Compressive Stress Distribution Research Articles

EXPERIMENTAL JUSTIFICATION OF THE PARAMETERS OF THE SOIL FOUNDATION MODEL OF LARGE-SIZE SLAB FOUNDATIONS OF MULTI-STORY BUILDINGS

In practice, the model of a linearly deformed layer of finite distribution capacity is the most widespread. The possibility of using this model for slab foundations should be confirmed by calculations with a scientific and technical justification of the accepted soil base model and its parameters. Based on observations of subsidence during the construction of a 16-story building on a slab foundation, the use of a model of the soil base in the form of a linearly deformed layer of finite distribution capacity and its parameters is demonstrated. A comparison of the measured and calculated values of the base deformation was made. The object of the study is the ground base and foundation of a 16-story residential building with an underground floor and a parking lot. During the construction, the subsidence of the building was monitored by the method of high-precision leveling of the II class. With the help of the SOFiSTiK software complex, modeling and calculation of the "foundation - foundation - building" system was performed. The soil base model is adopted as a linearly deformed layer of finite distributive capacity. The strength of the layer was limited by the size of the compressible layer. For the soil massif, the boundary conditions in the plan were adopted so that the influence of elm restrictions was minimal. The width of the model was initially set so that the distribution of compressive stresses along the depth was at an angle of distribution α=45º to the vertical from the edges of the loaded foundation. During further modeling, the distribution angle α was changed to 25º. The numerical calculation was performed using the finite element method, which is based on the solution of the theory of elasticity using the SOFiSTiK software calculation complex for the first and second groups of limit states. The possibility of applying the model of the soil base in the form of a linearly deformed layer of finite width for predicting the deformations of the building on a large-sized slab foundation based. It was established that the nature of the development of deformations determined by the calculation for the angles of distribution α=45º and α=25º is proportional to the nature of the development of subsidence determined during field observations. It has been demonstrated that the angle of distribution α=25º is optimal for modeling the soil massif of the foundation, ensuring the reliability of moment stress values.

Simulation and analysis of residual stress in 17-7 PH stainless steel welded joints using laser shock peening technology

To investigate the effect of power density on the residual stress distribution on the surface of 17-7 PH stainless steel welded joints during laser shock process, we utilized ABAQUS finite element software for analyzing its distribution under different laser shock power densities. The material was tested for residual stress using an X-ray stress diffractometer to verify the accuracy of the simulation results and lay the foundation for finding the optimal process parameters. The simulation results show that when the laser power density is 2.79 GW/cm2, the maximum residual compressive stress value on the surface of the sample after laser shock peening is −37.2 MPa; When the laser power density is 2.79 GW/cm2, the maximum residual compressive stress value on the surface of the sample is −94.1 MPa; When the power density reaches 5.17 GW/cm2, the maximum residual stress value on the surface of the laser shock peening sample is −144.8 MPa, and residual stress cavity is formed. The experimental results show that when the laser power density is 2.79 GW/cm2, the maximum residual compressive stress on the surface of the sample is −37.3 MPa; When the power density is 3.98 GW/cm2, the uniformity of compressive stress distribution on the surface of the sample is optimal, with a maximum residual compressive stress value of −99.0 MPa; When the power density is 5.17 GW/cm2, the maximum residual compressive stress value is −146.1 MPa, and residual stress cavity is formed on the material surface. The simulation results are close to the experimental results, and the model error ranges from 0.2% to 4.9%. The simulation results are accurate and reliable.

Study on surface integrity and crack propagation mechanism of Ti/Al composite plates enhanced based on water jet peening

This study investigates the mechanisms through which water jet (WJ) enhancement affects surface integrity and crack propagation in Ti/Al composite plates. Finite element models for both WJ enhancement and crack propagation were developed using ABAQUS, complemented by experiments analyzing the influence of different jet velocities on surface integrity parameters, such as residual stress and surface roughness. These parameters were then examined for their effects on the stress intensity factor (SIF), fatigue crack propagation rate (FCP), and crack propagation path.The results demonstrated a positive relationship between jet velocity and both surface roughness and maximum residual compressive stress in specimens treated with WJ enhancement. Specifically, as jet velocity increased from 300 mm/s to 350 mm/s, surface roughness rose approximately 4.2-fold to around 0.95813 μm, while maximum residual compressive stress increased from 1109.9 MPa to 1472.5 MPa. The uniform distribution of residual compressive stress contributed significantly to the reduction in the stress intensity factor.Additionally, the crack propagation rate was inversely correlated with jet velocity. The residual compressive stress induced by higher jet velocities effectively slowed crack propagation. The theoretical interpretation of residual compressive stress as an equivalent damping layer further validated the effectiveness of WJ enhancement in reducing crack propagation in Ti/Al composites.

QCT/FEA analyses of palateless splinted and unsplinted maxillary all-on-4 systems

The goal of the presented study was to determine the viability of using splinted and unsplinted maxillary implant-supported overdentures. The main physical quantity used to evaluate their differences was compressive stress in bone and equivalent (von Mises) stress in the implant and overdenture components. We took a 3D X-ray scan of the maxilla and imported the data into a QCT/FEA (Quantitative Computed Tomography-based Finite Element Analysis) software. The loading was done in three load cases. We designed both models of the overdentures in CAD, included the polyetheretherketone (PEEK) overdenture and analyzed the whole model of the reconstructed maxilla with implants. The results show worse (more concentrated) compressive stress distributions for the unsplinted locator variant. The splinted, bar-retained variant shows lower values of stress in all load cases. These findings and their potential for real-time selection of the optimal variant are then further discussed.

Horizontal mechanical performance of the upper beam frame with beam-beam connection of traditional wooden building

This paper presents the analytical model of the beam-beam connection (BBC) and studies the horizontal mechanical performance of the upper beam frame assembled by BBC. The different compressive stress distributions at the contact interfaces of the BBC with intersection angles 2π/4, 2π/5, 2π/6, 2π/7 and 2π/8 are analyzed when it rotates in clockwise and anticlockwise directions, also the deformation and friction characteristics of the BBC with intersection angles 2π/5, 2π/6, 2π/7 and 2π/8 when it rotates in two directions are discussed, then the analytical model of the BBC is proposed. Also, the moment-angle curves of the proposed model with multiple angles are checked by the results of the numerical models in Abaqus. Furthermore, the horizontal mechanical performance of the upper beam frame assembled by BBC is studied under in-plane load. The results show that frictional slip at the contact interfaces of BBC with angles 2π/5, 2π/6, 2π/7 and 2π/8 when it rotates in anticlockwise direction should be considered in modeling process, and it can be ignored of BBC with angles 2π/4, 2π/5, 2π/6, 2π/7 and 2π/8 when it rotates in clockwise direction. The results of the proposed model agree with those of the numerical model basically. The resistance increases with the number of the beams of frames, and the resistance characteristics of the hexagonal and octagonal frames are similar. The research results can be further applied to the model analysis of beam-column structures of the traditional Chinese wooden building.

Abrasive Wear Characteristics of 30MnB5 Steel for High-Speed Plough Tip of Agricultural Machinery in Southern Xinjiang Region

The high-speed plough tip is the core soil-touching component in southern Xinjiang field cultivation, but the interaction of the plough tip with the soil results in severe wear of the tip. The friction behaviour of sand and soil on plough tips was investigated with a homemade rotary abrasive wear tester in a one-factor multilevel test with three parameters: moisture content, velocity/rotational speed and friction distance. The objective was to study the friction behaviour of the sand soil and plough tip and analyse and characterise the wear amount, wear thickness and compressive stress distribution, three-dimensional wear morphology and microscopic wear morphology of the plough tips. The results show that with increasing speed, the wear amount changes more gently; with increasing soil water content, the soil adhesion force and lubricating water film increase so that the wear amount follows a second-order parabolic law; and with increasing friction distance, the wear amount gradually increases, and the wear rate also shows an upward trend when the plough tip is in the abrasive wear stage. The tip makes contact with the firmer soil with higher surface compressive stresses, causing the most wear. As the friction distance increases, sand particles become embedded in the contact surfaces, creating a groove effect along with spalling pits caused by fatigue wear. During the whole wear period, the groove effect is always accompanied by spalling pits appearing repeatedly. The analysis of the wear micromorphology of the plough tip shows that the number of flaking pits gradually decreases in the direction of soil movement, and the form of damage changes from impact wear to plough groove scratches. Abrasive wear interacts with corrosive wear to exacerbate plough tip wear.

The cross-sectional morphology of the proximal femoral diaphysis is defined by the anteversion angle.

Osteoporosis in postmenopausal women is one of the causes of femoral fractures and is prevented by the administration of bisphosphonates. Individual morphologies are considered to increase the risk of atypical fractures associated with long-term administration. To evaluate cortical bone morphology quantitatively, we established a method to measure the distance from the center point of a cross-section to the external and internal borders based on CT images. Using this method, 44 sides of a female femoral skeleton specimen were examined and areas of protrusion and thickening in the medial anterior and lateral posterior regions just below the lesser trochanter were identified. These positions strongly correlated with the anteversion angle, suggesting the involvement of the distribution of the load received from body weight defined by the angle. The finite element method was used to examine the relationships between the positions of these areas with compressive and tensile stress distribution areas in the one-legged standing condition. The medial anterior region and lateral posterior region protruded and thickened in response to compressive and tensile stress, respectively. In addition, a hierarchical relationship was observed between the anteversion angle, tensile stress distribution, protrusion, and thickening in femurs with thinning of cortical bone, indicating that morphogenesis occurs adaptively to loading. The present results demonstrate the usefulness of this method in considering the formation mechanism and function of the femoral diaphysis and suggest that bone remodeling is necessary to maintain adaptability.

Study on the effects of bilateral laser-assisted cutting on surface integrity and fatigue life of FeCoCrNiAl0.6 alloy

This study investigates the impact of various cutting parameters in both unilateral and bilateral laser-assisted cutting processes on the surface integrity and fatigue life of FeCoCrNiAl0.6 high-entropy alloy. By utilizing ABAQUS/FE-SAFE simulations and conducting laser-assisted cutting and fatigue tensile tests, differences in surface quality and fatigue life cycles of FeCoCrNiAl0.6 alloy samples under different cutting scenarios were evaluated. The results indicate that in high-speed laser-assisted cutting, an increase in laser speed leads to a progressive decline in surface quality for both unilateral and bilateral methods. Nevertheless, at a laser speed of 4000 mm/s, optimal surface quality is achieved in both approaches, with the bilateral method consistently providing superior results across varying speeds. Regarding residual stress, unilateral laser-assisted cutting at 4000 mm/s produces a surface residual compressive stress of 532 MPa, which is twice as high as that observed at 10000 mm/s. The bilateral method shows a symmetric distribution of residual compressive stress, with peak values of 567 MPa and 528 MPa on the front and back surfaces, respectively. In terms of fatigue life, bilateral laser-assisted cutting demonstrates enhanced performance at 4000 mm/s, achieving a fatigue life cycle that is 4.72 times longer than that of the unilateral method. Overall, bilateral laser-assisted cutting improves the fatigue life of the material through symmetric thermal effects and higher residual compressive stress, particularly at lower laser speeds and optimal cutting depths.

Effects of laser non-uniform shock peening on the microstructure and fatigue performance of SUS 304 stainless steel welded joints

Residual tensile stresses and microstructural heterogeneity in welded joints are primary factors that degrade fatigue performance. As an effective post-weld strengthening method, Laser Shock Peening (LSP) can address these issues. Given the personalized demands of different regions, this paper proposes a Laser Non-Uniform Shock Peening (LNUSP) technique. This approach involves applying high pulse energy to the weld zone (WZ) and heat-affected zone (HAZ), and low pulse energy to the base material (BM) to achieve a more uniform residual compressive stress distribution and refined microstructure, thereby improving overall performance and service life. Results indicate that LSP transforms residual tensile stresses on the weld surface into compressive stresses. Compared to original samples, uniformly LSP-treated samples, and locally LSP-treated samples, LNUSP-treated samples exhibit more uniform residual stress and hardness distribution. LSP significantly increases surface hardness, with LNUSP-treated samples achieving a maximum hardness of 308.3 HV. Additionally, LSP induces martensitic transformation in the BM and WZ areas, alters grain orientation, and promotes dislocation movement, resulting in dislocation tangling, dislocation networks, and twin structures, which refine grain size. Consequently, LSP markedly improves joint fatigue performance, delaying fatigue crack propagation. The fatigue life of LNUSP-treated samples is increased by 25.41 % compared to original samples, reaching levels comparable to high-energy large-area impacts. This enhancement is attributed to the uniform residual stress and refined grain structure.

An analytical model for predicting residual stress in shot peening with strain energy method

In this study a model by novel analytical approach is developed and experimentally verified for shot peening residual stress distribution. The residual stress field induced by single shot impact is calculated by using Glinka–Molski energy-based method and kinematic hardening model. The formulation of the compressive residual stress (CRS) distribution is often based on plane strain or plane stress. It can be determined from the derived relation presented in this paper, the final residual stress in the full coverage conditions is the average of the two strain and stress plane expressions proposed by previous researchers. The distribution of residual stress is one of the key differences between the profiles produced by the results of the current model. There is a significant distinction between surface residual stress and maximum CRS, because the CRS profile near the surface is more curved compared to profiles obtained in earlier analytical models. The experimental data obtained by XRD analysis indicate the correctness and precision of the current model. Another goal of this study is to increase the fatigue life of GTD-450 stainless steel by shot peening at two different peening intensities. The fatigue life of samples were obtained by rotary bending test. Analytical results that confirmed by experimental findings shown bigger maximum compressive residual stresses occurred in higher shot peening intensities. This incident can improved fatigue life by deeper plastically deformed layer.

Investigation of the Influence of Boundary Conditions on the Deformability of a Model of Soil Base of limited Width in The Form of a Linearly Deformable Elastic Half-Plane

Abstract The paper examines the available approaches to the distribution of vertical compressive stresses over the depth of the soil base from a uniformly distributed load on the surface. The paper investigates the effect of boundary constraints in plan of the model of a continuous linearly deformable (elastic) layer of finite width on its distribution capability and stress-strain performance from a loaded foundation on the surface. Numerical calculations of the stress-strain state of a uniformly loaded foundation with different relative bending stiffness (flexibility), which interacts with a layer of a certain depth (compressible depth) and strict horizontal constraints in terms of width (the width dimensions of the model), were performed using the SCAD software. Based on the analysis of the results of numerical calculations for the plane problem (plane-strain deformation), the width of the model of a linearly deformable layer of finite width, which considers the distribution of compressive loads over the depth at an angle of α≈20÷25° to the vertical from the edges of the loaded foundation, was justified. In this case, the width of the model according to the angle of distribution of α≈20÷25° has virtually no effect on the average settlements and the maximum moment forces of the foundation in comparison with the increase in the width of the model.

NUMERICAL STUDIES OF THE DISTRIBUTION CAPACITY AND DEFORMABILITY OF THE SPATIAL MODEL OF THE SOIL BASE IN THE FORM OF A LINEAR-DEFORMED LAYER

The article analyses the existing approaches to modelling the interaction between a structure and a soil foundation, which consider the joint deformation of the soil and the structure. The “base-foundation-structure” models can be created in one-dimensional, two-dimensional, or three-dimensional space. Each of these models has its own set of boundary conditions and calculation methodology The advantages and disadvantages of each model, during application in engineering calculations, are presented. The purpose of research is to substantiate the methodology for assigning the geometric parameters of a three-dimensional model of a soil foundation, represented as a linearly deformed layer of finite resolution, for adequate modelling of interaction in the "base- foundation-structure" system. A finite-element model of the interaction between the soil base and the slab foundation was built using the modern SCAD software package. The modelling was performed in three dimensions. The soil base is represented by volumetric finite elements with constant deformation characteristics. The foundation is modelled by plate finite elements In context of this research, the slab model of the foundation was assumed to be rigid to neglect stress redistribution in the above-ground part of the building. Based on the analysis of modern approaches to the assignment of geometric parameters to the model of the soil base represented by a continuous linearly deformed layer with finite overall dimensions, which is created in a three-dimensional problem statement, it was shown that today there is no single approach to modelling such a “base-foundation-structure” system. Numerical studies of the effect of rigid horizontal constraints in the plan on the stress-strain state of a uniformly loaded rigid foundation interacting with a linearly deformed layer (compressible thickness) of finite distribution capacity were carried out using the SCAD program. Based on the analysis of the results of numerical calculations for a three-dimensional problem, the minimum allowable sizes in terms of the model of a linearly deformed layer of finite distribution capacity, which considers the distribution of compressive stresses along the depth at an angle of α = 25º to the vertical from the edges of the loaded foundation, are substantiated. At the same time, the overall size of the model in the plan according to the distribution angle α = 25º has practically no effect on the average settlement and maximum moment forces of the foundation compared to the angle α = 45º. Keywords: slab foundation, soil foundation, linear-deformed model, distribution angle, stress-strain state.

Pile–Soil Interaction during Static Load Test

Abstract This study highlights the possibility of determining the shear stress distribution along the skin of a pile, which represents skin resistance. Geotechnical engineering is plagued by the challenge of designing appropriate piles as a sufficient foundation construction while being economically justified solution. Static load testing facilitates verification if the pile satisfies these requirements. In most cases, the pile skin resistance is undervalued. This study first introduces the general approach based on static load test results using an appropriate mathematical approach in the presence of linear, vertical shear stress distribution boundary conditions as well as phenomena such as pile shortening and Kirchhoff's principle. Moreover, a scientific approach for pile compression and shear stress distribution is presented. Further, the study expands upon previous work by applying mathematical calculus to displacement piles. The promising results indicate that further work on greater number of piles may lead to a better understanding of pile–soil interaction and a more accurate design process.

Comparative analysis of geometric imperfections and residual stresses on the global stability behavior of cantilever composite alveolar beams

Few studies addressed the influence of geometric and structural imperfections of steel alveolar I-sections on the stability behavior of composite beams under hogging moment. Therefore, this paper aims to study the sensitivity to geometric imperfection amplitude and residual stress distribution on their global stability. The research primarily focuses on comparing numerical results with experimental data in detail, which addresses four tests involving cantilever composite beams with castellated and cellular I-sections. It includes applying various residual stress patterns and geometric imperfection values to advanced numerical analyses as documented in the literature. Linear buckling analyses (LBA) and geometrically and materially nonlinear analyses with imperfections (GMNIA) are carried out using the ABAQUS software. Regarding the first positive eigenvalue from LBA analyses, the eigenvectors presented Web-Post Buckling (WPB) with a slight compressed flange lateral curvature, inserted as the initial geometric imperfection in the GMNIA analyses. However, when the residual stresses were implemented in the GMNIA analyses, some finite element models had different failure modes regarding the deformed configurations from LBA analyses, in which the failure modes were characterized by Lateral-Distortional Buckling (LDB), which was in agreement with the test results. As the beams reached LDB in an inelastic regime, residual stresses significantly affected their resistant capacity. This way, the distribution of compressive residual stresses in the flanges had the most critical influence on the global stability behavior of the analyzed beams, as these residual stresses favor the LDB occurrence. Finally, higher geometric imperfection amplitudes did not provide only lower ultimate loads, as when the instability phenomena are reached in an inelastic regime, the effect of global geometric imperfections becomes highly complex.

In vivo biomechanical dynamic simulation of a healthy knee during the single-leg lunge and its experiment validation

Biomechanical modeling of the knee during motion is a pivotal component in disease treatment, implant designs, and rehabilitation strategies. Historically, dynamic simulations of the knee have been scant. This study uniquely integrates a dual fluoroscopic imaging system (DFIS) to investigate the in vivo dynamic behavior of the meniscus during functional activities using a finite element (FE) model. The model was subsequently validated through experiments. Motion capture of a single-leg lunge was executed by DFIS. The motion model was reconstructed using 2D-to-3D registration in conjunction with computed tomography (CT) scans. Both CT and magnetic resonance imaging (MRI) data facilitated the development of the knee FE model. In vivo knee displacements and rotations were utilized as driving conditions for the FE model. Moreover, a 3D-printed model, accompanied with digital imaging correlation (DIC), was used to evaluate the accuracy of the FE model. To a better inner view of knees during the DIC analysis, tibia and femur were crafted by transparent resin. The availability of the FE model was guaranteed by the similar strain distribution of the DIC and FE simulation. Subsequent modeling revealed that the compressive stress distribution between the medial and lateral menisci was balanced in the standing posture. As the flexion angle increased, the medial meniscus bore the primary compressive load, with peak stresses occurring between 60 and 80° of flexion. The simulation of a healthy knee provides a critical theoretical foundation for addressing knee pathologies and advancing prosthetic designs.

Effect of beam-column depth ratio on seismic behavior of precast RC column-steel beam joint

To achieve the simultaneous horizontal casting of the joint and column in the factory, the authors proposed a new precast RC column-steel beam (RCS) joint. The overall behavior of the proposed joint has been investigated. However, the effects of various design parameters were unclear. This paper focused on the impact of the beam-column depth ratio on the proposed RCS joints. Three 2/3 scale interior RCS joint specimens were designed and tested under cyclic loading. Experimental results showed that the joint shear strength and ductility of the specimen improved as the beam-column depth ratio decreased. A large beam-column depth ratio could modify the bond condition of column bars. Moreover, a numerical study was conducted to further investigate the influential mechanism of the beam-column depth ratio. According to the distribution of compressive stress, the concrete strut was activated in the joint. The angle between the strut and the horizontal increased with the beam-column depth ratio, leading to less horizontal component to resist the joint shear force. The joint shear strength tended to be overestimated as the beam-column depth ratio increased by using current design methods. Ignoring the effect of the beam-column depth ratio in the design methods may cause significant errors in predicting the joint shear strength.

Investigating the Dynamic Mechanical Properties and Strengthening Mechanisms of Ti-6Al-4V Alloy by Using the Ultrasonic Surface Rolling Process.

The demand for titanium alloy has been increasing in various industries, including aerospace, marine, and biomedical fields, as they fulfilled the need for lightweight, high-strength, and corrosion-resistant material for modern manufacturing. However, titanium alloy has relatively low hardness, poor wear performance, and fatigue properties, which limits its popularization and application. These disadvantages could be efficiently overcome by surface strengthening technology, such as the ultrasonic surface rolling process (USRP). In this study, the true thermo-mechanical deformation behavior of Ti-6Al-4V was obtained by dynamic mechanical experiment using a Hopkinson pressure bar. Moreover, USRP was applied on the Ti-6Al-4V workpiece with different parameters of static forces to investigate the evolution in surface morphology, surface roughness, microstructure, hardness, residual stress, and fatigue performance. The strain rate and temperature during the USRP of Ti-6Al-4V under the corresponding conditions were about 3000 s-1 and 200 °C, respectively, which were derived from the numerical simulation. The correlation between the true thermo-mechanical behavior of Ti-6Al-4V alloy and the USRP parameters of the Ti-6Al-4V workpiece was established, which could provide a theoretical contribution to the optimization of the USRP parameters. After USRP, the cross-sectional hardness distribution of the workpiece was shown to initially rise, followed by a subsequent decrease, ultimately to matrix hardness. The cross-sectional residual compressive stress distribution of the workpiece showed a tendency to initially reduce, then increase, and finally decrease to zero. The fatigue performance of the workpiece was greatly enhanced after USRP due to the effect of grain refinement, work hardening, and beneficial residual compressive stress, thereby inhibiting the propagation of the fatigue crack. However, it could be noted that the excessive static force parameter of USRP could induce the decline in surface finish and compressive residual stress of the workpiece, which eliminated the beneficial effect of the USRP treatment. This indicated that the choice of the optimal USRP parameters was highly crucial. This work would be conducive to achieving high-efficiency and low-damage USRP machining, which could be used to effectively guide the development of high-end equipment manufacturing.

The influence of the geometric characteristics on the behavior of braces with restrained buckling - case study of perforated steel core.

Buckling restrained braces are elements that equip the building with additional capacity for resistance and stability when subjected to earthquakes. As an answer to the problem of the possible loss of stability of the buckling-preventing component, the “perforated-core buckling restrained braces” (PCBRB) is a concept that involves the introduction of gaps, in the core of the bracing, to control the plasticizing mechanism of the dissipative element. The research addresses the behavior of PCBRB groups where all the elements belonging to the same group have the same area and length of the section considered active dissipative. A numerical analysis environment was developed that simulates the support conditions and material behavior. Based on the results of the numerical analyses, the influence of the geometry (b/t ratio) of the section of the dissipative zone on the behavior and the mechanism of stress strain distribution in the bracing core. It can be noticed the development of over-resistance to the compressive stress and non-uniform distribution of stresses on the surface of the elements whose b/t ratio exceeds the value of 5.5; for the elements whose b/t ratio has a value lower than 1.75 local instability problems in the dissipative zone occurred.

Strength Analysis of Carbon Fiber Composite Flywheel Energy Storage Rotor Based on Progressive Damage Failure

Composite materials consist of a matrix and fibers, and their failure modes differ significantly from those of isotropic materials. In undamaged composite materials, under increasing loads, matrix damage typically occurs first. At this stage, the damaged area experiences a stiffness reduction, redistributing stress until failure occurs elsewhere. As matrix damage progresses, debonding between fibers and the matrix begins, leading to delamination failure. With further load increase, the fibers eventually fracture. Finite element simulation with stiffness degradation methods can be employed to study composite material damage. This involves gradually degrading damaged elements, ultimately revealing the final failure mechanism of the composite material. Advances in finite element software now allow for precise engineering simulations, widely applied in the field. Consequently, this method can be used to simulate and analyze the failure of composite material flywheel rotors, identifying the factors contributing to their failure. This study uses progressive damage theory to simulate the failure process, establishing rational failure criteria for composite materials and utilizing a finite element stiffness degradation model. Greater interference fit results in higher compressive stress and initial stress, making the compressive stress and initial stress distribution of composite material flywheel rotors dependent on the interference fit. The study also analyzes the critical speeds of flywheels with single‐ring and multiring rotors under different interference fits, revealing the influence of interference fit on the maximum speed of the flywheel.

Polarization Raman spectroscopy characterizations of microscopic stress in 3D angle-interlock woven composites during thermo-oxidative ageing

Investigating stress distribution of three-dimensional carbon fiber epoxy woven composites after thermo-oxidative ageing, especially the microscopic stress, is key to safety design of composite materials. Here, polarization Raman spectroscopy combined with the Raman stress sensitivity of carbon fiber was employed to characterize the microscopic stress in the carbon fiber along the warp and weft direction, as well as the microscopic stress mapping in the warp and weft interwoven interfaces. Under thermo-oxidative ageing, the carbon fiber was forced with compressive stress caused by the thermo-oxidative shrinkage of resin. The fitting lines of compressive thermo-oxidative ageing stress (TAS) distribution in the warp and weft were similar to the yarn alignment paths. Meta-regression analysis indicated that the compressive TAS in carbon fibers is positively correlated with ageing time. Furthermore, the correlation between the compressive TAS and ageing time in warp yarns is greater than that in weft yarns. The stress distributed unevenly with the synergistic effect of the structure and ageing time, and interfacial failure was generated where interfacial stresses exceeded the interfacial strength. The interfacial failure further propagated with ageing time, leading to matrix cracking.