Cracking Phenomena Research Articles

Failure analysis and deformation characteristics of shield tunnel obliquely crossing ground fissure under earthquake

In order to study the deformation law and failure characteristics of shield tunnel obliquely crossing ground fissure under earthquake action, taking the shield tunnel of Xi ’an Metro Line 8 crossing f3 ground fissure as the engineering background, the 1: 20 shaking table model test method was used to analyze the strain of shield tunnel, the contact pressure with surrounding rock soil, the dislocation of segment and the axial force of bolt in detail, and the seismic damage mechanism and failure characteristics of shield tunnel obliquely crossing ground fissure were obtained. The test results show that under the action of earthquake, the shield tunnel has complex three-dimensional deformation characteristics, among which the vertical deformation is the most obvious. The deformation is mainly concentrated in the location of the ground fissure. The tensile strain and contact pressure of the hanging wall of the tunnel segment are greater than the strain value and contact pressure of the footwall. Because the vertical deformation of the tunnel is the largest, the bolts at the vault and the arch bottom are most obviously pulled. Excavation after the test, it can be seen that the tunnel appeared the phenomenon of ring joint opening, lining cracking and other damage. Under the action of the earthquake, the shield tunnel across the ground fissure is mainly subjected to tensile failure. The failure area is within 10 m from the ground fissure in the hanging wall and footwall, and the total length is 20 m. The closer to the ground fissure, the more serious the damage. The research results provide a scientific and reasonable reference for the subsequent construction and disaster prevention and mitigation design of Xi ’an Metro.

Fatigue Life Analysis and Equal Life Optimization Design of Fluid End of Septuple Fracturing Pump

Abstract To determine the cause of failures phenomenon of fatigue cracks in the crossbore area of septuple fracturing pump 4 inch fluid end, optimal design the fluid end based on the idea of equal fatigue life to reduce non-uniformity and prolong fatigue life. Firstly, the static finite element analysis under 14 design conditions and 1 test condition are calculated, the results fulfill the static strength requirements. Next, based on the static of 14 actual working conditions, find cycle peaks through constant amplitude alternating load, the fatigue life and distribution rule were calculated. Then, increase the single side width increment e to 75mm, non-uniformity between 7 cylinders is reduced from 26.6% to 1.35%, the fatigue life is prolonged by 98.2%. Finally, by parameter optimization of the crossbore fillet radius Ru to 15mm and reducing the distance from the central axis of the suction cylinder to the top 25mm, the non-uniformity of the cylinder 4 is reduced from 20.07% to 7.67%, the fatigue life is prolonged by 40.9%, and it is prolonged by 179.4% totally. The results show that the analysis method by finding cycle peaks can accurately calculate the fluid end fatigue life. The equal fatigue life parameter optimization approach has obvious consult significance for reduce non-uniformity and prolong fatigue life of septuple fluid end.

Weakly confined slotted cartridge blasting in jointed rock mass

Directional fracture blasting can improve the smooth blasting effect of layered jointed rock masses. However, few studies have comprehensively considered the interaction between joints and slit blasting, and there is a lack of quantitative research and analysis on slit blasting. Therefore, this study combined slit blasting, pouring model test blocks for explosion testing, and numerical simulations for auxiliary research. Finally, practical engineering applications were conducted. The results showed that the weakly constrained PVC material has a high instantaneous strength under impact and can achieve a good energy accumulation guidance effect. The joint angle has a significant impact on the isolation effect of explosion stress and crack propagation. The isolation effect of the explosion stress gradually weakened with an increase in joint angle. The smaller the angle, the more vulnerable the crack propagation direction is to the “traction” of the joint and tends to the trend of the joint, and the more serious the phenomenon of crack turning, deviation and bifurcation. The results show that the explosion energy propagates preferentially from the cutting seam direction, and the stress in the cutting seam direction reaches the peak value first. The energy in the cutting seam direction has a strong transmission ability and a directional fracture effect on the joints, and the application of weakly restrained slotted pipes in layered rock tunnel blasting construction has a good effect.

Flow behavior and microstructural evolution of Al-1.2Mg-2.4Si-1.2Cu-0.6Mn alloy during hot compression

Thermal compression tests were conducted on Al-1.2Mg-2.4Si-1.2Cu-0.6Mn alloys with process parameters including deformation temperatures ranging from 400°C to 550°C and strain rates ranging from 0.05 s⁻¹ to 1 s⁻¹. The hot working properties of aluminum alloys were evaluated with intrinsic equations and machining diagrams. The results show that the processing safety zones of the alloy are 425–450℃ and 0.05–0.1 s−1, 450–475℃ and 0.1 s−1-0.5 s−1, and 475–500℃ and 0.5 s−1. The microstructure of the aluminum alloy following hot pressing was investigated through the use of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and backscattered electron diffraction (EBSD). When the deformation temperature of the alloy is below 450°C, the alloy organization exhibits a greater prevalence of inhomogeneous defects, which manifest as coarser granular regions in the micro-morphology. Upon reaching a deformation temperature of above 525°C, the deformed alloy organization exhibits an evident thermal cracking phenomenon. At the same temperature, an increase in strain rate is accompanied by a decrease in the Mg2Si phase and an increase in the precipitation of the Al(Fe,Mn)Si eutectic phase. Furthermore, the precipitated phase tends to become coarser. The presence of certain Mn-containing nanoparticle dispersions can impede the migration of subgrain grain boundaries, while simultaneously pinning dislocations and accelerating the generation of dislocation entanglement. This also can serve to inhibit the coarsening of the grains to some extent.

Determination of critical local straining conditions for solidification cracking at laser beam welding by experimental and numerical methods

AbstractThe phenomenon of solidification cracking has been the subject of numerous research projects over the years. Great efforts have been made to understand the fundamentals of hot cracking. It is generally agreed that solidification cracks form in the solidification range between the liquidus and solidus temperatures under the combination of thermal, metallurgical and mechanical factors. There is still a need to determine the time‐resolved strain distribution in the crack‐sensitive region in order to analyse the local critical conditions for solidification cracking phenomena. This was a strong motivation for the development of a measurement system used in this study to estimate the local strains and strain rates in the zone where the solidification crack is expected to occur. The laser beam welding experiments were conducted using the Controlled‐Tensile‐Weldability test (CTW test) to apply an external strain condition during welding to generate solidification cracks. The CTW test is a test method for investigating the susceptibility of laser‐welded joints to solidification cracking, in which the sample can be subjected to a defined strain at a defined strain rate during welding.In combination with experimental investigations, numerical simulations provide spatially detailed and time‐dependent information about the strain development during the welding process, especially regarding the critical conditions for solidification cracking. Therefore, this tool was also used in the present study to evaluate the accuracy of measurement methods and to estimate experimentally derived values and their concrete influence on the formation of solidification cracks. By integrating experimental methods and numerical simulations, this study investigates the spatially resolved and temporally changing development of strain during welding, with a particular focus on the critical conditions that lead to the formation of solidification cracks. The use of numerical simulations serves a dual purpose by validating the accuracy of measurement methods and examining experimentally determined values for their actual influence on the formation of solidification cracks. A three‐dimensional finite element (FE) model implemented with ANSYS is used to simulate strains and stresses during welding. The credibility of the model was first established by validation using experimental temperature measurements. Subsequently, structural simulations were carried out under external load. The results of the simulations showed commendable agreement with the strain measurements performed using the developed technique.

Analysis, Assessment, and Mitigation of Stress Corrosion Cracking in Austenitic Stainless Steels in the Oil and Gas Sector: A Review

This comprehensive review examines the phenomena of stress corrosion cracking (SCC) and chloride-induced stress corrosion cracking (Cl-SCC) in materials commonly used in the oil and gas industry, with a focus on austenitic stainless steels. The study reveals that SCC initiation can occur at temperatures as low as 20 °C, while Cl-SCC propagation rates significantly increase above 60 °C, reaching up to 0.1 mm/day in environments with high chloride concentrations. Experimental methods such as Slow Strain Rate Tests (SSRTs), Small Punch Tests (SPTs), and Constant-Load Tests (CLTs) were employed to quantify the impacts of temperature, chloride concentration, and pH on SCC susceptibility. The results highlight the critical role of these factors in determining the susceptibility of materials to SCC. The review emphasizes the importance of implementing various mitigation strategies to prevent SCC, including the use of corrosion-resistant alloys, protective coatings, cathodic protection, and corrosion inhibitors. Additionally, regular monitoring using advanced sensor technologies capable of detecting early signs of SCC is crucial for preventing the onset of SCC. The study concludes with practical recommendations for enhancing infrastructure resilience through meticulous material selection, comprehensive environmental monitoring, and proactive maintenance strategies, aimed at safeguarding operational integrity and ensuring environmental compliance. The review underscores the significance of considering the interplay between mechanical stresses and corrosive environments in the selection and application of materials in the oil and gas industry. Low pH levels and high temperatures facilitate the rapid progression of SCC, with experimental results indicating that stainless steel forms passive films with more defects under these conditions, reducing corrosion resistance. This interplay highlights the need for a comprehensive understanding of the complex interactions between materials, environments, and mechanical stresses to ensure the long-term integrity of critical infrastructure.

Early Stages of Crack Nucleation Mechanism in Fe39Mn20Co20Cr15Si5Al1 High-Entropy Alloy during Stress Corrosion Cracking Phenomenon: Pit Initiation and Growth

Early Stages of Crack Nucleation Mechanism in Fe39Mn20Co20Cr15Si5Al1 High-Entropy Alloy during Stress Corrosion Cracking Phenomenon: Pit Initiation and Growth

Circular Economy Opportunity Utilizing Fitness for Service Methodology for Aged HIC Defected Reboiler

The phenomenon of Hydrogen-Induced Cracking (HIC) is a cracking mechanism of carbon steel material as in ASME SA- 516 pressure containing equipment operating in a wet sour H2S environment. Such phenomenon is mainly driven by the diffusion of hydrogen atoms into the carbon steel due to corrosion reaction. The Structural integrity of an in-service equipment that contain a flaw or damage such as HIC could be scrutinised using Fitness For Service (FFS) assessments as quantitative engineering evaluations. The assessments are conducted using methodologies specifically prepared for pressurized equipment. These assessments provide standard procedure that can be used to determine if pressurized equipment containing flaws could continue to operate safely for certain period of time. FFS assessments are recognized and referenced by the API Codes and Standards such as API- 510, 570, & 653, and by National Board-23. Those assessments are considered suitable methodologies for evaluating the structural integrity of pressurized equipment as heat exchangers, pressure vessels, piping systems and storage tanks where inspection has revealed degradation and flaws in the equipment. The objective of this paper isto illustrate API-579 case study of HIC of fifty (50) years operating pressurized equipment, namely reboiler.

Cristobalite formation on high-temperature oxidation of 4H-SiC surface based on silicon atom sublimation

Two innovative high-temperature oxidation methods for 4H-SiC were developed, with observations made via Optical Microscope, Scanning Electron Microscope and Raman spectrum. We successfully fabricated fully crystallized cristobalite films through oxidation and annealing processes, unveiling the lateral growth mechanisms of crystal planes during annealing. The study also delved into the unusual effects of Si sublimation on the oxidation rate of cristobalite during its formation and investigated the stress-induced cracking phenomena observed when the film thickness exceeds 1 μm. Additionally, a novel step oxidation technique was introduced to suppress vapor phase oxidation of Si at high temperatures by employing a barrier layer, facilitating the swift production of amorphous SiO2 thick films. The exceptional surface and interface flatness exhibited by these films underscore their significant potential for applications in the realm of functional films.

On the role of surface stress in environment-assisted fracture

Abstract Environment effects in plasticity and fracture of metals, well studied for several decades, still pose many unanswered questions. A micro-mechanics explanation of how dislocation activity is influenced by the material surface state, that can answer these questions, has been elusive. We build on a recently discovered effect in metal cutting – organic monolayer embrittlement (OME) – wherein metal surfaces are rendered brittle by long-chain organic adsorbates, to explore how material state variables influence surface plasticity and fracture. In particular, cutting experiments with Al containing Self Assembled Monolayers (SAMs), show that the OME is controlled by surface stress (f) induced by the adsorbates. This is contrary to many instances of environment-assisted fracture which are usually attributed to surface energy changes, and wherein f is largely ignored. Other contributions include (a) a cantilever technique to measure surface stress, (b) demonstration of strong effect of SAM molecule chain length on f, (c) characterization of how dislocation activity at crack-tips is affected by adsorbate-induced f, and (d) large improvements in machining processes enabled by controlled environment-assisted fracture. We make the case that surface stress, due to adsorbates, likely influences all environmentally assisted cracking (EAC) phenomena, warranting a revisit of extant models of EAC.

Cracking modes and force dynamics in the insertion of neural probes into hydrogel brain phantom

Objective. The insertion of penetrating neural probes into the brain is crucial for advancing neuroscience, yet it involves various inherent risks. Prototype probes are typically inserted into hydrogel-based brain phantoms and the mechanical responses are analyzed in order to inform the insertion mechanics during in vivo implantation. However, the underlying mechanism of the insertion dynamics of neural probes in hydrogel brain phantoms, particularly the phenomenon of cracking, remains insufficiently understood. This knowledge gap leads to misinterpretations and discrepancies when comparing results obtained from phantom studies to those observed under the in vivo conditions. This study aims to elucidate the impact of probe sharpness and dimensions on the cracking mechanisms and insertion dynamics characterized during the insertion of probes in hydrogel phantoms. Approach. The insertion of dummy probes with different shank shapes defined by the tip angle, width, and thickness is systematically studied. The insertion-induced cracks in the transparent hydrogel were accentuated by an immiscible dye, tracked by in situ imaging, and the corresponding insertion force was recorded. Three-dimensional finite element analysis models were developed to obtain the contact stress between the probe tip and the phantom. Main results. The findings reveal a dual pattern: for sharp, slender probes, the insertion forces remain consistently low during the insertion process, owing to continuously propagating straight cracks that align with the insertion direction. In contrast, blunt, thick probes induce large forces that increase rapidly with escalating insertion depth, mainly due to the formation of branched crack with a conical cracking surface, and the subsequent internal compression. This interpretation challenges the traditional understanding that neglects the difference in the cracking modes and regards increased frictional force as the sole factor contributing to higher insertion forces. The critical probe sharpness factors separating straight and branched cracking is identified experimentally, and a preliminary explanation of the transition between the two cracking modes is derived from three-dimensional finite element analysis. Significance. This study presents, for the first time, the mechanism underlying two distinct cracking modes during the insertion of neural probes into hydrogel brain phantoms. The correlations between the cracking modes and the insertion force dynamics, as well as the effects of the probe sharpness were established, offering insights into the design of neural probes via phantom studies and informing future investigations into cracking phenomena in brain tissue during probe implantations.

Strength analysis and structural improvement of the connection between rear shock absorber support and frame of a city bus based on Hypermesh

Abstract In response to the phenomenon of cracking at the rivet holes of the plate connecting the rear shock absorber to the frame of the 6-meter leaf spring of the passenger bus, this article takes the rear shock absorber support and the frame as the research object. Firstly, CATIA software is used to model the object, and Hypermesh is used to divide the mesh to establish a fine element model. The Optistruct finite element solver is used to analyze the strength of the model, and the analysis results are imported into Hyperview 2019 for post-processing to analyze stress distribution and stress concentration. The simulation analysis results show that when a force of 6, 721 N is applied to the rear shock absorber support, the maximum stress value occurs at the rivet holes of the plate connecting the support to the frame, and the maximum equivalent stress value at this point is greater than the yield limit of the frame material, which is consistent with the crack location that occurs during actual vehicle operation. After adopting the strengthening scheme, the stress distribution of the frame is more uniform, greatly reducing stress concentration. The maximum stress value appears on the inner side of the right frame, and the maximum equivalent stress is less than the yield limit of the frame material, avoiding the crack phenomenon. The results indicate that this scheme can not only meet the performance requirements but also provide a reference for structural improvement and optimization design of the connection between the rear shock support and the frame.

Analysis of the manufacturing craft of the painted gold foils applied on the lacquerware of the Jin Yang Western Han Dynasty tomb in Taiyuan, Shanxi, China

Seven pieces of gold foils for surface decoration of the lacquerware were excavated in the late Western Han Dynasty tomb in the area of the Jin Yang (晋阳) Ancient City site in Taiyuan (太原), Shanxi (山西), China. These gold foils portray images of the carriage, the leopard, the tigers, the ox, and the dancer with fluttering sleeves, etc., with black lines outlining the contours and red paint depicting vivid patterns. The study used Stereo Microscopes, Metallurgical Microscopy, Environmental Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy (ESEM-EDS), and Laser Raman Spectroscopy (LRS) to analyse the thickness of the gold foils, the alloy composition, the composition of the paint and other surface attachments, and investigate the manufacturing process. As the results show, the thickness of the gold foils is about 26 μm. The composition is a gold-silver alloy with about 96% Au/(Au + Ag) (surface) and 98% Au/(Au + Ag) (cross-section). The metallurgical observation shows that the gold foils underwent heating and forging. The black lines on the front side are Chinese ink lines, with cracking and peeling phenomenon, and parallel polishing lines can be seen at the peeling places, while no polishing lines are observed on the back side. Some red paint made of cinnabar is above the black lines, and the binder is organic. Some lacquer residues are found on the back. According to the results of the study, the manufacturing process of the gold foils applied on the lacquerware is as follows: the gold foils are obtained by heating and forging, the front sides of the gold foils are polished, the shapes are carved out, and the gold foils are pasted on the lacquerware when the lacquerware’s surface is not yet dry. The gold foils are painted with black Chinese ink and red cinnabar pigment. The study’s results offer important references for understanding the manufacturing craft of the gold foils applied on the lacquerware in the late Western Han Dynasty of China and guide the conservation of the lacquerware decorated with painted gold foils.

Mastering the complex time-scale interaction during Stress Corrosion Cracking phenomena through an advanced coupling scheme

Stress corrosion cracking (SCC) failure is a multi-physics phenomena and is usually modelled at the microstructural level, which includes mechanical, chemical, and electrochemical contributions. In aggressive corrosive environments, materials prone to localized corrosion, can suffer heavy pitting corrosion. Subsequently, pit-to-crack transition events might be initiated. Respective mechanical assisted pitting corrosion propagation processes are determined by mechanical, chemical, and electrochemical properties as well as transport properties of ions at grain boundaries. Variations in the electrolyte exposure conditions (including the kinetics at the solid–liquid interface), different mechanical loading scenarios, grain-specific crystal anisotropies, and other local factors combine to produce a highly complex SCC-type interaction scenario at various time and length scales. Since corrosion is a slow process whereas brittle fracture is a rapid failure mechanism, the individual domain discretization-based solvers need to use distinct time steps and appropriate solver settings to become capable to accurately simulate such coupled events. In order to address the issues that arise while accounting for scaling effects in both time and space, and retaining coupled mechanistic interplay and including the aspects specified earlier, a sophisticated modelling method is necessary for the analysis of structural failure by SCC. In this work, a partitioned multi-physics computational approach is presented, using two separate single physics solvers coupled by the open-source coupling library preCICE. In the proposed computational setup, two separate software environments are used, with dedicated solver settings and different time steps, to simulate the mechanical fracture and dissolution-driven pitting corrosion for various loading and corrosion conditions, while also taking into account the effects of microstructural anisotropy. For a 2D polycrystalline model representing face-centered-cubic (fcc) material systems, selected numerical experiments are conducted that predict the evolution of fracture and crack path resulting from SCC. The framework has been further extended to simulate 3D problems as well. The corresponding results are evaluated to show the applicability of the proposed methodology.

Effect of open crack on axial compressor performance

To investigate the effects and mechanisms of rotor open crack on axial compressor performance, a steady 3D single-passage numerical simulation is used on NASA Stage 35. The results show that the crack leakage flow can affect the compressor performance, and the crack at the middle span has the most serious effect. At 100% rotating speed, there is a 1.2% decrease in peak total pressure ratio and a 0.36% decrease in peak efficiency. Besides, the stability margin is reduced by 26.9% relatively. The effect of crack is not only limited to the span range near it, and the main phenomena of cracks at different spans are various, concentrating in the aspects of vortex structure and stator passage flow. From peak efficiency to near stall condition, the effect of crack leakage flow is gradually strengthened, which leads to the flow blockage and reduces the working flow range of compressor. With the decrement of rotating speed, the reduction of stability margin increases gradually, but the influence span range of crack at low-speed narrows.

Segment Cracking and Damage Mechanism of Curved Shield Tunnels During Construction by Field Investigation and Modeling

This study was based on the field statistical results of segment cracking and damage of a curved shield tunnel engineering. Combined with the collected data of 11 related tunneling parameters of 120 segments in the curve section, the one-way analysis of the variance method was used to reveal the main tunneling parameters that affect the cracking and damage state of the segment. Then, the finite element analysis model was established to analyze the mechanism of jack thrust and yawing angle affecting segment cracking and damage. The main results are as follows: (1) The phenomenon of segment cracking and damage gradually becomes serious from the crown to the invert. (2) The jack thrust and shield machine yawing angle are the main factors affecting the cracking and damage state of the segment. For larger values of yawing angle and jack thrust difference, the cracking and damage state of the segment is more serious. (3) The first three segments near the jack are significantly affected by the jack offset angle and uneven jack thrust. During the construction of a curved shield tunnel, under the action of the jack offset angle and uneven jack thrust, the segment spring line is more likely to incur tensile cracking. (4) To ensure the normal stress state of the segment during construction, it is suggested to control the jack offset angle at not more than 0.5° and the jack thrust non-uniform coefficient [Formula: see text] of the left- and right-hand sides within 0.75.

Post‐tension retrofitting of RC dapped‐end beams: A numerical investigation

AbstractDapped‐end beams are frequently used in roofing and flooring systems of precast reinforced concrete buildings as well as in bridge constructions. Due to design flaws, deterioration, and construction mistakes, they may have unsatisfactory structural performance. Past experimental studies investigated the effectiveness of post‐tension strengthening techniques applied to dapped‐end beams, revealing them as effective solutions, even though a limited range of influencing parameters were considered. This paper numerically investigates the performance improvement provided by post‐tension interventions applied to dapped‐end beams. Numerical models were built through a refined FEM software simulating two experimental tests found in the literature. After the models' calibration, a post‐tension intervention was designed and implemented in the models, considering the level of prestressing as the main intervention's parameter. Afterwards, the behavior in the post‐intervention condition was analyzed to find changes in the failure modes and highlight the performance improvement concerning cracking phenomena and ultimate load‐bearing capacity. It is found that the level of tendons' prestress significantly improves the cracking load, which increases almost linearly with respect to it. Conversely, the significant gain in terms of ultimate load‐bearing capacity (up to 53%) shows only slight variations when the prestress level changes. Finally, accounting also for the reduction of deformation capacity for high prestressing levels, practical suggestions are provided regarding the optimal post‐tension choice.

Mechanisms driving fruit cracking in ‘Sinhwa’ pears (Pyrus pyrifolia Nakai) and effect of foliar fertilizer application on fruit quality

Fruit cracking poses a significant challenge to ‘Sinhwa’ pear cultivation and has potential economic repercussions for growers due to its adverse effects on yield and fruit quality. This study delves into the phenomenon of fruit cracking in ‘Sinhwa’ pears by conducting a comprehensive analysis of its causes and exploring the efficacy of foliar fertilization as a mitigation strategy. To reveal the conditions contributing to fruit cracking in ‘Sinhwa’ pears, moisture change regimes were systematically applied to 5-year-old ‘Sinhwa' trees from 2018 to 2020 during post-flowering and harvest periods. Alternating wet and dry conditions resulted in the highest fruit cracking rates, thus highlighting the importance of consistent soil moisture levels for mitigating cracking. Furthermore, the timing of fruit cracking and its histological characteristics in ‘Sinhwa’ pears were examined to understand the underlying causes. Microcracks appeared approximately 60 days after full bloom and preceded visible cracking, although notable changes in epidermis thickness and stone cell layer distribution were observed. Analysis of the nutrient content revealed differences in calcium and potassium levels between intact and cracked fruits, thus providing insights into potential nutritional influences on fruit quality. Potential mitigation strategies included foliar application of 0.3 % calcium chloride and 0.5 % potassium nitrate, and they demonstrated promising results in reducing fruit cracking rates compared to the control. Fruit characteristics, including mass and hardness, varied among the treatment groups, with treated trees showing notable increases in calcium content, which were correlated with decreases in fruit cracking incidence. To understand the molecular mechanisms underlying the effectiveness of foliar fertilization, gene expression levels associated with fruit cracking were analyzed by real-time PCR. Higher expression of heat-related expansion genes (Exp1 and Exp2) was observed in the treated fruits, particularly those in the calcium chloride and potassium nitrate treatments, suggesting the role of these elements in mitigating fruit cracking. This study provides valuable insights into the causes of fruit cracking in ‘Sinhwa’ pears and offers practical mitigation strategies, such as foliar fertilization. Moreover, the findings underscore the importance of maintaining consistent soil moisture levels and optimizing nutrient management practices to enhance fruit quality and minimize economic losses in ‘Sinwha’ pear cultivation.

Research on concrete early shrinkage characteristics based on machine learning algorithms for multi-objective optimization

Cracking phenomena in tunnel side wall structures (TSWS) increasingly jeopardize their longevity due to water leakage, reinforcement corrosion, and eventual collapse. The primary contributor, early-age shrinkage (EAS) induced by hydration reactions, significantly undermines structural stability and durability. The integration of expansion agents (EA) and fibers presents a low-cost, efficient strategy to counteract EAS-induced cracking. Despite its promise, limited research on the influencing factors constrains its broader application. This study delves into the impacts of EA content, the CaO–MgO ratio, and fiber reinforcement on flexural strength (FS), compressive strength (CS), and EAS, revealing a complex interplay where EA and CaO content detrimentally affect mechanical properties yet beneficially influence EAS. Results showed that EA and CaO content had negative effects on the mechanical properties, but had positive effect on EAS. Additionally, Random Forest (RF) was developed with hyperparameters refined via the firefly algorithm (FA) based on the experimental data. The validity of the built RF-FA models was verified by substantial correlation coefficients and low root-mean-square errors. Subsequently, a coFA-based firefly algorithm (MOFA) was proposed to optimize tri-objectives of mechanical properties, EAS, and cost simultaneously. The Pareto fronts were obtained effectively for the optimal mixture design. This study contributes to its practical implications, offering a scientifically grounded approach to enhancing TSWS concrete design for improved performance and durability.

Formation mechanism of inspection defects in hundred-ton class 55NiCrMoV7 die steel forging

Using an ultrasonic flaw detector, this study precisely located the dimensions and distribution characteristics of defects during the manufacturing process of 55NiCrMoV7 die steel forgings weighing hundreds of tons. The probing defects of the forging are predominantly concentrated in the central region, spanning approximately 4200 mm in length, 400 mm height and 1500 mm width. Detailed research on the characteristics of these probing defects was conducted through dissection sampling and scanning electron microscope analysis. The research results reveal that the maximum diameter of an individual defect can reach Φ10 mm, and localised cracking phenomena exist in specific areas within the forging. The flaws exhibit characteristics such as millimetre-sized, large, elongated MnS inclusions, with spacing between inclusions ranging from 200μm to 500μm. Furthermore, based on elemental analysis, the sulphur content from the surface to the core of the forging increased from 0.001% to 0.002% to a maximum of 0.0085%. Through analysis using thermodynamic and growth kinetics models, it was determined that in regions with higher sulphur content (S = 0.0085) at a certain distance from the steel ingot surface, the radius of MnS inclusions can reach up to 380μm under low cooling rates (1 K/min). After forging deformation, these can evolve into millimetre-sized MnS inclusions, leading to internal inspection defects. Therefore, we propose that reducing the sulphur content in the molten steel and increasing the degree of undercooling can effectively inhibit the precipitation and growth of MnS inclusions. Practical results indicate that this improvement strategy effectively enhances the inspection quality of the 55NiCrMoV7 die steel forgings weighing hundreds of tons.