Rajib Kalsar

This study presents a novel confined hot rolling technique for embedding optical fiber sensors into wrought metallic components, with the goal of enabling real time strain monitoring in extreme environments such as advanced nuclear reactors. Finite element analysis was used to investigate the stress–strain response of embedded fiber assemblies under various rolling conditions. Multi-pass rolling was found to reduce stress concentrations, shear gradients and roll separation forces compared to single-pass deformation. Guided by simulation results, experimental trials were conducted on a 316 stainless steel (SS316) plate with precision-machined channels housing sapphire optical fibers (compatible with higher temperature processing) within the tubes. The assemblies were hot rolled at 900 °C to achieve a 40% total reduction. Microstructural analysis confirmed progressive channel closure and bonding at both tube-matrix and fiber-tube interfaces, with no significant interfacial defects. For lower temperature applications, copper (Cu)-coated silica fibers were embedded into aluminum alloy 6061 (AA6061) plates using the same method. Optical backscatter reflectometry during thermal cycling of the rolled sample showed minimal optical attenuation and compressive residual fiber stresses after rolling. The integrated computational and experimental approach demonstrates a scalable and robust pathway for embedding optical sensors into structural metals for high temperature structural health monitoring.

Soft magnetic materials are critical to the performance, energy efficiency, and miniaturization of electric motors. While laminated soft magnetic materials have dominated the industry, the demand for soft magnetic composites (SMCs) is rapidly growing in applications requiring three-dimensional magnetic flux paths, reduced eddy current losses, and high-frequency operation. This study reports for the first time, in-situ friction stir forging (I-FSF), an innovative and single-step consolidation process for Fe-3.5Si soft magnetic powders. By leveraging pre-oxidized powders, the process generates oxide layers that enhance electrical resistivity. Unlike conventional sintering methods that require prolonged diffusion times, I-FSF promotes rapid densification and enables near-net-shape fabrication of dense SMC components with exceptional structural integrity in a single-step. The resulting components exhibit outstanding performance metrics, including tensile strength exceeding 650 MPa, saturation magnetization of 187 emu/g, and coercivity below 10 Oe, achieving the ideal balance between mechanical durability and magnetic efficiency. The proposed I-FSF process offers a simplified manufacturing route for producing advanced SMCs tailored for next generation electric motor applications, providing an alternative approach to magnetic material fabrication.

We report the fabrication of aluminum metal matrix composites (Al-MMCs) with hierarchical architectures via friction extrusion (FE), a scalable, single-step, solid-phase processing technique. Precursor pucks containing 0–15 vol% Al₂O₃ particles were extruded into fully dense AA6061-based composite rods. The FE induced a tree-ring-like architecture of concentric particle-rich and particle-lean bands, yielding refined grains in particle-rich regions and coarser grains elsewhere. At the nanoscale, magnesium in AA6061 selectively reacted with Al₂O₃ particles to form virus-like nodes, improving particle–matrix bonding. This multi-scale design strategy, combining mesoscale architecture, microscale grain refinement, and nanoscale interface engineering overcome the conventional strength–ductility trade-off. Tensile testing showed substantial increases in yield and ultimate tensile strengths while retaining high ductility ( > 20%). Enhanced strain hardening, driven by the accumulation of geometrically necessary dislocations at interfaces, contributed to the performance. The hierarchical microstructure produced by FE demonstrates a promising pathway for scalable fabrication of lightweight MMCs for structural applications requiring a combined high strength and ductility.