Experimental and numerical study of adding TiO2 nanoparticles effect on the thermomechanical behavior of welded joints of Steel buildings.

This study investigates the impact of titanium dioxide (TiO2) nanoparticles on the thermomechanical behavior of L-shaped welded joints in steel structures. Nanoparticles were incorporated into the weld metal at three weight ratios (0.5, 1.25, and 2 wt%) using the cold spray coating technique, and the samples were heat-treated across a wide temperature range (25-900 °C). Experimental results demonstrated that the addition of 2 wt% TiO2 nanoparticles significantly enhanced the ultimate load capacity by up to 25% compared to nanoparticle-free joints. The improvement was more pronounced in thicker steel sheets (30 mm), where uniform nanoparticle distribution and better stress dissipation were observed. The resistance recovery coefficient decreased from 94 to 97% at lower temperatures (25-400 °C) to 60-80% at 900 °C, with nanoparticle-enhanced samples showing superior retention of mechanical properties. Microstructural analysis confirmed the anatase phase of TiO2 with an average crystallite size of 20 nm and spherical morphology (20-40 nm). Computational fluid dynamics (CFD) simulations revealed that nanoparticle porosity and specific surface area critically influence heat transfer and pressure drop in coated welded joints, with optimal thermal performance achieved at higher specific surface areas. This work highlights the synergistic effects of TiO2 nanoparticles, sheet thickness, and thermal treatment on weld performance, offering a promising pathway for enhancing the durability and thermal management of steel structures in demanding applications.