Creep-rupture behavior of forged, thick section 9Cr-1Mo ferritic steel

Detailed investigations have been performed to examine the creep-rupture behavior of a 1000-mm diameter and 300-mm-thick tube plate forging of 9Cr-1Mo ferritic steel in quenched and tempered (Q + T), simulated postweld heat treatment (SPWHT), and thermally aged (TA) conditions. Creep tests were conducted over a wide stress range (50 to 275 MPa) at 793 and 873 K. The alloy exhibited well-defined primary, steady-state, and extended tertiary creep stages at all test conditions. At 793 K, no significant difference in the creep-rupture properties was noted between Q + T, SPWHT, and TA conditions. On the other hand, SPWHT specimens exhibited lower creep-rupture strength than that of Q + T specimens at 873 K. Applied stress (σ _a ) dependence of rupture life (t _r ) exhibited two-slope behavior. Both the Monkman-Grant (ε _s .t _r = C _MG) and modified Monkman-Grant (ε _s .t _r /ε _f = C _MMG) relationships were found to be valid for 9Cr-1Mo steel, where ε _s is the steady-state creep rate and ε _f is the strain to failure. The two-slope behavior was also reflected as two constants in the Monkman-Grant relationship (MGR) and modified Monkman-Grant relationship (MMGR) in the two stress regimes. Further, two creep damage tolerance factors (λ = 1/C _MMG) of 5 and 10 were also observed in the high and low stress regimes, respectively. The alloy exhibited high creep ductility, which was retained for longer rupture lives at low stresses, and the creep ductility increased with increase in test temperature. The failure mode remained trangranular under all test conditions. The extensive tertiary creep in the alloy has been attributed to microstructural degradation associated with precipitates and dislocation substructure. The creep-rupture strength of the forging was found to be lower than that of thin section bars and tubes.     

Atomic force microscopy: Unraveling the fundamental principles governing secretion and membrane fusion in cells

The story of cell secretion and membrane fusion is as old as life itself. Without these fundamental cellular processes known to occur in yeast to humans, life would cease to exist. In the last 15 years, primarily using the atomic force microscope, a detailed understanding of the molecular process and of the molecular machinery and mechanism of secretion and membrane fusion in cells has come to light. This has led to a paradigm shift in our understanding of the underlying mechanism of cell secretion. The journey leading to the discovery of a new cellular structure the ‘porosome’,—the universal secretory machinery in cells, and the contributions of the AFM in our understanding of the general molecular machinery and mechanism of cell secretion and membrane fusion, is briefly discussed in this article.     

Estimation of heat source model parameters for twin-wire submerged arc welding

Heat source models are mathematical expressions that represent the generation term in the fundamental heat transfer equation. Investigators have successfully demonstrated different heat source models for single-wire welding. The present investigation estimates the double ellipsoidal heat source model parameters for twin-wire application. The heat source model parameters have been estimated for varying set of welding conditions. It has been found that the heat source model parameters for twin-wire welding are different from the single-wire welding. Moreover, the heat source model parameters also depend upon process parameters. Effects of welding current, electrode polarity and wire diameter on the size of heat source model have been presented. Flux consumption is also found to play a significant role in deciding the heat source model parameters.     

Creep strengthening of low carbon grade type 316LN stainless steel by nitrogen

Nitrogen-alloyed 316LN stainless steel is used as a structural material for high temperature fast breeder reactor components. With a view to increase the design life of the components up to 60 years and beyond, studies are being carried out to develop nitrogen alloyed 316LN stainless steel with superior tensile, creep and low cycle fatigue properties. This paper presents the results from studies on the influence of nitrogen on the high temperature creep properties of this material. The influence of nitrogen on the creep behaviour of 316LN stainless steel has been studied at nitrogen levels of 0.07, 0.11, 0.14 and 0.22 wt%. Creep tests were carried out at 923 K at stress levels 140, 175, 200 and 225 MPa. Creep rupture strength increased substantially with increase in nitrogen content. The variation of steady state creep rate with stress showed a power law relationship. The power law exponent varied between 6.4 and 13.7 depending upon the nitrogen content. Rupture ductility was generally above 40% at all the test conditions and for all the nitrogen contents. It was observed that the internal creep damage and surface damage decreased with increase in nitrogen content. Fracture mode was found to generally shift from intergranular failure to transgranular failure with increasing nitrogen content.     

Identification and characterization of novel α-amylase and α-glucosidase inhibitory peptides from camel whey proteins

This study explores the inhibitory properties of camel whey protein hydrolysates (CWPH) toward α-amylase (AAM) and α-glucosidase (AG). A general full factorial design (3 × 3) was applied to study the effect of temperature (30, 37, and 45°C), time (120, 240, and 360 min), and enzyme (pepsin) concentration (E%; 0.5, 1, and 2%). The results showed that maximum degree of hydrolysis was obtained when hydrolysis was carried out at higher temperature (45°C; P < 0.05), compared with lower temperatures of 30 and 37°C. Electrophoretic pattern displays degradation of all protein bands upon hydrolysis by pepsin at various hydrolysis conditions applied. All the 27 CWPH generated showed significant AAM and AG inhibitory potential as indicated by their lower IC₅₀ values (mg/mL) compared with intact whey proteins. In total 196 peptides were identified from selected hydrolysates and 15 potential peptides (PepSite score > 0.8; http://pepsite2.russelllab.org/) were explored via in silico approach. Novel peptides PAGNFLMNGLMHR, PAVACCLPPLPCHM, MLPLMLPFTMGY, and PAGNFLPPVAAAPVM were identified as potential inhibitors for both AAM and AG due to their high number of binding sites and highest binding probability toward the target enzymes. CCGM and MFE, as well as FCCLGPVPP were identified as AG and AAM inhibitory peptides, respectively. This is the first study that reports novel AG and AAM inhibitory peptides from camel whey proteins. The future direction for this research involves synthesis of these potential AG and AAM inhibitory peptides in a pure form and investigate their antidiabetic properties in the in vitro, as well as in vivo models. Thus, CWPH can be considered for potential applications in glycaemic regulation.     

Effect of camel milk protein hydrolysates against hyperglycemia,hyperlipidemia, and associated oxidative stress in streptozotocin (STZ)-induced diabetic rats

This study investigated the effect of camel milk protein hydrolysates (CMPH) at 100, 500 and 1,000 mg/kg of body weight (BW) for 8 wk on hyperglycemia, hyperlipidemia, and associated oxidative stress in streptozotocin-induced diabetic rats. Body weights and fasting blood glucose levels were observed after every week until 8 wk, and oral glucose tolerance test (OGTT) levels and biochemical parameters were evaluated after 8 wk in blood and serum samples. Antioxidant enzyme activity and lipid peroxidation in the liver were estimated, and histological examination of the liver and pancreatic tissues was also conducted. Results showed that CMPH at 500 mg/kg of BW [camel milk protein hydrolysate, mid-level dosage (CMPH-M)] exhibited potent hypoglycemic activity, as shown in the reduction in fasting blood glucose and OGTT levels. The hypolipidemic effect of CMPH was indicated by normalization of serum lipid levels. Significant improvement in activity of superoxide dismutase and catalase, and reduced glutathione levels were observed, along with the attenuation of malondialdehyde content in groups fed CMPH, especially CMPH-M, was observed. Decreased levels of liver function enzymes (aspartate aminotransferase and alanine aminotransferase) in the CMPH-M group was also noted. Histology of liver and pancreatic tissue displayed absence of lipid accumulation in hepatocytes and preservation of β-cells in the CMPH-M group compared with the diabetic control group. This is the first study to report anti-hyperglycemic and anti-hyperlipidemic effect of CMPH in an animal model system. This study indicates that CMPH can be suggested for its therapeutic benefits for hyperglycemia and hyperlipidemia, thus validating its use for better management of diabetes and associated comorbidities.     

Theory and Practice of γ + α2 Ti Aluminide: A Review

Among the high temperature materials γ + α₂ Ti aluminide is the most promising material, which has unique characteristics of low density coupled with high temperature properties. However, the low room temperature ductility of the alloy has limited its commercial application. Many studies have been carried out on this alloy to understand the phase transformation and role of alloying elements. Several processing methodologies have been attempted and advantages of various routes have been explored. However, poor ductility at room temperature is still a concern. In the present paper a thorough review of relevant studies has been carried out and viable route for industrial processing has been suggested. This paper includes theoretical concepts behind limited ductility of alloy at room temperature and its processing difficulty through the conventional methods. Modification in binary Ti aluminide alloy through alloying addition, selection of suitable processing route and heat treatment are noted as important areas which can provide a practical solution for this alloy to bring it to industrial processing and application.     

Temperature and strain-rate effects on low-cycle fatigue behavior of alloy 800H

The effects of strain rate (4 × 10^-6 to 4 × 10^-3 s^-1) and temperature on the low-cycle fatigue (LCF) behavior of alloy 800H have been evaluated in the range 750 ° to 950 °. Total axial strain controlled LCF tests were conducted in air at a strain amplitude of ± 0.30 pct. Low-cycle fatigue life decreased with decreasing strain rate and increasing temperature. The cyclic stress response behavior showed a marked variation with temperature and strain rate. The time- and temperature-dependent processes which influence the cyclic stress response and life have been identified and their relative importance assessed. Dynamic strain aging, time-dependent deformation, precipitation of parallel platelets of M₂₃C₆on grain boundaries and incoherent ledges of twins, and oxidation were found to operate depending on the test conditions. The largest effect on life was shown by oxidation processes. On leave from the Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India.     

Theoretical investigation of a water‐gas‐shift catalytic membrane for diesel reformate purification

The novel application of a catalytic water‐gas‐shift membrane reactor for selective removal of CO from H₂‐rich reformate mixtures for achieving gas purification solely via manipulation of reaction and diffusion phenomena, assuming Knudsen diffusion regime and the absence of hydrogen permselective materials, is described. An isothermal, two‐dimensional model is developed to describe a tube‐and‐shell membrane reactor supplied with a typical reformate mixture (9% CO, 3% CO₂, 28% H₂, and 15% H₂O) to the retentate volume and steam supplied to the permeate volume such that the overall H₂O:CO ratio within the system is 9:1. Simulations indicate that apparent CO:H₂ selectivities of 90:1 to >200:1 at H₂ recoveries of 20% to upwards of 40% may be achieved through appropriate design of the catalytic membrane and selection of operating conditions. Under these conditions, simulations predict an apparent hydrogen permeability of 2.3 × 10^?10 mol m^?1 Pa, which compares favorably against that of competing hydrogen‐permselective membranes. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4334–4345, 2013     

吸湿对印制电路板层压板热膨胀系数的影响

水分对印制电路板的可靠性有重要影响.电路板中的水分子可以改变电路基板的热性能及热力学性能,从而影响电路板及元器件的正常功能.研究了吸湿对两种无卤PCB及两种含卤PCB层压板热膨胀系数的影响,评价了IPC-TM-650 2.4.24测试方法中预处理方法对吸湿样品的适用性.结果表明,PCB层压板中的水分对PCB层压板的热膨胀曲线有明显影响,但传统的热膨胀系数计算方法并不能显示这种影响,对此作了详细分析并提出了改进建议.同时,IPC测试方法中的预处理可以降低湿度对样品热膨胀曲线的影响,但不能完全消除.