Isothermal fatigue mechanisms in Ti-based metal matrix composites

Stress-controlled isothermal fatigue experiments were performed at room temperature (RT) and 548 C (in argon) on (0)8 SCS6/Ti 15-3 metal matrix composites (MMC's) with 15 and 41 volume percent SCS6 (SiC) fibers. The primary objectives were to evaluate the mechanical responses, and to obtain a clear understanding of the damage mechanisms leading to failure of the MMC's. The mechanical data indicated that strain ranges attained fairly constant values in the stress-controlled experiments at both RT and 538 C, and remained so for more than 85 percent of life. The fatigue data for MMC's with different volume fraction fibers showed that MMC life was controlled by the imposed strain range rather than the stress range. At RT, and at low and intermediate strain ranges, the dominant fatigue mechanism was matrix fatigue, and this was confirmed metallurgically from fractographic evidence as well as from observations of channel type dislocation structures in the matrix of fatigued MMC specimens. Reaction-zone cracks acted as important crack initiating sites at RT, with their role being to facilitate slip band formation and consequent matrix crack initiation through classical fatigue mechanisms. MMC life agreed with matrix life at the lower strain ranges, but was smaller than matrix life at higher strain ranges. Unlike the case of monotonic deformation, debonding damage was another major damage mechanism during fatigue at RT, and it increased for higher strain ranges. At high strain ranges at RT, fractography and metallography showed an absence of matrix cracks, but long lengths of debonds in the outer layers of the SCS6 fibers. Such debonding and consequent rubbing during fatigue is believed to have caused fiber damage and their failure at high strain ranges. Thus, whereas life was matrix dominated at low and intermediate strain ranges, it was fiber dominated at high strain ranges. At 538 C, the mean stain constantly increased (ratchetting) with the number of cycles. At high strain ranges, such ratchetting led to overload failure of the fibers, and debonding of the type at RT was very small. At intermediate strain ranges, fractography showed large areas of matrix cracks. However, in spite of this matrix dominated mechanism, the MMC life at elevated temperatures was significantly less than the matrix fatigue life at all strain ranges. The reason for this difference is still unclear, although metallographic and fractographic evidences suggest that internal crack initiation sites at Mo-ribbons and reaction-zone cracks may have played a critical role, with the former tending to dominate

In-phase thermomechanical fatigue mechanisms in an unidirectional SCS-6/Ti 15-3 MMC

The objective of this investigation was to identify the inelastic deformation and damage mechanisms under in-phase (IP) thermomechanical fatigue (TMF) in a unidirectional SCS-6/Ti 15-3 metal matrix composite (MMC). Load-controlled IP TMF tests were conducted at 300-538 C at various stress ranges in high-purity argon. A major emphasis of this work was to identify damage mechanism well before final fracture of specimens, rather than to generate life diagrams, to aid development of a realistic deformation/damage and life model

Inelastic deformation mechanisms in SCS-6/Ti 15-3 MMC lamina under compression

An investigation was undertaken to study the inelastic deformation mechanisms in (0)(sub 8) and (90)(sub 8) Ti 15-3/SCS-6 lamina subjected to pure compression. Monotonic tests were conducted at room temperature (RT), 538 C and 650 C. Results indicate that mechanical response and deformation characteristics were different in monotonic tension and compression loading whereas some of those differences could be attributed to residual stress effects. There were other differences because of changes in damage and failure modes. The inelastic deformation in the (0)(sub 8) lamina under compression was controlled primarily by matrix plasticity, although some evidence of fiber-matrix debonding was observed. Failure of the specimen in compression was due to fiber buckling in a macroscopic shear zone (the failure plane). The inelastic deformation mechanisms under compression in (90)(sub 8) lamina were controlled by radial fiber fracture, matrix plasticity, and fiber-matrix debonding. The radial fiber fracture was a new damage mode observed for MMC's. Constitutive response was predicted for both the (0)(sub 8) and (90)(sub 8) laminae, using AGLPLY, METCAN, and Battelle's Unit Cell FEA model. Results from the analyses were encouraging

Crystallization and kinetics studies of Ti20Zr20Cu60-xNix (x=10, 20, 30 and 40) metallic glasses

Synthesis and characterization of Ti20Zr20Cu60-xNix (x = 10, 20, 30 and 40) metallic glasses are reported in this paper. Glassy ribbons are produced by rapid quenching using the standard copper wheel roller technique in argon atmosphere. Their structural characterization is carried out by X-ray diffraction (XRD) and thermal behaviour (crystallization) study by differential scanning calorimetry (DSC). Results of XRD on both sides of each ribbon sample confirmed that each sample was indeed amorphous/glassy as only a very broad peak in XRD pattern was observed. Metallic glass Ti20Zr20Cu50Ni10 shows three crystallization peaks in non-isothermal DSC scans while other three samples show only a single crystallization peak. The activation energy of crystallization for each sample has been calculated using three available models, namely, those of Kissinger, Augis-Bennett and Ozawa. All the three models gave nearly similar activation energies for a given sample within 10%

Extended C-terminus and length of the linker connecting the G-domains are species-specific variations in the EngA family of GTPases

AbstractEngA is an essential protein involved in ribosome biogenesis. It is an unique GTPase, possessing two consecutive G-domains. Using sequence and phylogenetic analysis, we found two intriguing variants among EngA homologues – one with a shorter linker joining the G-domains and another with a longer linker, which additionally possesses an extended C-terminus. Interestingly, while the former variant is mainly restricted to firmicutes, the latter is found in nonfirmicutes. Chimeric proteins with interchanged linkers and extensions were generated to gauge the importance of these elements. Ribosome interaction experiments employing the chimeric proteins suggest that a precise combination of the linker and C-terminal extension are important features regulating EngA ribosome interactions in a variant-specific manner

Effects of oxytetracycline residues in Thai Koi (Anabas testudineus Bloch) collected from Sylhet, Bangladesh

The present study was conducted to determine the levels of oxytetracycline residues in Thai Koi (Anabas testudineus Bloch) collected from some local fish markets of Sylhet Sadar Upazilla, Bangladesh during March to August, 2016. For the purpose of the study, 24 fresh Thai Koi fish samples were randomly collected from four (4) local markets of Sylhet Sadar Upazilla. Concentration of oxytetracycline residues in collected fish samples were determined by High Performance Liquid Chromatography (HPLC) at the Food Toxicology Laboratory of Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research, Dhaka. The results showed that 9 (37.50%) samples with detectable amount of oxytetracycline residues (mean = 42.30±3.00 ppb) were found in Thai Koi. Oxytetracycline residues level below detection limit was also reported in 15 (62.50%) samples of Thai Koi during this study. The detected residues of oxytetracycline in this fish sample did not exceed the maximum residue limit (MRL) 100 ppb recommended by the European Commission. Though residue level of oxytetracycline is lower than the MRL but long term exposure could be hazardous for human health. For that reason, control of antibiotic usage in aquaculture, regular residue monitoring, legislations and regulations for the use of antimicrobials in aquaculture and food safety education are utmost things in this regard

Measurement of the state of stress in silicon with micro-Raman spectroscopy

Micro-Raman spectroscopy has been widely used to measure local stresses in silicon and other cubic materials. However, a single (scalar) line position measurement cannot determine the complete stress state unless it has a very simple form such as uniaxial. Previously published micro-Raman strategies designed to determine additional elements of the stress tensor take advantage of the polarization and intensity of the Raman-scattered light, but these strategies have not been validated experimentally. In this work, we test one such stategy [S. Narayanan, S. Kalidindi, and L. Schadler, J. Appl. Phys. 82, 2595 (1997)] for rectangular (110)- and (111)-orientated silicon wafers. The wafers are subjected to a bending stress using a custom-designed apparatus, and the state of (plane) stress is modeled with ABAQUS. The Raman shifts are calculated using previously published values for silicon phonon deformation potentials. The experimentally measured values for σxxσxx, σyyσyy, and τxyτxy at the silicon surface are in good agreement with those calculated with the ABAQUS model.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70888/2/JAPIAU-96-12-7195-1.pd

FISH BIODIVERSITY, THREAT STATUS AND CONSERVATION SIGNIFICANCE OF THE JAMUNA RIVER, BANGLADESH

Ovo istraživanje provedeno je kako bi se istražila raznolikost, brojnost i status zaštite riblje faune u rijeci Jamuna, pritoku rijeke Brahmaputra u Bangladešu. Ukupno je zabilježeno 55 ribljih vrsta koje pripadaju u 6 redova, 20 porodica i 41 rod, a koje su prikupljene s pet odabranih lokacija u blizini rijeke tijekom razdoblja istraživanja od studenog 2018. do listopada 2019. godine. Red Cypriniformes i Siluriformes zabilježeni su kao dominantne skupine u ribljoj fauni, a koje čine 34,55% i 30,91% od ukupno uočenih vrsta. Tijekom razdoblja ispitivanja zabilježene su različite vrste manjih autohtonih vrsta (SIS) i ukupno 26 vrsta s crvene liste Međunarodne unije za zaštitu prirode (IUCN). Shannon – Weaverov indeks (H), Simpsonov indeks dominacije (D), Simpsonov indeks raznolikosti (1-D), Margalefov indeks (d) i ravnomjernost (E) izračunati su kako bi se pokazala raznolikost vrsta, bogatstvo i ravnomjernost riba. Tijekom ispitivanog razdoblja i vrijednosti tih parametara su se kretale između 1,28-1,48, 0,26-0,33, 0,67-0,74, 1,22-1,46 i 0,77-0,86. Ovo istraživanje preporučuje akcijski plan gospodarenja i očuvanja ribe, posebno uspostavljajući i održavajući skloništa za ribe, zabranjujući neselektivni ribolov i upotrebu destruktivnih ribolovnih alata radi zaštite rastilišta i mrijestilišta riba kako bi se održala perspektiva biološke raznolikosti ribarstva u rijeci Jamuna.The present survey aimed to explore the fish fauna diversity, abundance and conservation status in the Jamuna River, a tributary of the River Brahmaputra, Bangladesh. During the study period from November 2018 to October 2019, a total of 55 species of fish were recorded, belonging to 6 orders, 20 families and 41 genera from the five selected stations near the river. Orders Cypriniformes and Siluriformes were recorded as the dominant group in the fish fauna community that comprises 34.55% and 30.91% of total species, respectively. Various types of Small Indigenous Species (SIS) and a total of 26 International Union for Conservation of Nature (IUCN) red-listed species were recorded. Population indices, viz. Shannon–Weaver index (H), Simpson’s dominance index (D), Simpson’s index of diversity (1-D), Margalef’s index (d) and Evenness (E), were applied to demonstrate the species diversity, richness and evenness of fish, and their overall values were 1.28-1.48, 0.26-0.33, 0.67-0.74, 1.22-1.46 and 0.77-0.86, respectively. To sustain the prospect of fisheries biodiversity in the Jamuna River of Bangladesh, different fish management and conservation plan of action specifically establishing and maintaining fish sanctuaries, banning indiscriminate fishing and the use of destructive fishing gears for the protection of the breeding and nursery grounds of fish should be taken into consideration with utmost priority

The STAR Photon Multiplicity Detector

Details concerning the design, fabrication and performance of STAR Photon Multiplicity Detector (PMD) are presented. The PMD will cover the forward region, within the pseudorapidity range 2.3--3.5, behind the forward time projection chamber. It will measure the spatial distribution of photons in order to study collective flow, fluctuation and chiral symmetry restoration.Comment: 15 pages, including 11 figures; to appear in a special NIM volume dedicated to the accelerator and detectors at RHI

Centrosome amplification disrupts renal development and causes cystogenesis

International audienc