Search Results (251)

In this paper, the different effects of laser shock peening (LSP) and laser shock peening without coating (LSPwC) on the morphology, microhardness and fretting-wear behavior of DD6 Ni-based single-crystal superalloy are investigated. The results show that the surface roughness of DD6 decreases slightly after LSP, while it increases after LSPwC due to surface remelting. Shock wave strengthening during LSP and LSPwC results in plastic deformation of the surface layer of DD6 samples. However, besides work hardening from shock wave, dispersion strengthening of oxide particles also occurs during LSPwC. Therefore, after LSPwC, the microhardness of the DD6 surface layer increases by 38.8%, higher than the increase of 27.7% after LSP. The fretting wear resistance of DD6 increases by about 42.8% and 58% after LSP and LSPwC, respectively. The surface roughness only affects the friction coefficient at the initial stage of fretting wear. The hardness increase caused by work hardening and the dispersion strengthening of surface oxides after laser strengthening is the key to the improvement of fretting wear resistance. The main wear mechanisms of untreated and LSP sample are oxidation wear, abrasive wear and adhesive wear, while the main wear mechanisms of LSPwC sample are oxidation wear and adhesive wear. Full article

Precipitation-hardenable stainless steels (PHSS) are widely used in various applications in the aeronautical industry such in as landing gear supports, actuators, and fasteners, among others. This research aims to study the pitting corrosion behavior of passivated martensitic precipitation-hardening stainless steel, which underwent passivation for 120 min at 25 °C and 50 °C in citric and nitric acid baths before being immersed in solutions containing 1 wt.% sulfuric acid (H₂SO₄) and 5 wt.% sodium chloride (NaCl). Electrochemical characterization was realized employing electrochemical noise (EN), while microstructural analysis employed scanning electron microscopy (SEM). The result indicates that EN reflects localized pitting corrosion mechanisms. Samples exposed to H₂SO₄ revealed activation–passivation behavior, whereas those immersed in NaCl exhibited pseudo-passivation, indicative of an unstable oxide film. Current densities in both solutions ranged from 10⁻³ to 10⁻⁵ mA/cm², confirming susceptibility to localized pitting corrosion in all test conditions. The susceptibility to localized attack is associated with the generation of secondary oxides on the surface. Full article

Nodular Cast Iron (NCI, also known as ductile iron) is widely used in important components such as crankshafts for automotive engines and internal combustion engines, as well as storage and transportation containers for spent fuel in nuclear power plants, due to its good comprehensive mechanical properties such as strength, toughness, and wear resistance. The effect of temperature on the fracture behavior of NCI was investigated using compact tensile (CT) specimens at different temperatures. The results showed that the conditional fracture toughness parameter (K_Q) of the NCI specimens firstly increased and then decreased with decreasing temperature. The crack tip opening displacement δ_m shows a significant ductile–brittle transition behavior with the decreasing of temperature. δ_m remains constant in the upper plateau region but sharply decreases in the ductile–brittle region (−60 °C to −100 °C) and stabilizes at a smaller value in the lower plateau region. Multiscale fractographic analysis indicated that the fracture mechanism changed from ductile fracture (above −60 °C) to ductile–brittle mixed (−60 °C to −100 °C) and then to completely brittle fracture (below −100 °C). As the temperature decreased, the fracture characteristics changed from ductile dimples to dimple and cleavage mixed and then to brittle cleavage. Full article

The initiation of ductile fractures in medium-strength AW5754 and high-strength AW6082 aluminum alloys at different quasi-static strain rates and under multiaxial stress states was investigated through a series of tensile tests using various specimen geometries. The sensitivity of the stress triaxiality locus to variations in the loading rate was examined for these two aluminum alloy families. Fractographic and elemental analyses were also conducted via SEM and EDS. Numerical simulations based on the finite element method (FEM) were performed using ABAQUS/Standard to determine the actual stress triaxialities and the equivalent plastic strains at fracture. The numerical approach was validated by comparing the simulation results with the experimental findings. These simulations facilitated the generation of a stress triaxiality locus through a curve-fitting process. Among the considered fitting functions, an exponential function was selected as it provided the most accurate relation between the equivalent plastic strain at fracture and the corresponding stress state across different strain rates. The results reveal different strain rate dependencies for the two alloys within a very low strain rate range. The resulting stress triaxiality loci provide a valuable tool for predicting fracture strains and for more accurately evaluating stress states. Overall, the findings of this study significantly advance the understanding of the fracture initiation behavior of aluminum alloys under multiaxial loading conditions and their sensitivity to various quasi-static loading rates. Full article

Cost reduction has always been a high priority target in modern management. Concentrating on material strength, the huge potential is recognized for cost reduction in finding the material fatigue coefficients by reduction the number and time required for testing specimens. The aim of this study is to evaluate the accuracy of several fatigue parameter estimation methods by comparing them with reference test data obtained for six different steel materials. In the literature, several estimation methods can be found. Those methods rely on tension or hardness tests. The concern is about the accuracy of those methods; therefore, a basic case was investigated involving estimation methods and comparing them to reference data from a physical test. The case was selected in a manner that allowed the verification of combined low and high cycle fatigue. As a result, the estimation methods produced a very wide range of fatigue life predictions, but some of them were quite accurate. This leads to the conclusion that estimation methods can be a step forward for finding the fatigue material properties; however, a study should be undertaken on which methods are the most suitable for the material family used. Full article

Body-centered cubic (BCC) metals, extensively utilized in low-alloy high-strength steels and heat-resistant alloys, exhibit a pronounced ductile–brittle transition (DBT) at cryogenic temperatures, marked by a well-defined yet narrow ductile–brittle transition temperature (DBTT) window. This paper overviews the research progress regarding the DBT mechanism of BCC metals. This mechanism was recently found to be related to the mobility of screw dislocation relative to edge dislocation, a decrease in which can induce a critical drop in the proliferation efficiency of dislocation sources. Furthermore, this paper summarizes the current research on the dilute solution softening effect of BCC metals, which has been frequently observed and studied in refractory alloys. The mechanism of this effect involves the low-temperature mobility of screw dislocations that could be promoted by specific solute atoms through kink pair nucleation. This offers a potential strategy for reducing the DBTT of low-alloy steels using a dilute solution, namely microalloying in metallurgy. However, the current understanding of the relationship between the macroscopic ductility of BCC alloys and the dilute solution softening effect is limited. This review aimed to draw attention to this relationship and strengthen related research. Full article

A hot compression simulation was conducted on the Al-7.62Zn-2.22Mg-0.90Cu-0.30Mn-0.09Er-0.13Zr alloy (7E97) within the temperature range of 300~460 °C and strain rate range of 0.001~10 s⁻¹ using a Gleeble-3500 hot simulator. A flow-stress constitutive equation and hot processing maps were established for the alloy, and the microstructural evolution of the alloy after hot deformation was investigated. It was found that the dominant dynamic softening mechanism of the alloy was dynamic recovery, accompanied by minor dynamic recrystallization. The optimal hot processing window for the alloy was determined to be in the ranges of 0.001~0.05 s⁻¹ and 350~410 °C. Full article

Advanced high-strength steels (AHSSs) are used as lightweight solutions for vehicles, mainly focusing on the Body-in-White. However, the implementation of such steels for chassis parts requires a profound knowledge of the key design parameters for these components, particularly those concerning fatigue performance. Manufacturing of chassis parts include mechanical cutting operations. Therefore, the deformation and damage induced at the cut edge may affect the fatigue resistance of the parts in service. To characterize and study this critical area, damage and micromechanical properties have been evaluated at the cut edge for three different AHSS grades, CP800, CP980, and DP600, analyzing the impact of cutting parameters and post-processing treatments, such as sandblasting. Large high-speed nanoindentation maps of 400 × 200 µm² have been carried out along the cut edge in the three different target zones: burnish, fracture, and burr. In the hardness maps, the deformation lines and the gradient of hardness with increasing distance from the cut edge are perfectly observed. Residual stresses at the target zones of the cut edges were measured using the FIB-DIC method for CP980 to complement the micromechanical study in these critical areas. The results found show that reduced cutting clearance leads to larger hardened zones and favorable compressive stress distributions, correlating with improved fatigue resistance. Hardened zones extending up to 100 µm from the cut edge and compressive residual stresses exceeding −300 MPa were observed at low clearance. These findings are consistent with numerical simulations and previous fatigue tests, highlighting the potential of combining high-speed nanoindentation and local stress analysis for optimizing shear cutting processes in AHSS components. Full article

Today, Powder Bed Fusion-Laser Based technology is widely used in many industrial fields, but some high-demanding applications are still not fully investigated, such as low temperatures. In basic physics research, experiments usually use low temperatures to reduce external influences and to increase the sensitivity of particle detectors, accelerators, etc. The production capabilities of this technology have become a standard for manufacturing such components, and the demand for high performance has led to the investigation of new materials, like GRCop-42. It possesses excellent thermal properties and strength at high temperatures, and although several works have been published in recent years, full research on its behaviour at low temperatures is still missing. The aim of the paper is to investigate the mechanical properties of GRCop-42, produced by PBF-LB, from low to room temperature, like Elastic Modulus and Poisson’s ratio, and correlate them with thermal conductivity in the as-built state and after heat treatment. The results showed that the material can maintain high strength even at low temperatures, without losing ductility and the ability to store strain energy; moreover, after heat treatment, it increases its thermal properties due to the way the precipitates are dispersed in the copper matrix. Full article

Magnetic Barkhausen noise (MBN) analysis is a non-destructive evaluation technique that offers significant advantages in assessing the magnetic properties of electrical steels. It is particularly useful for quality control in electrical steel production and for evaluating magnetic quality during core manufacturing and assembly. Despite its potential, MBN has not been widely used in electrical steel characterization. One obstacle is that the effects of silicon content in the electrical steel and the residual stress generated during its processing on MBN have not been thoroughly understood, limiting the practical application of the MBN technique in the electrical steel and electric motor industries. To address this knowledge gap, this paper investigates the MBN responses from four non-oriented electrical steel (NOES) sheets with varying silicon contents (0.88, 1.8, 2.8, and 3.2 wt%) but similar other elements. The measurements were performed both with and without applied tensile stress. It is observed that increasing the Si content increases the pinning density, which, together with the microstructure and texture, largely impacts the MBN response. In addition, the MBN energy increases with the applied stress, which can be attributed to the increase in the number of 180° domain walls (DWs) in the direction of stress. The rate of this MBN increase, however, differs among steels with different silicon concentrations. This difference is due to the combined effect of the DWs and pinning density. When the DW spacing becomes less than the jump distance between the pinning sites, no further increase in the MBN energy is observed with additional stress. The reported results provide a basis for the interpretation of MBN signals for varying wt% Si in NOES when residual stresses are present. Full article

The presence of mixed-mode stresses, combining both opening and shearing components, complicates fatigue life estimation when applying the Paris law. To address this, the crack path, along with Mode-I (opening) and Mode-II (shear) components, was numerically analyzed using Fracture Analysis Code (Franc2D) based on the linear elastic fracture mechanics (LEFM) approach. Accordingly, fatigue life and stress intensity factors (SIFs) under various biaxial loading ratios (λ) were calculated using the Paris law and compared with available data in the literature. The results show that crack growth is primarily driven by the Mode-I component, which exhibits the largest magnitude. Thus, the Mode-I stress intensity factor (K_I) was adopted for the numerical integration of the fatigue life equation. Furthermore, the influence of normal and transverse loads (σ_y and σ_x, respectively) on the crack path plane and SIF was examined for λ. The analysis revealed that lower λ values led to faster crack propagation, while higher λ values resulted in extended fatigue life due to an increased number of cycles to failure. The comparison demonstrated good agreement with reference data, confirming the reliability of the proposed modeling approach over a wide range of biaxial loading conditions. Full article

Superalloys are a class of materials renowned for their exceptional ability to retain mechanical properties at elevated temperatures. Nickel superalloys, with a nickel content ranging from 38% to 76%, and iron–nickel superalloys (15–60% iron, 25–45% nickel) are extensively employed within the aviation industry due to their resilience in harsh operating environments. These components encounter extreme temperatures during operation, significantly impacting their tensile strength and melting point. Furthermore, high-speed rotation and abrasive conditions necessitate materials with superior hardness. Consequently, material modifications are crucial to ensure that gas turbine components meet their required properties. Machine learning (ML) and deep learning (DL) offer promising solutions for the design of materials with tailored tensile strength, hardness, and melting point properties. This study investigates the efficacy of direct and inverse machine learning models in predicting crucial material properties and composition, respectively. The model with the most favorable prediction accuracy is identified through the systematic variation of key parameters. The findings show that a fully connected feed-forward Artificial Neural Network (ANN) with three hidden layers using ReLU activation functions performs better than the other models. This capability is leveraged to modify the composition of INCONEL-718, successfully achieving significant enhancements in tensile strength (1592 MPa), hardness (152 HRB), and melting point (1665 °C). Full article

A better residual stress prediction model can lead to more accurate life assessments, better manufacturing process design and improved component reliability. Accurate modeling of transformation-induced plasticity (TRIP) is critical for improving residual stress simulation fidelity in advanced manufacturing processes. In this work, a novel TRIP model is implemented within a finite element framework to predict residual stress in quenched AISI 4140 steel cylinders. The proposed model incorporates a dual-exponential normalized saturation function to capture TRIP kinetics. Residual stress characterization through X-ray diffraction (XRD) is employed to validate the predictive capability of the finite element model that couples the new TRIP model. In addition, the performance of the new TRIP model in predicting residual stress is compared with traditional TRIP models such as Leblond and Desalos model. Systematic comparison of finite element models incorporating different TRIP models reveals that traditional TRIP models exhibit more deviations from the measurements, while the new TRIP model demonstrates more accurate predictive accuracy, with both the axial and hoop residual stress distribution curves showing a better degree of agreement with XRD results. The findings of this study provide a reliable numerical simulation tool for optimizing the quenching process, particularly for improving fatigue life predictions of critical components such as gears and bearings. Full article

This study elucidated the effect of Ti–Mo microalloying on the hydrogen embrittlement (HE) resistance and fracture behavior of warm-rolled Fe-5.6Mn-0.16C-1Al (wt%) steel. After intercritical annealing, both steels, i.e., without and with Ti–Mo microalloying, showed ultrafine ferrite (α) and austenite (γ_R) duplex microstructure. The addition of Ti–Mo to 5.6Mn steel reduces the volume fraction of γ_R, facilitating the formation of (Ti, Mo)C carbides in α phase and further refining the final microstructure. The product of ultimate tensile strength (UTS) and total elongation (TEL) of 5.6MnTiMo can be as high as 35 GPa·% with an ultra-high yield strength of above 1.2 GPa. Furthermore, the addition of Ti–Mo also had a significant effect on the resistance to HE of medium Mn steels. Firstly, the limited (Ti, Mo)C carbides precipitated in γ_R could act as irreversibly trap sites to capture a considerable amount of H, effectively increasing the C_H (Diffusible Hydrogen Content). Additionally, 5.6MnTiMo displayed higher γ_R stability, resulting in a reduced susceptibility to HE. The H-assisted microcracks mainly formed inside γ(α′) and extended along γ(α′) grain boundaries, leading to intergranular cracking and premature fracture. Full article

This paper presents an experimental and numerical analysis of the mechanical behaviour of orthopaedic implants with crack-type defects, considering the principles and advantages of the modern X-FEM method, which was used due to limitations of traditional FEM in terms of crack growth simulation, especially for complex geometries. In X-FEM, the finite element space is enriched with discontinuity functions and asymptotic functions at the crack tip, which are integrated into the standard finite element approximation using the unity division property. Though rare, femoral component failures are well-documented complications that can occur after hip prosthetic implantation. Most stem fractures happen in the first third of the implant due to the loosening of the proximal stem and fixation of the distal stem, leading to bending and eventual fatigue failure. The main goal of this paper was to obtain accurate and representative models of such failures. Experimental analyses of the mechanical behaviour of implants subjected to physiological loads, according to relevant standards, using a new combined approach, including both experiments and numerical simulations was presented. The goal was to verify the numerical results and obtain a novel, effective methodology for assessing the remaining fatigue life of hip implants. For this purpose, the analysis of the influence of Paris coefficients on the total number of cycles was also considered. Hence, this simulation involved defining loads to closely mimic real-life scenarios, including a combination of activities such as ascending stairs, stumbling, and descending stairs. The tensile properties of the titanium alloy were experimentally determined, along with the Paris law coefficients C and m. The finite element software ANSYS 2022R2 version was used to develop and calculate the three-dimensional model with a crack, and the resulting stresses, stress intensity factors, and the number of cycles presented in the figures, tables, and diagrams. The results for the fatigue life of a partial hip implant subjected to various load cases indicated significant differences in behaviour, and this underscores the importance of analysing each case individually, as these loads are heavily influenced by each patient’s specific activities. It was concluded that the use of numerical methods enabled the preliminary analyses of the mechanical behaviour of implants under fatigue loading for several different load cases, and these findings can be effectively used to predict the possibility of Ti-6Al-4V implant failure under variable cyclic loads. Full article