An elastic–plastic finite element analysis (FEA) was performed for a Mode I plane-strain center-cracked plate (CCP) made of a titanium alloy and subjected to biaxial tension/compression loading. Two crack-tip configurations were considered: a mathematical notch (MN) and a finite radius of curvature (FRC). In the present study, both the J-integral and the plastic stress intensity factor (plastic SIF) were employed to characterize the elastic–plastic stress fields near the crack tip. The distributions of the J-integral and the plastic SIF were evaluated as functions of loading biaxiality and applied stress level. The analysis covered a biaxial stress ratio range extending from equibiaxial tension–compression to equibiaxial tension and included both small-scale yielding (SSY) and extensive plasticity conditions. The results reveal a pronounced coupling between loading biaxiality and crack-tip configuration effects on the fracture parameters. Opposite trends in the variation of the J-integral and the plastic SIF with respect to the biaxial stress ratio and crack-tip geometry were observed. In addition, a comparative assessment of SSY and extensive plasticity regimes was carried out for both crack-tip configurations. It was found that under extensive plasticity conditions the plastic SIF becomes dependent on the crack-tip radius of curvature, whereas under SSY conditions it remains essentially independent of crack-tip geometry.
In this study, the effect of aging temperature on the mechanical and fatigue properties of the Ti-5Al-5V-5Mo-1Cr-1Fe alloy treated by radial-shear rolling was investigated. Increasing the aging temperature from 450 up to 520 °C gave rise to coarsening of the microstructure and enhancing of the volume fraction of the a-phase from 58 to 71 %. As a result, the ultimate tensile strength decreased slightly, but both ductility and fatigue performance at a cycling frequency of 5 Hz increased. In the high-cycle fatigue regime, the regularities of the initiation and propagation of cracks, as well as the evolution patterns and ultimate sizes of the fracture surface zones were revealed. In addition, both critical level of stress intensity factors and general relationships between the crack propagation and the fatigue performance were assessed. The obtained results suggested that used combinations of radial-shear rolling and subsequent aging is a promising treatment for critical components made of the Ti-5Al-5V-5Mo-1Cr-1Fe alloy operated under low-frequency high-amplitude loads.
The mechanical characterization of welded joints is a critical step in assessing the structural reliability of stainless-steel components employed in marine, offshore, and industrial environments. Welding processes introduce significant local variations in microstructure and hardness, leading to heterogeneous mechanical properties that strongly influence fatigue life and structural performance. This study presents an integrated experimental–numerical methodology for the evaluation of local mechanical properties in AISI 316L butt-welded joints through minimally destructive hardness measurements. The approach combines two established hardness–property correlations to derive full true stress–strain curves for each region of the weld. These were subsequently implemented in a finite element model to reproduce the local and global deformation behavior during quasi-static tensile loading. Calibration was achieved using tensile tests on non-welded specimens, and a preliminary validation was conducted through Digital Image Correlation (DIC) strain measurements of both welded and base material specimens. Unlike most existing studies that focus on structural steels, this work investigates AISI 316L welds, austenitic stainless steel widely used in high-integrity applications, through a combined microhardness–FEM–DIC framework. The proposed methodology suggests the possibility to develop robust framework for correlating indentation hardness with mechanical response, offering a rapid, reliable, and potentially non-destructive route for assessing welded structures.
The paper addresses an actual fundamental mechanical problem – analysis of deformation behavior of a perfectly bonded layered metallic composite consisting of soft and hard components, being subjected to normal load and shear stress under mechanical equilibrium at prohibited interfacial slip. The problem is solved with the use of 3D crystal‑plasticity (CP) simulations using the DAMASK Spectral Solver package. By doing so, microstructure-inherited stress and strain fields were calculated, visualized, and analyzed. The results obtained provide an insight into the patterns of stress and strain localization as well as their evolution within and between mated soft/hard phases with different microstructure at the onset of subsurface deformation processes. The latter corresponds to the pre‑sliding regime beneath dry tribological contact zones. The resulting effective shear-to-normal stress ratio responses exhibited significant differences that depend on the microstructure and mechanical properties of both interfaced materials that compose a tribological pair.
Methods have been developed for inducing service-related defects—dents (using flat and spherical indenters) and scratches (using a steel blade)—under controlled impact conditions, based on the combined use of a testing system and an acoustic emission signal recording system. Critical values of loads and displacements have been established for each type of indenter (induced defect). A 4 mm thick STEF model fiberglass laminate was used as the test material. Samples measuring 150 mm × 20 mm × 4 mm were cut from the sheet of material in the warp and weft directions. Simulated external defects were applied to the specimens: a dent at a load of 0.85 times the breaking load, and a scratch at a load of 1 kN and a depth of 0.5 mm. Compression tests (ASTM D 3410/GOST 33519—2015) were carried out on groups of specimens cut along the warp and weft, without defects, and with defects including a cylindrical indentation, a spherical indentation and a scratch. The test results showed that the most dangerous defect is the ball indentation, which leads to a 20% reduction in compressive strength for weft-direction samples and a 12% reduction for warp-direction samples. Scratches and cylinder indentations had virtually no effect on the compressive strength values, and the difference in values can be explained by statistical variation. Acoustic emission signals were also recorded and analyzed during the compression testing.
Steel fibers are commonly used to compensate for the tensile weakness of concrete. However, the interaction of steel fibers with conventional reinforcing bars after a crack has been formed is poorly understood. Most fracture studies use a cut through the thickness of the material that cuts through any fiber in its path, whereas a real crack would maintain the bridging action. In this study, the true mode I fracture toughness (KIC) of steel-fiber-reinforced concrete beams with longitudinal steel bars is determined using a matrix-crack (MC) approach where short fibers are not broken through a natural pre-crack, and compared with companion beams prepared with a conventional through-thickness crack (TTC). Reinforced concrete (RC), normal strength concrete (NC), and fiber-reinforced concrete (FRC) beams with a steel fiber volume fraction of 1.0%, two ratios of notch depth to beam depth (a/d=0.25 and 0.5), and two reinforcement layouts were tested under four-point bending. Incorporation of steel fibers delayed crack propagation and improved ductility, increasing the ultimate load-carrying capacity by up to 50% and the modulus of toughness by nearly 94% relative to fiber-free beams. All cases showed higher first-cracking loads and better post-cracking load maintenance for MC specimens than for TTC specimens, confirming that the MC approach provides a more realistic representation of fiber bridging. KIC increased with a/d in plain reinforced beams, due to the growing moment arm of the steel closing force, but decreased with a/d in fiber-reinforced beams, indicating that fiber-bridging efficiency weakens as the crack deepens. The results support the MC method as a more reliable approach for assessing the intrinsic fracture toughness of fiber-reinforced RC members.
Concrete production contributes approximately 8-10% of global CO₂ emissions necessitating sustainable alternatives. This study investigates hybrid nano-modified composite cement concrete with Ordinary Portland Cement (OPC) partially replaced by Ground Granulated Blast-furnace Slag (GGBS, 30-35%) and Fly Ash (10-15%) by weight of cement, nano-reinforced using Graphene Oxide (GO, 0.01-0.05%) and Carbon Nanotubes (CNT, 0.1-0.3%) by weight of cement. Eight mixes were designed and evaluated for fresh properties, mechanical performance (compressive, split tensile, and flexural strength at 7, 28, and 56 days), and microstructure (SEM, XRD, and EDAX). Nanomaterials were dispersed using magnetic stirring to ensure uniform distribution. Optimal formulations achieved significant enhancements, specifically, GO 0.03% reached 34.5 MPa compressive (+23.2%) and 15.6 MPa flexural (+108%); CNT 0.1% achieved 33.53 MPa compressive (+19.8%) and 3.23 MPa tensile (+31.8%); the hybrid (GO 0.03% + CNTs 0.1%) demonstrated 33.9 MPa compressive (+21.1%) and 14.92 MPa flexural (+98.9%). Early-age strength improved by 69-77%, compensating for slower pozzolanic reactions associated with GGBS and Fly Ash. Microstructural characterization revealed densified C-S-H gel, refined ITZ (from 20-50μm to 10-15μm), reduced porosity (from 12.3% to 7.8%), enhanced crystallinity, and optimal Ca/Si ratios (1.36-2.14). Environmental assessment showed 39.2% CO₂ reduction and a 50.7% improvement in carbon intensity. The hybrid approach provides a viable route to sustainable, high-performance concrete for infrastructure applications.
The tribocorrosion behavior of boronized 13Cr4Ni and 16Cr5Ni martensitic stainless steels (MSS) in 3.5 weight percent NaCl is examined in this work. Samples were tempered at 600 °C for two hours and boronized at 950 and 1000°C for six hours. Hard surface layers (≈1680–1805 Hv) with case depths of 35-90 µm were generated by boronizing. Icorr increased from 0.6-0.9 µA/cm² (bare) to 4.3-8.1 µA/cm² (boronized) and then to 14.3-27.1 µA/cm² under tribocorrosion. Potentiodynamic polarization showed a shift in corrosion potential by around 200–310 mV toward more active values. The coefficient of friction (COF) in dry sliding varied from 0.49 to 0.78, and wear rates ranged from 3.5 to 5.1 × 10⁻6 mm³/Nm. At 950 °C, wear rates decreased by 25 to 27% because of higher fracture toughness (3.3 to 3.9 MPa√m). Due to electrolyte lubrication, COF decreased to 0.28-0.49 (16-33% lower) under tribocorrosion. When compared to bare MSS, boronized samples showed noticeably better wear resistance, with wear reduction of 60-80%. Under tribocorrosion, wear mechanisms changed from sticky abrasive in dry sliding to mixed abrasion, adhesion, and tribo-oxidation, controlled by cyclic passivation–depassivation. Boronizing, particularly at 950°C, improves overall tribocorrosion performance despite decreased corrosion resistance by balancing hardness and toughness.
Shear strength represents an important mechanical property. For the additively manufactured polymers nowadays, there is not a valid standard to determine the shear strength. Finite element analysis of 145 shear specimen geometries was performed. Then an AI-based optimal shape prediction methodology was developed using supervised machine learning, where a Multiple Linear Regression model was trained on selected design parameters to accurately predict shape performance and efficiently explore new design configurations. The ratio between maximum shear stress and maximum normal stress in the shear plane was considered the parameter to be optimized.
The dependences connecting the values of the residual stress components in the contact interaction zone of the steel indenter and the surface of the composite plate with the impact energy are presented. These quantitative relations are first obtained on the basis of an original experimental method developed earlier by the authors of this article. It is also established that the upper limit of applicability of the developed approach to residual stress quantifying has been expanded to the impact energy of 75 J. New results are presented that make it possible to estimate the distribution of the residual stress components over the thickness of the composite plate. The required results are obtained by drilling probe holes from the side opposite to the contact dimple. These data are essential to create a methodology for assessing the residual strength of composite plates with impact damage based on the use of residual stress values as a design parameter.
This study develops stress intensity factor (SIF) solutions for cladded WWER reactor pressure vessel nozzles subjected to pressurised thermal shock loading. Although finite element analysis is widely used for fracture assessment, analytical or semi-analytical SIF formulations remain important for fast evaluation, including online stress monitoring, probabilistic fracture mechanics, and screening of transient scenarios. The proposed approach combines an influence coefficient method based on three-dimensional finite-element J-integral evaluation with least-squares refinement of shape coefficients. A stress decomposition procedure is applied to address the stress discontinuity at the ferritic base metal–austenitic cladding interface. The resulting coefficients are validated against finite element reference solutions for representative pressure and thermal loading cases and show good agreement over the investigated range of crack sizes and aspect ratios. The developed solutions provide a practical tool for engineering assessment of through-clad and underclad defects in cladded WWER nozzle regions.
Mechanical and electronic components, mainly in aerospace and rotating machinery environments, are generally subjected to Sine-on-Random (SoR) excitations, where deterministic sinusoidal tones are superimposed on a broadband random vibration. While international testing standards require the validation of components under these complex profiles, the numerical evaluation of fatigue damage poses a major analytical challenge. The time-domain rainflow counting method is computationally prohibitive. Conversely, frequency-domain spectral methods rely on Gaussian assumptions that are explicitly violated by SoR loads, leading to inaccurate damage estimates. To bridge this gap, researchers have developed two main strategies: practical approaches that synthesize an equivalent random Power Spectral Density (PSD) based on damage or energy equivalence, and rigorous theoretical methods deriving analytical cycle distributions. This paper evaluates and compares the available methodologies, aiming to highlight the benefits and limitations of each. Ultimately, this comparative study serves as a practical guide for engineers to select the most appropriate tool for fatigue damage assessment under SoR vibrations
Epoxy adhesives are known to have good strength and chemical resistance; however, they tend to be brittle, restricting their use in structural applications. This study examines the effect of low-concentration graphene and hybrid graphene–SiO₂ reinforcement on the mechanical and fracture behaviour of epoxy nanocomposites. Composites containing 0.1–0.4 wt.% graphene and hybrid systems with 0.05–0.2 wt.% graphene combined with SiO₂ were synthesised using in-situ polymerisation and ultrasonic dispersion to ensure uniform filler distribution. Tensile, flexural, and fracture tests were performed following ASTM standards. The mechanical properties of epoxy composites are significantly improved by adding nano fillers when used at optimal concentrations. From the single filler systems, epoxy with 0.3 wt. % graphene achieved the highest enhancement of tensile and flexural strengths compared to pure epoxy. Greater enhancement was also found in the hybrid composites with a combination of 0.15 wt.% graphene and 0.15 wt.%. SiO2 resulted in an increase of 53% and 22% for tensile strength and flexural strength, respectively. All nano composite specimens showed a higher fracture toughness, with the best improvement of 71.1% found for the composite mix containing 0.2 wt.% graphene and 0.2 wt.% SiO2. Scanning Electron Microscopy (SEM) images indicated stronger interfacial bonding, more crack deflection and less brittleness when the filler loadings were optimized. The excessive filler content caused agglomeration due to which the performance was lowered. The structural strength and fracture resistance of the epoxy nanocomposites were significantly improved when Graphene is combined with SiO2 and this combination created a strong synergistic effect. A finite element simulation was carried out to understand the impact of filler addition on the flexural strength of nanocomposites and results were compared with experimental outcomes.
This study develops stress intensity factor (SIF) solutions for cladded WWER reactor pressure vessel nozzles subjected to pressurised thermal shock loading. Although finite element analysis is widely used for fracture assessment, analytical or semi-analytical SIF formulations remain important for fast evaluation, including online stress monitoring, probabilistic fracture mechanics, and screening of transient scenarios. The proposed approach combines an influence coefficient method based on threedimensional finite-element J-integral evaluation with least-squares refinement of shape coefficients. A stress decomposition procedure is applied to address the stress discontinuity at the ferritic base metal-austenitic cladding interface. The resulting coefficients are validated against finite element reference solutions for representative pressure and thermal loading cases and show good agreement over the investigated range of crack sizes and aspect ratios. The developed solutions provide a practical tool for engineering assessment of through-clad and underclad defects in cladded WWER nozzle regions.
The focus of this research was to investigate the effects of carbon nanofiber (CNF) reinforcement on the mechanical performance, interfacial characteristics, and abrasive wear behavior of short glass fiber/polyphenylene sulfide (GF/PPS) hybrid nanocomposites intended for high-performance tribological applications. Melt processing was used to fabricate GF/PPS hybrid nanocomposites with 0, 0.4, and 0.8 wt% CNFs, which were then methodically characterized. Through it-it interactions between CNFs and the polymer matrix, FTIR measurements demonstrated enhanced interfacial compatibility while confirming the retention of the PPS chemical structure. The addition of CNFs demonstrated improved fiber-matrix adhesion and load transmission capability by increasing composite density, decreasing void content, and considerably improving interlaminar shear strength (23.7%) and hardness (20%). Studies on two-body abrasive wear showed significant decreases in wear loss and coefficient of friction (CoF), with the 0.8 wt% CNF-filled composite showing the best tribological performance because a stable and continuous lubricating tribo-film was formed. Applied load mostly controlled the CoF behavior, while sliding velocity and abrasive grit size primarily affected wear loss, according to statistical ANOVA data. With prediction errors under 6.5% and coefficient of determination (R2) values between 73% and 77%, regression models demonstrated strong predictive power. The change from severe micro-cutting, matrix deterioration, and fiber pull-out in unfilled composites to mild ploughing and protective tribo-layer development in CNF-reinforced composites was further validated by worn surface morphology. The CNF modified GF/PPS hybrid nanocomposites are promising materials for automotive transmission components, bearing cages, thrust washers, gears, and power plant chute liners operating under extreme abrasive wear conditions, as evidenced by the synergistic improvement in mechanical strength, interfacial bonding, and tribological stability.
The purpose of this work is to validate the N-SIF (Notch-Stress Intensity Factor), SED (Strain Energy Density) and ENS (Effective Notch Stress) approaches for the fatigue design of austenitic stainless steel welded joints. Literature fatigue data for cruciform welded joints, originally expressed in terms of nominal stress, were first re-analysed through a finite element model in terms of N-SIF. The resulting fatigue limit was then used to determine the SED critical radius required for the application of the SED approach. The same dataset was subsequently reprocessed in terms of SED. Finally, a second finite element model was implemented to calculate the ENS values. The N-SIF and SED approaches led to a more unified representation of the fatigue behaviour compared to nominal stress, showing a noticeable reduction in data scatter. In contrast, the ENS method exhibited a significant dispersion for the investigated joints, possibly due to material-specific effects and to the geometric regularisation introduced by the fictitious notch radius. Although the available dataset is limited to root failures in cruciform joints, the results suggest promising applicability of fracture-mechanics-based local approaches to austenitic stainless steel welded joints, while indicating that further validation of the ENS method is required.
This review paper aims to systematically examine the effects that the most common thermal and thermochemical surface hardening treatments - specifically surface hardening, carburising, and nitriding - have on the fatigue strength of mechanical components, which has historically been the primary cause of failure during service. Following a brief description of the heat treatments and the mechanical and metallurgical effects they produce on components, a predictive model of the fatigue strength of surface-hardened mechanical components subjected to bending stresses is presented, using the local fatigue limit approach. The parameters used in the model are the microhardness profile of the hardened zone, the distribution of residual stresses in the hardened layer, the fatigue strength of the base material, and the stress state induced by external forces. The proposed model was validated for three real-world cases: surface hardened specimen with a notch, smooth carburised specimen and smooth nitrided specimen. The results provide important insights from both an academic and industrial perspective. In fact, they allow for the determination of which parameters must be controlled to increase the fatigue strength of surface-treated mechanical components.
The effects of nanoscale TiC (n-TiC) reinforcement on Al7075 composites made by stir casting with 0%, 1%, 2%, 3%, and 4% reinforcement are examined in this work. The existence of n-TiC particles in the aluminum matrix was verified by microstructural investigation. When compared to un-reinforced alloy (Al7075), the mechanical, tribological, and wear properties were greatly improved by the addition of n-TiC; hardness, tensile strength, and wear resistance increased by 28.57%, 24.41%, and 33.69%, respectively. Molybdenum wire was used as the electrode material in an experimental investigation of the produced nano composites' machinability characteristics during Wire Electrical Discharge Machining (WEDM). Two machining attributes, Material Removal Rate (MRR) and Surface Roughness (SR), are examined in connection to the combinational values of pulse time ON, pause time OFF, as well as peak current, which are chosen as the changeable input process elements. The results of the experiment showed that as pulse on time and peak current levels increased, so did MRR and Ra values. Under these circumstances, the wire electrode has maximum current, which makes it simple to remove more material and produce a moderate surface finish. The ANOVA results show that the "Pulse ON Time" has the biggest impact (47.01 %) on MRR and 36.64% impact on surface roughness values compared to the other factors, making it the most important parameter. The confirmatory test results revealed that the errors in MRR and Ra values were within acceptable limits. In the present research work, Taguchi methods have been successfully implemented to identify the optimum machining conditions for Al7075/n-TiC composites.
17-4 PH specimens were produced using the three-step process referred to as Material Extrusion Additive Manufacturing (MEAM), which involves printing components with a composite feedstock of metal powder and polymers, followed by a debinding process to remove the polymer, and a final sintering process to obtain the finished metallic part. The process enables the production of metallic components at a limited cost and with reduced safety issues in comparison to other additive manufacturing processes. With the goal of exploring and evaluating the fatigue properties of 17-4 PH MEAM specimens, two experimental campaigns were designed. The first with the objective of assessing the effect of thickness on the fatigue performance of smooth specimens, and the second aimed to investigate the notch effect on the fatigue limit of different notched specimens. The smooth specimens were fabricated with a thickness ranging between 1 and 5 mm, while the notched specimens were fabricated with a thickness of 3 mm, with 90° and 30° notch opening angles. The mechanical properties of the smooth series proved not to be affected by the thickness, neither for quasi-static nor cyclic response. On the contrary, the fatigue behavior of the notched specimens was significantly influenced by the presence of the notch, with sharper notches exhibiting a more negative impact. Moreover, the findings revealed that the fabrication of specimens characterized with thin sections, small geometrical features, and acute notches presented significant challenges, posing a severe issue regarding the practical applicability of MEAM for real-life complex geometries.
By controlling welding parameters and adjusting process conditions, three typical defects-oxide inclusions, tunnel defects, and lack-of-penetration defects-were intentionally introduced during the friction stir welding (FSW) of aluminum alloys. A comparative analysis of fatigue S-N curves between sound joints and joints with the three types of defects was conducted to systematically evaluate the impact of different defect types on the fatigue performance of welded joints. The results demonstrated that all three defects significantly reduce the fatigue life of the joints, with lack-of-penetration defects having the most pronounced effect, followed by tunnel defects and oxide inclusions. Fracture surface analysis using SEM, EDS, and Microhardness testing confirmed that defects act as the primary crack initiation sites—the sound joint initiated cracks at the arc-textured surface, whereas cracks in all defective joints originated from the defect regions. Building on these fractographic findings, the intrinsic micro-mechanism responsible for the systematic decrease in the S-N curve slope —from 7.14 for the sound joint to 2.74 for the LOP defect joint—was elucidated: the geometric sharpness and interfacial bonding state of a defect compress the crack initiation stage, shifting the dominant failure mode from initiation-dominated to propagation-dominated, which in turn manifests as a reduction in m.
