Influence of Multi-Holes on Fatigue Behaviors of Cast Magnesium Alloys Based on In-Situ Scanning Electron Microscope Technology.

The low cycle fatigue tests on the crack initiation and propagation of cast magnesium alloys with two small holes were carried out by using in-situ scanning electron microscope (SEM) observation technology. The fatigue crack propagation behaviors and fatigue life, which are affected by two small artificial through holes, including the distances between two holes and their locations, were discussed in detail based on the experimental results and the finite element analysis (FEA). The results indicated that the fatigue multi-cracks occurred chiefly at the edges of two holes and the main crack propagation was along the weak dendrite boundary with the plastic deformation vestiges on the surface of α-Mg phase of cast AM50 and AM60B alloys. The fatigue cracking characteristics of cast AZ91 alloy depended mainly on the brittle properties of ß-Mg17Al12 phase, in which the multi-cracks occurred still at the edges of two holes and boundaries of ß-Mg17Al12 phase. The fatigue crack initiation position of cast magnesium alloys depends strongly on the radius of curvature of through hole or stress concentration factor at the closed edges of two through holes. In addition, the fatigue multi-cracks were amalgamated for the samples with titled 45° of two small holes of cast Mg-Al alloys when the hole distance is less than 4D (D is the diameter of the small hole).

Surrogate endpoint for overall survival in assessment of adjuvant therapies after curative treatment for hepatocellular carcinoma: a re-analysis of meta-analyses of individual patients' data.

The gold standard endpoint to evaluate the effect of treatment for hepatocellular carcinoma (HCC) is overall survival (OS), but it requires a longer follow-up period to observe. This study aimed to identify whether disease-free survival (DFS) could be used as a surrogate endpoint for OS to assess the efficacy of adjuvant therapies after curative treatment (surgical resection and ablation) for HCC patients. A systematic review was conducted to identify trials about curative treatment combined with or without adjuvant therapies (interferon, IFN; or transarterial chemoembolization, TACE) for HCC. Total of 2211 patients' data from 17 trials were analyzed. At the individual study level, DFS was strongly correlated to OS (ρ = 0.988 and 0.930, 95% CI: 0.965-0.996 and 0.806-0.976 for the studies comparing Radiofrequency ablation (RFA) + TACE to RFA alone; and for the studies comparing curative treatment + IFN to curative treatment alone, respectively). At the trial level, the effects of treatment on DFS and OS were also strongly correlated to each other (R = 0.815 and 0.854, 95% CI: 0.536-0.934 and 0.621-0.948, respectively). In conclusion, DFS could be used as a potential surrogate endpoint for OS to assess the effect of adjuvant therapies after curative treatment for HCC.

Microarc Oxidation Coating Combined with Surface Pore-Sealing Treatment Enhances Corrosion Fatigue Performance of 7075-T7351 Al Alloy in Different Media.

Rotating bending fatigue tests have been performed to evaluate the corrosion fatigue performance and its influence factors of 7075-T7351 Al alloy in different media, namely air and a 5.0 wt % NaCl aqueous solution. All samples were coated by microarc oxidation (MAO) coating technology; some samples were followed by an epoxy resin pore-sealing treatment. Microscopic analyses of the surfaces and fracture cross-sections of samples were carried out. The results reveal that the sample with a MAO coating of 10 µm thickness and pore-sealing treatment by epoxy resin possesses optimal corrosion fatigue performance in the different media. The MAO coating with a pore-sealing treatment significantly improves the corrosion fatigue limit of 7075-T7351 Al alloy.

Improvement on the Fatigue Performance of 2024-T4 Alloy by Synergistic Coating Technology.

In this paper, rotating bending fatigue tests of 2024-T4 Al alloy with different oxide coatings were carried out. Compared to the uncoated and previously reported oxide coatings of aluminum alloys, the fatigue strength is able to be enhanced by using a novel oxide coating with sealing pore technology. These results indicate that the better the coating surface quality is, the more excellent the fatigue performance under rotating bending fatigue loading is. The improvement on the fatigue performance is mainly because the fatigue crack initiation and the early stage of fatigue crack growth at the coating layer can be delayed after PEO coating with pore sealing. Therefore, it is a so-called synergistic coating technology for various uses, including welding thermal cracks and filling micro-pores. The effects of different oxide coatings on surface hardness, compressive residual stress, morphology and fatigue fracture morphology are discussed. A critical compressive residual stress of about 95-100 MPa is proposed.

Investigations on the mechanical properties of conducting polymer coating-substrate structures and their influencing factors.

This review covers recent advances and work on the microstructure features, mechanical properties and cracking processes of conducting polymer film/coating- substrate structures under different testing conditions. An attempt is made to characterize and quantify the relationships between mechanical properties and microstructure features. In addition, the film cracking mechanism on the micro scale and some influencing factors that play a significant role in the service of the film-substrate structure are presented. These investigations cover the conducting polymer film/coating nucleation process, microstructure-fracture characterization, translation of brittle-ductile fractures, and cracking processes near the largest inherent macromolecule defects under thermal-mechanical loadings, and were carried out using in situ scanning electron microscopy (SEM) observations, as a novel method for evaluation of interface strength and critical failure stress.

Ultra-high sensitivity of super carbon-nanotube-based mass and strain sensors.

Based on the molecular structure mechanics method, the dynamic properties of super carbon nanotubes (STs), together with ST-based mass and strain sensors, are investigated. The following results are obtained: (a) the fundamental frequency of the STs is found to be lower than that of the single-wall carbon nanotube (SWCNT); (b) the STs may be a potential ultra-high sensitivity mass sensor with a sensitivity about 10(-24) g, which is much higher than that of SWCNT-based mass sensors (10(-21) g); (c) the ST-based strain sensor has a sensitivity as high as 887 Hz/nanostrain, which is also higher than that of SWCNT-based strain sensors. The obtained results suggest that the STs could be used to design the new generation of sensors due to its high sensitivity and ultra-low density.

The effective modulus of super carbon nanotubes predicted by molecular structure mechanics.

A super carbon nanotube (ST) is a kind of hierarchical structure constructed from carbon nanotubes (named as CNT arm tubes). With the detailed construction of a Y-junction considered, the effective mechanical properties of ST structures are studied by the molecular structure mechanics (MSM) method. The Young's modulus and shear modulus of STs are found to depend mainly on the aspect ratio of CNT arm tubes instead of the chirality of the ST. A scale law is adopted to express the relation between the effective modulus (Young's modulus or shear modulus) and the aspect ratio of the CNT arm tubes. The Poisson's ratio of the ST is affected by both the aspect ratio of the CNT arm tubes and the chirality of the ST. The deformation of the ST comes from both the bending and the stretching of the CNT arm tubes. The Y-junction acts as an reinforcement phase to make the bending and stretching couple together and induce large linearity in ST structures.