Volume 68, Issue 3

Ti- x ZrO 2 (x: 10 and 20, wt.%) composites are produced at high density (98.2 %) by spark plasma sintering (SPS), and the corrosion and wear resistance of each composite is examined according to the change in the amount of reinforcement. SPS process under the sintering conditions is achieved at a sintering temperature of 1,000 °C for 10 min under a pressure of 30 MPa. Microstructural characterization reveals out that ZrO 2 particles as the secondary phase are homogeneously distributed in the metallic matrix and no new phase is formed between metal (Ti) and ceramic based materials (ZrO 2 ). Mechanical test findings indicate that a reinforcement level of 20 wt.% ZrO 2 reaches its highest value (933 HV) among the materials studied. Potentiodynamic measurements reveal that the corrosion resistance of the composites increases due to the increasing amount of ZrO 2 in their interaction with the Ringer’s solution. Also, it is determined that as ceramic reinforcement increases, microhardness increases, and not only the coefficient of friction but also the wear rate decreases during tribological interaction with the 20 wt.% ZrO 2 particles counterpart material under dry friction conditions.

Side door support beams are widely used to protect against side impacts, which are among the most critical threats to the safety of vehicle passengers. This study aimed to evaluate the crashworthiness of side door beams under Euro NCAP side pole impact conditions, considering three materials (aluminum alloy 6061-T6, aluminum alloy 5083-H116, A36 steel), three thicknesses (1.5, 2.0, 2.5 mm), and four beam angles (0°, 15°, 22.5°, 30°). Key crashworthiness parameters, including absorbed energy, specific energy absorption (SEA), reaction force, deformation characteristics, and velocity absorption time (VAT), were assessed. The results showed that the model designed with aluminum alloy 5083-H116, 15° beam angle, and 1.5 mm thickness achieved the highest SEA of 2.0043 kJ kg −1 , while the model defined with A36 steel, 0° beam angle, and 1.5 mm thickness achieved the maximum absorbed energy of 779.69 J. The reaction forces varied significantly between 20.6 kN (aluminum alloy 5083-H116, 0° beam angle, 1.5 mm thickness) and 30.5 kN (aluminum alloy 6061-T6, 30° beam angle, 2.5 mm thickness). Overall, the findings suggest that aluminum alloys, particularly aluminum alloy 5083-H116, are advantageous for lightweight crash-absorbing structures, while thickness optimization is necessary for balancing occupant protection and structural durability.

This study examined the effects of hydrogen-related degradation on the static and dynamic fatigue strength of high-strength bolts for propulsion motors during electro-galvanization. Two-bolt types were prepared with different baking treatments: B 0h (no baking) and B 8h (baking at 200 °C for 8 h). Baking did not significantly affect the mechanical strength ( p  < 0.01) but did increase the elongation of B 8h by 25.3 %. In high-cycle fatigue tests, B 8h exhibited a fatigue life of up to 6.3 times longer than that of B 0h . These results indicate that baking effectively mitigates hydrogen-related degradation and enhances the high-cycle fatigue life, ductility, and toughness of electro-galvanized 42CrMo4 steel bolts.

In tilt-up construction, cable and pulley systems (riggings) are used to lift precast panels from horizontal to vertical positions. Accurate prediction of cable tensions is essential for structural integrity and operational safety. This study develops a generalized nonlinear system of equations to model diverse rigging configurations for tilt-up erection. A dynamic analysis is included to evaluate the influence of crane hook velocity on cable tension. The equations are solved using MATLAB’s symbolic “solve” function, and a dynamic factor is introduced to quantify inertial contributions across operational scenarios. Validation was performed through simulations in Working Model software. Results show that the dynamic factor significantly affects cable tensions at moderate to high lifting velocities, particularly beyond 75° of rotation, while at lower velocities it increases static tensions by 1.33–1.59 times depending on panel height. To mitigate overload risks, the effect of hook inclination was analyzed, identifying a safe range between 85° and 95°. The formulation accommodates both aligned and misaligned inserts, covering multiple rigging layouts with 1–8 rows and 1–8 columns. This approach provides a foundation for more advanced computational tools, enhancing accuracy and safety in tilt-up panel erection.

In this study, a commercially extruded CuNiSiCr alloy was subjected to a solution treatment at 900 °C for 60 min, followed by rapid cooling using conventional water quenching and cryogenic cooling methods. The samples were then aged at 450 °C for 0–240 min. Metallurgical analyses revealed the presence of Ni/Cr-rich metal silicides within the α-Cu matrix, and it was determined that Cr-rich precipitates did not fully dissolve during the solution treatment due to their high-temperature stability. Electrical conductivity measurements showed a decrease in conductivity values after quenching in the supersaturated matrix, but significant increases in conductivity were observed with aging time. Cryogenic cooling accelerated the precipitation kinetics, enabling the attainment of higher conductivity (24.09 MS m −1 ) and hardness (247 HV) values in a shorter time. Using the Avrami kinetic model, precipitation volume fractions and phase transformation rates were calculated, confirming that cryogenic cooling accelerates the aging process. The findings demonstrate that cryogenic cooling combined with appropriate aging optimizes the microstructure and phase distribution of the CuNiSiCr alloy, improving key properties such as electrical conductivity and mechanical hardness, thereby providing superior performance for commercial applications.

With the growing adoption of commercial off-the-shelf (COTS) components in aerospace applications, the spontaneous growth of tin whiskers from pure tin coatings has emerged as a critical reliability issue. These whiskers, formed as stress-driven, typically single-crystalline structures, are prone to inducing short circuits and electrical discharges in typical space-relevant environments such as thermal vacuum conditions. This study investigates whisker growth behavior in representative COTS components soldered onto printed circuit boards, subjected to both thermal vacuum cycling and air ambient thermal cycling. The experimental results demonstrate that whisker formation was observed in all tested package types under both conditions. 0603-packaged multilayer ceramic capacitors were particularly susceptible, while whiskers tended to emerge at the bent leads of SOP and TO-packaged devices. Under thermal vacuum, ceramic capacitors exhibited significantly longer whiskers, suggesting that the suppression capability of the nickel barrier layer may be limited under such environments. Comprehensive analysis indicates that the primary driving forces for whisker growth include cyclic thermal stresses caused by mismatched thermal expansion coefficients between the coating and substrate, along with localized stress concentrations arising from grain orientation differences. The influence of intermetallic compound (IMC) layers was relatively minor. Additionally, thinner oxide films formed under vacuum conditions promote more rapid whisker growth.

The mechanical properties of AlSi10Mg alloy fabricated by laser powder bed fusion (LPBF) were investigated under different strain rates and post-processing conditions, including shot peening (SP) and stress relief (SR). Tensile tests were performed at quasistatic (0.1 s −1 ) and dynamic (0.015 s −1 ) strain rates on as-built and post-processed specimens. The results revealed that SP significantly increased the yield strength by 7.10 %, reaching 249.59 MPa, due to the induced compressive residual stresses. However, while SP slightly improved the ultimate tensile strength (UTS) by 0.25 %, it also reduced elongation at break by 18.06 %, indicating a trade-off between strength and ductility. Conversely, SR improved ductility by reducing internal stresses, leading to an elongation at break increase of 574.01 %, with a slight reduction in yield strength. The combination of SP and SR exhibited a synergistic effect, achieving a balance between strength and ductility. Strain rate sensitivity (SRS) analysis indicated that stress-relieved specimens performed better under dynamic loading conditions. These findings highlight the potential of post-processing techniques in tailoring the mechanical behavior of LPBF-produced AlSi10Mg alloys. The balanced properties achieved through combined treatments make this material particularly suitable for high-performance aerospace and automotive applications, where strength and ductility are critical under varying operational conditions.

In this study, the repair of AISI 304 stainless steel was performed using wire arc additive manufacturing (WAAM), and its effects on microstructure, hardness, and wear behavior were investigated. Five samples were fabricated using either plain 304 stainless steel wire or filler wires containing different WC and FeCrC particle ratios. Microstructure characterization using OM, SEM, EDS, and XRD revealed that WC additions led to grain refinement and increased carbide formation. Particularly in the 50WC sample, fine and uniformly distributed carbides contributed to an increase in both hardness and wear resistance. XRD results supported the formation of hard carbide phases such as Fe–Cr–C and Fe–W–C, in agreement with microstructural analyses. Microhardness tests showed the highest value (∼700 HV 0.1 ) in the 50WC sample, while the lowest was observed in the plain 304 wire and substrate. Ball-on-disc wear tests revealed that WC-containing samples had the lowest specific wear rates, primarily due to the presence of hard and homogeneously distributed carbide phases that enhanced surface hardness and wear resistance. The findings demonstrate that particle-filled wire reinforcements in WAAM significantly enhance mechanical and tribological performance in repaired stainless steel components.

Optimizing structural systems for multiple natural frequencies is a significant challenge due to the high nonlinearity and sensitivity of these problems to configuration changes. As traditional search algorithms often struggle, this study employs a Bayesian-reinforced search algorithm to address these complexities. The highly nonconvex nature of the search space for these problems also makes constraint handling crucial for effective performance. To this end, a new constraint handling approach was developed using the fly-back mechanism integrated with a quadratic search technique. The developed strategy is integrated with interactive search algorithm. The search capability of the proposed integrated method was evaluated on a suite of structural optimization problems, including planar, spatial, and dome structures. The numerical results demonstrate that the developed approach significantly reduces the required computational cost while yielding promising results in terms of solution accuracy and process stability.

Functionally Graded Materials (FGMs) improve fatigue resistance in leaf springs subjected to cyclic loading by optimizing the distribution of material properties throughout the component, thus enhancing both performance and durability. These materials feature a gradual variation in composition and structure, enabling customized mechanical properties that better resist the stresses and strains encountered during repeated loading cycles. This study focuses on the design of a monoleaf spring composed of an FGM composite that combines carbon fiber–reinforced polymer with 50R steel, analyzed using finite element analysis (FEA). The investigation examines the spatial distribution of von Mises stress and strain energy across the thickness of the functionally graded monoleaf spring. Three different grading functions are employed: a straightforward power-law function (P-FGM), a modified symmetric power-law function (S–P-FGM), and a Sigmoid function (S-FGM). The parameter k in the power-law functions was varied (0.2, 0.5, 1, 2, 5 and 10) to understand its influence on stress distribution and strain energy. Results indicate that the spring’s performance improves with increasing k , with the highest value, k  = 10, yielding the greatest strain energy storage capacity, making it ideal for applications demanding high energy absorption and resilience. Additionally, at k  = 10, the FGM exhibits the highest margin of safety (MOS), reflecting superior strength and reliability. Among the functions tested, P-FGM and S–P-FGM provide the best results in terms of margin of safety and strain energy, while the S-FGM function performs the least effectively. Ultimately, the optimal design for a monoleaf spring is an FGM composite of carbon fiber–reinforced polymer and 50R steel with a power exponent k  = 10, offering excellent strain energy capacity, strength, and safety margin, thereby significantly enhancing spring performance.

Concrete applications in heat piles (used in ground source heating systems) and nuclear waste repositories present unique challenges due to the thermal loads imposed on the concrete. These loads significantly affect the mechanical properties and long-term performance of the concrete, ultimately influencing the efficiency of heat piles and the safety of nuclear waste storage. This study investigated the fracture toughness (KIC) and cohesive fracture properties of concrete made with environmentally sustainable cement under high-temperature loading. The fracture toughness (FT) test results showed that FT values decreased by 27.8 % for specimens with a notch crack inclination angle of β  = 0°, and by 31.6 % for specimens with β  = 30° at 500 °C loading. SEM and 3D image processing analyses revealed a clear exponential relationship with increasing temperature. Microcracks became more extensive and interconnected, forming a network throughout the cement paste at 500 °C. These microcracks initially developed in the interfacial transition zone (ITZ), with significant debonding of the aggregate from the cement paste observed, leading to an overall reduction in ITZ strength. Cohesive zone model (CZM) analysis using NLQ elements with FRANC2D showed that the highest traction opening and traction sliding occurred in the β  = 0° specimens at 500 °C loading.

This study investigates the mechanical performance of AA5182 aluminum alloy joints produced using resistance spot welding (RSW), adhesive bonding, and hybrid RSW–adhesive techniques. The joining processes were carried out under controlled and automated conditions, with adhesive layers applied at six different thicknesses ranging from 0.50 to 1.25 mm. Tensile T-peel tests were employed to evaluate joint strength and quality. The results revealed that spot-welded joints exhibited the lowest peel strength (220.5 N), mainly due to localized stress concentration at the weld nugget. Adhesive joints demonstrated a progressive increase in strength with thickness, reaching a maximum of 327.2 N at 1.25 mm. The highest performance was observed in hybrid joints, which combined the mechanical interlocking of spot welds with the load distribution of adhesives. The maximum load in hybrid joints reached 616.7 N, corresponding to an improvement of approximately 180 % compared to spot welding and 88 % compared to adhesive bonding alone. Fractographic analyses indicated brittle fracture at weld nuggets, mixed cohesive/adhesive failure in bonded joints, and combined fracture mechanisms in hybrid joints. These findings confirm that hybrid joining provides superior mechanical behavior and represents a promising solution for lightweight structural applications in the automotive and aerospace industries.

Friction stir welding (FSW) provides an effective solution for joining dissimilar aluminum alloys like AA5083 and AA6061-T6, which are prone to issues like porosity and cracking when welded using conventional fusion methods. This study investigates the use of real-time acoustic emission (AE) monitoring to evaluate weld quality and detect defects such as piping and pinholes during the FSW process. Key AE parameters, including RMS, Hits, Amplitude, Counts, and AE Fast Fourier Transform (FFT) spectra, were examined alongside waveform characteristics. Mechanical testing revealed that defect-free joints achieved a tensile strength of 256 MPa and 82 % joint efficiency, whereas the presence of piping and pinhole defects lowered the strength to 235 MPa and 201 MPa, respectively. Microstructural analysis confirmed the formation of finer grains and higher hardness (93 Hv) in the stir zone of defect-free welds. AE Parametric monitoring showed marked increases in signal intensity in defective welds, especially those with pipping and pinhole defects, validating its potential for defect identification. Shifts in AE FFT spectra peak amplitude frequencies and distinct burst-type waveforms further demonstrated the capability of AE analysis to characterize weld conditions. These findings highlight the effectiveness of AE techniques as a nondestructive, real-time tool for monitoring weld integrity in industrial applications.

This study investigates the comparative performance of four different supervised machine learning algorithms for the prediction of maximum thrust force F z max during the drilling process of aluminum 5083 H111 alloy. Accurate prediction of the forces generated during drilling operations is of great importance for extending tool life, increasing hole quality and improving production efficiency. In this direction, a total of 27 experimental conditions were created including three different cutting speeds (80, 100, 120 m min −1 ), three different feed rates (0.06, 0.09, 0.12 mm tooth −1 ) and three different cooling strategies (dry, air, liquid) and the maximum thrust force was measured for each condition. Artificial neural networks (ANN), decision trees (DT), random forest (RF) and extreme gradient boosting (XGBoost) algorithms were trained with the obtained data set and evaluated by MAE, RMSE and R 2 performance metrics. The findings revealed that the XGBoost algorithm achieved the lowest error rates (MAE: 56.742 N, RMSE: 67.179 N) and the highest explanatory power ( R 2 : 0.929) compared to other models. These results show that ensemble-based methods can be used as reliable and effective estimation tools in production processes.

This study investigates the mechanical and wear behavior of sisal fiber reinforced polyester composites containing 5 wt.% calcium carbonate (SFCC) and 5 wt.% kaolin (SFKL) fillers. Composites were fabricated via hand lay-up with 30 wt.% alkali-treated sisal fibers. Mechanical testing revealed that SFCC exhibited a tensile strength of 118 MPa, a flexural strength of 165 MPa, an impact strength of 9.8 kJ m −2 , and a Rockwell hardness of 92 HRM, whereas SFKL showed superior performance with a tensile strength of 124 MPa, a flexural strength of 172 MPa, an impact strength of 10.4 kJ m −2 , and a hardness of 94 HRM. Wear tests using a pin-on-disk tribometer under varying load, sliding distance, and velocity, analyzed via Taguchi L9 orthogonal arrays and analysis of variance, indicated that applied load is the most dominant factor (SFCC: 76.63 %; SFKL: 76.24 %), followed by sliding distance, while sliding velocity had negligible effect. Specific wear rates increased sharply with applied load, ranging from 0.0633 to 0.2233 for SFCC and from 0.0557 to 0.195 for SFKL. Scanning electron microscopy analysis revealed smoother worn surfaces with shallow grooves and limited fiber pull-out in SFKL compared to SFCC. Overall, kaolin-filled sisal fiber composites exhibited superior mechanical and tribological performance, making them promising for structural panel applications.

This study investigates the effects of refined boron additives on the microstructure, hardness, and wear behavior of brake pads. Conventional materials such as Novolak resin, copper, alumina, graphite, brass, zirconium silicate, and sulfates were combined with boric acid and borax decahydrate at varying weight fractions. Samples were fabricated via pressing, and microstructure, density, hardness, and wear were evaluated. Porosity increased with higher boron content, leading to lower density, while hardness initially increased and then decreased beyond certain concentrations (maximum at 2.5 wt.% for boric acid and 5 wt.% for borax decahydrate). A linear relationship between hardness and wear resistance was observed. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and 3D profilometry analyses revealed microcracks, oxide tribolayers, and plastic deformation at wear track edges. Overall, the incorporation of boron at optimal concentrations significantly improved frictional performance of the brake pads.