable diagnostic yield and clinical impact on the management of patients with chronic diarrhea