High Stress Concentration Research Articles

Investigations on Fatigue Life of Ball Pin After Laser Shock Peening

ABSTRACTIn the present work, laser shock peening (LSP) was applied on critical areas of ball pins made of 41CrS4 steel to extend their fatigue life. The treatment introduced compressive residual stresses up to a depth of 1 mm with maximum value of −592 MPa on the ball pin surface. This led to a suppression of fretting fatigue in the conical section of the ball pin under lower stress amplitudes and overall fatigue life improvement by a factor of 2.4. After LSP, the crack propagation speed was slowed down to 0.001 μm/cycle down from 0.1 μm/cycle. At high stress amplitudes, the location of the main fatigue crack shifted into a notched part of the ball pin. The combined effect of high stress amplitude and stress concentration changed the elastic strain dominated high cycle fatigue to plastic strain dominated low cycle fatigue where the LSP treatment had no significant impact on the fatigue life.

Metallurgical Investigation and Failure Analysis in GTD-111 Stage 2 Buckets From an Industrial F-Class Gas Turbine

Abstract A utility experienced cracking in multiple stage 2 buckets (S2Bs) in a large F-class power generation gas turbine after only 7348 h and 31 starts following a standard repair and rejuvenation heat treatment cycle. The blades were cast from a directionally solidified (DS) superalloy and the cracking was found in the shroud section of the blade in the Z-notch region. A detailed failure investigation was conducted to determine the failure mechanism and most likely contributing factors to root cause in terms of design, operation, fabrication, and metallurgy. Three blades, two with visible cracks and one without cracks, were subjected to nondestructive and destructive evaluation. Methods consisted of visual inspection, three-dimensional scanning, physical measurements, chemical analysis, optical metallography, LED surface topological evaluation, and scanning electron microscopy. The failure mechanism was determined to be due to creep with damage propagating along the grain boundaries in a high stress concentration area. Evaluation of precipitate structure and size also confirmed this area exhibited the highest temperature during operations. High temperature creep testing was also conducted in material from the two different casting houses to confirm metallurgical risk did not have a significant impact on creep performance. An evaluation of the operational profile of an entire fleet of GE 7FA units showed that the failed 7F.03 S2Bs were in the highest operating temperature base loaded units. The findings from this work will help better define key factors that influence the high temperature performance of nickel-base superalloys used in the hot section of industrial power generating turbines.

Mining-Induced Earthquake Risk Assessment and Control Strategy Based on Microseismic and Stress Monitoring: A Case Study of Chengyang Coal Mine

As large-scale depletion of shallow coal seams and increasing mining depths intensify, the frequency and intensity of mining-induced earthquake events have significantly risen. Due to the complex formation mechanisms of high-energy mining-induced earthquakes, precise identification and early warning cannot be achieved with a single monitoring method, posing severe challenges to coal mine safety. Therefore, this study conducts an in-depth risk analysis of two high-energy mining-induced earthquake events at the 3308 working face of Yangcheng Coal Mine, integrating microseismic monitoring, stress monitoring, and seismic source mechanism analysis. The results show that, by combining microseismic monitoring, seismic source mechanism inversion, and dynamic stress analysis, critical disaster-inducing factors such as fault activation, high-stress concentration zones, and remnant coal pillars were successfully identified, further revealing the roles these factors play in triggering mining-induced earthquakes. Through multi-dimensional data integration, especially the effective detection of the microseismic “silent period” as a key precursor signal before high-energy mining-induced earthquake events, a critical basis for early warning is provided. Additionally, by analyzing the spatiotemporal distribution patterns of different risk factors, high-risk areas within the mining region were identified and delineated, laying a foundation for formulating precise prevention and control strategies. The findings of this study are of significant importance for mining-induced earthquake risk management, providing effective assurance for safe production in coal mines and other mining environments with high seismic risks. The proposed analysis methods and control strategies also offer valuable insights for seismic risk management in other mining industries, ensuring safe operations and minimizing potential losses.

Exploring the Relationship Between Foot Position and Reduced Risk of Knee-Related Injuries in Side-Cutting Movements

Background: Knee-related injuries often result from poor movement patterns that destabilize the joint and increase stress on knee structures. Understanding the influence of foot positioning on knee biomechanics is critical for identifying high-risk movement patterns and preventing injuries. Methods: Twenty healthy male participants performed side-cutting movements at three different foot progression angles. One participant’s data were used to develop and validate a knee finite element model with high-speed dual fluoroscopic imaging (DFIS). Combined with a musculoskeletal analysis, the model simulated internal knee loads under various foot-positioning conditions. Results: The analysis revealed that, as the external foot progression angle increased, the ankle plantarflexion decreased, while the ankle internal rotation and knee valgus moments increased. Higher stress concentrations were observed on the ACL, lateral meniscus, lateral tibial cartilage, and medial collateral ligament, particularly at the femoral–tibial ACL attachments. Conclusion: The findings suggest that a toe-out foot position elevates the risk of knee injuries by increasing stress on key structures, whereas a toe-in position may enhance joint stability, reduce the ACL injury risk, and promote favorable muscle activation patterns.

Phytohormone pretreatment mitigates the negative impacts of salt stress on the germination of common buckwheat seeds (Fagopyrum esculentum)

ABSTRACT Salinity is one of the major abiotic stresses that affect crop production in worldwide. Seed germination is the most sensitive stage affected by salinity. Common buckwheat (Fagopyrum esculentum Moench) is a widely cultivated minor-crop with huge economic importance in China. However, little is known about the effect of plant hormones during seed germination under salt stress. In this study, our results shown the germination rate decreased with increasing NaCl concentration. The effect of four different synthetic phytohormones (ethephon; gibberellin, GA3; 6-benzylaminopurine, 6-BA; and naphthalene acetic acid, NAA) at different concentrations on the germination of seeds under low (50 mmol L−1 NaCl) and high (100 mmol L−1 NaCl) concentration of salt stress have been investigated. Pretreatments with ethephon, GA3 and 6-BA have alleviated the adverse effects of salt stress during seed germination, whereas pretreatment with NAA has aggravated the adverse effects due to salt stress. The most effective treatments for alleviating the adverse effect of salt stress on common buckwheat seed germination were 100 mg L−1 of ethephon, 100 mg L−1 of GA3, and 200 ug L−1 of 6-BA. This study provides a new insight for cultivation of common buckwheat especially the seed germination of common buckwheat in saline environments.

Effect of polyethylene microplastics on anammox sludge characteristics and microbial communities

Microplastics (MPs), a class of emerging pollutants, pose significant potential risks to microbial metabolism and ecology. By adding different concentration gradients of polyethylene (PE), the effects of PE on the nitrogen removal efficiency and bacterial colony structure of anammox granular sludge (AnGS) were examined. The results of the 40 d experiment with various concentrations (0.05~1.0g/L) of PE MPs on AnGS showed that the elimination of ammonia and nitrite nitrogen was less affected than in the control group. Analysis of extracellular polymer (EPS) content revealed a decreasing trend in EPS content under high stress concentrations (0.2~1.0g/L) compared to the control, and protein/polysaccharide (PN/PS) showed a similar situation, suggesting that the stability of AnGS was compromised by elevated PE concentrations. Specific anammox activity (SAA) indicated a declining trend with increasing polyethylene microplastic (PE MP) concentrations between 0.2 and 1.0g/L, and the nitrogen removal performance of AnGS decreased. From the micro-morphological point of view, the AnGS subjected to 0.5g/L stress formed blocky large particle aggregates. PE MPs were adsorbed on the surface of AnGS and combined with it to form dense particles, and both particle size and mechanical strength of the granular sludge increased proportionally the concentration of PE MPs. High-throughput sequencing data indicated that exposure to 0.5g/L PE MPs stress enhanced the complexity of the microbial community structure in AnGS, while reduced the relative abundance of the anammox bacteria Candidatus Brocadia and Planctomycetes by 2.2% and 4.2%, respectively.

Mechanical strengthening and corrosion behavior of friction stir welded dual-phase Fe50Mn30Co10Cr10 high entropy alloy

This study explores the mechanical strengthening and corrosion behavior of friction stir welded joints in dual-phase Fe50Mn30Co10Cr10 high entropy alloy (HEA). The influence of microstructural evolution on the joint's mechanical properties was analyzed, along with an assessment of its corrosion resistance using electrochemical quantitative analysis. Additionally, the corrosion mechanisms of HEAs were explored by analyzing corrosion morphology. The results show that the nugget zone exhibits a low fraction of HCP phase, yet refined grains contribute to higher hardness compared to the base metal. The presence of multiple dislocations, HCP phases, and partially fine grains enhanced hardness in thermal-mechanical affected zone and heat affected zone, despite coarse grain does not favor hardness in these zones. Although fracture occurred in the heat affected zone due to inadequate inhibition of coarse grains on the crack propagation, the TRIP effect increased the joint's tensile strength to 97.1 % of the base metal. Reduced Mn segregation and grain refinement in the nugget zone promote the formation of thicker and more uniform passivation films, which exhibit superior corrosion resistance compared to the base metal. Conversely, a high fraction of HCP phase in the base metal elevated its tensile strength but reduced elongation by inducing high stress concentrations near phase boundaries. And the combined effects of component segregation, a high fraction of HCP phase, and bulk grain boundaries accelerate base material dissolution.

High-power narrow-linewidth tunable blue laser diode array utilizing a blazed grating external cavity

High-power, narrow-linewidth blue laser sources have been in high demand for applications in laser pumping and spectral beam combining. In this paper, a blue laser source, consisting of 12 transistor-outline (TO) packaged laser diodes (LD), is established through space beam combining. An improved external cavity (EC) utilizing a blazed grating (BG), a beam splitter, and a beam expander is investigated. Through injection feedback and mode competition, a laser output, with 31.2 W power, 445.04 nm central wavelength, 0.18 nm full-width at half maximum (FWHM) linewidth, is achieved at a driving current of 3.0 A. A tunable range of 3.6 nm is observed at 2.0 A driving current. Additionally, the effect of the deformation of the aluminum-coated grating under a high-intensity blue laser is examined. The external cavity requires a moderately efficient blazed grating and prevents potential damage caused by high absorption and thermal stress concentration. The system exhibits excellent temporal stability in both output power and spectrum. Moreover, wavelength-locking experiments using both a volume Bragg grating (VBG) and a surface grating (SG) are conducted to serve as comparative tests for this study. Compared with volume Bragg gratings, blazed gratings offer spectral tunability and are insensitive to temperature perturbations and mechanical stress. Compared with surface gratings, blazed gratings offer a relatively high threshold and stable performance at high driving currents. Furthermore, blazed gratings are more cost-effective than VBGs, providing a competitive advantage. To the best of our knowledge, it’s the first blue laser source with over 30 W output and 0.18 nm FWHM linewidth utilizing a blazed grating external cavity.

Study of the residual stress distribution in SiCp/Al composites under thermal cycling conditions

In this study, a three-dimensional random representative volume element model was constructed using the finite element method combined with Python script to investigate the residual stress distribution in SiCp/Al composites with varying volume fractions, particle shapes, and particle size under thermal cycling conditions. The model has two different particle morphologies: spheres and irregular polygons. The results show that the irregular polygonal SiC particles exhibit higher residual stresses than spherical particles before and after thermal cycling due to their complex load transfer pathways and higher stress concentration at particle corners, which makes them more consistent with the characterization of SiCp/Al composites under practical application conditions. As the volume fraction of SiC particles increases, the particle spacing decreases, hindering the release of thermal stresses through plastic deformation. Notably, the relief rate of residual stress reached 53% in the 12 vol% SiCp/Al composites, with the stress decreasing from 698 MPa to 328 MPa after 50 thermal cycles. In contrast, the reduction rate for 18 vol% composites is only 13% after thermal cycling. Furthermore, compared to larger particles (7.3 µm, 8.9 µm), the smaller particles (4.3 µm, 5.9 µm) exhibit a more uniform stress distribution and lower thermal stresses before and after thermal cycling. Consequently, our work provides a significant theoretical basis for the design and application of SiCp/Al composites, especially for the application of materials under extreme temperature changes.

Stress Concentration Modelling in Internal Stiffeners of Ship-to-Shore Quay Cranes Legs Due to Structural Heightening

This paper presents a study on the modelling and estimation of stress concentration at the tips of leg stiffeners in ship-to-shore (STS) quay cranes, which is intensified in those on the sea-side leg extensions, which are more prone to crack formation, notably following structural heightening of the cranes. A computer-simulated database was generated, incorporating mechanical parameters and geometric features that impact stress concentration. These variables can then be integrated as inputs into a multiple linear regression model (MLR). This methodology offers an alternative to the finite element method (FEM) for the computation of stress concentration and deformations. At the same time, the statistical significance of the parameters influencing this scenario is determined, ensuring a comprehensive assessment of their impact on the studied phenomenon. The research underscores the importance of incorporating stress concentration and structural geometry considerations into crane design or modification, given their crucial role in preserving the remaining lifecycle of the structure. Crack initiation is significantly intensified in regions characterised by high stress concentrations, particularly in areas where there are geometric changes at the tips of the stiffeners, where local stiffness is altered. All of this is in combination with work cycles under the supported loads.

Metagenomic insight into the enrichment of antibiotic resistance genes in activated sludge upon exposure to nanoplastics

Activated sludge is an important reservoir for the co-occurring emerging contaminants including nanoplastics (NPs) and antibiotic resistance genes (ARGs). However, the impacts and potential mechanisms of NPs on the fate of ARGs in activated sludge are not fully understood. Herein, we used metagenomic approach to investigate the responses of ARGs, host bacteria, mobile genetic elements (MGEs), and functional genes to polystyrene (PS) NPs at environmentally relevant (0.5 mg/L) and high stress concentrations (50 mg/L) in activated sludge. The results showed that 0.5 and 50 mg/L PS NPs increased the relative abundance of ARGs in the activated sludge by 58.68% and 46.52%, respectively (p < 0.05). Host tracking analysis elucidated that the hosts of ARGs were significantly enriched by PS NPs (p < 0.05), with Proteobacteria being the predominant host bacteria. Additionally, the occurrence of new ARGs hosts and the enrichment of MGEs and functional genes (i.e., genes related to SOS response, cell membrane permeability, and secretion system, etc.) indicated that PS NPs promoted horizontal gene transfer (HGT) of ARGs. Finally, path modeling analysis revealed that the proliferation of ARGs caused by PS NPs was primarily attributed to the enhancement of HGT and the enrichment of host bacteria. Our findings contribute to a comprehensive understanding of the spread risk of ARGs in activated sludge under NPs pollution.

Combining transcriptome and metabolome analyses to reveal the response of maize roots to Pb stress

As a major food crop, maize (Zea mays L.) is facing a serious threat of lead (Pb) pollution. Research into its Pb tolerance is crucial for ensuring food security and human health, however, the molecular mechanism underlying the response to Pb remains incompletely understood. Here, we investigated the transcriptomic and metabolome of two maize lines (BY001, a Pb-resistant line; BY006, a Pb-sensitive line) under different concentrations of Pb stress (0, 500, 1000, 2000 and 3000 mg/L). The results showed that BY001 performed well, whereas the BY006 exhibited minimal development of lateral roots upon exposure to high concentration of Pb. The antioxidant enzyme activity of BY001 remained relatively stable, while that of BY006 declined significantly. Transcriptomic analysis revealed that under high concentration of Pb stress, BY001 produced 5057 differentially expressed genes, whereas BY006 produced 3374. Functional annotation showed that these genes were primarily involved in carbohydrate metabolism, root growth, and plant resistance to external Pb stress. Further untargeted metabolomics indicated that Pb stress triggered distinct alterations in the levels of 47 diverse metabolite types across 13 distinct classes, particularly amino acids, carbohydrates, and organic acids. A conjoint omics analysis suggested that the pathways of starch and sucrose metabolism, as well as cutin, suberin, and wax biosynthesis in BY001, play a key role in the Pb resistance. These findings elucidate the biological mechanisms employed by maize to counter the effects of Pb stress, and provide a basis for breeding of maize cultivars with low Pb accumulation or tolerance.

An asymmetric pinching damaged hysteresis model for glubam members: Parameter identification and model comparison

The performance of glue laminated bamboo (glubam) members is governed by the nonlinear response at their joints, where high deformation levels and stress concentrations are developed. Numerous phenomenological models are presently employed to describe the hysteresis behavior of these joints, while these models always have an excessive number of parameters, and the physical interpretation of these parameters is often challenging. Moreover, some hysteresis models cannot capture all hysteresis features such as asymmetry, pinching, and damage. Consequently, this paper introduces a novel phenomenological-based hysteretic model named Asymmetric Pinching Damaged (APD) model, and implemented it in Abaqus by combining connector and spring elements in series or parallel. This model encompasses asymmetry, pinching, and strength degradation for bamboo joint components, with parameters that possess clear physical meanings and are readily comprehensible. This study also presented a parameter identification framework coupling the Parallel Genetic Algorithm (PGA) and Bayesian Neural Network (BNN). By merging the FE modeling and optimizing algorithms with the interactive application of ABAQUS and Python software platforms, the integrated identification framework is capable of performing multi-threaded parallel computation of finite element models considering the BNN-based uncertainty quantification, thus greatly improving the efficiency of parameter identification.

Concept of Expert Software for Welding of Nodes from Inland Vessels

The structural integrity and safety of the vessels depends significantly on the quality of their welded joints, particularly at specific nodes where high-stress concentrations are common. This research leverages computer-aided design, artificial intelligence and materials science advancements to develop an innovative software tool that integrates expert knowledge, and best practices, for inland vessel welding. The proposed expert software system offers several key features, including the visualization of specific ship nodes, their parameters, as well as the residual stresses and strains that are specific to each node. By integrating these functionalities, the software aims to minimize human error, reduce inspection time, and ultimately improve the overall structural reliability of inland vessels.

Effects of Length-to-Width Ratio on Magnetic and Microstructural Properties of Die-Upset Nd-Fe-B Magnets.

In this study, the effects of the length-to-width ratio on the magnetic and microstructural properties of die-upset Nd-Fe-B magnets were examined. A die-upset magnet with a uniform shape and no significant cracking was successfully developed. During the die-upset process, the applied pressure was not uniform across the magnet and varied depending on its shape and position. In the case of the magnet with a 4:1 ratio, which had the largest length-to-width ratio, there was a higher concentration of stress at the edges compared to the center, resulting in easier grain deformation and growth at the edges, which led to the lowest remanence and (BH)max. As the length-to-width ratio approached 1:1, the grain size increased slightly, reducing the coercivity; however, the magnets maintained a uniform grain-size distribution. The change from a rectangular to a square pressing surface resulted in a more uniform stress distribution, particularly at the center and corners, which improved the consistency of the magnetic properties across different regions of the magnet. Consequently, an 11.9% enhancement in (BH)max, reaching 285.6 kJ/m3, was achieved in the 1:1 ratio die-upset magnet, which is attributed to the uniform grain size and improved grain alignment.

Effect of friction stir processing on grain refinement and superplastic properties of binary Al-8 wt.% Si to Al-30 wt.% Si alloys

ABSTRACT As-cast binary Al–Si alloys containing ∼8, 12, 20, and 30 wt.% Si, representing the hypoeutectic, eutectic (12 wt.% Si), and hypereutectic compositions, were subjected to severe plastic deformation by friction stir processing (FSP) for grain refinement to 2.3–2.7 μm by dynamic recrystallization. Tensile tests conducted by differential strain rate test technique over the strain rates of 10−4 – 10−2 s−1 and test temperatures in the range of ∼840–530 K led to strain rate sensitivity index (m) varying from ∼0.04 to 0.40 depending on temperature, strain rate, and alloy composition. The constant initial strain rate tests conducted at 10−4 s−1 and 840 K exhibited a maximum elongation of 250% in the hypereutectic Al–20Si alloy, but the same increased linearly with m irrespective of alloy composition. Generally, with increasing Si content, the activation energy for deformation increased from 104.7 ± 14.4 kJ/mol for eutectic Al–12Si to 310.4 ± 32.3 kJ/mol for hypereutectic Al–30Si, which increased further to 572 ± 148 kJ/mol over the higher temperature range of 840–800 K. Analysis of observed deformation and microstructure behaviour supports the occurrence of superplasticity, whereby the accommodation of grain boundary sliding by grain boundary migration led to enhanced grain growth or else the local high-stress concentration at the particle-matrix interface led to cavity formation. There was no evidence of dynamic recrystallization during high-temperature tensile deformation but the flow softening observed is ascribed to the occurrence of concurrent cavitation.

Fast low-temperature irradiation creep driven by athermal defect dynamics

The occurrence of high stress concentrations in reactor components is a still intractable phenomenon encountered in fusion reactor design. Here, we observe and quantitatively model a non-linear high-dose radiation mediated microstructure evolution effect that facilitates fast stress relaxation in the most challenging low-temperature limit. In situ observations of a tensioned tungsten wire exposed to a high-energy ion beam show that internal stress of up to 2 GPa relaxes within minutes, with the extent and time-scale of relaxation accurately predicted by a parameter-free multiscale model informed by atomistic simulations. As opposed to conventional notions of radiation creep, the effect arises from the self-organisation of nanoscale crystal defects, athermally coalescing into extended polarized dislocation networks that compensate and alleviate the external stress.

Computed tomography-driven analysis of particle breakage using a coupled FDM–DEM approach

This study proposes a refined approach for simulating the mechanical behavior of soils under high stress by integrating the finite difference method–discrete element method (FDM–DEM) with in situ experiment. This novel framework incorporates advanced technologies such as flexible membrane and X-ray computed tomography (CT) to enhance the predictive capabilities of the simulation with physical insight. The FDM–DEM model adeptly simulates irregular particle shapes, capturing their interactions and the dynamics of particle breakage. The use of flexible membrane within the model further enriches this approach by enabling the capture of deformation responses in granular materials during shearing. Moreover, the adoption of CT technology facilitates continuous optimization of the simulation process. Validation through in situ experiments has confirmed the model’s effectiveness. The ability of the model to predict areas of high stress concentration—and their correlation with observed particle breakage patterns—underscores the utility of the enhanced FDM–DEM framework as a robust predictive tool for understanding the behavior of granular materials under shearing.

Study of GTA-Welded Joints of ZW61 Magnesium Alloy — Effect of Welding Current on the Microstructure and Mechanical Properties

An attempt has been made to weld ZW61 magnesium alloy extruded plates by gas tungsten arc welding (GTAW). In this paper, the zone with the largest average grain size in the welded joint was the fusion zone (FZ) rather than the heat-affected zone (HAZ). The grains of the FZ were nearly equiaxed, and their average size increased gradually with the increase of welding current. Simultaneously, the mechanical properties of the joints decreased with the increase of welding current under the set conditions of this experiment. The optimum mechanical properties of the joints were obtained at a welding current of 100 A. Their ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) were 230 MPa, 103 MPa, and 19.2%, respectively, while the joint efficiency (σb / σb BM) was only 77.7%. The fracture locations of all the joints were found in the FZ. Excessive grain size was one of the significant factors contributing to the weakness of this zone. In addition, the semicontinuous second phase on the grain boundary induced high-stress concentrations, contributing to the fracture of the welded joint. The tensile properties of the joints can be improved by limiting heat input.

Investigating the impact of notch shapes on oxide–oxide ceramic matrix composites strength: A computational approach

AbstractThis study utilizes finite element analysis (FEA) to explore the effect of standardized notch shapes—triangular, circular, and rectangular on the tensile behavior of oxide–oxide (O–O) ceramic matrix composites (CMCs) across various temperature ranges. Findings reveal that unnotched samples exhibited a superior equivalent stress of ∼425 MPa, closely aligning with experimental values. However, under elevated temperatures of 1000°C and 1200°C, degradation occurs, reaching up to 54% decrease at 1200°C. Notched samples demonstrate similar behavior, with all notches acting as stress concentrators. Analysis of single and double notches highlights that circular notches have the most significant stress concentrators due to their smooth surfaces and lack of sharp edges, in contrast to rectangular and triangular notches. Although all notch types influence stress concentration, the absence of non‐sharp corners in circular notches limit stress dissipation, resulting in higher stress concentrations. This trend persists under high temperature as well. The study emphasizes the critical need for a thorough assessment of notch effects, considering their position, orientation, shape, and size, as they significantly affect the mechanical properties of O–O CMCs.