Bhattacharyya, Abir

The present study explores the creep and high-temperature tensile performance of the P92/304L dissimilar weld joint. The gas tungsten arc welding (GTAW) technique was used to prepare the dissimilar weld joint between P92 creep strength enhanced ferritic (CSEF) steel and 304L austenitic stainless steel (SS) by utilizing ERNiCrMo-3 filler metal. After welding, tensile strength was evaluated at 450, 550, 650, 750, and 850 °C temperature to examine the performance of the dissimilar weld joint at elevated temperatures. The high-temperature tensile test result indicated that the ultimate tensile strength (UTS) decreased from 439 to 58 MPa, and yield strength (YS) fell from 155 to 41 MPa during the test from 450 to 850 °C. After high-temperature tensile strength, the creep performance of the P92/304L dissimilar weld joint has also been investigated at 650 °C in the stress range of 100-200 MPa. All the creep specimens failed from the P92 steel parent metal region during the creep test at different conditions. The maximum creep life of 706.9 h was observed for the specimen tested at 650 °C under 100 MPa. The minimum creep life of 11.9 h was observed for the specimen tested at 650 °C under 200 MPa. The relationship between the rupture time and applied stress followed the logarithmic equation as log (tr) = log (14.39695) + (− 5.79039) log (σ). The softening of the parent metal matrix due to the consumption of the solid solution strengthening W and Cr elements and the coarsening of the precipitates were the main reasons behind the creep failure at 650 °C in the stress range of 100-130 MPa. The plastic deformation caused by the grain boundary sliding was mainly responsible for creep failure at 650 °C in the stress range of 150-200 MPa. © ASM International 2023.

Axial-torsion low cycle fatigue (LCF) experiments were conducted on 304LN stainless steel under in-phase triangular (IPT), 90° out-of-phase triangular (OPT), 90° out-of-phase sinusoidal (OPS), and 90° out-of-phase trapezoidal (OPZ) loading paths with same applied axial strain (ε) and equivalent shear strain amplitude ([Formula prsented]), to study the material's cyclic stress response (CSR) under each strain path and to further correlate the responses with dislocation substructure and martensite formation. The CSRs exhibited primary hardening followed by softening and a secondary hardening. Both primary and secondary hardening were found to increase, and the softening was found to decrease as per the following sequence IPT < OPT < OPS < OPZ. Electron backscattered diffraction (EBSD) revealed that both deformation-induced Martensite (DIM) fraction and Kernel average misorientation (KAM) increases in the same sequence for different paths, indicating the tendency of formation of DIM increases and the propensity of recovery decreases in the same order. The cyclic stress response and DIM formation under non-proportional loadings are rationalized by (i) higher non-proportionality of strain path for OPS than OPT for same equivalent strain amplitude, and (ii) greater equivalent strain amplitude in OPZ than OPS. A greater fraction of planes subjected to combined resolved shear and tensile stress under OPS path than OPT path leads to a greater DIM formation in the OPS path than OPT path, reflecting the effect of non-proportionality factor. A greater magnitude of resolved shear and normal strain, and high tensile normal stress causes higher DIM formation and hardening in the OPZ path as compared to OPS path, reflecting the effect of equivalent strain amplitude. © 2025 Elsevier Ltd

Measurement of stress-strain response under different deformation modes is important for developing constitutive models of soft polymers. However, such measurements on soft and compliant polymers are challenging using traditional techniques due to generation of unwanted stress concentrations leading to premature failure during loading. In this study, a non-contact digital image correlation (DIC) technique along with a novel experimental setup were used to accurately measure the strain field on a specimen surface subjected to finite strain. Polydimethylsiloxane (PDMS) elastomers of three different base polymer to hardener ratio were characterized under three different deformation modes— uniaxial compression, uniaxial tension, and simple shear—over strain rates ranging between 10−3/s–10−1/s. The resulting strain fields exhibited uniformity across all the deformation modes up to finite strains. While the lower strain rate experiments are minimally affected by strain acceleration and inertia effects, the specimens loaded under higher strain rate (10−1/s) are initially affected by strain acceleration during loading, which precluded reliable determination of Young's moduli and shear moduli from the initial slope of the stress-strain responses. The Poisson's ratio calculated from the ratio between measured axial and lateral strains was close to 0.5 at small strains, and exhibited a close match with that calculated from Young's modulus (E) to shear modulus (G) ratio (E/G), validating linear elasticity theory at small strains. The tangent moduli for all the compositions were found to be practically strain-rate insensitive in the region of steady strain rate. © 2025 The Authors

Neural Network (NN)-based models showed robust capabilities while predicting cutting force during end milling of Carbon Fiber Reinforced Polymer (CFRP) Composites. NN models can effectively handle numerous factors and the inherent nonlinearities associated with the end milling of CFRP composites. However, a systematic approach is necessary to determine the quality and quantity of experimental cutting force data, which is critical for NN model training. This paper presents a physics-informed experimental design or Physics-Informed Advisor (PIA) that systematically determines cutting conditions for end milling experiments to generate training datasets. The PIA recommends the radial depth of cut and fiber orientation angle values to capture the process mechanics adequately and minimize experimental efforts. The cutting constant relationships of the Mechanistic force model are established using two independent Feed Forward Neural Networks (FFNN) trained using datasets from end milling experiments performed at cutting conditions determined using PIA. The predictions of the proposed approach are compared with the traditional Mechanistic force model presented in the literature and experimentally measured values. It is shown that integrating PIA with FFNNs enables an accurate estimation of cutting forces with reduced experimental efforts in generating training datasets.

This study investigates the effect of filler materials on the structural integrity of dissimilar welded joints (sDSS 2507/IN625) employed in marine subsea manifold applications. Multi-pass gas tungsten arc welding (GTAW) using ER2594 and ERNiCrMo-3 fillers investigates microstructure evolution, solidification mechanisms, mechanical characteristics, residual stresses, and corrosion behavior. Optical and scanning electron microscopy revealed an unmixed zone (peninsula/island-shaped) at the weld interface and weld zone (WZ) in both filler weldments. Segregation of Mo, Nb, and Ni was observed in the interdendritic region of ERNiCrMo-3 filler WZ, whereas the skeletal ferrite matrix of ER2594 filler WZ revealed the existence of the Laves phase (Fe2Nb form). Electron beam scattered diffraction (EBSD) investigation showed austenitic solidification for ERNiCrMo-3 and fully ferritic solidification for ER2594 with distinct dendrite formations. Inhomogeneity has been observed in microhardness maps, with ER2594 and ERNiCrMo-3 WZ averaging 310 ± 7 Hv0.5 and 270 ± 10 Hv0.5, respectively. ERNiCrMo-3 (165 ± 5 J and 180 ± 3 J) and ER2594 (100 ± 3 J and 110 ± 6 J) fillers exhibited distinct effects on toughness in the weld cap and root due to laves phase precipitation. Additionally, ER2594 (750 ± 6 MPa) and ERNiCrMo-3 (790 ± 7 MPa) fillers exhibited lower tensile strength than base metals. The structural integrity of WZ can be better understood by residual stress analysis, which showed compressive cap pass and tensile root pass residual stresses for both fillers. In a 3.5 wt% NaCl solution, both fillers exhibited outstanding corrosion resistance in marine conditions. These findings improve subsea manifold structure integrity and performance in corrosive marine environments.

A novel back-stress deconvolution method based on nonlinear-kinematic hardening plasticity theory is proposed to determine the minimum number of back-stresses required to model the low cycle fatigue (LCF) hysteresis loops of 316L(N) stainless steel at room temperature. The deconvoluted back-stresses at different threshold plastic strains corroborate that, three back-stresses can simulate the back-stress vs plastic strain response for all cycles at ± 0.6 % strain amplitude. The variation of kinematic hardening parameters with cycles indicates dynamic evolution of material microstructure and gross microstructural heterogeneity during LCF. The simulated stress–strain hysteresis loops show excellent match with the experiments.

Low-cycle fatigue (LCF) tests were performed at ambient temperature on annealed single-phase Cu–30 wt% Zn (70/30 brass) at strain amplitudes of 0.4 %, 0.7 %, 1.0 %, and 1.2 % to investigate the effect of strain amplitude on the cyclic stress response. The cyclic stress response exhibits primary hardening, softening, and secondary hardening. The primary hardening and softening increases, while the secondary hardening decreases with increasing strain amplitude. Internal stresses determined from stress-strain hysteresis loops show that back-stress hardening and softening dominate the primary hardening and softening, whereas friction stress is almost constant, leading to Masing behavior. Electron backscatter diffraction (EBSD) analysis revealed that Kernel Average Misorientation (KAM) and low-angle grain boundary (LAGB) fraction increase with increasing strain amplitude, indicating an increase in geometrically necessary dislocation (GND) density and recovery of dislocation substructure with increasing strain amplitude. The recovered substructure determined by softening of back stress reveals the formation of planar slip bands, and the slip band intersection increases with increasing strain amplitude, indicating that Cu-Zn 70/30 is a purely planar slip alloy. During secondary hardening, friction stress increases, and unrecovered corduroy substructure forms. The back stress components were determined based on a modified Chaboche model for different strain amplitudes to calculate the intergranular and intragranular back stresses evolution with increasing cycles and increasing strain amplitudes, and correlated with microstructural evolution. There is competition between the evolution of intergranular and intragranular back stress due to heterogeneous dislocation distributions during cyclic softening. © 2025 Elsevier B.V., All rights reserved.

A low-carbon medium-Mn steel is designed utilizing CALPHAD approach to leverage the transformation induced plasticity (TRIP) for the enhancement of strength-ductility combination. The as-cast steel produced by vacuum induction melting, was hot forged, and was subsequently hot-rolled and air-cooled to room temperature (HRAC). The hot-rolled plate was subjected to two different thermomechanical processing routes- (i) inter-critical annealing (IA) to obtain partial austenitization followed by air cooling (S1 or HRIA), and (ii) annealing above the upper critical temperature to obtain full austenitization and subsequent air cooling (S2). Both steels were cold-rolled followed by IA and subsequent water quenching to room temperature (S1-IA and S2-IA, or CRIA) to obtain different microstructures. The steels were characterized for phase fractions and recrystallization, grain boundary characteristics, and dislocation densities. The HRIA steel showed greater strain-hardening but lower ductility than the CRIA steels due to HCP-martensite mediated TRIP. The CRIA steels exhibited same UTS × TE≈20.5 GPa%. S1-IA exhibited higher yield and tensile strength, but lower uniform elongation than S2-IA, despite having higher austenite volume fraction. The higher yield strength is attributed to the higher dislocation density of ferrite in S1-IA, in which TRIP activates at a higher stress due to smaller austenite grains size. The lower yield strength, and easier initiation of TRIP in S2-IA are attributed to a more recrystallized ferrite with lower dislocation density, and coarser austenite grains, respectively. However, the higher C of retained austenite in S2-IA increases its stability requiring larger tensile strain for continuation of TRIP effect leading to higher uniform elongation than S1-IA. © 2025 Elsevier B.V., All rights reserved.