Search Results (367)

Impact toughness of three different samples was evaluated using an instrumented Charpy pendulum combined with fractography performed using scanning electron microscopy (SEM) to analyze the effects of heat treatment and vanadium as alloying element. Samples were made from Mn16V with water quenching and aging (WQA), as well as from Mn16V and Mn16 with WQA and additional aging (WQAA). It was concluded that vanadium reduced impact toughness, whereas the additional aging had practically no effect. Full article

This research examines how atmospheric plasma spraying torch power and coating thickness jointly affect the adhesion strength, microstructure, porosity, and flexural behavior of $A{l}_2{O}_3$ coatings on 100Cr6 steel substrates. Optical microscopy, SEM and EDS mapping, 3D surface-roughness analysis, Vickers hardness testing (HV2) on polished cross-sections, and three-point bending of extracted beams were employed to develop a processing–structure–property map. This multi-technique approach enables the cross-validation of processing–structure–property relationships and supports a robust identification of the optimal power–thickness condition by jointly considering porosity (densification), adhesion strength, flexural response and failure mode. All conditions resulted in an average surface roughness Ra of approximately 1.0 µm. Increasing torch power to 45 kW generally reduced cross-sectional porosity, except at 500 µm, where globular pores appeared. Hardness (HV2) increased with power and peaked at the intermediate thickness (500 µm); adhesion up to 63 MPa was recorded for the 300 µm/45 kW coating. Flexural strength was highest at 500 µm and was consistently greater at 45 kW than at 39 kW. Fractography showed a shift in failure mode from interface-driven delamination at 39 kW to more cohesive, tortuous intra-coating cracks at 45 kW, aligned with improved splat bonding and crack-path deflection. An intermediate thickness of 500 µm deposited at 45 kW is thus identified as an optimal condition to balance densification and crack-path tortuosity, leading to enhanced hardness and flexural performance. Full article

Threaded component fatigue failure is a severe issue in cyclically loaded mechanical systems, and the service life in these systems is controlled primarily by stress concentration at the thread root, especially in loading regimes dominated by bending. Rounded thread profiles such as knuckle threads have been thought to improve fatigue performance, although this is mostly due to the assumption being made on the basis of axial loading, the numerical stress analysis, and/or isolated stress-concentration analyses. This paper presents an experimental study on the fatigue behavior of knuckle-thread and conventional screw-thread specimens manufactured from AISI 1045 steel under rotating bending loading to determine the effects of thread geometry on fatigue life and damage mechanisms. Fatigue testing was conducted at varying stress levels to develop comparative stress–life (S–N) curves, the analytical relation being used in determining the stress-concentration factor, and standard literature techniques have been used in the analysis of fracture-surface in order to investigate the behavior of crack initiation and propagation. Results indicate that knuckle threads exhibit a lower stress concentration factor (K_t ≈ 1.59) than screw threads (K_t ≈ 2.11), resulting in longer fatigue life at the same nominal stress level, particularly in the high-cycle life regime. Fractographic research also indicates that knuckle threads enhance delayed crack initiation and more evenly distributed circumferential crack propagation, but screw threads show highly localized crack initiation and rapid radial propagation of cracks, resulting in earlier unstable fracture. These findings provide new experimental evidence that the improved fatigue performance of knuckle threads during rotating bending is linked to fundamental change in fatigue damage mechanism rather than to stress alleviation alone, thereby offering quantitative supporting guidance in designing fatigue-sensitive threaded components to experience cyclic bending. Full article

This study investigates the as-cast Mg-8Gd-1Y-2Sm-1.2Zn-0.5Mn (wt.%) alloy with high rare-earth content. Solution treatments were conducted at 480 °C, 520 °C, and 560 °C for 6–10 h. Microstructure and mechanical properties were characterized using OM, XRD, SEM-EDS, and compression testing. The as-cast alloy shows a dendritic structure with continuous grain-boundary phases (Mg₅RE, W, and LPSO), exhibiting a compressive yield strength of 145 MPa, ultimate strength of 238 MPa, and fracture strain of 12.66%. Solution temperature has a critical influence on phase dissolution and grain refinement. Notably, the overall plasticity of the material did not show a significant dependence on the specific solution temperature or holding time within the studied range. Treatment at 520 °C produces the most balanced microstructure: clear grain boundaries, extensive phase dissolution, refined grains, and enhanced solid-solution strengthening. Specifically, 520 °C for 10 h results in the finest and most uniformly distributed residual phases, a homogeneous matrix, the highest compressive strength, and suitable conditions for subsequent aging, thus being identified as optimal. Fractography reveals a transition from quasi-cleavage in the as-cast state toward enhanced ductility after solution treatment. However, small cleavage facets after 10 h are attributed to stress concentrations from rare-earth-rich regions and reduced deformation compatibility due to retained LPSO phases. Full article

Interfacial adhesion between selective laser-melted (SLM) AlSi10Mg and polyimide (PI) insulating coatings is often limited by mismatched physicochemical properties. To improve adhesion, Al-rich and Si-rich microstructured surfaces were fabricated on the XY plane (perpendicular to the build direction) and the Z plane (parallel to the build direction) by acidic and alkaline etching, exploiting the characteristic microstructure of SLM AlSi10Mg. Surface topography, chemical composition, and wettability were characterized, and interfacial mechanical performance was evaluated by shear and pull-off tests. The microstructures increased surface roughness and improved wettability. The shear strength rose from 2.6 ± 1.5 MPa for the polished surface to 43.2 ± 8.6 MPa. The polished surface showed a pull-off strength of 2.2 ± 0.25 MPa. In pull-off tests, failure mainly occurred within the dolly/adhesive/PI system, indicating that the interfacial tensile strength exceeded the strength of the adhesive system; the maximum measured pull-off strength was 29.0 ± 1.3 MPa. Fractography predominantly showed cohesive failure in PI on Al-rich microstructures. Si-rich microstructures exhibited mixed failure, including fracture of the Si skeleton and tearing of PI, together with interfacial microcracks. Full article

Addressing technical challenges in personalized fabrication and mechanical regulation of bioresorbable vascular scaffolds, this study pioneers an electric field-driven melt jetting rotational printing technique to fabricate polycaprolactone (PCL) scaffolds (Ø3–8 mm). Multiscale characterization confirms a rhombic mesh macrostructure with uniform fibers and fusion-enhanced nodal junctions, demonstrating synergistic control of electrohydrodynamic forces and surface tension over microfiber deposition. Mechanical testing reveals triphasic tensile behavior (elastic-plastic-fracture), where 5 mm scaffolds exhibit 38% enhanced peak load due to superior interfacial bonding and densified geometry, while 8 mm counterparts suffer premature failure from structural weakening. Fractography identifies brittle fracture initiation at stress-concentrated nodes versus ductile dominance in straight segments, confirming co-regulation by intrinsic material properties and architecture. Compression tests demonstrate characteristic load-holding-recovery behavior, with 20% increased load-bearing capacity and enhanced elastic recovery in larger scaffolds. This work establishes a structure–property correlation framework for optimizing degradable vascular implants, providing novel methodologies and theoretical foundations for clinical compatibility. Full article

The joining of dissimilar steels is crucial for designing lightweight, high-performance structures but poses significant challenges due to uneven material properties. This study optimizes the butt-welding process for a dissimilar pair of S355J2 and Strenx 700E steels. Cold Metal Transfer welding was employed, and the effects of surface preparation, linear energy, and joint gap on joint integrity were systematically investigated via tensile testing, digital image correlation, fractography, and microhardness analysis. The results demonstrate that mechanical surface cleaning combined with a low linear energy of 0.334 kJ/mm and a 0.5 mm gap yields optimal performance. This parameter set produced a joint with a tensile strength of 616 MPa, representing a 32% increase compared to uncleaned samples, and promoted uniform plastic deformation across the joint. Microstructural analysis confirmed a narrower heat-affected zone and the absence of significant softening in the high-strength steel. Full article

This study investigates hydrogen embrittlement mechanisms at the interfaces of explosively welded joints between 304L austenitic stainless steel and carbon/low-alloy steels (St41k, 15HM), focusing on the unique properties of local melting zones (LMZs) formed during joining. Advanced microstructural characterization, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and microhardness testing, was combined with controlled electrochemical hydrogen charging. Results demonstrate that while base materials suffered substantial hydrogen-induced degradation—blistering in carbon steels and microcracking in stainless steel—the LMZ exhibited exceptional resistance to hydrogen damage. Compositional analyses revealed that the LMZ possessed intermediate chromium (4.8–8.8 wt.%) and nickel (1.7–3.6 wt.%) contents, reflecting mixing from both plates, and significantly higher microhardness compared to adjacent zones. The superior hydrogen resistance of the LMZ is attributed to their refined microstructure, increased density of hydrogen trapping sites, and non-equilibrium phase composition resulting from rapid solidification. These findings indicate that tailoring the process of the LMZ in clad steel joints can be an effective strategy to mitigate hydrogen embrittlement risks in critical hydrogen infrastructure. Full article

Delamination remains a critical failure mode in carbon fiber-reinforced polymer (CFRP) composites, particularly under cyclic loading in aerospace and automotive applications. This study explores whether nanoscale reinforcement with graphene-based materials can enhance delamination resistance and identifies the most effective nanofiller type. Two distinct graphene nanospecies—reduced graphene oxide (rGO) and carboxyl-functionalized graphene nanoplatelets (HDPlas)—were incorporated at 0.5 wt% into CFRP laminates and tested under static and fatigue mode I loading using double cantilever beam (DCB) tests. Both nanofillers enhanced interlaminar fracture toughness compared to the neat composite: rGO improved the energy release rate by 36%, while HDPlas achieved a remarkable 67% enhancement. Fatigue testing showed even stronger effects, with the fatigue threshold energy release rate rising by 24% for rGO and 67% for HDPlas, leading to a fivefold increase in fatigue life for HDPlas-modified laminates. A compliance calibration method enabled continuous monitoring of crack growth over one million cycles. Fractography analysis using scanning electron microscopy revealed that both nanofillers activated crack bifurcation, enhancing energy dissipation. However, the HDPlas system further exhibited extensive nanoparticle pull-out, creating a more tortuous crack path and superior resistance to crack initiation and growth under cyclic loading. Full article

This study explores Friction Stir Spot Welding (FSSW), a well-established solid-state joining technique, for high-strength aluminum alloys like AA2024-T4, which present significant challenges for conventional welding techniques. This research focuses on the impact of relatively low rotational speeds, specifically within a range of 700 to 1300 rpm, on the mechanical and microstructural properties of the welded joints. By employing a short dwell time of 3 s, this study aims to enhance productivity in the automotive and aerospace industries. The experimental work evaluated the joints’ thermal cycles, macrostructure, microstructure, hardness and load-carrying capacity. Results indicated a linear relationship between rotational speed and heat input. Although all welds exhibited a significant grain size reduction in the stir zone (SZ) compared to the base material (29.7 ± 6.1 μm), the SZ grain size increased with rotational speed, ranging from 4.7 ± 1.4 to 8.3 ± 1.3 μm. This study identified 900 rpm as the optimal parameter, achieving the highest load-carrying capacity (7.35 ± 0.4 kN) and a high SZ hardness (99 ± 1.5 HV). These findings confirm that joint strength is a balance between grain refinement and thermal softening. The presence of precipitates and the fractography of the tensile–shear tested specimens were also investigated and discussed. Full article

This work studies the hydrogen embrittlement (HE) behaviour of Dual-Phase steels with varying martensite content. Steels with martensite contents of 25 ± 5, 50 ± 4 and 78 ± 7% were realised by intercritically annealing an as-received DP steel. These steels were charged with hydrogen and consequently subjected to an in situ slow strain rate tensile test to characterise the embrittlement. It was found that the steel with 50% martensitic content showed the most ductility in air, but the highest embrittlement of 86 ± 10%. The extent of embrittlement does not increase further from the point that martensite forms a continuous network in the microstructure. The presence of martensite on the surface is linked to the formation of brittle crack initiation sites in these steels. Furthermore it was found that the anisotropic banded structure in the annealed steels promotes brittle crack propagation along the direction of banding, which originates from rolling process. This research shows that anisotropic martensite distributions as well as surface martensite should be avoided when developing rolled steels, to maximise HE resistance. Full article

Improving the operational parameters of machinery necessitates the use of materials with higher mechanical characteristics. Strength characteristics, particularly fracture toughness, are strongly linked to the material’s microstructure. This article presents the results of a study examining the effect of microstructure on the mechanical properties and fracture toughness of G17CrMo5-5 cast steel in its basic and rare-earth modified variants. The addition of rare-earth elements (REEs) to the melt resulted in a reduction and homogenization in grain size, as well as a reduction in the size and shape of non-metallic inclusions. For modified cast steel, there were no grains with a chord size above 120 μm and inclusions with a diameter above 5.5 μm. Changes in the microstructure of modified cast steel resulted in a slight increase in strength properties. It significantly increased the fracture toughness: for unmodified cast steel at a temperature of −20 °C, the fracture toughness increased from 94 kN/m to 416 kN/m for modified cast steel. Fracture fractographic analysis using non-contact microroughness measurement techniques or measuring the width of the stretch zone allowed for the calculation of fracture toughness without the need for a conventional test. Fracture toughness calculated based on fractographic analysis can be determined for brittle fracture and brittle fracture preceded by plastic growth. Numerical simulations of the loading of specimens tested for fracture toughness allowed us to determine the effect of the REE steel modification on the stress field distribution ahead of the crack front. The modification resulted in a change in the opening stress distribution and the location of its maximum at each temperature. The use of REE modification is an effective approach for homogenizing the microstructure and increasing the fracture toughness of cast steel, especially when the material operates at temperatures in the interval of the fracture mechanism change. Full article

The study of the behaviour of steel reinforcement in high temperatures is essential to understanding the performance of structural concrete after a fire. A special case is presented by steel reinforcements that are exposed to high temperatures after losing all or part of the nominal coating that protects them. In this work, detailed research has been carried out to understand the behaviour of two types of steel, B500SD (carbon) and EN 1.4301 (stainless), exposed to high temperatures. For this purpose, different heating temperatures (450, 800 and 1150 °C) and two types of cooling (rapid in water and slow at room temperature) were used. Mass loss and tensile strength were evaluated, and the ductility indices of these steels were analysed in detail, accompanied by a discussion with a statistical analysis and fractography. The results indicate that stainless steel performs better than carbon steel in a fire. The B500SD reinforcement exhibited a decrease in yield strength of up to 239 MPa (↓ 55%) compared to the reference specimen when heated to 1150 °C. Additionally, it has been observed that rapid cooling results in a more pronounced decrease in ductility in B500SD steel. However, slow cooling led to an increase in ductility in the three indices studied (Cosenza, Creazza and Ortega), with the presence of micro-void coalescence in the fractography corroborating the results. Thus, this research holds great practical interest in decision-making for the selection of structural materials, as it assesses the physical–mechanical behaviour of reinforced concrete after exposure to high temperatures. Full article

Triply periodic minimal surface (TPMS) sandwich structures made from PLA, reinforced with flax fibers, offer a bio-based approach to lightweight design, but their performance is sensitive to material-extrusion parameters. This study investigates the combined effects of layer height (0.16, 0.24, and 0.28 mm) and extrusion temperature (200, 220 °C) on the flexural behavior of gyroid-core PLA–flax sandwiches. Six parameter combinations were fabricated by fused filament fabrication and tested in three-point bending to obtain flexural strength and strain at failure. Post-fracture optical microscopy related mesostructure and failure mechanisms to macroscopic response. The highest strength (≈23 MPa) was found at 0.28 mm/200 °C, while the greatest strain at failure (≈0.06 mm/mm) occurred at 0.16 mm/200 °C. Two-factor ANOVA showed the significant main and interaction effects of temperature and layer height on both metrics. Fractography revealed a transition from interfacial delamination at lower temperatures and thinner layers to a more localized, cohesive rupture as interlayer bonding improved with higher temperature and thicker layers. Complementary compression tests revealed a core-dominated cellular collapse, with first-collapse stresses ranging from 6.3 to 8.2 MPa and a significant dependence on layer height and temperature (ANOVA). A gate-to-gate sustainability assessment indicated that layer height dominates printing time, energy demand, and CO₂ emissions, with 0.28 mm minimizing energy per unit property. Measured part masses were 4–6% below slicer predictions, consistent with typical FFF porosity. The results provide TPMS-specific process windows that balance mechanical performance and energy efficiency for PLA–flax sandwiches. Full article

The significant advancement in additive technologies has made it possible to manufacture metal components in diverse shapes and sizes. Despite this progress, numerous processes and phenomena, along with the implications of producing components layer by layer on their performance under stress, remain inadequately explored. These factors not only affect microstructure but subsequently also the mechanical properties. The positioning of objects within the 3D printer’s workspace can thus significantly play a crucial role in their operational functionality, reliability, and safety of the equipment in an application. This article studies anisotropic properties and the influence of the printing orientation of aluminum alloy (AlSi10Mg) cylindrical tensile samples fabricated through an additive approach on their mechanical properties under tensile loading. Tensile testing of specimens covering seven different spatial orientations in the workspace of a 3D printing machine was performed according to ISO 6892-1 international standard. Minimum and maximum tensile properties (yield and ultimate tensile strength) have been observed in Y-sample and X-sample series, respectively. In contrast, elastic modulus of the 3D printed specimens was minimal for X-sample series, and maximal for Y-sample series. Fracture surfaces of the samples in seven basic spatial orientations were evaluated in synergy with the mechanical testing results determined by optical, electron microscopy, and electron backscatter diffraction (EBSD) textural analysis to find correlation between the strength of the samples and the orientation of grains, their size and morphology. Furthermore, thermodynamic and Scheil–Gulliver simulation has been employed in order to explain the formation of intermetallic phases during additive manufacturing and further justifying observations in microstructure and mechanical properties. The disparity in texture intensity between these regions for samples Y(3) is likely responsible for localized mechanical incompatibilities and strain heterogeneity, resulting in preferential crack paths and reduced mechanical strength compared to the sample Z(3), which presented a more randomized orientation distribution with less distinguishable texture zones, enabling better strain accommodation and more uniform plastic deformation, which correlates with its higher tensile and yield strength. Full article