Characterization on microstructure of interface and failure analysis of SiC fiber reinforced Ti-17 composites under tension load

From IOP Publishing via Jisc Publications RouterHistory: ppub 2021-05, open-access 2021-05-01Publication status: PublishedAbstract: In this study, the ultimate tensile strength of unidirectional SiC-fiber/Ti-17 composites was measured in the as-produced condition at room temperature. Fracture and interfacial reaction zone was characterized by using laser confocal microscopy, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy. Elemental distribution maps of the interfacial reaction layer and titanium matrix were quantitatively examined by electron probe micro-analyzer (EPMA). Micromechanical properties of SiC fiber and titanium matrix was inspected by Nano-indentation. The Fracture failure mechanisms was show that the key microstructural parameters which dominate damage initiation, damage growth and fracture behavior of the composites were explained in detail

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Effet de surface en plasticite cyclique

Available from INIST (FR), Document Supply Service, under shelf-number : TD 84021 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

EXPERIMENTAL STUDY REGARDING ADHESIVE THICKNESS-DEPENDENCE OF STRENGTH FOR LIGHTWEIGHT ALLOY ADHESIVELY BONDED JOINTS

The effect of the adhesive thickness on the overall strength of single lap joints made by lightweight aluminum alloy was experimentally studied. The relation between the overall strength and the adhesive thickness is influenced by some intrinsic characteristics of adhesives,one of which is the adhesive toughness addressed by the present study. The results show that the variation of overall strength corresponding to relatively ductile adhesive is more remarkable compared to that corresponding to relatively brittle adhesive,especially in the comparatively small adhesive thickness range. When the adhesive thickness is larger than the critical thickness,the overall strength of the single lap joints appears equal to the bulk shear strength of the adhesives. The present experimental results agree with the previous model prediction

Anisotropic high cycle fatigue property estimation for laser additive manufactured Ti6Al4V alloy dependence on tomographic imaging of defect population

Improvement of fatigue properties of additive manufactured metals is subject to the regulation of process-induced microstructure and defect population. Here, the high cycle fatigue properties of the annealed Ti6Al4V alloy manufactured by two types of laser powder bed fusion (L-PBF) processes, in orthogonal sample orientations, were studied. The fatigue performance of this alloy was also estimated dependence on the investigation of microstructure and defects using optical microscopy, X-ray diffraction, scanning electron microscopy and micro computed tomography. The results demonstrated that the fatigue properties were degraded by the negative effect of prior-β columnar grain boundaries and defects, wherein the surface keyhole governed the pronounced fatigue scatter and anisotropy due to its geometrical parameters and anisotropy severity along the building direction. The projection size √area of keyholes was well applied in the fatigue property estimation. The theorical fatigue limits were estimated individually due to the keyhole anisotropy, and provided conservatively in the improved Kitagawa-Takahashi diagram based on the modified El-Haddad model and the extreme size of keyholes. A relation derived from Paris law was proposed for fatigue life prediction, and to well establish a linear fitting correlating fatigue life with the projection size of surface keyholes and stress amplitude range with the achievement of the alleviation of fatigue anisotropy and scatter. The research provides a reference for the non-destructive estimation of fatigue properties in terms of tomographic imaging of defect population

Feasibility of Penetrant Testing on Surface Axial-Radial Cracks of GH4169 Super Alloy Turbine Disk

The post emulsifiable and water-washable fluorescent penetrant testing were carried out with ZL-27A and ZL67 respectively. Ultrasonic cleaning by detergent were used for 30 minutes before penetrant. The parts were immersed and drained for 60 minutes. The macroscopic and microscopic characteristics of cracks were researched using the split mirror and scanning electron microscope. The results show that the outgrowth of high temperature oxidation plugs up the forging cracks. Thus the penetrant testing is not effective in detecting this type of cracks

Wave velocity measurement in the through-thickness direction of the anisotropic material plate with ultrasonic polar scan

Ultrasonic polar scan (UPS) records the amplitude in transmission for a wide range of incidence angles, providing a UPS image with characteristic contours reflecting the acoustic parameters of the material. This study focused on a newly developed wave velocity measurement of the DD6 single-crystal material plate by analyzing the UPS image to realize the ultrasonic thickness measurement of the DD6 single-crystal material plate accordingly. Firstly, considering transducer contour size compensation, the UPS images are obtained by numerical simulation on the DD6 single-crystal material plates with different crystal orientations. Secondly, the fitting equations are obtained by analyzing the UPS images to calculate wave velocity in the thickness direction. Finally, a 5-joint UPS scanner is designed to validate the accuracy of wave velocity simulation results experimentally, and it indicates a good agreement with conventional ultrasonic velocity measurement. The measurement results demonstrated that the UPS method could evaluate the wave velocity in the through-thickness direction of the DD6 single-crystal material plate with high precision

Failure Analysis of a Cylindrical Roller Bearing Caused by Excessive Tightening Axial Force

The premature failure of a cylindrical roller bearing took place during service, with a total operation time of 100 h. The failure cause was analyzed by macroscopic and microscopic observation, metallographic analysis, hardness testing, tightening axial force influence analysis, and test verification. The results show that failure modes of the bearing are contact fatigue spalling, wear, and fatigue fracture. The outer ring, inner ring, rollers, and cages all have suffered relatively heavy damage in the sides corresponding to the bearing side with laser marking. Excessive load, induced by the excessive tightening axial force, derived from the lock nut, is the cause of the bearing failure. The failure mechanism is that excessive tightening axial force caused a great deformation and cylindricity increase of the inner ring raceway, which induced high local contact stress between one side of the ring raceways, as well as the corresponding ends of the rollers, resulting in the bearing failure. At last, measures for prevention of this failure are put forward as follows: controlling the tightening axial force within the range of technical requirement, increasing the convexity of the inner ring raceway and rollers, and decreasing the grinding undercut size of the inner ring

Evolution of the Microstructure and Mechanical Performance of As-Sprayed and Annealed Silicon Coating on Melt-Infiltrated Silicon Carbide Composites

In this study, silicon coating was deposited on melt-infiltrated SiC composites using atmospheric plasma spraying and then annealed at 1100 and 1250 °C for 1–10 h to investigate the effect of annealing on the layer. The microstructure and mechanical properties were evaluated using scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, nano-indentation, and bond strength tests. A silicon layer with a homogeneous polycrystalline cubic structure was obtained without phase transition after annealing. After annealing, three features were observed at the interface, namely β-SiC/nano-oxide film/Si, Si-rich SiC/Si, and residual Si/nano-oxide film/Si. The nano-oxide film thickness was ≤100 nm and was well combined with SiC and silicon. Additionally, a good bond was formed between the silicon-rich SiC and silicon layer, resulting in a significant bond strength improvement from 11 to >30 MPa