Search Results (141)

In the industrial practice of metal forming, the consistent and reasonable characterization of the material behavior under the coupling effect of strain, strain rate, and temperature on the material flow stress is very important for the design and optimization of process parameters. The purpose of this work was to establish an appropriate constitutive model to characterize the rheological behavior of a hot-formed steel plate (22MnB5 steel) produced through the TSCR (Thin Slab Casting and Rolling) process under practical deformation temperatures (150–250 °C) and strain rates (0.001–3000 s⁻¹). Subsequently, the material flow behavior was modeled and predicted using the Johnson–Cook flow stress constitutive model. In this study, uniaxial tensile tests were conducted on 22MnB5 steel at room temperature under varying strain rates, along with elevated-temperature tensile tests at different strain rates, to obtain the engineering stress–strain curves and analyze the mechanical properties under various conditions. The results show that during room-temperature tensile testing within the strain rate range of 10⁻³ to 300 s⁻¹, the 22MnB5 steel exhibited overall yield strength and tensile strength of approximately 1500 MPa, and uniform elongation and fracture elongation of about 7% and 12%, respectively. When the strain rate reached 1000–3000 s⁻¹, the yield strength and tensile strength were approximately 2000 MPa, while the uniform elongation and fracture elongation were about 6% and 10%, respectively. Based on the experimental results, a modified Johnson–Cook constitutive model was developed and calibrated. Compared with the original model, the modified Johnson–Cook model exhibited a higher coefficient of determination (R²), indicating improved fitting accuracy. In addition, to predict the material’s damage behavior, three distinct specimen geometries were designed for quasi-static strain rate uniaxial tensile testing at ambient temperature. The Johnson–Cook failure criterion was implemented, with its constitutive parameters calibrated through integrated finite element analysis to establish the damage model. The determined damage parameters from this investigation can be effectively implemented in metal forming simulations, providing valuable predictive capabilities regarding workpiece material performance. Full article

Digital twin models utilising point cloud data have received significant attention for efficient bridge maintenance and performance assessment. There are some studies that show finite element (FE) models from point cloud data. While most of those approaches focus on modelling by solid elements, modelling of some civil structures, such as bridges, requires various uses of beam and shell elements. This study proposes a systematic approach for constructing shell element FE models from point cloud data of thin-walled structural members. The proposed methodology involves k-means clustering for point cloud segmentation into individual plates, principal component analysis for neutral plane estimation, and edge detection based on normal vector variations for geometric structure determination. Validation experiments using point cloud data of a steel corner specimen revealed dimensional errors up to 5 mm and angular errors up to 6°, but static load analysis demonstrated good accuracy with maximum displacement errors within 3.8% and maximum stress errors within 7.7% compared to nominal models. Additionally, the influence of point cloud data quality on FE model geometry and analysis results was evaluated based on geometric accuracy and point cloud density metrics, revealing that significant variations in density within the same surface lead to reduced neutral plane estimation accuracy. Furthermore, toward practical application to actual bridge structures, on-site measurements and quality evaluation of point cloud data from a steel plate girder bridge were conducted. The results showed that thickness errors in the bridge data reached up to 2 mm, while surface deviation RMSE ranged from 3 to 5 mm. This research contributes to establishing practical FE modelling procedures from point cloud data and providing a model validation framework that ensures appropriate abstraction in structural analysis. Full article

This study focuses first on the synthesis through an aza-Michael addition reaction of original linear diamine prepolymers and original amine/acrylate thermoset adhesives, and second on their thermal, mechanical and adhesion characterization. The major advantage of the aza-Michael addition reaction is that it takes place at room temperature, without a solvent and without a catalyst. Using the aza-Michael addition reaction, linear secondary diamine prepolymers were first synthesized with a control of the molecular weight, ranging from 867 to 1882 g mol⁻¹. Then, aza-Michael reactions of diamine prepolymers with three different acrylates allowed the synthesis of new amine/acrylate thermoset adhesives. All the thermoset adhesives were characterized by rheology and thermal analysis, leading, once the crosslinking aza-Michael reaction had occurred, to soft thermoset networks with glass transition temperatures ranging from −23 to −8 °C, gel point times ranging from 40 min to 4 h, and a polar component of the surface energy ranging from 3 to 17 mJ m⁻². Functionality of the acrylates directly influences the crosslinking rate, and a decreasing master curve is obtained when reporting crosslinking rate versus gel point time. Crosslinking density is controlled by the diamine prepolymer chain length. In a second step, thermoset adhesives were applied as thin films between two galvanized steel plates, and adhesion properties were evaluated through a lap-shear test. Results showed that the adhesive strength increases as the dynamic viscosity and molecular weight of the diamines prepolymer increases. Increasing the diamines prepolymer chain length results in an increase in strain at break, a decrease in the shear modulus, and a decrease in the maximum lap-shear strength. It is also observed that the adhesive strength decreases when the adhesive film thickness increases. Moreover, thermoset adhesives with high polarity and a surface energy similar to the surface energy of the substrate will favor high adhesion and a better adhesive strength of the assembly. Lastly, the nature of the acrylates and diamines prepolymer chain length allow tuning a wide range of adhesive strength and toughness of these original soft thermoset adhesives. Full article

Ti/a-C:Cr multilayer films were deposited on 316L stainless steel (SS316L) substrates using medium-frequency alternating current magnetron sputtering, with a single-layer a-C:Cr film also prepared on a titanium substrate. The influence of sputtering pressure on the film’s structure and properties was systematically investigated. Film morphology and microstructure were analyzed via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). At a pressure of 1.4 MPa, the interfacial contact resistance (ICR) of SS316L bipolar plates (BPPs) coated with the films reached as low as 3.30 mΩ·cm², while that of titanium BPPs was 2.90 mΩ·cm². Under simulated proton exchange membrane fuel cell (PEMFC) cathode conditions (70 °C, 0.6 V vs. SCE, 0.5 M H₂SO₄, 5 ppm HF solution), the corrosion current density, Icorr, reached optimal values of 0.69 μA·cm⁻² for SS316L and 0.62 μA·cm⁻² for titanium. These results demonstrate that parameter optimization enables SS316L BPPs to functionally replace titanium counterparts, offering significant cost reductions for metal BPPs and accelerating the commercialization of PEMFC technology. Full article

Objectives: To introduce a novel method for apical lesion sampling using a protected paper point device and to evaluate its effectiveness and robustness during the sampling process in vitro. Methods: A prototype for apical sample collection was developed as an adaptation of the Micro-Apical Placement System—the device features a highly tapered screw head with a thin, hollow, stainless-steel tube and an internal wire piston. Standardized 5 mm paper points (ISO 10; PD Dental, Switzerland) served as carrier material. The prototype was tested using 30 × 3D-printed, single-rooted tooth models inoculated using two bacterial strains (Staphylococcus epidermidis and Escherichia coli) to simulate apical and intraradicular bacterial infections, respectively. The sampling process involved collecting and analyzing samples at specific timepoints, focusing on the presence or absence of E. coli contamination. Following sample collection, cultural detection of bacterial presence was performed by incubating the samples on agar plates to confirm the presence of E. coli. Samples were collected as follows: S0 (sterility control of the prototype), P0 (sterility control of the tooth model), P1 (apical sample collected with the CAPS (controlled apical sampling) device, and P2 (contamination control sample to check for the presence of E. coli inside the root canal). Results: Handling of the CAPS prototype was straightforward and reproducible. No loss of paper points or complications were observed during sample collection. All sterility samples (P0, S0) were negative for tested microorganisms, confirming the sterility of the setup. P2 samples confirmed the presence of E. coli in the root canal in all trials. The P1 samples were free from contamination in 86.67% of trials. Conclusions: The CAPS method for apical sampling demonstrated advances in the successful and precise sample collection of apically located S. epidermidis and will be a useful tool for endodontic microbiological analysis. Its user-friendly design and consistent performance highlight its potential for clinical application, contributing to more accurate microbial diagnostics and later patient-specific therapeutic approaches in endodontic treatments. Full article

Thin steel plates with stiffeners are widely used in shipbuilding, aeronautics, and civil construction due to their lightness and structural strength. This study presents a numerical model developed using ANSYS Mechanical APDL with SHELL281 finite elements to evaluate the deflection of thin steel plates with trapezoidal-shaped box-beam stiffeners, known as hat-stiffened plates. The structure is analyzed under a uniformly distributed load perpendicular to the plate, with simply supported boundary conditions. The constructal design method combined with the exhaustive search technique is employed to optimize the geometry. A volume fraction of 30% is used, transferring material from the reference plate (without stiffeners) to the stiffeners, defining parameters such as number, height, and thickness—considered degrees of freedom. The stiffener angle is fixed at 120°. The results show that increasing stiffener height and reducing thickness generally improve structural performance by reducing deflections. The best configuration with transverse stiffeners reduced deflection by 97.15% compared to the reference plate, and by 79.27% compared to the best longitudinal configuration from previous studies. Therefore, transverse stiffeners were more effective than longitudinal ones. This study highlights the importance of stiffener orientation and geometry in the structural optimization of thin steel plates. Full article

This study investigates the effect of welding speed on the microstructure and mechanical properties of pulsed laser lap-welded 0.2 mm 316L stainless steel sheets, commonly used in fuel cell bipolar plates. Welding speeds ranging from 6 to 26 mm/s were tested while other laser parameters remained constant. Results show that increasing welding speed reduces heat input, overlap factor, and weld dimensions. A transition from full to partial penetration occurs beyond 6 mm/s, with no visible heat-affected zone. The weld microstructure features columnar ferrite near fusion boundaries and globular ferrite in the center. Tensile–shear tests reveal that welds maintain higher strength than the base metal up to 22 mm/s, with all fractures occurring in the base material. An optimal speed range of 10–14 mm/s ensures defect-free joints with improved mechanical performance. These findings provide practical guidance for thin-gauge stainless steel welding in fuel cell applications. Full article

This study investigates the forming process (stamping) of bipolar plates which have applied a novel ultra-thin (0.1 mm) super ferritic stainless steel, i.e., SUS470, whose chromium is sufficiently high for corrosion resistance. A three-dimensional finite element model of the stamping process was developed using the commercial software ABAQUS version 2022. The model incorporated optimized die parameters obtained through Central Composite Design (CCD). This model was used to analyze the effects of key forming parameters, including stamping speed and friction coefficient, on the distribution of stress, strain, and thickness reduction during the stamping process. The finite element modeling (FEM) results disclose that the inner corner of the flow channel is a critical defect-prone region, exhibiting stress concentration, uneven strain distribution, and severe thinning. The optimal forming quality can be achieved at a stamping speed of 100 mm/s and a friction coefficient of 0.185 among all varied options. Further, a comparative study of single-stage, conventional two-stage, and optimized two-stage stamping strategies based on previous investigation demonstrates that the optimized two-stage stamping process can effectively alleviate stress and strain concentrations at the corners, significantly reduce thinning problems, and enhance the uniformity and stability during stamping. In summary, this study provides theoretical support for the design of the forming process (stamping) of high-performance super ferritic stainless steel bipolar plates, which is beneficial to subsequent practical engineering application. Full article

The development of bipolar plate materials with enhanced corrosion resistance and surface conductivity is critical for the commercial application of proton exchange membrane fuel cells (PEMFCs). The corrosion behavior and surface conductivity of electrochemically nitrided 446 stainless steel with and without the pretreatment of Cr-enrichment were investigated in the simulated PEMFC anode and cathode environments (i.e., 0.5 mol L⁻¹ H₂SO₄ + 2 ppm HF solution bubbled with hydrogen or air at 80 °C) using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma–mass spectrometry (ICP-MS), and electrochemical measurement techniques. Extending the nitriding time from 5 to 30 min enhances the surface conductivity but reduces the corrosion resistance. After the pretreatment and 30 min of nitridation, a thin film formed on the specimen surface, which mainly consists of Cr-nitrides and -oxides with atomic fractions of 0.42 and 0.37, respectively. The Cr-enriched and nitrided specimen shows spontaneous passivation in both the simulated cathode and anode environments and higher corrosion potentials, lower passive current densities, and larger polarization resistances in comparison with the directly nitrided specimens. Its stable current densities are about 0.26 and −0.39 μA cm⁻² after 5 h of polarization tests at 0.6 V_SCE in the cathode environment and at −0.1 V_SCE in the anode environment, respectively. Its contact resistance is about 5.0 mΩ cm² under 1.4 MPa, which is close to that of the specimen directly nitrided for 120 min and slightly decreases after the potentiostatic polarization tests. These results indicate that Cr-rich pretreatment improves not only the corrosion resistance and surface conductivity of nitrided specimens but also the efficiency of electrochemical nitridation. Full article

This research was carried out for selected alloy (bearing) and non-alloy (tool) steel. The steels were subjected to austempering. The hardening temperature range was from 100 °C to 180 °C. The use of acoustic emission in connection with the artificial neural network (ANN) enabled the analysis and identification of phase changes occurring in steels during austempering. Classification of acoustic emission events was carried out with the help of their energy values and with the use of an artificial neural network. On this basis, it was observed that in the process of isothermal hardening of steel at the applied temperatures, complex transformations of austenite into martensite and bainite occur. In addition, it was found that the research methods used enabled the identification of signal components originating from the phase transformation causing the formation of thin-plate martensite midrib. The use of acoustic methods in the field of bainitic transformation creates the possibility of their application in the industry. Full article

This study investigates a novel steel grid shear wall (SGSW) structure with lightweight and discrete lateral-resistance members, focusing on its structural behavior in lateral resistance. By comparing the characteristics of the thin steel plate shear wall, the mechanism of the steel grid components in both the tension zone and compression zone was briefly described. The formulas of lateral-resistant capacity and initial stiffness of the SGSW were derived through the static equilibrium method. Then, the influence laws of the span–height ratio, steel member spacing and section size of the steel members on the lateral-resistant performance of the SGSW were determined through a parametric analysis. In addition, the accuracy of the calculation formula was validated. The results showed that the strains of the steel grid components in different positions were all the same when the bending stiffnesses of the edge members were significantly large. The lateral-resistance capacity of the SGSW increased with the span-to-height ratio, while it decreased as the spacing between the steel components increased. Compared with the effects of web height, web thickness and flange width, increasing the flange thickness exhibited the best effects on improving the lateral capacity. As the flange thickness increased from 7 mm to 13 mm, the lateral-resistant capacity showed an improvement of 35.45%. Additionally, the formula derived in this study demonstrated high accuracy and reliability, with the error not exceeding 8% between the formula calculation and the simulation results. Full article

Axial force and deformation during drilling significantly impact the hole quality of thin-walled high-strength steel components. This study analyzed the drilling process of thin-walled AF1410 steel, focusing on axial force, deformation, drill cap formation, and hole exit edge characteristics. The effects of cutting speed (12.6–37.7 m/min) and feed rate (0.01–0.1 mm/r) were also examined. Initially, the steel plate undergoes elastic, outward bulging deformation. Axial force, driven by elastic resistance, rises from 114.9 N to 322.1 N as feed rate increases from 0.025 mm/r to 0.1 mm/r, with minimal influence from cutting speed. As drilling progresses, axial force increases slowly. Near the hole exit, plastic deformation occurs beneath the drill bit, causing material to yield and form a drill cap. This results in a sharp rise in axial force, with maximum values increasing from 314.2 N to 525.3 N at higher cutting speeds and from 314.2 N to 840.1 N at higher feed rates. The formation characteristics of the drill cap directly affect hole edge defects, with larger thickness and width leading to more pronounced burrs. Full article

The failure mode of thin-walled C-channel beams typically manifests as premature local buckling of the compression flange, leading to insufficient utilization of material strength in both the flange and the web. To address this issue, this study adopts the approach of increasing the number of bends to reinforce the flange and adding V-shaped stiffeners in the middle of the web to reduce the width-to-thickness ratio of the plate elements, thereby delaying local buckling and allowing for greater plastic deformation. However, the challenge lies in the irregular cross-sectional shape and complex buckling patterns. Therefore, this paper aims to explore a suitable cross-sectional form to expand the application of stainless steel members. Subsequently, three-point bending tests were conducted on the optimally designed stainless C-channel beam with folded flanges and mid-web stiffeners. The finite element simulation results were compared and analyzed with the experimental results to validate the model’s effectiveness. After verifying the correctness of the finite element model, this study conducted numerical parameterization research to investigate the effects of the shear span ratio, complex edge stiffeners, web height–thickness ratio, and V-shaped stiffener size on the shear performance of stainless steel folded flange C-beams. The results show that changing the shear span ratio has a significant impact on the shear capacity and vertical deflection deformation of components; increasing the web height–thickness ratio can enhance the shear capacity of the component; elevating the V-shaped stiffener size can slightly improve the shear capacity of components; and for the stainless steel C-shaped beam with folded flanges and intermediate stiffening webs, adding edge stiffeners cannot remarkably promote the shear capacity of the component. Full article

This article shows the behavior of the corrosive effect of acid mine water on carbon steel metal alloys. Mining equipment, composed of various steel alloys, is particularly prone to damage from highly acidic water. This corrosion results in material thinning, brittle fractures, fatigue cracks, and ultimately, equipment failure. For this purpose, a set of carbon steel metal plates similar to those found in mine facilities were immersed into mine leachates of an AMD (Acid Mine Drainage) polluted river from the Tharsis Mine (Huelva, Spain). In these leachates, physicochemical variations occur, directly correlated with the alterations produced in the metal plates, manifested with the appearance of dissolved materials and particulate matter. Weight loss of up to 37 g in 30 weeks for plates of about 140 grs occurred and an increase in EC up to 45.64 mS/cm from 5.40 mS/cm and an increase in TDS from 2600 mg/L to 17,100 mg/L. STATGRAPHICS Centurion, a powerful data analysis tool was used for performing the time series analysis that was used for the first time to statistically define the corrosion effects on metal alloys. As a result, a significant variability in the physical and chemical factors of the leachates was observed due to the redox and precipitation–dissolution processes occurring within the system: an increase in total dissolved solids (TDS), electrical conductivity (EC) and temperature (T) (the corrosion process is an exothermic reaction) and a decrease in pH. It was also demonstrated that the longer the exposure time, the plates noticeably lost more material and became further weakened. Finally, these results allowed the formulation of a simple algorithm to define weight loss as a function of exposure time to acidic water. Full article

The P91 martensitic steel and 304L austenitic stainless steels are two mainly used structural steels in power plants. The major problem in conventional multipass tungsten inert gas (TIG) welding of P91/304L steel is high heat input and joint distortion, increased cost and time associated with V groove preparation, filler rod requirement, preheating and welding in multiple passes, and labor efforts. Hence, in this study, a novel approach of robotically operated activated flux TIG (A-TIG) welding process and thin AlCoCrFeNi_2.1 eutectic high entropy alloy (EHEA) sheet as the interlayer was used to weld 6.14 mm thick P91 and 304L steel plates with 02 passes in butt joint configuration. The joints were qualified using visual examination, macro-etching, X-ray radiography testing and angular distortion measurement. The angular distortion of the joints was measured using a coordinate measuring machine (CMM) integrated with Samiso 7.5 software. The quality of the A-TIG welded joints was compared to the joints made employing multipass-TIG welding process and Inconel 82 filler rod in 07 passes. The A-TIG welded joints showed significant reduction in angular distortion and higher productivity. It showed a 55% reduction in angular distortion and 80% reduction in welding cost and time compared to the multipass-TIG welded joints. Full article