Circumferential Compressive Stresses Research Articles

Stress evolution in enamel coating/Ni-based alloy systems during isothermal oxidation

This paper utilizes a coupled chemomechanical model that integrates chemical reactions, diffusion, and mechanical deformation to describe the high-temperature interfacial reactions and stress evolution within an enamel coating/Ni-based super-alloy system. Through finite element simulation, we conduct a comprehensive analysis of multiple reactions and processes at the interface. Experimental characterization of the concentration distribution of various elements is employed to verify the accuracy of the proposed chemomechanical model. Additionally, the simulation reveals that the interface region experiences compressive circumferential stress, which can potentially lead to interfacial failure due to buckling. On the other hand, the enamel coating undergoes tensile circumferential stress, resulting in the formation of vertical surface cracks. These findings hold practical implications for the development of advanced coatings with enhanced durability and performance. Future research can further optimize coating design and enhance the reliability of high-temperature applications based on these results.

Suppressing wrinkles in thin-walled dome parts: A novel deep drawing method with active stress control

The occurrence of wrinkling defects in deep drawing thin-walled dome parts is primarily attributed to circumferential compressive stress. With a decrease in the thickness-to-diameter ratio, preventing wrinkling becomes increasingly challenging during the forming process. This study proposes a novel deep drawing method that effectively suppresses wrinkles in thin-walled dome parts through the utilization of a local reverse bulging tool for active stress control. An analytical model is developed to describe this novel deep drawing method, enabling analysis of the radius variations in the reverse bulging area and the corresponding reverse bulging force. Numerical simulations are carried out to investigate the effect of the reverse bulging loading path on the stress-strain distribution. Furthermore, experimental trials are performed under various loading conditions to explore the impact of loading paths on forming defects and thickness distributions of the formed parts. The findings indicate that the radius of rigid tools and the reverse bulging force play pivotal roles in achieving the desired reverse bulging effect. As the punch stroke increases, the radius of the reverse bulging area decreases, while the reverse bulging force exhibits a pattern of initial increase followed by a subsequent decrease. By employing an appropriate reverse bulging loading path, the circumferential stress at the reverse bulging area transitions from compressive stress to tensile, effectively suppressing the occurrence of wrinkles. This research provides valuable experimental guidance for implementing the novel deep drawing process for dome parts.

Research on the Residual Stress Field of a Compression Bushing-Lug Plate in Cold Expansion Strengthening

The accurate acquisition of the residual stress field is the key to clarifying the cold expansion strengthening mechanism of compression bushings, optimizing the extrusion process parameters, and improving the structural fatigue life. In the actual cold expansion strengthening process, the resultant distribution of residual stresses is influenced by the relative extrusion amount, mandrel structure, material properties, and extrusion speed. In this article, the distribution patterns of residual stress after cold extrusion are investigated through a combination of finite element simulation and experimental measurements using a micro-region stress tester. To examine the redistribution law of the stress field of cold expansion reinforcement under external load, the compression bushing-lug-plate-reinforced structure is loaded and unloaded. The results show that large circumferential residual compressive stresses are distributed in the hole wall of the compression bushing after cold expansion. Radial residual stresses are also compressive stresses, although the values are small. In addition, the reinforced structure after cold extrusion presents a large difference in the stress redistribution rules compared with cold extrusion after the load is applied and removed.

Evaluation of segmental lining response during shield tunnel construction based on field measurements and 3D FEM simulation

Lining safety can be threatened more severely at the construction stage than at the service stage, because the loads at the construction stage are larger. This study presents an in-situ experiment for measuring the loads acting on the lining and the internal forces of the lining to investigate the lining response during both the construction and service stages. A three-dimensional (3D) finite element method (FEM) model that could simulate the main relevant components of the shield tunnel construction process was employed to gain further insight into the mechanisms of the lining response. The influences of the key segment position and assembly sequence on the lining behavior were examined through a comprehensive parametric analysis. The results showed that during the assembly stage, the insertion of a key segment resulted in the most significant increase in the axial force, followed by the assembly of an adjacent segment. The lining responses were significantly influenced by the key segment, particularly during the construction stage, whereas the assembly sequence had a limited effect on the lining responses. During the construction stage, the closer the key segment to the tunnel invert, the greater was the axial force and the smaller was the bending moment of the lining. During the construction stage, the closer the key segment to the tunnel invert, the smaller was the axial force of the tunnel lining and the greater was the bending moment. The circumferential compressive stress reached its maximum value at the joint interfaces. Finally, the jack thrust force was the greatest at the tunnel invert. The key segment should not be placed at this location.

Failure Mechanism of Integrity of Cement Sheath under the Coupling Effect of Formation Creep and Temperature during the Operation of Salt Rock Gas Storage

Maintaining the integrity of the cement sheath is essential for the sealing of underground gas storage. The formation creep, temperature changes, and operating pressure changes during the operation of underground gas storage can cause changes in the stress of the cement sheath, which probably induces the failure of the cement sheath’s integrity. A creep model taking the effects of stress and temperature into account is developed to study the cement sheath’s integrity in creep formation, and the feasibility of creep simulation via finite element method is verified. The finite element method is used to analyze the effects of formation creep, temperature, operating pressure, and the cement sheath’s elastic modulus on the cement sheath’s integrity. The result shows that the coupling effect of formation creep and temperature increases the cement sheath’s failure risk; both the formation creep and the decrease in cement sheath temperature increase the Von Mises stress on the cement sheath, increasing the risk of the cement sheath’s shear failure. The decrease in cement sheath temperature decreases the circumferential compressive stress on the cement sheath and raises the risk of the cement sheath’s tensile failure. Shear failure of the cement sheath occurs at high operating pressure upper limits. The operating pressure is less than 70 MPa, or the cement sheath’s elastic modulus is less than 3 GPa, which can prevent the failure of the cement sheath’s integrity during the operation of underground gas storage.

Simulation Research on Residual Stress of Swage Autofrettage-processed High-Pressure Cylinder

The vital component of the high-pressure pump is the high-pressure cylinder, which undergoes pulsating cyclic loads during operation. This exposure can lead to fatigue cracking and limit the pump’s overall performance. To address this issue, a swage autofrettage treatment method for the high-pressure cylinder is proposed based on the principles of autofrettage technology. The structure parameters of the mandrel are designed to optimize its role in the treatment process. Subsequently, a swage autofrettage simulation model is established, considering the Bauschinger effect to analyze the distribution of residual stress about the mandrel interference percentage. The results demonstrate that the swage autofrettage treatment improves the stress distribution in the high-pressure cylinder, causing the inner wall surface to undergo a circumferential residual compressive stress. Within a specific range, the Bauschinger effect becomes more significant as the mandrel interference percentage increases. This study provides insights for enhancing the durability and performance of high-pressure cylinders while adhering to mechanical engineering standards.

Study on the Residual Stress Distribution of Bi-Directional Cold Expansion Process Performed on Open Holes

AbstractTraditional unidirectional cold expansion technology usually generates non-uniform distribution of residual stress in the thickness direction of holes, which is harmful to the improvement of fatigue life of holes. The present work proposed a bi-directional cold expansion procedure to realize the homogenization of residual stress in the thickness direction of the cold expanded hole, thereby further improved antifatigue performance of cold expanded hole. For this aim, a series of finite element (FE) simulations were carried out to investigate the effectiveness of the bi-directional cold expansion procedure and optimize the process parameters. The results showed that the optimized bi-directional cold expansion process generated a more uniform distribution of residual circumferential compressive stress in the thickness direction comparing to the simplified bidirectional cold expansion process using a single mandrel. For the Aluminum alloy 7050-T7451, when the first interference level I1 = 1.8%, the largest and the most uniform residual circumferential compressive stress was achieved, which suggested the best anti-fatigue performance.

Effect of cryogenic machining-strengthening process on enhanced surface integrity and fatigue properties of ZK61M magnesium alloy

Excessive heat and fatigue are important factors affecting the machinability and service performance of magnesium alloy. Cryogenic processing is an effective method to reduce the temperature of the tool and the component, thus improving the machinability of magnesium alloys. The fatigue of workpieces is affected by machining and strengthening processes. However, the current studies on cryogenic processing hardly comprehensively consider the effect of cutting and rolling. To investigate the effect of cryogenic air and pre-cutting processes on rolling, the sequential cutting and rolling experiments were conducted on ZK61M magnesium alloy under dry and two cryogenic cooling conditions. Effects of coolant during sequential machining and rolling processes on forces, surface roughness, microstructure, hardness and residual stresses were investigated. The fatigue properties of ZK61M in the cryogenic processes were also studied. The results show that the rolling force is affected by the coolant lubrication and the surface hardening generated by the previous process. Cryogenic rolling can effectively reduce the surface roughness, increase the circumferential residual compressive stress and reduce the axial residual compressive stress. The feed force of the dry turning followed by rolling with liquid nitrogen (ST + NR) process is the smallest, which is 136.4 N. And the surface roughness (Ra) is also the smallest, which is 0.42 μm, 46.8 % lower than the traditional process. Meanwhile, the ST + NR process can prolong the fatigue life of ZK61M magnesium alloy by 62.9 % compared with conventional process. Moreover, the surface roughness and residual stress have significant influences on fatigue life of ZK61M magnesium alloy, followed by the depth of work hardening layer, and finally the surface hardness. Cryogenic cutting and strengthening process can effectively suppress the initiation and propagation of fatigue cracks.

Analysis of Bearing Safety and Influencing Factors of Supporting Structures of Hydraulic Tunnels in Cold Regions Based on Frost Heave

In order to study the bearing safety and influencing factors of the support structures of hydraulic tunnels in cold regions under the action of low-temperature frost heave, a mechanical model of the support structure and surrounding rock was established. Taking a hydraulic tunnel of a hydropower station in Xinjiang as the research object, a combination of field measurement and a numerical simulation method was adopted to study the bearing safety of the support structure during a period of freezing weather. Based on this model, the effects of different thermal expansion coefficients, temperature differences, and surrounding rock porosity on the bearing safety of the support structure in the low-temperature region were studied. From the calculation results, it was concluded that the simulation results of the numerical model established by using the mechanical model in this paper were in good agreement with the actual measurement results of the project. The circumferential freezing and compressive stresses at the arch waist of the supporting structure of the project were the largest, and significant plastic strain was generated near the arch waist. The displacement at the arch of the supporting structure was the largest, while the weak points were at the arch waist and arch top of the supporting structure. The coefficient of thermal expansion, greater temperature difference, and increased porosity of the surrounding rock all led to an increase in the rock freezing and swelling force to varying degrees, thus reducing the load-bearing safety of the supporting structure. The research results could provide a theoretical basis and a reliable mechanical and numerical simulation model for establishing the bearing safety of tunnels in the cold region.

ИССЛЕДОВАНИЕ ОСТАТОЧНЫХ НАПРЯЖЕНИЙ, ВОЗНИКАЮЩИХ ПРИ ИНКРЕМЕНТАЛЬНОМ ФОРМООБРАЗОВАНИИ

In this article, studies have been carried out to determine the magnitude of residual stresses arising during incremental shaping of a truncated cone, depending on the angle of inclination of its formative. To assess the residual stresses the method of cutting rings was used, according to the results of which it was found that the rings, cut out along the height, manufactured conical parts, when cutting are closed. This indicates the formation of compressive circumferential stresses during incremental shaping. There is also an insignificant axial displacement of the ring ends after cutting rings, which indicates the presence of axial residual stresses, the value of which is negligibly small compared to the value of circumferential stresses. As the degree of deformation increases during incremental shaping (increasing the taper angle), the magnitude of residual stresses decreases.

SECONDARY BUCKLING OF A HEATED CIRCULAR PLATE

Upon heating, a circular plate with immovable edge exhibits buckling, which results in ax-isymmetric postcritical bending. Progressive axisymmetric bending due to increasing thermal load in the postbuckling range leads to substantial redistribution of the stresses in the plate and occurrence of high compressive circumferential stresses in a narrow zone adjacent to the plate edge. In this case, secondary buckling can occur resulting in unsymmetric stress-strain state. The aim of the present work is to study stability behavior of the postbuckling axisymmetric equilibrium configurations of a circular plate subjected to uniform temperature rise. The plate edge is assumed to be immovable in the radial and transverse directions and elastically re-strained against bending rotation, which allows one to model the boundary conditions between two extremes of clamped and simply supported. The stability analysis is performed by the semi-analytical finite element method, where unknown displacements are approximated by truncated Fourier series in the circumferential coordinate. The geometrical nonlinearity is taken into ac-count in a quadratic approximation using the Fӧppl – von Karman nonlinear plate theory. To find equilibrium states of the plate, an iterative algorithm is proposed which requires determination of the coefficients of the first and second variations of the total potential energy. Stability of the equilibrium states is examined using the criterion of positive defineteness of the Hess matrix of the plate finite-element model. The critical temperature rise at which secondary buckling occurs is determined. The post-buckling nonlinear deformation characterized by local winkling near the plate edge is studied. The effect of boundary conditions and temperature-dependent material properties on the critical thermal load and secondary buckling modes is discussed.

Effect of blank quenching on shear spinning forming precision of 2219 aluminum alloy complex thin-walled components

The quenching-spinning (Q-S) process, i.e., shear spinning after blank quenching, has been increasingly utilized to form 2219 aluminum alloy complex thin-walled components. However, the changes in material property, shape and stress of the blanks after quenching will affect the spinning forming precision. In this study, the rules and mechanisms of these effects are investigated based on a combined finite element (FE) model including blank quenching and component spinning process. The results indicate that the increase of material strength and the existence of distortion of the quenched blank lead to a notable increase in the non-uniformity of the circumferential compressive stress in the spinning area and the increase of the flange swing height during spinning. These changes result in an increase in the wall thickness and component-mandrel gap of the components. The quenching residual stress has little effect on wall thickness and roundness but can noticeably reduce the component-mandrel gap. This is because that the existence of quenching residual stress of the blank can lead to the decrease of the maximum circumferential compressive stress of the workpiece in spinning and an obvious drop in the maximum compressive stress after reaching the stress peak. Quenching distortion is the main factor affecting the roundness. Moreover, the optimized installation way of the blank for spinning is obtained.

Optimization of machining parameters applied in hard turning of large components for cooling lubrication methods

The increasing demands concerning renewable energy have required ever-bigger projects, as seen with wind turbine cases; in these large projects, the surface contact presents high load and wear resistance requirements. The cooling and lubrication methods in machining are highlighted due to the reduction of costs and environmental impacts. In functional hardened surfaces, it is critical to understand the integrity aspects once they significantly affect the durability of the component. This work clarifies, how the machining parameters of feed, depth of cut, velocity of cut, minimum quantity of lubrication, and abundant cooling affected the machined surface in a large component, with a discussion about microstructural altered layer, residual stresses, and Sa, Sq, and Sz statistical parameters. The results indicated that the minimum quantity lubrication and abundant cooling produced highly compressive circumferential residual stresses. Both methods produced surfaces free of significant microstructure altered layers. The altered surface layer was very thin when detected, with a thickness of up to 2.35 µm. On optimal conditions, the minimum quantity lubrication, in relation to abundant cooling, presented residual stresses 37% higher, a thickness of altered layer 74% lower, and Sa and Sz roughness, respectively, 47% and 11% lower and Sz 12% higher.

Simulation Analysis and Verification of Temperature and Stress of Wheel-Mounted Brake Disc of a High-Speed Train

During the braking process, a large amount of heat energy is generated at the friction surfaces between the brake disc and pads and rapidly dissipates into the disc volume. In this paper, a three-dimensional thermo-mechanical coupling model of high-speed wheel-mounted brake discs containing bolted joints and contact relationships is established. The direct coupling method is used to analyze the temperature and stress of the brake discs during an emergency braking event with an initial speed of 300 km/h. A full-scale bench test is also conducted to monitor the temperatures of the friction ring and bolted joints. The simulation result shows that the surface temperature of the friction ring reaches its peak value of 414 °C after 102 s of braking, which agrees well with the bench test result. The maximum alternating thermal stress occurs in the bolt hole where the maximum circumferential compressive stress is − 658 MPa and the maximum circumferential tensile stress is 134 MPa. During the braking process, the out-of-plane deformation of the middle part of the friction ring is larger than that of the edge, which increases the axial tensile load of the connecting bolt. This work provides support for the design of brake discs and connecting bolts.

Possible mechanism of spallation in rock samples under uniaxial compression

In uniaxial compression, rocks are often observed to have spallation failure at the lateral surface of the sample developing parallel to the direction of loading. While easily explained by a 2D concept of axial crack growth in uniaxial compression, the real 3D mechanism cannot be explained this way, as 3D crack growth in uniaxial compression is restricted to the size of the initial defect due to the phenomenon of wing wrapping. The wing wrapping can only be overcome in biaxial compression with the magnitude of the intermediate principal stress exceeding 5–8.5% of the axial load (depending on the type of crack-producing defect). In uniaxial compression, the role of the intermediate principal stress is played by the circumferential compressive stress induced due to the end constraint owning to the presence of end friction. The results of Finite Element modelling show that zones of biaxial compression are formed at the lateral surface near the sample ends. The sizes of the zones and the maximum magnitude of the circumferential stress depend upon the friction coefficient and the Poisson’s ratio of the rock. The modelling also revealed the presence of zones of tensile circumference stress which can potentially induce splitting failure.

Orientation and Residual Stress Distributions in Thick Melt Spun Polystyrene and Polycarbonate Filaments

Abstract A study of orientation development and residual stresses in thick melt spun polystyrene filaments and polycarbonate filaments described. Linear relationships between spinline stress and mean birefringence under different melt spinning conditions were obtained. These results were used together with models of the dynamics of melt spinning to predict the characteristics of thick melt spun filaments. Birefringence distrbutions and residual stresses were computed. High orientations and compressive circumferential residual stresses were predicted at the larger radii and low orientation and tensile circumferential and radial residual stress in the fiber core are obtained. The distribution of birefringence across the thickness of thick melt spun filaments was measured by determining changes of retardation across a wedge. The birefringence distributions were correlated with severity of quench and model prediction. Thick melt spun fibers were peeled and found to have fibrillar cores.

Deformation mode and wall thickness variation in conventional spinning of metal sheets

In the conventional spinning of metal sheets, the deformation mode and wall thickness variation have a critical effect on forming stability, quality, and accuracy. Although it is widely accepted there is near-constant wall thickness during conventional spinning, there is actually a certain degree of variation in wall thickness during this process. The nature of this variation has yet to be fully understood, which makes it difficult to precisely control wall thickness during conventional spinning. In this study, we investigated and predicted the deformation mode and wall thickness variation in the conventional spinning of a 1060 aluminium alloy plate. It is found that there are three deformation modes that change sequentially in conventional spinning: shear deformation, compression-shear deformation, and tension-shear deformation. These modes correspond, respectively, to the wall thickness variation of (a) sine-law reduction, (b) a reduction intermediate between sine-law reduction and no reduction, and (c) wall thickening. These dynamic changes in deformation mode and wall thickness variation are caused by a decrease in stress triaxiality in the forming region, which is induced by a decrease in the constraint from the flange region to the forming region. We quantified this constraint by calculating the bending rigidity of the flange region, which represents the resistance to the elastic bending deformation that occurs once the flange loses its stability. Then, we developed a formula with the bending rigidity of the flange region as an independent variable to predict the deformation mode and wall thickness variation that occurs during the conventional spinning of 1060 aluminium alloy. Moreover, we determined the effects of the processing parameters on the deformation, and then used a process-related correction factor to incorporate these effects into the above predictive model. By this model, the effects of processing parameters on the change in the deformation mode during spinning were revealed. The model was also used to modify the traditional flange wrinkling model, in which the wall thickness is assumed to be constant. This modified wrinkling model considers the actual variation in wall thickness, which enabled us to accurately determine the maximum circumferential compressive stress on the flange. Thus, the predictive accuracy and applicability of the modified wrinkling model for characterizing the conventional spinning of 1060 aluminium alloy was far superior to that of the traditional wrinkling model. These results increase the understanding of deformation behavior in conventional spinning, thereby providing important guidance for improved processing design and forming accuracy.

Bond Behavior of Reinforced Concrete Considering Freeze-Thaw Cycles and Corrosion of Stirrups.

In relatively cold environments, the combination of freeze–thaw and steel bar corrosion is a key factor affecting the durability of concrete. The adjustment of the stirrup ratio would change the mechanical performance of surrounding concrete, while the circumferential compressive stress can further improve the bonding performance. Hence, based on eccentrically tensioned specimens, the influence of corrosion of stirrups and freeze–thaw of concrete on bond properties is discussed in this paper. The monotonic pull-out test of reinforced concrete specimens is carried out to study the variation rules of bond strength and slip between steel bar and concrete under the coupling action of corrosion rate, freeze–thaw times and stirrup spacing. Based on the experimental data, the empirical formula for the ultimate bond strength is obtained, and a bond–slip constitutive model is established considering the stirrup spacing, stirrup corrosion rate and freeze–thaw times. Then, a refined finite element pull-out specimen model is established by ABAQUS simulation, and the numerical simulation results are compared with the real test ones, so as to make up for the deficiencies in the test and lay the foundation for further finite element analysis.

Large ellipsoid parts manufacture using electromagnetic incremental forming with variable blankholder structure

Large ellipsoid parts are prone to wrinkle when forming by using traditional stamping. Aiming to solve the wrinkling problem in large parts, the EMIF method with a variable blank holder is proposed in this paper. The numerical simulation has shown that the sheet material near the blank holder is, as a consequence of stamping, subjected to circumferential compressive stress. When the drawing height was 100 mm, the sheet metal was notably wrinkled. In the electromagnetic forming (EMF) process, the sheet region facing the coil becomes thinner. However, the sheet metal thickness corresponding to the coil edge increases with the increase in forming height. If the EMF forming height is 150 mm, the sheet, which is in contact with the smooth mold, is deformed without a wrinkle. Compared to traditional stamping, the EMF can significantly reduce the sheet metal wrinkling, improving the deformation height of the sheet metal smooth area.

Local Elasto–plastic Buckling of Isotropic Plates With Cutouts Under Tension Loading Conditions

The motivation of the presented study was the observation of the existence of local loss of stability “tension buckling” in the experimental tests of composite and metallic plates with cut-outs subjected to tension. Because of this, the numerical analyses of the aluminum plate with elliptical or circular cutouts at the center and subjected to tensile load are studied in the paper. Although the whole structure is uniformly stretched, the circumferential compressive stresses in the vicinity of the cutout edge are observed. First of all, the linear buckling analysis is carried out for different sizes of the holes. Based on these results, the size of the hole is chosen, where the circumferential stress magnitude in the vicinity of the cutout is the lowest or even comparable to the yield stress of the material. The computations are made for three different values of thickness. Finally, the nonlinear buckling analysis is carried out without and with the plasticity effects included. Generally, in the case of the circular and vertically oriented elliptical cut-out, the loss of stability in the tensed plate is always observed. However, in elastic-plastic analyses, the values of the critical parameters significantly differ from the results obtained for elastic buckling. Finally, the critical geometries for further experimental tests were defined.