Mechanic of Advanced and Smart Materials

Abstract In this research, the effect of manganese content on the microstructure and tensile properties of dual-phase steels was studied. At first, three low-carbon steels with fixed carbon and silicon and variable amount of manganese (0.76-2.3wt.%) were produced by melting and casting method. Then the cast steels were hot rolled in several stages to create sheets with a thickness of 2 mm. To create dual-phase ferritic-martensitic structure in steels, they were subjected to intercritical annealing process at three different temperatures of 750, 775 and 800 ℃ for 20 minutes and then quenched in cold water. According to the variables of intercritical annealing temperature and manganese content, different ratios of volume fraction of ferrite and martensite phases were created in steels. In order to study the role of manganese in dual-phase steels, these steels were subjected to microstructure and tensile properties. The relationship between tensile properties and microstructure was cleared.

Increasing Mn at a constant intercritical annealing temperature significantly increased the martensite volume fraction. Meanwhile, the effect of annealing temperature on the volume fraction of martensite was less. The uniaxial tensile test on steels showed that manganese reduces the ductility of steels due to the increase of martensite volume fraction, while it increases their strength. The effectiveness of tensile strength was more than yield strength.

Abstract Ultra-precision machining refers to the process of manufacturing very high-precision parts that are required in industries such as aerospace, medicine, optics, and electronics, where nanometer tolerances, fine surface coatings, and precise geometries are essential. In this research, the nano-machining process of polycrystalline nickel-iron-chromium alloy has been investigated using the molecular dynamics method. Investigating the effects of cutting speed and cutting depth parameters on this process by the response surface method shows that by reducing the cutting speed from 400 to 10 m/s, the cutting depth from 5 to 0.5 nm, the values of cutting forces, normal forces and the Von Mises stress of the workpiece decreases by 65.9, 23.4 and 25.58 percent, respectively. When the cutting depth was set to 0.5 nm and the cutting speed was 10 m/s, the temperature reached 308.82 K. At this state, the machining forces—including cutting forces and Thrust force —were measured at 152.42 and 221.2 (eV/n), respectively. This configuration minimizes the machining forces, resulting in an optimized state for the machining process. The investigation of structural changes using the radial distribution function shows that increasing the cutting speed from 10 m/s to 400 m/s, while maintaining a cutting depth of 2.75 nm, results in an increase of 10 units in the radial distribution function. This change has contributed to the structural alterations of the workpiece.

Abstract Laser bending of metal sheets is one of the most common forming processes and is widely used across various industries. Perforated sheets, due to their geometric discontinuities, encounter serious challenges during mechanical bending operations, which lead to ovalization of the holes and reduced dimensional accuracy. In this study, laser bending of 2-mm-thick perforated 304 stainless steel sheets is performed using a CO₂ laser, based on an experimental design developed through the response surface methodology and the Box–Behnken algorithm. For this purpose, the effects of process parameters—including laser power, scan speed, and laser beam diameter—on the percentage of hole ovalization are investigated. The results show that increasing the laser power and beam diameter increases ovalization, while increasing the scan speed reduces it. Analysis of variance of the statistical model indicates the significance of the main effects, interactions, and second-order terms of the parameters. Parameter optimization reveals that, in order to achieve minimum ovalization (0.22%), the laser power, scan speed, and beam diameter should be set to 87 W, 75 mm/min, and 2 mm, respectively.

Abstract Airborne particulate matter, such as fine dust and aerosols, poses serious threats to respiratory health. Conventional polymer filters suffer from limited reusability and sterilization challenges. This study presents the design, fabrication via Selective Laser Melting (SLM), and characterization of a cylindrical porous filter made from Ti-6Al-4V alloy with a graded conformal Gyroid topology. The structure features graded channel spacings (inner wall: 206 µm, mid-region: 396 µm, outer wall: 463 µm; weighted mean: 415 µm) and an effective open porosity of ~65%. The design was optimized in nTopology software to enhance cell overlap and particle trapping while maintaining airflow permeability. The sample (OD=15 mm, ID=9 mm, H=10 mm) was fabricated from Ti-6Al-4V powder (15–45 µm) and characterized after stress-relief annealing at 600°C. Results include optical metallography (acicular α phase in β matrix), metallographic measurements (mean layer spacing of 415 µm), Vickers microhardness (mean 327 HV), bulk density (4.18 g/cm³), and bulk porosity (~5.5%).

Abstract Noise pollution, particularly the low-frequency noise generated by wind turbines, is recognized as an environmental challenge that may have adverse effects on human health. In this study, the effect of blade cone angle (0°–10°) on the low-frequency noise of a horizontal-axis wind turbine was investigated. To this end, the flow field around the turbine was first simulated for wind speeds ranging from 5 to 10 m/s using the Reynolds-Averaged Navier–Stokes (RANS) equations coupled with the Shear Stress Transport (SST) turbulence model. Subsequently, the turbine noise, generated by sources located on and around the blades, was predicted using the Ffowcs Williams–Hawkings (FW–H) equation. The results showed that varying the blade cone angle from 0° to 10° changed the turbine power output by less than 5%; however, it had a significant influence on the propagation of low-frequency noise. It was also found that at a blade cone angle of 5°, the turbine not only achieved higher power output but also exhibited a lower peak sound pressure level than the planar turbine (0° blade cone angle 0°).

Abstract Developing low-cost recycled filaments with desirable mechanical properties is a major challenge in the additive manufacturing industry. This research investigated the feasibility of producing 3D-printer filament from recycled high-density polyethylene (HDPE) bottle caps and characterized its shape-memory behavior. Unlike previous studies that neglected the residual stress history from production and spooling, this study demonstrated the inherent error in conventional testing methods by measuring the initial curvature angle and its variation after stress relaxation. The fabricated 1.75 mm filament was subjected to shape-memory bending tests, and the results were compared with those of commercial PLA, ABS, and TPU filaments. The recycled filament, with a shape-recovery ratio of about 80%, behaved similarly to PLA and outperformed ABS. Furthermore, the necessity of a stress-relaxation step in testing protocols was confirmed by observing a non-zero initial angle and unwanted shape recovery after stress relaxation in all samples. The fabricated filament also exhibited a lower density than the other materials, providing a key competitive advantage. Additionally, economic analysis revealed a significant cost reduction compared to commercial counterparts. It is concluded that high-value smart materials do not require expensive resources; recycling bottle caps is presented as an environmentally friendly solution with high application potential, affordability, and significant added value.

Abstract This paper presents a comprehensive vibrational and static analysis of a soft actuator considering nonlinear effects. Fluidic channels embedded within a soft beam are considered a soft robotic actuator, exhibiting nonlinear characteristics due to the inherent properties of the soft material. The analytical process is based on Hamilton's principle, and the numerical solution has been carried out using the finite element software ANSYS, utilizing the Fluid-Structure Interaction (FSI) and Pre-stress Modal tools. Initially, time-dependent inlet pressure is applied, and the resulting pressure distribution within the soft fluidic actuator (SFA) is extracted over the time domain. Following the validation of results obtained from finite element software and analytical methods, the feasibility of using this actuator as an artificial muscle in a robotic fish has been examined, leveraging the phenomenon of resonance and analyzing its behavior under real-world conditions. The findings indicate that utilizing this type of actuator in the robotic fish's tail enables functional similarity to a real fish after 8 seconds. However, by applying the proposed method and tuning the operating frequency closer to the system’s natural frequency, the robot can immediately exhibit movements resembling those of a biological fish.

Abstract Given the inherent susceptibility of laminated composites to delamination damage, numerous strategies have been introduced in recent years to enhance delamination resistance. One emerging approach is the use of 3D-printed interlayers; however, despite promising results in enhancing delamination resistance, the effect of interlayer cellular architecture on mode II interlaminar fracture toughness (ILFT) has not yet been investigated. Accordingly, this study designed an interlayer composed of PVA filament, with a thickness of 0.4 mm and a hexagonal cellular architecture. Also, to comparatively evaluate the effectiveness of the interlayer cellular architecture, the results were compared with those of the authors’ previous study, and the effect of replacing the square geometry with the hexagonal geometry was assessed while maintaining the materials and design parameters constant. The results demonstrated that the hexagonal interlayer increased the maximum load-bearing capacity by 25% and 34% compared with the control specimen and the square structure, respectively. Moreover, based on the compliance calibration method, the initiation and propagation values of ILFT (G_IIC^(ini.) and G_IIC^(prop.)) increased by 164% and 88%, respectively. Meanwhile, the G_IIC^(ini.) and G_IIC^(prop.) improved by 160% and 17%, respectively, compared with those of the square structure, indicating the superiority of the hexagonal geometry in controlling the propagation of delamination damage. Fractographic analysis further revealed that crack deflection and pinning, together with the deformation and breakage of the PVA filaments, altered the failure pattern and enhanced delamination resistance. Overall, the findings underscore the decisive role of the cellular architecture of 3D-printed interlayers in the interlaminar performance of composites.