Rocks used in historical buildings exhibit a wide range of chemical compositions due to the diversity of volcanic activities and the complexity of their formation processes. The structural integrity and chemical form of these rocks can be significantly deformed when exposed to various environmental factors (wind, rain, earthquakes, fires, etc.). In particular, fires can have destructive effects on the mineral composition of these rocks. When building stones used in historical structures are exposed to high temperatures, chemical changes occur. These chemical changes can cause immediate damage to the structures and also reduce their resistance to environmental factors. To pre-emptively identify the chemical changes occurring in structures after a fire and to enhance the fire resistance of the rocks, preliminary laboratory studies are necessary. In this context, pyroclastic rocks collected from the Ni & gbreve;de region (Turkey) were subjected to thermal treatment at 450 degrees C, 650 degrees C, and 1000 degrees C based on the chemical changes observed through thermogravimetric analysis (TGA). Phase changes in the samples (as-received, 450, 650, and 1000 degrees C) were detected using X-ray diffraction analysis, microstructural changes were examined with scanning electron microscopic (SEM) analysis, and chemical changes were identified using SEM-energy-dispersive X-ray spectroscopy (EDS) and X-ray fluorescence (XRF) analyses. Significant changes were observed in the chemical composition, mineralogical structure, and texture of the rocks when subjected to thermal treatment. TGA analysis showed that chemical changes occurred at 450 degrees C and 650 degrees C. It has been determined that silicon and iron-containing minerals undergo phase changes depending on the increase in temperature (transformation of jarosite into Opal-CT and magnetite into hematite).
This study focuses on the corrosion-wear (tribocorrosion) performance of selective laser melted (as-built SLM) Inconel 718 in natural seawater and quantifies the benefit of a solution heat treatment and double aging (SHT + DA). Potentiodynamic polarization and potentiostatic tribocorrosion tests were conducted while continuously monitoring friction response, and the damaged surfaces were analyzed to clarify the dominant degradation mechanisms. Compared with the as-built condition, the SHT + DA condition exhibited a substantial reduction in corrosion current density (approximate to 30-65%), together with a similar to 50% lower friction coefficient and markedly reduced material loss, indicating a significantly mitigated corrosion-wear synergy under sliding. Microstructural characterization shows that SHT + DA promotes a more homogeneous microstructure with strengthened gamma '/gamma '' precipitation and a higher hardness (from 280.3 HV0.3 to 503.6 HV0.3), which provides improved load-bearing capacity during contact and supports more stable passivation during tribocorrosion. Overall, the results demonstrate that solution heat treatment and double aging reduce the sensitivity of SLM Inconel 718 to coupled mechanical-electrochemical degradation and improve surface durability for chloride-containing service.
Under the complex downhole conditions of torque and pressure, the friction-welded joint of a drill pipe becomes the critical region for fracture failure due to inherent stress concentration and welding residual stress. Traditional homogeneous material models fail to accurately predict the crack propagation behavior of friction-welded drill pipe joints. This study investigates the crack-tip stress-strain fields and propagation paths at various locations of a friction-welded drill pipe joint through a computational model that accounts for its inherent mechanical inhomogeneity across the tool joint, pipe body, and heat-affected zone. First, the mechanical properties of the friction-welded drill pipe joint were characterized in detail using a microhardness tester. Then, a numerical model with continuously varying material properties along spatial positions was developed using the USDFLD user subroutine, ensuring the continuous transition of mechanical properties across the joint region. Finally, the extended finite element method was employed to analyze the influence of inhomogeneous mechanical properties on the crack propagation paths in the tool joint, pipe body, and heat-affected zone. The results show that the inhomogeneous mechanical properties of the friction-welded joint cause the crack propagation path to deflect toward the region with lower material strength, and the total crack propagation length is affected by the mechanical strength near the crack tip.
Hydroxyapatite (HA) is a bioactive ceramic widely applied in dental, bone replacement, and implant therapies because of its excellent biocompatibility and chemical similarity to natural bone. Despite these advantages, its poor strength, limited thermal stability, low crystallinity, and unfavorable surface morphology restrict its use in demanding, load-bearing implants. Improving these properties without compromising biocompatibility remains a key challenge in developing reliable biomedical materials. In this study, HA-titanium (Ti) composites were synthesized by the wet precipitation method and examined to understand how Ti content and processing temperature influence their structural and functional characteristics. Scanning electron microscopy (SEM) revealed distinct morphological changes: low Ti concentrations promoted finer, more uniform particles, whereas higher Ti content and elevated temperatures led to agglomeration, grain coarsening, and the appearance of rod-like TiO2 structures. X-ray diffraction (XRD) showed that crystalline HA was preserved at lower temperatures, with partial Ti addition into the HA lattice. At higher temperatures, reflections of rutile and anatase TiO2 phases emerged, indicating limited Ti solubility and the onset of phase segregation. Fourier-transform infrared (FTIR) spectroscopy confirmed these trends, with characteristic HA phosphate bands present across all samples, alongside band shifts, broadening, and diminished OH peaks that reflected lattice distortion. The growth of Ti- O bands at higher calcination temperatures further supported TiO2 formation. Collectively, these findings highlight that carefully controlled Ti incorporation enhances the crystallinity, thermal stability, and morphology of HA, while excessive Ti or high temperatures promote TiO2 segregation. Optimizing these parameters can pave the way for stronger, more reliable HA-Ti composites tailored for orthopedic, dental, and load-bearing implants that better serve patient needs.
A study was conducted on high-temperature hardness of multifunctional polyphenylene sulfide (PPS)-matrix composite containing carbon fibers (CFs), graphite flakes (Gr), and polytetrafluoroethylene (PTFE). The PPS matrix offers excellent mechanical properties, thermal stability, and chemical resistance at high temperatures. Carbon fibers are added as reinforcement to improve strength and stiffness. Graphite flakes and carbon fibers are good thermal conductors for thermal management. PTFE and graphite are solid-state lubricants for tribological improvements. Thus, CF/Gr/PTFE/PPS material is truly multifunctional due to the attractive combined mechanical, thermal, and tribological properties of its constituents. The high temperature referred to the temperature near, at, and above the composite glass transition. The Rockwell hardness (M scale) was determined from room temperature to 155 degrees C. Hardness of the composite was found to decrease monotonically with increasing temperature, particularly above its glass transition temperature. At high temperature, rigid carbon fibers and graphite carried significant indentation load and constrained segmental chain mobility, thus preserving composite hardness. The injection-molded PPS-matrix composite had flow-induced carbon fiber orientation. The composite with transverse fibers had the highest transverse hardness, while the composite with randomly oriented fibers saw an increase in hardness. The composite hardness was directionally dependent and had a linear relationship with its yield strength at high temperature, but its proportionality changed above and below its glass transition. The relationship enables subsequent prediction of composite tribological behavior based on basic yield property and provides insight into the roles of high temperature and plastic yielding on friction and wear.
Measuring residual stress is critical for assessing the structural integrity and performance of fiber-reinforced plastic (FRP) laminates. The incremental hole-drilling (IHD) method, a common technique for this purpose, relies on calibration constants that are typically determined through computationally intensive finite element (FE) analyses for each unique laminate configuration. While deep operator networks (DeepONet) can serve as efficient surrogate models, the optimal strategy for composing the necessary training data has not been fully established. In this work, a simple yet effective strategy for training data selection is proposed, which is shown to reduce error in predicted stress by 12.4-15.2% over uniform random selection. Further analysis of training data length with the proposed selection strategy shows that acceptable test error, within the inherent uncertainty of the IHD method, can be achieved using just a small fraction of the possible laminate configurations. In this study, strategically selecting only 15 laminate configurations for training, out of the 70 possible laminate configurations, provided acceptable accuracy for complex residual stress profiles, including steep gradients. These findings provide a practical framework for developing reliable surrogate models, making computationally demanding residual stress analyses more accessible for the design and validation of composite structures.
The present study investigated the various aspects of mechanical behavior, microstructure evolution, and formability of a SS430/AA1050 clad sheet at three different elevated temperatures with or without lubrication. Tensile experiments revealed a reduction in tensile strength and ductility of the SS430 layer at elevated temperatures, while the AA1050 layer showed a decrease in strength but an increase in its ductility when compared to that at room temperature. The average normal anisotropy was also increased for both layers of the sheet, enhancing overall clad sheet formability. At elevated temperatures, recovery and recrystallization influenced texture intensity significantly, especially in AA1050, resulting in a more random distribution of grain orientation; however, the texture of SS430 became stronger after deformation. With MoS2 as lubrication, friction values decreased notably for both layers, reducing sticking friction during forming operations. Forming limit diagrams demonstrated improved limit strains under lubrication, with major strain at the plane strain condition increasing more than 65% at 300 degrees C compared to the dry conditions. Deep drawing experiments of the clad sheet revealed that the lubricant significantly improved drawability at all temperatures. Also, the use of lubrication increased the limiting draw ratio, with a maximum draw ratio of 2.0 achieved at 300 degrees C. An analytical model was also developed to predict the required punch force in the deep drawing of the clad sheet based on the Barlat-89 anisotropic yield criterion. The results achieved by numerically and analytically were observed to be in good agreement with the experimental results.
This study investigates the impact toughness of additively manufactured 316L stainless steel using the bound metal deposition (BMD) technique and explores the influence of process parameters including print orientation, outer wall thickness, skin overlap percentage, and printing sequence. Charpy V-notch impact tests were conducted on samples produced with varying configurations, followed by predictive modeling using machine learning (ML). The results demonstrate that a 45 deg printing orientation and increased outer wall thickness significantly enhance impact energy absorption, with a peak value of 49.89 J. The optimal skin overlap was found to be 0%, yielding the most uniform material structure and highest toughness across both infill-first and outer-wall-first strategies. A ridge regression model was developed to predict impact energy based on printing parameters, achieving modest predictive accuracy (mean R-2 = 0.151) due to dataset size and variability. Although predictive power was limited, the study highlights the potential of ML in parameter optimization for metal additive manufacturing. These findings provide valuable insights for improving the mechanical performance of 3D-printed metal components, particularly in impact-critical applications.
High-performance stainless steels have been utilized in reusable rockets to achieve significant reductions in manufacturing and maintenance costs. In this study, the effect of silver doping on the mechanical and tribological properties of 316L stainless steel under cryogenic conditions was experimentally investigated. Three silver mass concentrations of 5 wt%, 10 wt%, and 15 wt%, were selected, and the corresponding microstructural characteristics were analyzed using optical microscopy, energy-dispersive spectroscopy, and electron backscatter diffraction. The cryogenic environment of rocket turbopumps was simulated by immersing the specimens in liquid nitrogen. Rockwell hardness, impact fatigue strength, and tribological performance were subsequently evaluated under both room-temperature and low-temperature conditions, with additional tribological tests conducted under water lubrication for comparison. The results indicated that silver preferentially segregated at austenite grain boundaries, leading to grain refinement and the formation of ductile accommodation regions within the hardened matrix. Silver doping enhanced cryogenic ductility and impact fatigue resistance by promoting plastic deformation capability. Owing to the intrinsic lubricating properties of silver, a self-lubricating film was formed at the sliding interfaces, resulting in reduced friction coefficients and wear-rates. Although silver addition slightly reduced hardness and toughness, its grain-stabilizing effect and interfacial lubricity led to an overall improvement in the cryogenic performance of 316L stainless steel. This work provides useful insights for the development of durable and highly reliable materials for reusable rockets and other cryogenic engineering applications.
The effect of specimen shape on the fracture angle in tensile testing of copper alloy sheets was investigated. Specimens with a width-to-thickness ratio of more than 30 were investigated, and it was found that relatively thick and narrow copper alloy sheets exhibited a fracture angle oblique to the loading direction. In contrast, the fracture angle was perpendicular to the loading direction in the thinner and wider specimens. To understand the mechanism of the change in fracture direction, digital image correlation (DIC) analysis was performed. The DIC analysis showed that the oblique localizations of the strain rate appeared in two directions in any thickness and width after diffuse necking. In thick specimens, one of the localizations was selected by the oblique fracture. In contrast, two localizations remained until the perpendicular fracture in thin and wide specimens. The analysis of the ratio of local strain rate revealed that the length strain over width strain was basically unchanged until fracture. However, in a few cases, the length strain over width strain drastically changed just before the fracture. These results suggest that the remaining two localized strain rates and the change in the strain state lead to the perpendicular fracture in thin and wide specimen. Regarding the edge of the specimen, the fracture angle tends to be oblique. This is presumably due to the less constrained condition of the edge, which is the possible reason for the oblique fracture of the narrow specimen.
The effects of crack size and specimen size on plane strain fracture toughness values of materials, measured using compact tension C(T) specimens, are examined through the analysis of elastic strain energy stored in the net-section at fracture. A large body of experimental data shows that there is a strong crack (or ligament) size effect on plane strain fracture toughness data that were experimentally obtained using compact tension C(T) specimens. The size effect is significant at relatively small crack sizes, but it gets stronger as a/W approaches unity. This dependence exists in both brittle and ductile materials, ruling out any effect of ligament plasticity. In this work, the net-section-based analysis of fracture behavior, enforcing constancy of crack tip fracture stress at all crack lengths, reveals that the measured fracture toughness should vary with crack size and specimen width. It is indeed found that in most materials, fracture occurs at a constant crack tip fracture stress, which is nearly equal to the tensile strength. A few exceptional cases have been noted, but even in these cases, fractures, at all crack lengths, still occurred at constant crack tip fracture stresses that are lower than tensile or bend strengths. Experimental fracture toughness data from ceramics, metals, and biomaterials have been used to demonstrate the crack and specimen size effects on toughness. It is shown that the expressions developed by the net-section stress analysis can predict the fracture toughness variations with crack/specimen size, quite accurately, with constant crack tip fracture stress as the fracture criterion. The results suggest that fracture toughness, measured using the C(T) specimen, is not a material property.
The present work investigates the effect of rare earth Lanthanum oxide (La2O3) nanoparticles on the microstructure, mechanical properties, and residual stress of Al 4047 alloy wall fabricated via cold metal transfer-based wire and arc additive manufacturing (CMT-WAAM). Results from microstructural analyses reveal that without La2O3 nanoparticles, the structure consists of coarse columnar crystals and dendrites, while the addition of La2O3 nanoparticles leads to significant refinement, promoting fine equiaxed dendrites and a reduction in pores. Energy dispersive spectroscopy (EDS) mapping confirms the uniform distribution of La2O3 nanoparticles, which aids in enhancing nucleation during solidification. Mechanical results show that walls with nano-La2O3 exhibit a uniform and increased microhardness and tensile strength, with improvements being more pronounced in the deposition direction than in the build direction. Although the presence of nanoparticles led to reduced ductility, as evidenced by lower elongation and finer, more uniformly distributed dimples were observed in the fractographic analysis. Adding La2O3 nanoparticles decreased residual stress in the wall, with higher compressive stress in the bottom layers from repeated heating, while the top layers experienced tensile stress from rapid cooling.
Welding procedures in high-hardenability steels often lead to adverse microstructural changes, resulting in a sharp decline in mechanical properties within the weld metal zone and the heat-affected zone. Due to the limited tensile strength Rm of commercially available welding consumables, which in many cases do not exceed 1000 MPa, the reduction in mechanical properties can reach up to 60% in steels with hardness levels of 600 HBW. Martensitic boron steels are among the materials with the highest mechanical strength indices and are used both in components exposed to abrasive wear and in ballistic protection. Consequently, welding techniques often produce joint zones with functional properties (e.g., ballistic resistance or resistance to abrasive wear) that fail to meet the required performance of the base material. Only through advanced welding techniques, the use of high-quality fillers, and subsequent heat treatment can the highest mechanical strength indices be achieved in the weld zone. This article presents the results of tests on the resistance of 450 HBW grade steel welded joints to dynamic loads. The research demonstrated that, when subjected to firing using intermediate 7.62 x 39 mm ammunition (43 model, PS bullet) from a distance of 10 m, a minimum plate thickness of 5 mm ensures material continuity across all characteristic zones of the welded joint.
This study examines the corrosion resistance of H13 tool steel exposed to ionic molten salt solution through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques. H13 steel samples were produced via selective laser melting (SLM) with three different build orientations (0 deg, 45 deg, and 90 deg) using the Build Processor v3.2 machine. Nyquist and Bode plots, along with polarization curves, were used to assess the impact of orientation on corrosion resistance. The findings were supported by microstructure analysis of the corroded samples using optical and scanning electron microscopies. The phase angle and the impedance modulus increased with building orientation, with the 0 deg orientation showing the highest values. Polarization resistance values were 1704 Omega cm(2), 1540 Omega cm(2), and 1430 Omega cm(2) for 0 deg, 45 deg, and 90 deg, respectively, demonstrating superior corrosion resistance for the 0 deg orientation. Results highlight the critical impact of SLM build orientation on corrosion resistance, providing insights for future corrosion mitigation strategies for alloys.
Welding dissimilar metals such as Inconel 625 and 316L stainless steel presents significant challenges due to differences in their thermal conductivity, melting points, and mechanical behavior, often leading to defects like cracks, porosity, and incomplete fusion. These are particularly critical in demanding environments such as underwater, aerospace, and nuclear applications, where joint integrity and reliability are essential. To address these challenges, this study investigates the feasibility and optimization of Ultrasonic Vibration-Assisted Laser Welding (USALW) for joining Inconel 625 and 316 L stainless steel. A Box-Behnken design under Response Surface methodology (RSM) was used to conduct experiments and analyze the effects of input parameters such as laser power, ultrasonic power, shielding gas flowrate, and weld bead clearance and on output responses such as tensile strength, weld penetration, impact toughness, and corrosion resistance. To enhance prediction accuracy and parameter optimization, a hybrid Interpretable Artificial Intelligence (IAI) framework was developed, combining a Recurrent Neural Network (RNN) for predictive modeling, Local Interpretable Model Agnostic explanations (LIME) for interpretability, and Moth Flame Optimization (MFO) for solution optimization. The proposed IAI model achieved high accuracy (R-2 > 0.99) and effectively identified the most influential process parameters. The optimized welds demonstrated significant improvements in mechanical and corrosion properties. This integrated approach not only improves weld quality but also provides transparency and reliability in the predictive modeling of complex welding processes.
This study investigates the effects of post-rolling cooling methods (quench cooling, air cooling, and furnace cooling) on the microstructure and properties of Ti-Zr microalloyed steel via laboratory rolling tests. The microstructure is transformed from the lath martensite/bainite to the ferrite-dominated microstructure by decreasing the cooling rate and increasing the average grain size to 3.55 mu m in furnace-cooled steel. Concurrently, transmission electron microscopy-based analysis reveals that the precipitate volume fraction increases from 0.038% to 0.106%, with the average size decreasing from 33.5 nm to 6.8 nm, enhancing the precipitation strengthening effect from 23 MPa to 121 MPa. Quench cooling forms a multiphase microstructure (martensite/bainite + ferrite), which reduces the yield ratio, while dislocation tangling in martensite decreases plasticity. Notably, quench-cooled steel exhibits high impact energy (151 J) despite low elongation. This is attributed to synergistic toughening by high dislocation density (10(14) m(-2)) and retained austenite. Furnace-cooled steel balances strength (yield-716.5 MPa, tensile-787.6 MPa), elongation (18.9%), and 0 degrees C impact energy (133 J), thereby demonstrating cooling rate-controlled synergy between strengthening-toughening mechanisms in Ti-Zr microalloyed steel.
Conventional recycling through remelting is an energy-intensive route and causes permanent material loss. In contrast, solid-state techniques like friction stir consolidation (FSC) and friction stir backward extrusion (FSBE) have emerged as energy-efficient, sustainable alternatives for metal scrap recycling. While prior studies have primarily focused on consolidation or extrusion of bulk material, this study introduces a product-centric approach for the direct fabrication of bimetallic tubular components from AA-6063 T6 chips. This approach involves FSC followed by FSBE within the same die using two different tools, resulting in the recycling of chips in the form of bimetallic tube fabrication. The bonding efficacy of the fabricated product was evaluated through push-out tests and flattening tests. This approach enables adequate frictional heat and plastic deformation, resulting in continuous intermetallic compound layer formation at the interface. The residual voids after each step were analyzed through X-ray computed tomography scans. The void fraction was reduced to zero after extrusion from the void fraction of similar to 0.21% following the second compaction. This approach demonstrates a scalable, energy-efficient pathway for recycling metal chips into bimetallic tubular components, highlighting its potential for sustainable and material-efficient manufacturing, aligning with industrial needs.
Bidirectional silica fabric-based polymer composite laminates were fabricated using resin transfer molding followed by oven curing. To evaluate the effects of environmental exposure, samples were cut as per testing requirements, and a substrate was surface-coated with a 300-mu m-thick polyurethane (PU) layer. Both PU-coated and uncoated samples were subjected to hot-wet conditioning in a climatic chamber for 100 days under critical conditions of 65 degrees C and 85% relative humidity (RH). In this study, density, thermal conductivity, pull-off adhesion, scratch resistance, and various mechanical strengths at room temperature and 100 degrees C were measured before and after conditioning. For uncoated composites, a significant effect of hot-wet conditioning on mechanical strengths, with reductions ranging between 15 and 30%, was observed. When compared between uncoated and coated composites, coated composites exhibited an additional reduction in tensile strength, flexural strength by 14-25%, and interlaminar shear strength decreased from 53 MPa (uncoated, after conditioning) to 46 MPa (after coating & conditioning), although compression and in-plane shear strengths were relatively unaffected. Furthermore, coated samples experienced over a 35% reduction in scratch resistance and pull-off adhesion strength (declined significantly from 8.1 MPa to 5.1 MPa), while density and thermal conductivity remained unchanged. These degradations were attributed to the formation of micro-crevices between the composite substrate and the PU coating, resulting in cavitation damage and matrix degradation. Based on these findings, PU coatings are not recommended for outdoor applications wherein environmental conditions are 65 degrees C and 85% RH.
The mechanical properties and microstructure of different diffusion bonded trials of 316 H stainless steel were compared to analyze the correlation between the mechanical properties and the microstructure of the bonded material. The results show that the percentage coverage of grain growth across the bond interface can be correlated to the ductility and the ultimate tensile strength of the bonded material. This correlation could be used to help identify whether or not a bond is of good quality. Additionally, the effects of bonding temperature and time can be seen on the quality of diffusion bonded 316 H stainless steel. With an increase in temperature and time, the percentage coverage of the bond line increased as well as the ductility of the material. When prioritizing ductility at high temperatures, bonding conditions of 1150 degrees C for 1 h at an 8 MPa interface pressure with a 3-hour annealing time under vacuum provided the best results.
TiO2 nanocomposites doped with Zn have been prepared via the sol-gel method. These nanocomposites with various doping percentages exhibited multi-phase structures with promising photocatalytic efficiency for the removal of pollutants, manifested by methylene blue degradation. Common characterization techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and UV-Vis spectroscopy, were employed to characterize the prepared samples. The identified phases are the rutile tetragonal and wurtzite hexagonal crystal structures of TiO2 and ZnO, respectively, while the doped samples tend to exhibit multi-phase structures of rutile, anatase, zincite, spinal, and inverse spinel cubic phases. Doping significantly influenced the energy gaps, which ranged from 2.9 eV to 3.45 eV. SEM morphological studies confirmed that the average size of the nanoparticles was around 150 nm, while the size of the crystallites varied with doping, ranging from 18 nm to a maximum of approximately 42 nm at a 5 wt% of Zn doping, which is manifested as the optimal doping amount that enhanced the properties of the nanocomposite. However, further increases in doping concentration resulted in the creation of additional scattering centers, which negatively impacted photocatalytic efficiency. The optimal doping ratio resulted in a photocatalytic efficiency of about 98%.
