Search Results (283)

A hollow steel structure with a hat cross-section was axially compressed under impact or quasistatic conditions. The hat height and hat width were 40 mm. The thickness was 0.6, 0.8, and 1.0 mm. The effect of the reinforcing member attached to the main structure on the collapse behavior was experimentally investigated. The formation of buckling lobes was observed, and the energy absorption performance was evaluated. The addition of the internal reinforcing member achieved increased compressive force, exhibiting a stepped force variation. This step became more pronounced as the wall thickness increased, and it was larger under impact conditions. When the height of the reinforcing member was 20 mm, or the hollow shape is square, a higher crush strength was achieved, with a very regular collapse pattern. To explain the increase in compressive force by using the reinforcing member, the deformation energy was calculated by considering the deformed shapes and the mechanical properties of the material. The calculated increase ratio of 3.18 was comparable with the experimental result of 3.54. The strain measurement at the hat top of the structure during the initial compression revealed that the damage, where the strain level is greater than 0.003, was successfully delayed at the reinforced section in the partially reinforced structure. Full article

Four alpha-beta titanium alloys, containing increased beta stabilising elements when compared to the well established Ti-6Al-4V, were previously characterised for their low cycle fatigue behaviour and resistance to cold dwell sensitivity. The same four alloys are now assessed for high cycle fatigue performance, employing plain cylindrical and notched specimen geometries. Fatigue strength under load-controlled cycling was measured under two contrasting mean stress conditions, a fully reversed R = −1 waveform and a positive mean stress waveform of R = 0.3. The role of microstructure and micro-texture are considered to explain the relative high cycle fatigue behaviour of each alloy and in particular the mechanisms responsible for fatigue crack initiation. The data are subsequently employed to construct “safe stress” range-mean diagrams. Full article

Aluminum alloying was considered difficult at excessively high aluminum mass fractions. For high-aluminum steel subjected to aluminum alloying under vacuum conditions, a positive trend was observed between the aluminum content and the aluminum yield. As the aluminum content increased from 5 to 5.5, the aluminum yield rose from 89.56% to 95.76%. Theoretical calculations were performed to determine that the saturated vapor pressures of pure aluminum were 267 Pa, 440 Pa, and 704 Pa at 1600 °C, 1650 °C, and 1700 °C, respectively. In consideration of aluminum volatility and temperature effects, the maximum aluminum yield was obtained at 1600 °C under 267 Pa. During smelting in a vacuum induction furnace, fine inclusions (1–5 μm) were counted for 82.4% of the total inclusions, whereas large inclusions (>20 μm) were recorded at only 0.98%. This phenomenon was attributed to the fact that the rising time of small-sized inclusions was 2500 times longer than that of large ones. Full article

Ultra-high-strength steel (UHSS) cross-members with a high height-to-width ratio are prone to forming defects, such as splitting and wrinkling, due to localized stress concentration during the drawing process. In this study, the addendum geometry in first-stage of a two-stage drawing process was optimized to improve the formability of a cross-member made of 1 GPa-grade UHSS. The optimization was performed using the Sigma module of AutoForm, and Latin hypercube sampling was adopted for the design of experiments. The punch opening width, upper bar radius, wall angle, and lower die radius of the addendum were selected as design parameters, and multi-objective optimization was conducted to simultaneously minimize the maximum failure index and maximum wrinkle value, the two AutoForm forming-defect indicators used in this study. In the initial design, the maximum failure index was 1.044, exceeding the splitting criterion of 1.0; however, this value was reduced to 0.961 in the optimized design, thereby mitigating the risk of splitting. In addition, the maximum wrinkle value was reduced by 11.7% compared with that of the initial design. Pareto analysis was performed to quantitatively evaluate the effects of the design parameters on the forming defects, and the results confirmed that the punch opening width and lower die radius were the dominant parameters affecting both splitting and wrinkling. These results demonstrate that die addendum geometry optimization is effective for reducing splitting and wrinkling in 1 GPa-grade UHSS cross-members. Full article

In this work, the focus is laid on the mean stress effect on the fatigue strength of thin-walled rectangular hollow section T-joints made of high-strength steel S960 M x-treme. The specimens are cyclically tested at a stress ratio of R = −1 and R = 0.1 in both as-welded and ground (weld-profiled) conditions. In the context of nominal stress evaluations, the ground specimens demonstrate a distinct advantage in contrast to the as-welded condition, exhibiting an increase of +33% at R = 0.1 and +16% at R = −1. Based on the experimental results, a corresponding Haigh diagram is evaluated, revealing a notable difference in the mean stress sensitivity, with M₁ = 0.58 for the as-welded condition and M₁ = 0.39 for the ground condition. Finally, mean stress factors are presented, enabling feasible application in the fatigue design of welded and post-treated structures. The resulting factors are compared with values from the literature for steel applications, showing an increased mean stress influence using high-strength steel as the base material. Full article

This study systematically investigates the effect of trace Ti addition on the impact toughness and underlying deformation mechanisms of high-Mn austenitic steel from 298 K to 4.2 K through instrumented Charpy impact testing, dynamic J-R curve analysis, and multi-scale microstructural characterization (SEM, TEM). The results show that Ti addition leads to the formation of Ti(C,N) precipitations, which act as microcrack initiation sites and significantly reduce the impact-absorbed energy at room temperature (298 K) from 249 J to 189 J. However, as the temperature decreases to liquid nitrogen (77 K) and liquid helium (4.2 K) temperatures, the impact toughness of the Ti-added steel does not deteriorate further and remains comparable to that of the Base steel. This temperature-dependent behavior originates from a transition in the dominant deformation mode. At room and moderately low temperatures, deformation is primarily governed by dislocation slip, whose strong interaction with coarse precipitates leads to premature cracking. At cryogenic temperatures, the significantly reduced stacking fault energy (SFE) shifts the deformation mechanism to the predominant formation of high-density nano-twins. These dense deformation twins enhance the matrix via the dynamic Hall–Petch effect and mitigate the detrimental effect of precipitates by alleviating interactions between dislocations and precipitates. Full article

Physics-based constitutive modelling remains a cornerstone for predicting ductile damage and fracture in metallic materials, particularly where microstructural mechanisms govern macroscopic response. Over the past two decades, a wide range of crystal plasticity, porous plasticity, and void-based fracture models have been proposed to capture deformation localisation, void growth, and coalescence under complex loading paths. However, these developments are often presented in isolation, obscuring their shared physical assumptions and limiting their transferability across material systems and length scales. This article provides a microstructure-sensitive perspective on the constitutive modelling of ductile damage and fracture, with particular emphasis on crystal plasticity-based frameworks, void growth and coalescence mechanisms, and interface-driven fracture. Rather than attempting an exhaustive review, this review highlights the unifying concepts, modelling trade-offs, and recurring challenges related to parameter identifiability, scale bridging, and predictive robustness. It further clarifies how physics-based constitutive descriptions can be systematically integrated into modern fatigue and fracture assessments and situates these developments relative to emerging data-assisted and machine-learning-enhanced modelling strategies. By reframing established constitutive models within a coherent physical narrative, this perspective aims to support more transparent model selection, improve interpretability, and guide future developments in the multiscale damage and fracture modelling of metallic materials. While these frameworks offer enhanced microstructure sensitivity, their parameter richness and experimental calibration demand currently limit widespread industrial deployment, motivating ongoing work on reduced-order and data-assisted variants. Full article

Fatigue properties of low-alloy steels, LAS, are well defined in air and at the beginning of life. However, the potential influence from thermal ageing under conditions relevant for the nuclear industry is uncertain. In this study, the fatigue properties of LAS base and weld metals, aged at 345 °C for 215,000 h, are compared to as-delivered archive reference materials. In the weld material, ageing appears as an increase in yield and ultimate tensile strength. Ageing also manifests as an inclined strain–cycle (ε-N) fatigue curve, where fatigue life decreases in the low-cycle fatigue region and conversely increases in the high-cycle fatigue region. The results further show that both as-delivered and aged weld metals exhibit a significantly shorter fatigue life in the low-cycle fatigue region and a longer fatigue life in the high-cycle fatigue region when compared to the ASME Code best-fit curve. Full article

This study explores the use of machine learning to predict high-cycle fatigue (HCF) behavior and fatigue crack growth rate (FCGR) in Co-Cr-Mo alloys manufactured through laser powder bed fusion. Two machine learning (ML) models: extreme gradient boosting (XGB) and deep neural networks (DNN), are implemented to estimate HCF and FCGR across three distinct scanning strategies. The raw datasets for HCF and FCGR are taken from previously performed experiments. The HCF dataset is augmented using a Gaussian Mixture Model, while the FCGR dataset is used in its raw form. Following hyperparameter optimization, both models exhibited quite similar accuracy on validation datasets. Their performance is assessed during testing using mean squared error (MSE) and R² scores. The DNN model demonstrated higher accuracy in HCF predictions by achieving higher R² scores. The DNN performs better because it can handle more complex patterns effectively due to its multiple neurons and deeper multilayer architecture. In contrast, the XGB model performed better in FCGR predictions and yielded higher R² scores compared to XGB. The good agreement with the experimental dataset shows that these two ML techniques are effective in predicting HCF and FCGR behavior. Full article

Ni@TiO₂ core–shell nanoparticles were synthesized by magnetron sputtering and their structure verified by HRTEM and EDS analysis. The thermal stability of these particles was investigated using in situ TEM annealing and compared with that of pure Ni nanoparticles. While pure Ni particles sinter at 450 °C and exhibit significant growth at 800 °C, Ni@TiO₂ nanoparticles remain stable up to 700 °C, with the sintering onset between 700 and 800 °C. A simple thermal-mismatch model was applied to explain the stabilizing effect of the TiO₂ shell, demonstrating that differences in thermal expansion between Ni and TiO₂ generate interface stresses sufficient to crack the shell after the amorphous–rutile transformation. The TiO₂ coating effectively delays Ni coalescence by 250 °C relative to bare Ni, highlighting its role as a protective shell against high-temperature sintering. Full article

A spherical-cylindrical pressure hull is a new form of pressure-resistant structure that is distinguished from traditional large deep-sea equipment. The residual stresses and deformations introduced by out-of-tolerance welded joints pose a great threat to structural safety under deep-sea service conditions. In this paper, the angular joint of the spherical-cylindrical structure is optimized as a skirted butt joint, and the simulation method is employed to focus on the changes in stress and deformation in the two structural models before and after applying 20 MPa external pressure. The results identify that under hydrostatic pressure, the stress level in the skirt model decreases significantly compared to the residual stress of welding, while the stress in the fillet model increases slightly at the local location. After unloading, the structural stress and deformation return to the post-weld state. The effect of heat treatment on stress relief is very significant and can improve the bearing capacity of the structure. Full article

This study investigates the progressive and critical variations in the outer minor-axis length of 6063-T5 aluminum alloy elliptical-square tubes, each with one of four outer major-to-minor axis length ratios (1.5, 2.0, 2.5, and 3.0), subjected to cyclic bending. The variations in the outer minor-axis length and the critical conditions leading to structural instability were systematically examined. Experimental observations revealed that the relationship between the changes in outer minor-axis length and the number of cycles could be divided into three distinct stages: (1) a rapid increase during the first stage, (2) a gradual and stable growth during the second stage, and (3) a saturation stage where further increase became negligible before final failure. The results showed that higher controlled curvature values corresponded to greater critical variations in the outer minor axis length, while larger axis-length ratios also led to increased critical variations. Furthermore, a modified version of the empirical ovalization model originally proposed by Lee et al. for SUS304 stainless steel circular tubes was employed. Nonlinear regression using the least-squares method yielded fitting parameters that describe the relationship between changes in the outer minor-axis length and the number of bending cycles during the first and second stages. In addition, a logarithmic-linear correlation was established between the critical change in the outer minor-axis length and the controlled curvature. The strong agreement between theoretical predictions and experimental results confirms the reliability and accuracy of the proposed empirical model and its parameterization. Full article

Metallic seismic dampers are an effective tool for reducing structural damage during seismic events. While previous reviews have often focused on cataloging device types, this review presents a deep analysis of the underlying science governing their performance. Particular emphasis is placed on advanced computational methods, such as non-linear kinematic hardening (e.g., Chaboche) and micromechanical damage models (e.g., GTN), which are essential for accurately predicting low-cycle fatigue and fracture. Furthermore, advances in materials science are analyzed, ranging from low-yield-strength (LYS) steels to self-centering shape memory alloys (SMAs). Finally, the influence of manufacturing processes (including additive manufacturing) is explored, and critical future challenges in design, modeling, and long-term durability are identified. This analysis provides a foundational resource for researchers seeking to advance beyond simple phenomenological design toward physics-based prediction of damper performance. Full article

In alignment with the European Union’s 2050 carbon-neutrality targets, the automotive industry is intensifying efforts to adopt lightweight materials that ensure structural integrity without compromising safety. Press-hardened steels (PHS), offering a combination of ultra-high strength and formability, are at the forefront of these developments. Standard PHS grades rely on Ti–B microalloying; however, further alloying with Nb and V has been proposed to enhance hydrogen embrittlement resistance via microstructural refinement and hydrogen trapping. This study investigates hydrogen transport and mechanical degradation in a Ti–Nb–V microalloyed PHS compared to a conventional Ti-only 22MnB5 grade. Electrochemical permeation, thermal desorption, and mechanical testing were employed to characterize hydrogen diffusivity, solubility, and trapping mechanisms. The Ti–Nb–V variant demonstrated lower hydrogen diffusivity, higher solubility, and improved resistance to delayed fracture, attributable to the presence of fine NbTiV precipitates. Full article

Under cyclic loading, almost immediately after its onset, a surface layer forms where hardening and softening processes occur. The interaction of plastic deformation traces with each other, and with other structural elements, leads to the formation of a characteristic microstructure on the surface of a component subjected to cyclic loading. The set of factors (conditions) acting during cyclic loading determines the nature of slip band accumulation, the integral structurally sensitive fatigue parameter, expressed as the slope of the left side of the fatigue curve linearized in logarithmic coordinates, and the location of the breaking point on the fatigue curve in the high-cycle region. A combined review of numerous data on the fatigue of metals, obtained under various combinations of factors, and the generalization of these results through a normalization procedure for obtaining the relative (recalculated) parameters of fatigue, allows us to derive a universal method for “S-N” curve prediction. However, extensive generalization decreases the prediction accuracy for specific cases; therefore, it is proposed to form limited generalized dependencies corresponding to specific operating conditions. This paper evaluates the accuracy of fatigue limit prediction using generalized and limited-generalized relationships of fatigue recalculated parameters for various fatigue curves obtained from independent experimental data. Full article