Stress Concentration Area Research Articles

Anti-Seismic Performance Research of Complicated Nodes Involved in Ultra-Limited Steel Structures Subjected to Rare Occurrence Earthquakes

This study focuses on the seismic performance of complicated nodes in the ultra-limited steel structure under rare occurrence earthquakes. The Xi’an Urban Exhibition Center (Chang’an Cloud) is chosen as the engineering background, and the ANSYS (18.0) analysis software is employed. Based on the overall importance and the extent of post-damage impacts, the critical nodes are selected for structural design. The research aims to develop simplified and reliable structural forms that can withstand the most adverse conditions at both the overall nodes and local component levels. Stress distribution under the most unfavorable scenarios is calculated to achieve the seismic design objectives of the overall structure. The research results indicate that localized stress concentration areas can reach or exceed the yield strength of the steel, which enters the plastic phase. The Von Mises stresses in the remaining nodes are lower than the yield strength of the steel. The overall performance is excellent without significant plastic deformation. Thus, the design requirements for non-yielding performance under rare seismic events are met. The conclusions can provide reliable references for the critical structural techniques and seismic design of complicated nodes.

Spatiotemporal evolutions of gas pressures in coal seam during gas extraction under mining disturbance

A 3D geometric model is established based on a fluid‒solid coupling model for purpose of identifying the influences of mining disturbances on the distribution of gas pressures in front of a working face during gas extraction. Then, the stress distribution and gas extraction process are simulated using COMSOL software. The spatiotemporal evolutions of gas pressures in front of the working face are analyzed from the dimensions of point, line, surface, and volume. A comparative analysis has been conducted to explore the distribution patterns of gas pressure in fractures and pores. The results show that under mining disturbance, the stresses in front of the working face create a stress-relaxation area, a stress concentration area, and an original stress area. Moreover, a low stress concentration is located near the boreholes. In the early stage of gas extraction, corresponding to the stress distribution, the gas pressures present a depressurization area, pressure concentration area, and almost undisturbed area. As the time increases after mining, the effects of mining disturbances gradually decrease, and the range of the gas pressure concentration area steadily shortens and shifts toward the front of the working face. Under the same temporal conditions, the gas pressure in pores is higher than that in fractures. At the onset of mining, the pore gas pressure is even greater than the initial pressure. Furthermore, during the identical extraction period, the “concentration area” of pore gas pressure is situated farther away from the coal wall of the working face compared to the “concentration area” of fracture gas pressure. These results of the study provide theoretical support for arranging drainage boreholes, enhancing gas extraction efficiency, safeguarding against gas accidents.

Full-field dynamic strain reconstruction of rotating compressor blades based on FBG sensors

Abstract Rotating compressor blades experience complex alternating loads during service, altering their stress–strain distributions and peak stress positions over time. Accurate measurement of these strains is crucial for identifying the areas of stress concentration. This paper presents a structural health monitoring system using fiber Bragg grating (FBG) sensors to record dynamic strains on laboratory-scale rotating blades, and a tailored full-field strain reconstruction methodology, which successfully identifies the magnitude of the strains and the areas of stress concentration of the blades at different rotational speeds. First, dynamic strain at selected blade points was monitored using FBG sensors, with raw signal data enhanced by the empirical wavelet transform method to reduce noise and clarify signals. An analytical framework was developed to relate blade rotational velocity to signal period, enabling precise speed calculation and accurate strain analysis. The improved-Kriging interpolation technique was then used to reconstruct comprehensive strain profiles. A comparative analysis showed an average strain relative error of 7.4% between predicted and actual values, demonstrating the methodology’s robustness and precision.

Vibration fatigue of film cooling hole structure of Ni-based single crystal turbine blade: Failure behavior and life prediction

The vibration fatigue failure behavior and fatigue life of the film cooling hole (FCH) structure of Ni-based single crystal superalloy were investigated at high temperature. The vibration fatigue test of the FCH specimens were carried out based on the paired staircase method. The cracks are mostly initiated in the stress concentration area at the edge of the FCH, and may also be initiated in non-stress concentrated areas with large defects. At high temperature, the crack initiation mechanism of the FCH specimens of Ni-based single crystal superalloy is oxidative cracking nucleation in stress concentration area, and the crack propagation mechanism is the competition mechanism of dislocation slip and dislocation climbing. Based on the Fatigue Indicator Parameter (FIP) of the critical plane method, a vibration fatigue life prediction model for FCH structures considering stress concentration and high temperature oxidation damage is proposed. The life prediction model proposed in this paper is applied to the vibration fatigue life prediction of FCH specimens. The deviation between the predicted results and the experimental results is within 2.5 times at 850℃, and the deviation is within 2 times at 980℃. Besides, the life prediction method proposed is compared with other two FIP life prediction methods, and the high accuracy and effectiveness of the proposed life prediction method are verified.

Compressive and Bending Properties of 3D-Printed Wood/PLA Composites with Re-Entrant Honeycomb Core

This study investigates the mechanical behavior of sandwich structures comprising a re-entrant honeycomb core structure created using wood/polylactic acid (PLA) filaments via fused deposition modeling (FDM) technology. The sandwich structures were manufactured with different face layer thicknesses (0 mm, 0.8 mm, and 1.6 mm) and various core topologies. Material characterizations included bending tests, compressive tests, and finite element analysis (FEA) to identify stress concentration areas. In-plane and out-of-plane re-entrant honeycomb core structure specimens were tested to examine the bending properties. In addition, flatwise and edgewise compressive tests were performed to investigate the structures' compressive properties. Furthermore, the modulus of elasticity for each specimen was determined using the finite element technique (FEM). The results reveal that increasing the thickness of the face layer significantly enhances the structure's resistance to bending forces. Furthermore, specimens with an in-plane orientation demonstrated better bending strength compared to those with an out-of-plane orientation due to increased material underloading. In flatwise compressive tests, specimens without a face layer exhibited the highest strength, attributed to their greater displacement. In contrast, edgewise compressive tests showed significant buckling behavior of the face sheet, the maximum stress increased proportionally with the thickness of the face layer, reaching its peak at a skin thickness of 1.6 mm. The findings are validated by ANSYS analysis, which closely mirrors the experimental results, providing insight into flexural modulus, modulus of elasticity, and stress concentration. These findings indicate that architected core structures could be efficiently utilized to improve bending/compressive characteristics and failure mechanisms, providing valuable insights into the mechanical response of sandwich structures for different industrial applications.

Research on seismic characteristics of supercharged boiler based on measured boundary

Supercharged boilers are susceptible to seismic impact loads, which can cause severe structural responses and exceed their ultimate bearing capacity. Compared with the traditional simplified structural model for earthquake resistance research in cold state, this paper establishes a real and complete three-dimensional physical model of the supercharged boiler base, and uses the reverse calculation method to obtain the boundary conditions of the boiler based on the temperature of the experimental measurement points. The temperature field and pressure field of the boiler are reconstructed, combined with the coupling method of thermal mechanical solid multiple physical fields. Using time-domain data of peak acceleration in various directions under typical earthquakes as external input loads, this study explores the seismic characteristics of boilers in the X, Y, and Z directions using time-domain analysis methods, and clarifies the vibration response mechanism in the stress concentration area of the tube sheet. The results show that the measurement and simulation error of the temperature of the inner and outer walls of the drum is 0.10 %; The individual effects of thermal stress and mechanical stress account for 107.56 % and 66.46 % of the total stress, respectively. Thermal stress plays a dominant role, while mechanical stress produces impedance effects; Under the action of an earthquake, the tube sheet undergoes reciprocating oscillation motion, and the impedance effect generated by the flexibility of the tube bundle gradually attenuates. The local stress in the X and Y directions increases by 7.70–8.27 MPa, while the local stress concentration phenomenon occurs in the Z direction due to low damping and stiffness.

Modeling of Stress-Strain State and Coseismic Effects of Epicentral Zone of Tangshan Earthquake (Southeastern China)

The paper presents the results of numerical modeling and analysis of stress-strain state of the epicentral zone of the strong earthquake in the north-east of China, which occurred on 27.07.1976 with Ms=7.8. Many present-day works continue to discuss the reasons for such a strong earthquake, which occurred in tectonic conditions ‒ far from interplate boundaries, inside the Tangshan tectonic block bounded by tectonic faults. However, published new geodynamic, seismological, geophysical and geodetic data provide confidence in the determining role of fault tectonics in this region. Based on the analysis of the results of modeling of the stress-strain state preceding the Tangshan earthquake with coseismic geophysical and geodetic data, we propose a model of earthquake rupture formation. The results of comparison of independent estimates of shear stresses with the results of modeling in the sources of strong earthquakes suggest that the areas of tectonic stress concentration are localized in the interfault rupture of the Tangshan fault, reaching maximum values at the termination of fault ruptures σi ≈ 50 MPa и τxy ≈ 20 MPa. The hypocenter of the main seismic event (taking into account the error of coordinate determination) is located in the region of stress intensity 35‒50 MPa and the ratio of main stresses σxx/σyy ≈ 8–10. It should be expected that these zones are the starting site of rupture, the extent of which depends on the amount of accumulated elastic potential energy of tectonic stresses in the adjacent region. For the Tangshan earthquake, this area corresponds to a high intensity of stresses exceeding 30 MPa in a band with a length more than 30 km and a width reaching 4.5 km.

Prediction of dominant roof water inrush windows and analysis of control target area based on set pair variable weight - Forward correlation cloud model

Coal mining disturbs the roof overlying rock, forming a channel for roof water inrush. This process destroys the primary seepage state of the deep aquifer, resulting in waste and pollution of deep water resources and posing a significant threat to coal mining. Therefore, through field measurement and numerical simulation, this paper comprehensively analyzes the development law of coal seam mining overlying rock fracture, and determines the influence range of coal seam roof water inrush. Then, a set pair variable weight - forward associated cloud prediction model is constructed to predict the dominant water inrush window and seepage channel of coal seam roof, and the key protection area of coal mining roof water inrush is delineated. The results show that with the continuous advance of the coal face, the stress shifts to both sides of the face, forming a stress concentration area, and the vertical fissure develops intensively, which becomes the main channel of water inrush. After the development is stable, it is comprehensively determined that the fissure production ratio of the coal seam is 11.7, and the fracture zone extends to the aquifer area are the water inrush source. Then, through the prediction model, the edge of the danger area near the high-risk area is defined as the advantage window of coal seam roof water inrush, and the result is consistent with the actual water inrush event. Therefore, the target of water inrush in roof is determined, and the effective measures of water reduction mining are put forward. This study is of great significance for protecting deep water resources, ensuring mine safety, and creating efficiency and increasing income.

Hydraulic horizontal slit-stress synergistic unloading fracturing in coal seams

Solving the problem of gas extraction from low-permeability coal seams is an urgent issue in the global coal industry, and exploring green and efficient mining methods has potential applications in this field. In this study, the No. 9 coal seam of the Guizhou Longfeng Coal Mine was selected as the research object. The method of using a hydraulic horizontal slit to create a compensation space and then synergizing it with the coal body’s own stress to decompress and increase the permeability of the coal body was studied through similarity simulation and numerical simulation experiments. This study showed that the slit can cause the overall development, expansion, and penetration of coal seam fissures. Thereby, a large number of fissures are produced in the coal seam and its upper rock layer, which form, as a whole, a “positive trapezoid” shape. The three stages of the slit produced 165, 487, and 1572 fissures, which unpressurized and increased the penetration of the coal and rock body. The slit causes the upper coal body to lose its support, and the original stress balance of the coal and rock is broken, forming a decompression zone. At the same time, the coal body below starts to expand and deform after losing the vertical stress. The decompression zone gradually expands up and down, and the stress on both ends of the compensation space becomes larger, forming a stress concentration area. After the overall displacement of the coal seam caused by the slit, a “positive triangle” area is formed. In the upper part of the area, six displacement dividing lines are created, which form five areas. The displacement shows the distribution characteristics of a large displacement in the middle and a small displacement at both ends. The results of the similarity simulation and numerical simulation experiments were verified. The study provides a new way of thinking for effectively preventing coal and gas protrusion and improving mining efficiency.

Comparative analysis of armid fiber reinforced polymer for strengthening reinforced concrete beam‐column joints under cyclic loading

AbstractThis research investigates the structural performance and failure mechanisms of beam‐column joints reinforced with aramid fiber‐reinforced polymer to bolster the durability and seismic resilience of concrete structures. It meticulously selects and proportions materials such as ordinary Portland cement Grade 53 cement, fine and coarse aggregates meeting IS: 383–1970 standards, and water conforming to IS: 456–2000 specifications. Tests confirm the high quality of ordinary Portland cement, crucial for optimal beam‐column joint performance, while carbon fiber‐reinforced polymer enhances structural integrity with its lightweight composition and substantial tensile strength (3800 MPa–4200 MPa). Failure analysis reveals that non‐aramid fiber reinforced polymer wrapped beam‐column joint specimens predominantly failed due to concrete crushing, whereas aramid fiber‐reinforced polymer‐wrapped specimens failed due to fracture in the aramid fiber‐reinforced polymer composite, emphasizing stress concentration areas. This study underscores the pivotal role of stress distribution in failure mechanisms and underscores the significance of robust reinforcement design in bolstering structural resilience. These insights advance retrofitting strategies and reinforce techniques aimed at enhancing the longevity and seismic resistance of concrete structures.

Research on influence of stress concentration on metal magnetic memory signal for stress evaluation

Abstract Based on the magneto-mechanical effect and stress concentration effect, this paper takes the failure of ferromagnetic components caused by stress concentration as the research background, artificially creates stress concentration by prefabricating U-shaped defects, and discusses the H p (y) signal distribution law of prefabricated U-shaped defect samples and the difference in H p (y) signal between specimens with different tip SCFs. Results show that the H p (y) signal has an apparent mutation in the stress concentration area, and when the stress concentration factor was the same, the magnetic field intensity gradient K becomes higher as tensile load increasing. As stress concentration factor increasing, the K value of the stress concentration area also increases gradually. Based on theoretical model of H p (y) signal, it can be known that the K value can be used to judge the sample stress concentration degree with the results in this study.

Force analysis and optimization design of flexible connection shafts with centerline passing

Abstract In response to the design and research of downhole signals transmitted through cables for drilling instruments, the wire passing structure of the cross screw motor is particularly crucial. A preliminary analysis and summary of the material characteristics and stress analysis of its bending tube were conducted. The analysis shows that, under the premise of verifying the strength composite design requirements of its mechanical structure and material performance, the bending tube is subjected to multiple effects of working conditions such as internal stress and alternating load, Gradually forming dangerous cross-sections and stress concentration areas, thereby increasing the risk of fatigue fracture failure. In addition, structural design and material adjustments were made to the stress concentration area, optimizing and improving the contact head structure of the flexible tube. This was verified through material performance analysis, further improving the service life of the flexible tube.

WITHDRAWN: Monolithically stacked VIA-free liquid metal circuit for stretchable electronics

Researchers are eagerly developing stretchable conductors because they constitute basic building blocks for stretchable electronic devices in the fields of wearable electronics, soft robotics, and human–machine interfaces. Though various stretchable conductors with high stability are being devised, fabricating stretchable stacked circuits with them leads to new challenges. The most critical problem is evoked by vertical interconnection access (VIA) structures, which inevitably become stress-concentrated areas when stretched. Consequently, stretchable circuits become much more unstable when manufactured as stacked circuits than single-layered circuits. Here, we demonstrate a monolithically stacked VIA-free stretchable liquid metal circuit that is mechanically one-body-merged and electrically stacked-circuit-designed. The circuit has no vertical structures, which endows extreme electromechanical stability with various features. It is realized by unique combinations of liquid metal conductor and selective surface treatment. The stacked circuit can be elongated over 1,100 % strain, demonstrating negligible difference in stretchability compared to a single-layered circuit. The circuit also possesses various distinctive characteristics of security, choosability, and extendability. As proof, we demonstrate an encryption element, a choosable circuit, an extendable circuit, and other functional circuits. We expect the proposed stacked circuit to give directions to stretchable stacked electronics with various functionalities.

Vibration fatigue behavior and failure mechanism of Ni-based single-crystal film cooling hole structure under high temperature

Film cooling hole structures significantly influence vibration fatigue performance of Ni-based single crystal turbine blades. This study investigates the vibration fatigue behavior and failure mechanism of film cooling hole structure of Ni-based single crystal superalloy at high temperature by using the plate specimens with film cooling holes. The vibration fatigue cracks are all initiated at the edge of the film cooling hole on specimen surface, and the macroscopic crack path is a straight line path. At the microscopic scale, the crack path at 850 °C is a Zigzag path, but the crack path at 980 °C still shows a straight line path. The crack initiation of the specimen shows the oxidation crack nucleation in the stress concentration area under the coupling effect of high temperature and alternating stress. The macroscopic crack propagation direction at high temperature depends on the stress gradient direction of the resolved shear stress. At the microscopic scale, the crack propagation at 850 °C is the dislocation slip-climb mechanism, and the crack propagation at 980 °C more inclined to produce only the dislocation climb mechanism. The vibration fatigue cracks have the temperature dependence. The high temperature environment promotes the activation of slip system and the enhancement of dislocation mobility, the microscopic raft structure promotes the crack propagation along the γ phase with a large number of dislocations, the oxidation crack promotes the oxygen to enter the alloy matrix, which accelerates the Mode-I crack propagation.

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.

Research on Pipeline Stress Detection Method Based on Double Magnetic Coupling Technology.

Oil and gas pipelines are subject to soil corrosion and medium pressure factors, resulting in stress concentration and pipe rupture and explosion. Non-destructive testing technology can identify the stress concentration and defect corrosion area of the pipeline to ensure the safety of pipeline transportation. In view of the problem that the traditional pipeline inspection cannot identify the stress signal at the defect, this paper proposes a detection method using strong and weak magnetic coupling technology. Based on the traditional J-A (Jiles-Atherton) model, the pinning coefficient is optimized and the stress demagnetization factor is added to establish the defect of the ferromagnetic material. The force-magnetic relationship optimization model is used to calculate the best detection magnetic field strength. The force-magnetic coupling simulation of Q235 steel material is carried out by ANSYS 2019 R1 software based on the improved J-A force-magnetic model. The results show that the effect of the stress on the pipe on the magnetic induction increases first and then decreases with the increase in the excitation magnetic field strength, and the magnetic signal has the maximum proportion of the stress signal during the excitation process; the magnetic induction at the pipe defect increases linearly with the increase in the stress trend. Through the strong and weak magnetic scanning detection of cracked pipeline materials, the correctness of the theoretical analysis and the validity of the engineering application of the strong and weak magnetic detection method are verified.

The effects of environments and adhesive layer thickness on the failure modes of composite material bonded joints

In this study, a structural adhesive was used to bond unidirectional prepreg and fiber fabric in a single lap joint. The mechanical properties of the structural adhesive were investigated under room temperature dry state (RTD) and elevated temperature wet state (ETW, 71 ℃/85% RH), and different adhesive layer thicknesses (0.5 mm, 1.0 mm, 1.5 mm, and 2.0 mm). The fracture surfaces of the bonded joints were examined using scanning electron microscopy (SEM), and finite element simulations were conducted to observe the failure modes and failure paths. Additionally, the specimens were immersed in water and hydraulic oil, and their tensile shear strength was tested to evaluate their liquid sensitivity. The experimental results indicated that with increasing adhesive layer thickness, the strength of the specimens decreased by 21% in the RTD and by 52% in the ETW. The strength differences between different environments were minimal for adhesive layer thicknesses of 1 mm and 1.5 mm. The shear strength of the specimens decreased after immersion in water and hydraulic oil, with reductions of 43.78% and 39.21%, compared to the room temperature dry respectively. SEM observations of the bonded joint sections revealed that the primary failure modes were adherend failure and adhesive layer failure. Finite element simulations indicated that fiber tearing and crack initiation occurred in stress concentration areas during loading, leading to structural failure.

Oxidation behavior and failure mechanisms of enamel coatings at different temperature

This work studies the prolonged high-temperature oxidation behavior and failure mechanisms of enamel coatings at three distinct temperatures: 600 °C, 800 °C, and 1000 °C. The evolution of the coating’s microstructural morphology was characterized, and the kinematics of porosity, crystal precipitation, and oxide layer thickness were measured. The results indicated that at 600 °C and 800 °C, the coatings exhibit strong oxidation resistance and retain their mechanical integrity. However, at 1000 °C, the coatings rapidly deteriorate due to formation of Cr microcrystalline bands and the diffusion of oxidation layer, leading to volume expansion and element segregation. These factors result in the formation of voids and stress concentrations. The precipitation of crystals further exacerbates localized stress and microcracks, increasing the brittleness and enlarging the stress concentration areas, ultimately causing coating spallation. The effects of cooling rate on the long-term oxidation lifetime of the coatings were also examined. The findings of this work suggest that the temperatures below 800 °C are suitable for long-term application of the enamel coatings, while exposure to 1000 °C results in their rapid failure.

Failure analysis-based mass reduction of an aluminium alloy engine mounting bracket using Design of Experiments approach

In this study, mass reduction of an engine mounting bracket has been performed without changing the failure mode. Firstly, failure modes were determined experimentally using failure loads provided by the vehicle manufacturer. Then critical stress concentration areas and suitable mass reduction regions were determined by using Finite Element Analysis (FEA) for these load cases. A structural optimisation process was carried out using Design of Experiment-Response Surface Methodology (DOE-RSM) to minimise the mass while keeping the failure load as constant as possible. When the stress values obtained from the preliminary structure are compared with the values obtained from the optimised part, it was seen that this target has been mostly achieved. A total mass reduction of 4.31 % was achieved in the new part through failure mode analysis. Furthermore, it was found that a financial saving of 129,000 Euro could also be achieved.

Stress transfer paths and damage modes of layered coal-rock mass under static loading

In order to explore the distribution characteristics of nonlinear mechanical behavior and the tendency of damage and failure of deep in situ coal-rock mass, a layered composite thin plate coal-rock mass model is established based on thin plate theory and finite element method. The continuity of interlayer stress and displacement is maintained by transfer matrix function, and the maximum shear stress is calculated by Mohr-Coulomb strength criterion. The distribution characteristics of stress, displacement, energy and maximum shear stress of coal-rock mass under static load are obtained. The analysis results are as follows : ① The torsional stress concentration areas of τxz and τyz are formed on the boundary of coal-rock interface, and the principal stress concentration areas of σx, σy and σz are formed in the center and center of the boundary, and the shear stress distribution of τxy is formed on the diagonal line. ② The maximum shear stress of the long axis has a strengthening effect on the shear failure, and each layer forms a stress state of alternating tension-shear-compression-shear. It first destroys in the middle of the coal-rock interface and boundary, and then destroys along the long side and short side. ③ The coal-rock mass presents a ′ X ′ -type shear zone along the radial and axial. The shear failure occurs first, followed by the principal stress compression failure. The cracks are preferentially developed in the direction perpendicular to the minimum principal stress, and the stepped ′ V ′ -shaped failure characteristics are formed under the action of shear and tensile stress.