https://ajme.aut.ac.ir/ AUT Journal of Mechanical Engineering en daily 1 Thu, 01 Oct 2026 00:00:00 +0330 Thu, 01 Oct 2026 00:00:00 +0330 https://ajme.aut.ac.ir/article_6032.html The study explores the behaviour of systems under both free and forced vibrations of spherical sandwich panels supported by an elastic foundation exposed to various impact load profiles. The panels consist of multilayer composite face sheets formulated based on the first-order shear deformation theory, and a soft core characterized by a higher-order theory employing third-order in-plane and second-order transverse displacement fields. By calculating the mechanical energy components, and introducing a higher-order element with nine nodes and 15 degrees of freedom for each node, the element stiffness and mass matrices were determined. Boundary conditions are simulated through distributed virtual springs. A free vibration problem is evaluated to extract the structure’s natural frequencies and mode shapes. Using the Newmark method, time response of displacement, velocity, acceleration, and phase planes are calculated for various impact profiles, specifically for half-sine pulses. This comprehensive analysis of sandwich panels' dynamic response under various impact loads reveals that the load profile critically determines structural behavior, essentially governing the boundary between safe operation and potential failure. For example, sudden loads like rectangular pulse emerged as the most critical case, causing extreme discontinuous responses across all dynamic parameters, and gradual loads (Gaussian/exponential) proved optimal for sensitive applications by generating smooth, controlled structural responses and providing ideal performance for stability-critical systems. https://ajme.aut.ac.ir/article_6036.html This article proposes architectural strategies and comfort conditions for designing nearly zero-energy buildings (NZEBs) across different climatic regions of Iran, based on the Köppen-Geiger classification method and passive design techniques. According to the Köppen-Geiger climate classification, Iran's climate is divided into nine zones. The primary climatic zones considered in this study include Bwh, Bwk, Bsk, Bsh, Csa, Cfa, Csb, Dsa, and Dsb. The impact of climatic conditions on the design of nearly zero-energy buildings was analyzed using the Köppen-Geiger method. the selected cities within the mentioned climate zones were analyzed by the Climate Consultant software (CCS) in EPW format, utilizing the ASHRAE Standard 55 and also PMV (Predicted Mean Vote) comfort model. By inputting weather data from selected cities into CCS, output results including comfort conditions, natural ventilation, cooling, heating, and other parameters across the nine climatic zones were obtained. Additionally, during designing NZEBs, passive architectural parameters such as window shading, passive solar radiation, and internal heat generation in these nine climate zones were examined. The results showed that the BWh climate (Yazd) provides the highest thermal comfort at 19.7%, while the CFa climate (Anzali) provides the lowest thermal comfort at 3.6%. In the BWh climate, window shading, evaporative cooling, and internal heat gain have better conditions for comfort compared to other climates, with percentages of 16.8%, 25.8%, and 22.5%, respectively. https://ajme.aut.ac.ir/article_6046.html This research aims to investigate the external aerodynamics of the IKCO-DENA+ car, which leads to the annoying sound inside the cabin. In this research, the sources of aerodynamic noises were identified using wind tunnel tests on a 2/5 scaled model. Smoke flow visualization of the flow around the car for finding out aerodynamic characteristics and noise sources has been conducted. The results obtained from visualization showed that six different factors can be considered as a source of noises, including 1.the distance between the side mirror and the body, 2. the aerodynamic form of the side mirror, 3. the rear passenger quarter window, 4. the shark antenna, 5. car handles, and 6. indentation design feature on the rear door of the car. Then, within the next steps, the surface modification solutions regarding the identified noise sources were tested. In addition, Measurements using hot wire anemometry and pressure sensors were performed at different velocities of 18, 36, 54, 72, 90, 108 and 118.8 km/h. The results showed that surface modification related to quarter window led to a reduction of the flow disturbances and the aeronoise level on the car’s rear door glass significantly. Furthermore, modifying the side mirror of the car has considerably improved the aerodynamic behavior within the area of the front door glass. Consequently, these two modifications reduced pressure disturbances by 9% and 5%, respectively. https://ajme.aut.ac.ir/article_6048.html For many years, biodiesel has been seen as an alternative fuel with the ability to eventually replace diesel. Products that are emitted when engines undergo a complete combustion reaction provide no direct health risks to humans. Due to certain fuel characteristics, biodiesel performs poorer during combustion process than diesel fuel. As a result, smoke emissions, complete combustion products like CO2, and incomplete combustion products including HCs, CO, and NOX are released into surrounding. An attempt has been made to enhance combustion and emission performance of CRDi-VCR type diesel engine using B20 neem biodiesel with a novel nanoparticle mixture of Al2O3 and ZnO as nano fuel additives for various dosing levels. B20 Neem biodiesel with nano additives was tested on a CRDi-VCR type diesel engine at a constant speed of 1500 rpm at various loads. Due to higher oxidation rate of hydrocarbon molecules, the nano additive reduced CO emissions in studies while improving the thermal conductivity, mass dissipation, and heat transfer of the tested nano fuels. Due to the improvement in the combustion reaction, CO2 emission increased with product of complete combustion. Brake specific fuel consumption was reduced at full load condition with the addition of 25 ppm NPs. Also, neem biodiesel fuel results in appreciably improved brake thermal efficiency, lower values of smoke opacity, and lower CO, NOX and HC emissions. https://ajme.aut.ac.ir/article_6055.html In this study, the convective transport of a temperature-dependent magneto-micropolar fluid over a stretching surface embedded in a porous medium is examined. The formulation accounts for viscous dissipation, internal heat generation or absorption, and radiative heat transfer modeled through the Rosseland diffusion approximation, which is appropriate for optically thick media. The governing equations, developed without the use of similarity transformations, are solved using the Optimal Homotopy Analysis Method (OHAM). The resulting velocity, microrotation, and temperature fields are illustrated through graphical and tabulated data across a broad range of physical parameters. Validation against existing literature demonstrates the reliability of the present approach. Quantitative analysis shows that the microrotation boundary layer decreases by approximately 18–25% with increasing micropolar parameter, while thermal boundary layer thickness increases by about 10–14% under stronger radiative effects. Moreover, micropolar fluids exhibit a thinner momentum boundary layer compared to Newtonian fluids under identical conditions. Specifically, the Newtonian case yields a thinner layer relative to the micropolar case . Overall, the results provide valuable insights into micropolar fluid behavior with practical implications in porous and radiative flow systems. https://ajme.aut.ac.ir/article_6066.html This study evaluates the sensitivity of modal parameters to incomplete adhesion in single-lap adhesive joints by comparing the vibrational behavior of fully bonded joints and joints with a macroscopic partial bond (≈50% loss of bonded area in the overlap). Beyond prior studies on crack-like or delamination-type defects, often using intrusive or destructive inspections, the present work targets a practically relevant macroscopic manufacturing flaw within a fully non-destructive modal testing framework. An integrated experimental–numerical approach is employed: aluminum 7075-T6 beams bonded with epoxy 828 are tested using impact-hammer excitation and laser Doppler vibrometer, and responses are processed in MATLAB and MEscope to extract natural frequencies and damping ratios. A three-dimensional finite element model in Abaqus/CAE is refined via limited experimental calibration. Results show 3–15% reductions in the first eight bending natural frequencies of defective joints relative to intact ones, with stronger effects in higher modes due to dominant stiffness loss over minor mass reduction. The damping ratio increases about sevenfold (0.0032 to 0.0236) in the defective specimen, attributed to frictional dissipation at the unbonded interface and contact nonlinearities supported by mode-shape analysis. These quantified shifts in frequency and damping establish modal parameters as reliable, non-destructive indicators of incomplete adhesion in single-lap joints and provide a basis for vibration-based structural health monitoring and defect detection in adhesively bonded components in aerospace, automotive, and multi-material structures. https://ajme.aut.ac.ir/article_6156.html This study investigated the reinforcing effect of aluminum oxide and titanium dioxide nanoparticles, used individually and as hybrid fillers, on the mechanical performance of natural rubber/styrene–butadiene rubber vulcanizates reinforced with carbon black. The composites were fabricated by conventional compounding and compression molding following ASTM standards. Mechanical performance was evaluated through tensile strength, compression set, hardness, and scanning electron microscopy. A total of 100 specimens were prepared and classified into two groups according to nanoparticle loading. The results demonstrated that hybrid incorporation of aluminum oxide and titanium dioxide nanoparticles produced superior reinforcement compared with the use of titanium dioxide alone. The optimum formulation, containing 10 parts per hundred rubber of aluminum oxide and 8 parts per hundred rubber of titanium dioxide, achieved the highest tensile strength of 27.93 ± 0.71 MPa and the maximum hardness of 72 ± 5 International Rubber Hardness Degrees. The lowest compression set (19.65 ± 1.60%) was obtained with titanium dioxide alone, whereas the hybrid system maintained a low compression set (24.66 ± 1.30%) while simultaneously providing substantial improvements in tensile strength and hardness. Scanning electron microscopy revealed a uniform nanoparticle distribution with limited agglomeration and good interfacial adhesion, explaining the enhanced mechanical behavior. These findings demonstrate that hybrid aluminum oxide–titanium dioxide nanoparticles are effective reinforcing fillers for high-performance rubber composites. https://ajme.aut.ac.ir/article_6045.html Additive manufacturing of biopolymer composites is rapidly advancing biomedical engineering. By combining synthetic polymers with natural biopolymers, inorganic ceramics, nanomaterials, and bioactive molecules, AM enables patient-specific constructs with high geometric precision and tunable biological performance. These materials support applications across hard and soft tissues, including bone regeneration, cartilage repair, wound healing, vascular grafts, and cancer modeling. Despite this progress, major barriers remain: mechanical-degradation mismatches, limited vascularization in thick constructs, photoinitiator-related cytotoxicity, and inter-laboratory variability that reduces reproducibility and slows clinical translation in real-world settings. Broader adoption is further constrained by the lack of standardized protocols and clear regulatory pathways. We compare AM modalities (extrusion, vat photopolymerization, and powder-bed processes) through a cost-benefit lens, outlining when each optimally balances resolution, throughput, sterility, and cell compatibility. To address these gaps, recent work (2020–2025) is shifting the field from static scaffolds toward adaptive, intelligent, and sustainable platforms, leveraging 4D printing, nanotechnology-enabled reinforcement and bioactivity, AI-driven design optimization, and greener feedstocks such as sustainable biopolymers. Notably, 2025 reports on multi-material bioprinting for neural tissues show improved print fidelity and bioactivity, enabling more realistic microvascular networks and neural interfaces. By synthesizing these advances and critically evaluating current limitations, this review proposes strategic directions for AM to mature into a clinically relevant, globally sustainable manufacturing approach. Biopolymer composites are not incremental upgrades; they are pivotal enablers of next-generation regenerative medicine. https://ajme.aut.ac.ir/article_6157.html This study presents the modeling, simulation, and control of a novel Micro Single-Rotor UAV (MSRUAV) with an onboard FPV camera for real-time video transmission. The proposed design addresses the high manufacturing costs and mechanical complexity of conventional multirotors by employing a single brushless motor and four servo‑actuated fins for attitude/position control. A comprehensive six‑DoF flight dynamics model is developed, incorporating translational and rotational equations of motion and aerodynamic drag. A cascaded PID‑P‑PI architecture serves as the baseline controller. To enhance disturbance rejection under turbulent wind conditions, a Fuzzy Inference System (FIS) is integrated into the position loop for the real‑time gain scheduling based on error and derivative. Numerical simulations are conducted under indoor (no wind) and outdoor (turbulent) environments, utilizing step and helical trajectory references. Indoor results show that the FIS‑enhanced controller achieves 14.2% lower RMSE and faster settling than the conventional cascaded controller. Under outdoor conditions with 5‑knot mean winds, the FIS controller demonstrates superior vertical tracking while the conventional controller exhibits better horizontal disturbance rejection. Monte Carlo simulations with 200 random wind conditions confirm the improved robustness of the FIS‑cascaded controller, maintaining stable trajectory tracking up to mean wind speeds of approximately 11.6 knots. Overall, the findings indicate that fuzzy‑enhanced control offers an effective and practical solution for improving MSRUAV position control under environmental perturbations, suitable for cost‑sensitive surveillance, inspection, and emergency response. https://ajme.aut.ac.ir/article_6167.html Although the one-dimensional continuous wavelet transform (1D-CWT) often suffers from redundant scales when applied to structural damage detection, it remains a valuable tool due to its flexibility in selecting optimal wavelet functions for improved accuracy. This paper investigates the capability of the 1D-CWT to accurately identify the most effective wavelet scales tailored for damage detection in laminated composite curved beams, a complex structural element widely used in aerospace and civil engineering. The finite element method (FEM) is utilized to obtain detailed mode shapes of these curved beams, providing representative input signals for wavelet transform analysis. To address the challenge of redundant scales, we propose employing the standard deviation of wavelet coefficients as a sensitive and robust index to pinpoint scales that most effectively highlight damage-induced changes. This quantitative metric enables a systematic selection of optimal scales, improving detection performance. Comprehensive numerical simulations complemented by experimental validations confirm that this approach significantly enhances damage localization accuracy. Overall, the results demonstrate that incorporating the standard deviation criterion into the 1D-CWT framework enhances its practicality and reliability, thereby positioning it as a powerful tool for structural health monitoring of laminated composite curved beams. https://ajme.aut.ac.ir/article_6168.html Carbon fiber-reinforced polymer (CFRP) composites are extensively used in aerospace, automotive, and marine structures due to their high stiffness-to-weight ratio; however, their dynamic performance is highly sensitive to delamination damage and laminate configuration. Recent advances in nanotechnology indicate that carbon nanotube (CNT) reinforcement can significantly enhance matrix-dominated properties and improve damage tolerance. This study investigates the vibration behavior of delaminated CNT-reinforced CFRP composite plates by examining the combined effects of CNT content, delamination size, stacking sequence, and boundary conditions. Natural frequencies and mode shapes are predicted using finite element modeling in ANSYS and an analytical Rayleigh–Ritz formulation implemented in MATLAB. Experimental modal testing is also conducted to validate the numerical and analytical results. Cross-ply, angle-ply, and quasi-isotropic laminates with CNT weight fractions of 0%, 0.5%, and 1.0% are analyzed under simply supported, clamped–clamped, and free–free boundary conditions. The results demonstrate that CNT reinforcement significantly increases natural frequencies and mitigates stiffness degradation induced by delamination, with quasi-isotropic laminates showing the highest sensitivity to CNT enhancement. For all configurations, natural frequencies decrease monotonically with increasing delamination size, while clamped boundary conditions consistently yield the highest frequency values. Excellent agreement is observed among finite element, analytical, and experimental outcomes. These findings provide valuable insights for vibration-based design and damage-tolerant optimization of CNT-enhanced composite structures in advanced engineering applications. https://ajme.aut.ac.ir/article_6170.html Metal Additive Manufacturing (MAM) has emerged as an advanced manufacturing technology capable of producing complex geometries with high material utilization, design flexibility, and reduced manufacturing waste. The increasing industrial adoption of MAM in aerospace, automotive, biomedical, and energy sectors has accelerated research on process optimization, material performance, and defect mitigation. This review critically examines major metal additive manufacturing processes, including Powder Bed Fusion (PBF), Directed Energy Deposition (DED), Wire Arc Additive Manufacturing (WAAM), and Binder Jetting, with emphasis on their process mechanisms, material characteristics, and industrial applications. Despite substantial advancements in process development and industrial implementation, several technical challenges like residual stresses, porosity, cracking, anisotropy, distortion, and surface irregularities arise which are systematically discussed along with their formation mechanisms and mitigation strategies. This review critically examines major metal additive manufacturing processes with emphasis on residual stress development, defect formation mechanisms, material behaviour, and process–microstructure–property relationships. The review further discusses commonly used metallic materials including titanium alloys, stainless steels, aluminum alloys, nickel-based superalloys, cobalt-chromium alloys, and metal matrix composites. In addition, industrial applications, advantages, limitations, post-processing techniques, and defect mitigation strategies associated with metal additive manufacturing are comprehensively reviewed. Recent developments in intelligent manufacturing, in-situ monitoring, process optimization, and data-driven manufacturing approaches are also discussed to highlight future research opportunities and technological advancements in metal additive manufacturing. https://ajme.aut.ac.ir/article_6212.html Aircraft warning spheres are installed on overhead power transmission lines to improve conductor visibility for low-flying aircraft and helicopters, thereby reducing the risk of aerial collisions. Conventional installation and replacement operations are generally carried out using helicopters, cranes, or scheduled transmission-line outages, resulting in high operational costs, increased safety risks, and interruptions to power delivery. To address these limitations, this study presents the design, development, and experimental validation of a mobile robotic platform capable of autonomously installing and removing aircraft warning spheres while travelling directly on overhead transmission-line conductors. The proposed robot combines a compact conductor-traversing mechanism with a dedicated quick-release clamping device and a suspended capsule-shaped battery module that improves stability under inclined operating conditions and wind-induced disturbances. Mechanical analyses were conducted to determine the required characteristics of the clamping system, and numerical simulations were performed to evaluate the robot's mobility, stability, and mechanical performance. The results demonstrated that the robot could reliably travel along the conductor, transport the warning sphere to the target location, complete the installation process, and safely return to its initial position. The experimental results agreed well with the numerical predictions, confirming the effectiveness of the proposed mechanical design and its practical applicability. The proposed robotic platform provides a safer, more efficient, and cost-effective alternative to conventional maintenance methods while reducing operator exposure to hazardous high-voltage working environments. https://ajme.aut.ac.ir/article_6213.html This study investigates the effect of alkali-treated abaca fiber (Musa textilis Née) mass fraction (10 wt.%, 15 wt.%, and 20 wt.%) on the mechanical response and fracture morphology of unsaturated polyester composites fabricated via compression molding, compared against an untreated 20 wt.% abaca fiber composite as the control. Composite specimens were characterized according to ASTM D638 and ASTM D6110 standards, complemented by Scanning Electron Microscopy (SEM) analysis. Results demonstrated a progressive enhancement in tensile strength with increasing treated fiber fraction, rising from 10.90 ± 1.17 MPa for the untreated 20 wt.% control to 23.90 ± 2.90 MPa for the 20 wt.% alkali-treated composite, representing a 119.3% improvement attributable to surface modification. Young's modulus similarly increased from 188.98 ± 25.64 MPa (control) to 286.85 ± 13.36 MPa (20 wt.% treated). Impact energy absorption and toughness reached maximum values of 15.48 ± 2.72 J and 0.1190 ± 0.0200 J/mm² at 20 wt.% treated fiber loading, corresponding to improvements of 96.9% and 92.0% over the untreated control, respectively. SEM analysis confirmed that the 20 wt.% treated composite exhibited optimized interfacial bonding, characterized by minimal void content and a predominance of fiber fracture over pull-out, whereas the untreated control displayed dominant fiber pull-out due to weak interfacial adhesion caused by natural impurities. Alkali treatment combined with 20 wt.% fiber loading is identified as the configuration for lightweight structural applications. https://ajme.aut.ac.ir/article_6220.html In this study, the production process for lithium-based Grease using treated waste engine oil as the base oil was investigated. Waste engine oil was collected and purified by settling, filtration, thermal dewatering, acid treatment, neutralization, and post-treatment filtration to ensure suitability for grease production. Grease compositions were developed using Minitab’s Extreme Vertex Mix Design software, varying the proportions of treated engine oil, lithium hydroxide (LiOH), Graphite, and calcium carbonate. Fourteen formulations were prepared, and samples were tested according to ASTM standards for dropping point, oil separation, evaporation loss, and copper corrosion resistance. The best formulation was determined to be 81.66% treated base Oil, 11.67% LiOH, and 6.67% additives, which delivered superior thermal performance. Findings revealed that LiOH content was directly correlated with thermal stability, and that both LiOH and the additive contributed to reduced oil separation and evaporation loss. Mixing temperature also affected stability, with 160°C yielding better structural integrity than 200°C. All samples maintained low evaporation loss across temperature variations. The study demonstrates that recycled waste engine oil can serve as a reliable, cost-effective, and environmentally friendly raw material for grease production, contributing to circular economy goals and offering a viable solution for industrial-scale manufacturing. https://ajme.aut.ac.ir/article_6229.html Fused Deposition Modeling (FDM) inherently induces inter-raster voids, which act as stress concentrators and significantly compromise the mechanical and dynamic integrity of printed components. This research presents a novel hybrid framework that integrates semi-empirical characterization with analytical modeling to quantify porosity and predict its effect on the vibrational behavior of Polylactic Acid (PLA) beams. Moving beyond simplified circular approximations, a data-driven geometric model employing the Superellipse function was developed to map the actual void morphology based on Scanning Electron Microscopy (SEM) and G-code toolpaths. These quantitative porosity estimates were subsequently incorporated into a stiffness-reduction constitutive model within the context of Classical Laminate Theory (CLT). Experimental validation, utilizing Digital Image Correlation (DIC) and modal analysis, confirmed the model's accuracy (porosity range: 1.3%–1.9%). Crucially, the findings reveal a direction-dependent frequency response: while the 0° raster angle maintains relative frequency stability due to a balanced reduction in mass and stiffness, the 90° raster angle exhibits a disproportionate stiffness decay, resulting in a precipitous drop in natural frequencies (up to 27%). This study establishes porosity not merely as a defect, but as a critical design parameter for predicting the dynamic performance of FDM structures.