Effect of 475oC embrittlement on the fatigue behaviour of a duplex stainless steel

The low cycle fatigue behaviour of a duplex stainless steel was studied in standard heat treated and embrittled (by aging at 475°C for 100 hours) condition by mechanical testing, scanning and transmission electron microscopy. The fatigue crack initiation behaviour was studied in the embrittled condition by interrupting stress-controlled fatigue tests, identifying the crack initiation sites and relating them to the crystallographic parameters obtained from EBSD-OIM scans. The aging treatment at 475°C resulted in the precipitation of a' in the ferritic phase. Impact energy drops from 260 Joules in the annealed condition to 8 Joules in the aged condition. The drop in impact energy was caused by the inability of the ferritic phase to form deformation twins in the embrittled condition, which was confirmed by TEM examination. From the low cycle fatigue experiments conducted at A C/2 = 4. Ox 10-', 6. Ox 10-', 8.Oxl0-3 and 1.Ox10"2, it was established that the deformation curves in the annealed condition has three discernible stages: (i) cyclic hardening, (ii) cyclic softening and (iii) cyclic saturation and in the aged condition has two discernible stages: (i) cyclic hardening, and (ii) cyclic softening till final failure for all values of strain amplitude. A change in slope is observed in the cyclic stress-strain curve in the aged condition as compared to the standard heat treated condition. In the range of strain amplitude employed, in the aged condition, fatigue life is longer at lower plastic strain amplitude, decreases and becomes similar at intermediate plastic strain amplitude and becomes shorter at higher plastic strain amplitude in comparison to the standard heat treated condition. The gradual decrease in fatigue life with increase in plastic strain amplitude in the aged condition was attributed to the rapid cyclic softening caused by disappearance of the a' precipitates. From the fatigue crack initiation studies conducted at Ao12 = 400 MPa and 500 MPa, it was established that the crack initiation sites are the slip markings corresponding to { 111 } plane traces in the austenitic grains at Dof2 = 400 MPa and more cracks were observed to initiate at E3 CSL boundaries in the austenitic grain at Do12 = 500 MPa in the aged condition. The major resistance to crack growth came from the ay phase boundary

Storage Stability of Sandesh – an Indian Milk Sweet

Storage stability of sandesh, one of the popular Indian milk sweets was determined in terms of its moisture adsorption isotherms by gravimetrically at 20 and 30°C using saturated salt solutions in the range of 11.2 and 97.2%. The isotherms obtained were of sigmoid shape and of the BET type. Out of three sorption models fitted to the experimental data, Caurie model was found superior in interpreting the moisture adsorption characteristics of sandesh with low relative deviation percent and high coefficient of determination. The values of isosteric heat of sorption as calculated from Clausius–Clapeyron equation was found to increase with decreasing moisture content at lower moisture content and approached the value of heat of vaporization of free water above 17.25% (db).

Numerical simulations of miscible channel flow with chemical reactions

We study the pressure-driven miscible displacement of one fluid by another in a horizontal channel in the presence of an exothermic chemical reaction. We solve the continuity, Navier-Stokes, and energy conservation equations coupled to convective-discussion equations of the reactant and product. The viscosity is assumed to depend on the volume fraction of the reactant and product as well as the temperature. The effects of relevant parameters such as the Reynolds number, Schmidt number, Damköhler number and viscosity ratio of the reactant and product are studied. Our results indicate that increasing the intensity of the chemical reaction by increasing the Damköhler number and decreasing the dimensionless activation energy increases the displacement rate. We have also found that increasing Reynolds number leads to more pronounced instabilities and roll-up phenomena, which in turn promote rapid displacement of the resident fluid inside the channel. Variation of the relative significance of the heat of reaction and the Schmidt numbers of the reactants and products, however, has a negligible influence on the displacement rates for the parameter ranges considered in the present work

475°C Embrittlement and Room Temperature Fatigue of Duplex Stainless Steel

Duplex stainless steels (DSSs) are two-phase materials consisting of both the ferritic and the austenitic phase. The alloys are prone to embrittlement particularly in the temperature range between 280°C and 512°C. This so-called 475°C embrittlement is caused by a decomposition of the ferritic phase into a chromium-rich α' and an iron-rich α phase. The objective of this study is to develop a better understanding of the embrittling process of DSS of type SAF 2205. Embrittled and non-embrittled DSS was fatigue tested in stress-controlled tests at 475°C and in strain-controlled tests at room temperature. The high temperature fatigue tests were stopped at different cycle numbers in order to characterize the changing material conditions by means of room-temperature tensile tests and scanning electron microscopy pictures of the fracture surfaces

Multi-kilowatt single-mode ytterbium-doped large-core fiber laser

We have demonstrated a highly efficient cladding-pumped ytterbium-doped fiber laser, generating >2.1 kW of continuous-wave output power at 1.1 µm with 74% slope efficiency with respect to launched pump power. The beam quality factor (M2) was better than 1.2. The maximum output power was only limited by available pump power, showing no evidence of roll-over even at the highest output power. We present data on how the beam quality depends on the fiber parameter, based on our current and past fiber laser developments. We also discuss the ultimate power-capability of our fiber in terms of thermal management, Raman nonlinear scattering, and material damage, and estimate it to 10 k

A Monetary Business Cycle Model for India

A New Keynesian monetary business cycle model is constructed to study why monetary transmission in India is weak. Our models feature banking and financial sector frictions as well as an informal sector. The predominant channel of monetary transmission is a credit channel. Our main finding is that base money shocks have a larger and more persistent effect on output than an interest rate shock, as in the data. The presence of an informal sector hinders monetary transmission. Contrary to the consensus view, financial repression in the form of a statutory liquidity ratio and administered interest rates, does not weaken monetary transmission

Nuclear equation of state at high density and the properties of neutron stars

We discuss the relativistic nuclear equation of state (EOS) using a relativistic transport model in heavy-ion collisions. From the baryon flow for $Au + Au$ systems at SIS to AGS energies and above we find that the strength of the vector potential has to be reduced moderately at high density or at high relative momenta to describe the flow data at 1-10 A GeV. We use the same dynamical model to calculate the nuclear EOS and then employ this to calculate the gross structure of the neutron star considering the core to be composed of neutrons with an admixture of protons, electrons, muons, sigmas and lambdas at zero temperature. We then discuss these gross properties of neutron stars such as maximum mass and radius in contrast to the observational values.Comment: 17 pages, 5 figures, to be published in Phy. Rev.