Monotonic and cyclic fracture behaviour of AISI 304LN stainless steel

Fracture behaviour of AISI 304LN stainless steel and its weldment has been studied employing J-integral approach with and without superimposed cyclic load reversals in order to assess their structural integrity under simulated seismic loading condition and to compare their fracture behaviour in cyclic vis-à-vis monotonic loading. Conventional J- integral tests were carried out on specimens having notch in LC and CL configurations. Cyclic J-R experiments have been conducted (i) under displacement control with various combinations of R-ratio and incremental plastic displacement, and (ii) under load control (henceforth called cyclic fracture tests) for various magnitudes of monotonic peak loads. All cyclic J-R and cyclic fracture tests were carried out using specimens with LC orientation. Examinations of fracture surface and crack tip profiles have been made to understand the micro-mechanisms of fracture. In addition, acoustic emission (AE) methods were used synergistically with fracture toughness tests to detect the onset of crack initiation. Characterization of microstructures and mechanical properties like, tensile and hardness values are necessary supplements in this study. The obtained results and their analyses lead to the following inferences: (a) microstructure of the selected steel reveals predominantly austenite whereas its weldment exhibits austenitic matrix with 12-15% δ-ferrite (b) the strength and hardness of the selected weldment are higher than that of the base metal. The results of fracture studies under monotonic loading conditions showed that (a) average fracture toughness values for LC and CL orientations are similar with J Q values of 1107 and 1062 kJ/m 2 respectively and (b) fracture toughness values of weldment are almost 50% lower than that of the base metal. The cyclic fracture behaviour of the selected steels leads to the following conclusions: (a) under displacement controlled cyclic J-R tests, fracture toughness is found to degrade with (i) decrease in stress ratio from -0.5 to -1.0 and (ii) decrease in plastic displacement from 0.5 mm to 0.1 mm and (b) under load controlled cyclic fracture tests the steels are found to fail in a limited number of load cycles even when the load amplitude is sufficiently below the collapse load estimated from monotonic tests. Examination of the fracture surfaces and crack tip profiles revealed that degradation in initiation fracture toughness and their resistance to crack propagation at R<0 is due to re-sharpening of the crack tip during compressive loading. Synergistic analyses of fracture test and AE results assist to demarcate the region of blunting, crack initiation and crack propagation under both monotonic and cyclic J-R tests. In generalization, it can be said that fracture resistance of the selected steels under cyclic loading is considerably lower than that obtained from monotonic J-integral experiments and the initiation fracture toughness value obtained from AE parameters provide a conservative estimate

Evolved Gases and Unified Kinetic Model for Low-temperature Thermal Decomposition of Rice Straw Hydrolysis Residue for Possible Value Addition

Low-temperature thermal decomposition (LTTD) of Rice straw hydrolysis residue (RSHR) was studied using thermogravimetric analysis and Fourier Transform Infrared spectroscopy (TGA-FTIR) at different heating rates. During thermogravimetry, the maximum rate of mass loss of 135% per min was observed at 339 °C ( Tmax ) for heating rate of 50 °C per min. Tmax decreased to 323, 315, and 299 °C with decrease in heating rate to 40, 30, and 20 °C min−1, respectively. LTTD of RSHR yields volatile oxygenated organics – acids, esters, aldehydes, ketones, alcohols and phenols – as revealed by the FTIR spectra of evolved gases. At increased decomposition temperature, carbonyl moieties were less conjugated. The main gaseous products of LTTD were carbon dioxide, carbon monoxide, and methane. Kinetics of LTTD of RSHR was analysed using thermogravimetry results. Activation energy of LTTD followed a Lorentzian distribution with respect to residual mass fraction (RMF). Dependence of LTTD rate on RMF was found to adhere to the truncated Sestak and Berggren model

Type-I thermal leptogenesis in Z3Z_3-symmetric three Higgs doublet model

Our present work explores the possibility of neutrino mass generation through {\em Type-I see-saw} mechanism and provides an explanation of the baryon asymmetry of the Universe via thermal leptogenesis in the framework of $Z_3$-symmetric three Higgs doublet model (3HDM) augmented with three right-handed neutrinos. Here the thermal leptogenesis is initiated by the out-of-equilibrium decay of the lightest heavy neutrino $N_1$. The constraints arising out of the scalar sector put strong bound on the model parameter $\tan \beta$, which in turn takes part in the computation of the lepton asymmetry $\epsilon$. Lepton asymmetry being converted partially into the baryon asymmetry by electroweak sphelaron processes, will account for the required baryon asymmetry satisfying the current data. We therefore analyse the parameter space consistent with the constraints arising from neutrino oscillation, lepton asymmetry and baryon asymmetry together, last one being the most stringent one.Comment: 37 pages, 10 captioned figures, 1 table, Accepted for publication in EPJ

Resonant leptogenesis in (2,2) inverse see-saw realisation

In this present work, we uphold the standard model (SM) augmented with two right-handed (RH) neutrinos along with two singlet neutral fermions to generate active neutrino masses via (2,2) inverse see-saw mechanism. All entries of the neutrino mass matrix are taken to be complex to make this study a general one. We also investigate if the parameter points compatible with the neutrino oscillation data simultaneously satisfy the experimental bounds coming from the lepton flavour violating (LFV) decays : $\mu \to e \gamma,~ \tau \to e \gamma, ~ \tau \to \mu \gamma$. This study also explores the prospect of producing the baryon asymmetry of the universe through resonant leptogenesis. Here the resonant leptogenesis is induced by the lightest pair of degenerate mass eigenstates. Upon solving the coupled Boltzmann equations, one can divide the multi-dimensional model parameter space into three parts, where the parameter points are compatible with the neutrino oscillation data, constraints coming from the LFV decays and last but not the least, the observed baryon asymmetry of the universe.Comment: 29 pages, 2 tables, 7 captioned figure