Effects of Rapid Cooling on Properties of Aluminum-Steel Friction Stir Welded Joint

In this study, dissimilar sheets including AA3003 aluminum and A441 AISI steel were welded via cooling-assisted friction stir welding (FSW). Three different cooling mediums including forced CO2, forced water, and forced air were employed, and a non-cooled sample was processed to compare the cooling-assisted condition with the traditional FSW condition. The highest cooling rate belongs to CO2 and the lowest cooling rate belongs to the non-cooled sample as FSW. The best macrograph without any segregation at interface belongs to the water-cooled sample and the poorest joint with notable segregation belongs to the CO2 cooling FSW sample. The CO2 cooling FSW sample exhibits the smallest grain size due to the suppression of grain growth during dynamic recrystallization (DRX). The intermetallic compound (IMC) thickening was suppressed by a higher cooling rate in CO2 cooling sample and just Al-rich phase was formed in this joint. The lowest cooling rate in the FSW sample exhibits formation of the Fe rich phase. The IMC layers were thicker at the top of the weld due to closeness with the heat generation source. The water cooling sample exhibits the highest tensile strength due to proper mechanical bonding simultaneously with optimum IMC thickness to provide appropriate metallurgical bonding. Fractography observation indicates that there is a semi-ductile fracture in the water cooling sample and CO2 cooling sample exhibits more brittle fracture. Hardness evaluation reveals that the higher the cooling rate formed, the higher the hardness in stir zone, and hardness changes in the aluminum side were higher than the steel side

Four-dimensional printing of acrylonitrile butadiene styrene – thermoplastic polyurethane shape memory polymers with excellent material and interfacial adhesion performance

There are a limited number of thermoplastics with intrinsic shape memory effect (SME) that are four-dimensional (4D) printable. Development of other shape memory polymers (SMPs) entails synthesis with a complicated chemical experimental lab effort. In this paper, for the first time, a novel layered multi-material structure is developed based on a deep comprehension of SMEs’ macromolecular requisites. The fused deposition modeling (FDM) method is used for the four-dimensional printing of layered structures whose base materials show no SME. Commercial acrylonitrile butadiene styrene (ABS), toughened ABS-thermoplastic polyurethane (TPU) blend, and TPU, all with no SME, are used to fabricate bi-layers of ABSTPU blends and TPU with different volumetric proportions. Different thermo-mechanical tests, including dynamic mechanical thermal analysis (DMTA), and constrained and free shape recovery, are conducted. Also, the interfacial properties of the layered 4D printed structure are assessed by the mean of shear testing and scanning electron microscopy (SEM). Experimental results reveal that the 4D printed bi-layer composites possess a high level of programmability, SME (90–96%), and perfect interfaces without any porosity and detachment between layers. The results of this research can potentially eliminate the desperate need for SMPs for 4D printing and broaden the opportunity to have smart parts using commercial thermoplastics

Aggregation study of Brownian nanoparticles in convective phenomena

The explanation of abnormal enhancement of transported energy in colloidal nanoparticles in a liquid has sparked much interest in recent years. The complexity comes from the inter-particle phenomenon and cluster formation. The process of nanoparticle aggregation, which is caused by convective phenomena and particle-to-particle interaction energy in a flow, is investigated in this research. Therefore, the probability of collision and cohesion among clusters is modelled, as stated in this research. ANSYS-Fluent 17 CFD tools are employed to implement a new method of nanoparticle aggregation, new essential forces, new heat law and cluster drag coefficient. The importance of the interaction forces is compared to drag force, and essential forces are considered in coupling between nanoparticles and fluid flow. An important parameter is defined for the surface energy density regarding the attractive energy between the double layer and surrounding fluid to capture the cohesion of particles. Particles’ random migration is also presented through their angular and radial displacement. The analyses for interactions show the significance of Brownian motion in both particles’ migration and coupling effects in the fluid. However, nanoparticles are pushed away from walls due to repulsive forces, and Brownian motion is found to be effective mainly on angular displacement around the tube centreline. The attractive energy is found to be dominant when two clusters are at an equal distance. Hence, the cluster formation in convective regions should be taken into account for modelling purposes. A higher concentrated region also occurs midway between the centreline and the heated wall.http://link.springer.com/journal/10973hj2020Mechanical and Aeronautical Engineerin