Influence Of Stress Concentration Research Articles

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 Hp(y) signal distribution law of prefabricated U-shaped defect samples and the difference in Hp(y) signal between specimens with different tip SCFs. Results show that the Hp(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 Hp(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.

The Influence of Stress Concentration Caused by Surface Dimples on Tribochemical Reaction of Solid Lubricants Encapsulated in Surface Dimples

The Influence of Stress Concentration Caused by Surface Dimples on Tribochemical Reaction of Solid Lubricants Encapsulated in Surface Dimples

Review on stress evolution and crack propagation mechanism of double-crack specimens

The distribution pattern of cracks in rock masses, known as the geometric distribution, holds significant significance in understanding the progressive failure mechanism and stress concentration can lead to instability and even failure of the specimens. However, the macroscopic and microscopic mechanisms of crack coalescence and the failure of the sample are not yet clear. Thus, the discrete element method was used to investigate the influence of stress distribution on the fracture coalescence and failure of dual-crack specimens with different arrangements under uni-axial compression in this study. The obtained results were compared and analyzed with laboratory test results. The results show: When the double-crack specimens are under overlapping arrangement, the stress concentration area only appears at the end of the crack, which is conducive to crack propagation, resulting in no coalescence. However, if the two preexisting cracks were arranged in a co-planar or non-overlapping manner, the stress concentration of the sample would not only occur at the end of the cracks, but also between the cracks. As the stress increases, the cracks will gradually expand and connect, forming shear coalescence and mixed mode coalescence (shear and tensile) respectively. In addition, the arrangement of cracks greatly changes the influence of stress concentration on the failure mode of the specimen, leading to the possibility that the coalescence of the specimen may occur in three periods: before, during, and after the peak stress. The findings of this research hold immense importance in comprehending the mechanisms behind the coalescence and failure of rock fractures. Moreover, they provide valuable insights for the analysis and design of rock engineering projects, offering practical guidance for ensuring stability.

Topology optimization of UAV structure based on homogenization of honeycomb core

In this paper, a new optimization design strategy is explored to achieve a rapid design of lightweight structures for unmanned aerial vehicles (UAVs) using honeycomb sandwich panels. Based on the existing performance equivalent method of honeycomb core material, an effective mechanical property homogenization model of honeycomb material is proposed and applied to finite element analysis. A finite element model is established to analyze the mechanical response of honeycomb sandwich panels under different bending loads, and the rationality of the model is verified by mechanical tests. The error between the simulation results and the experimental results is about 10%. Based on the variable density method and rational approximation of material properties interpolation method, a topology optimization model with the minimum structural flexibility as the objective is constructed. By comparing with the experiment-based design scheme, it is found that the optimized design scheme has a more reasonable structure and better performance. The optimized design can effectively reduce the structural weight and improve the load transfer path while ensuring structural stiffness. In this way, the influence of stress concentration and large deformation on the structure is avoided, which is of great significance for the design of UAV structures.

Experimental Study on the Influence of Stress Concentration on the Flexural Stability of Aluminum Hollow Tube

Solid sections are gradually replaced by the hollow sections in most of the structural applications in various engineering fields due to their attracting features such as light-weight and high specific strength. In the present investigation, one such attempt was made to investigate in detail about the flexural capability of an aluminum hollow tube (AHT) with square cross section. The objective of the investigation is to study about the influence of stress concentration on the flexural behavior of the hollow tube. The type of stress concentration considered in the investigation was through hole of different cross section and quantity. Three-point bending test with concentrated load is conducted on the specimens of hollow tube with different types of stress concentration such as circular hole, square hole and perforations. The load was applied manually during the bending test. The bending test was carried out on all specimens for various support span of 110, 130, 170 and 200 mm respectively. The output measures of the study are maximum bending load, deflection and flexural stiffness. The maximum bending load capacity around 5.7 kN was observed for AHT with circular hole with support span of 90 mm. The maximum deflection measured at the mid span of the beam increases rapidly when the aspect ratio increases from 73.33 to 93.33, whereas after which the variation of deflection is marginal for the increase in aspect ratio from 113.33 to 133.33. This was due to the effect of spring back, which dominates more on the bending behaviour at shorter span between the supports

Assessment of Fatigue Life for Corroded Prestressed Concrete Beams Subjected to High-Cycle Fatigue Loading

Millions of in-service concrete bridges around the world are exceeding their design life. Corrosion may lead to a sudden fracture of prestressing steels, and understanding the fatigue behavior of corroded prestressed concrete (PC) bridges is essential. Accordingly, an effective fatigue analytical model for corroded PC beams is needed. In this study, an experimental investigation of the fatigue behavior of corroded PC beams, was carried out. Thirteen PC beams had experienced acceleration corrosion before high-cycle fatigue testing. All beams failed due to fatigue fracture of the corroded tensile steel bars, and three-dimensional laser scanning results indicated that the fracture occurred at the minimum cross sections with a severe corrosion pit. A segmented linear analytical model to evaluate fatigue response and predict fatigue life was developed which considers fatigue irrecoverable plastic strain of concrete, stress concentration, and longitudinal variation in the cross-sectional areas of corroded steel bars. There is an acceptable agreement between the numerical and experimental results of corroded PC beams. The proposed model can reasonably predict the evolution of strains in concrete, corroded prestressing steel, and rebars in PC beams under high-cycle fatigue loading, thereby allowing fatigue life prediction. Further analysis studied the influence of degree of corrosion in prestressing wires/rebars, stress concentration and longitudinal variation in cross-sectional areas of corroded steel bars, load ranges, and partial prestressing ratios (PPRs). It was found that, to reasonably estimate the fatigue life of corroded PC beams, the influence of stress concentration must be considered with the proposed impact factor. A higher corrosion degree, load range, or PPR shortens the fatigue life of corroded PC beams.

Mechanical Behavior and Failure Process of Hard Rock with Rock Bridge under Uniaxial Compression Test

Abstract The mechanical properties of rock mass are mostly controlled by the structural plane. Rock bridge has an important effect on the failure and stability of rock mass with structural plane. In this paper, the uniaxial compression test of hard rock containing rock bridge is carried out, accompanied by acoustic emission (AE) and high-speed video monitoring. Within the scope of this study, the results show that the uniaxial compressive strength (UCS) of sample with rock bridge increases with the rock bridge length. Under the same stress condition before peak, the strain of the sample decreases with the increase of the rock bridge length (RBL). Under the influence of stress concentration, the cracking of the sample starts from the prefabricated crack tip. The peak AE count of the sample decreases with the increase of RBL. The AE cumulative energy of the sample increases with the increase of RBL. The number of cracks in the sample before the peak is small, and the rapid increase of cracks is mainly concentrated in the main fracturing stage after the peak, while after reaching the residual stage, the increase rate of various types of microcracks in the sample is relatively slow. The numerical simulation results show that the number of all kinds of cracks in the sample before the peak is small, and the number of tensile cracks in the sample is very close to the total number of cracks under different RBLs. With the increase of RBL, the tensile/shear crack ratio decreases. The internal cracks of the sample are mainly concentrated at the peak stress and postpeak stage. The research results of this paper are of great significance to the engineering excavation and safe construction of jointed rock mass engineering.

Effect of stress concentration and deformation temperature on the tensile property and damage behavior of a B4Cp/Al composite

In the present work, the influence of stress concentration and deformation temperature on the mechanical behavior of boron carbide particles reinforced aluminum matrix (B4Cp/Al) composites fabricated by powder metallurgy was investigated via the tensile test and finite element simulation based on the real microstructure. The results demonstrate that a uniform particle distribution and a good interface bonding between the particles and matrix are found in the 5 wt% B4Cp/6061Al composite. When the deformation temperature decreases from 298 to 77 K, the tensile property and notch sensitivity ratio of the notched composite increases. Combined with the microstructure observation and stress/strain evolution, the fracture mechanism of the notched composite at 77 K was revealed. Specifically, there is a difference in stress and strain distributions induced by deformation temperature in the initial stage of deformation of the notched composite. The matrix damage tends to occur from the notch and propagate to the high strain regions near the particles. Furthermore, there is a high possibility of particle fracture or interface debonding in the notched composite due to the high matrix stress at 77 K. This work provides the experimental and theoretical basis for the application of particle-reinforced aluminum matrix composites with stress concentration under cryogenic environments.

Influence of stress concentration on fatigue life of corroded specimens under uniaxial cyclic loading

Corrosion has a significant deteriorative effect on fatigue life of aged ship and offshore structures; hence reliable numerical fatigue life analysis of aged ship structures is crucial for safe operation. The reliability of the fatigue damage assessment techniques depends on the quality of the S-N curve which should account for corrosion degradation. In this paper, the different factors affecting the randomness of stress concentration and fatigue life of corroded specimens have been studied. It was demonstrated that the Stress Concentration, which results from the distinctive thickness variation of the corroded specimens, significantly depends on the mean and minimum thickness of the corroded plate. The equivalent thickness of a typical plate, which has the same fatigue strength of the corresponding corroded one under the same cyclic load, was investigated. A time-dependent S-N curve of corroded structures considering the deterioration of material mechanical properties was proposed. The corroded surfaces were modeled using random spatial distributions and the effect of corrosion degradation on the material mechanical properties was taken into account. The numerically estimated fatigue life and the proposed S-N curve were compared with experimental fatigue test results. The comparison showed good agreement between the experimental results and the adopted approaches for fatigue life assessment.

Fatigue Life of Welded Structures under Random Load Study on Frequency Domain Method

In this paper, based on the finite element software, the residual stress of the structure weld is obtained through simulation analysis. The influence of stress concentration is considered by using the mean square stress concentration factor; and the S-N curve equation of the structure is derived. then, the stress power spectrum density of dangerous parts is obtained by random response analysis; Then, the vibration mode of the welded structure is obtained by random response analysis, and the acceleration power spectral density of the structure is input, and then the stress power spectrum density of the dangerous part is obtained Finally, the appropriate stress probability density distribution model is selected to predict the fatigue life with S-N curve equation and Miner damage accumulation theory. The results show that the fatigue life predicted by this method is very close to that of rain flow counting method.

Prediction of fatigue damage in ribbed steel bars under cyclic loading with a magneto-mechanical coupling model

As a ferromagnetic material, the magnetization of ribbed steel bars will change with the development of fatigue damage under cyclic loading, which can be used to evaluate the fatigue damage state of steel bars. However, the quantitative relationship between fatigue damage and the variation in magnetization is still unclear, and the existing magneto-mechanical model cannot be applied to ribbed steel bars directly. To accurately predict the magnetization and the fatigue damage state during fatigue, it is also necessary to consider the influence of stress concentration caused by ribs on stress and fatigue life. This paper proposes a magneto-mechanical model suitable for ribbed steel bars, which use the Neuber law and Coffin-Manson relationship to determine the stress range and fatigue life under stress concentration. Additionally, the magnetic induction intensity of the HRB400 ribbed steel bar in the tensile fatigue test was measured to verify the proposed model, and the mechanism of the magnetization change trend during fatigue was analyzed in detail. Through the fatigue damage formula based on the magnetic indicator, the simulation and experimental comparison results show that the proposed model can effectively describe the fatigue damage state of ribbed steel bars in the fatigue.

Modeling of deformation and fracture of porous media taking into account their morphological composition

This paper investigates the mechanical behavior and fracture of porous materials with an aluminum matrix. The purpose of the work was to create numerical models of failure of representative volume elements of such materials and to reveal the dependences of the nature of the failure processes on their structural morphology. Representative volume elements of these materials are random non-uniform structures of closed-cell and open-cell types. To create three-dimensional geometric models of the closed-cell structures, methods of sequential synthesis the possibility of their mutual intersection were used. For creation of models of interpenetrating structures of the open-cell type, methods based on the analytical determination of surfaces separating the two phases are used. In this paper, three approaches to fracture mechanics of representative volume elements of porous materials were studied and implemented. The first approach is an implementation of the elastic model and damage accumulation based on elastic properties degradation in accordance with the criterion of maximum stresses with reduction of the stiffness matrix coefficients in individual elements. The second approach is an implementation of the same model, but with removal of the failed elements. The third approach is based on the Johnson-Cook elastic plastic behavior and fracture model. Numerical modeling of the representative volumes was carried out with finite element analysis using each of the above approaches. The influence of the internal structure of the representative volumes of the porous materials on the processes of deformation and failure was studied on the example of several structures of open-cell and closed-cell types. The influence of stress concentrators on the distribution of stresses in representative volumes and character of their subsequent failure has been studied.

Study on corrosion fatigue properties and fracture characteristics of 7075 aluminum alloy FSW joint

Taking 7075-T6 aluminum alloy friction stir welding joint as the research object, the microstructure, 3.5 wt % NaCl solution corrosion fatigue life and corrosion fatigue fracture characteristics were studied, and the corrosion fatigue performance and fracture process of 7075 aluminum alloy friction stir welding joint were analyzed. The results showed that: the S-N curve equation of corrosion fatigue of 7075-T6 aluminum alloy friction stir welded joint is lgN=5.845-0.014S, With the increasing of stress amplitude, the corrosion fatigue life decreased greatly. The corrosion fatigue crack originated in the thermal affected zone of the joint, gradually expanded and finally broke in the welded core zone of the joint. There were multiple crack sources in the corrosion fatigue fracture, and with the influence of stress concentration, the crack source originated in the corrosion pit. The high stress aggravated the corrosion damage of the corner part of the sample, led to more serious corrosion than that of the plane position. Obvious intergranular fracture and fatigue striation appeared in the crack growth zone. Under the combined action of corrosive medium and alternating load, the crack growth zone suffered the most serious corrosion, and the anodic dissolution occurred at the grain boundary, resulting in the morphology characteristics of “rock candy” and “ant nest”. Instantaneous fault zone was brittle fault,and there were a lot of cleavage steps and secondary cracks in this zone, the pore morphology appeared in the second phase particle distribution region.

Local Fracture of Nanolaminates: Edge Chipping Test

The fracture resistance of domestic and foreign nanolaminate ceramics was studied by the EF (edge fracture) method. This method provides for indentor chipping of rectangular specimen edges, which permits evaluating such fracture resistance characteristics, as chipping resistance and edge toughness. There is no way of experimental determining the stress intensity factor effected as the penetration of a Vickers indentor into the polished specimen surface and measurement of crack sizes that are formed near the angles of its imprint. The influence of stress concentrations in the indentor–specimen surface contact zone on the fracture resistance of ceramics was assessed. Different test stress concentrations were produced with conical diamond indentors of different tip radii. Studies on domestic titanoaluminous carbide Ti3AlC2 specimens demonstrated that with a reduction in stress concentration levels (indentors with increasingly larger tip radii), its edge toughness grew to a smaller extent than that of Y2O3 and TS Mg-PSZ ceramics. It is indicative of the limited sensitivity of an examined material to stress concentrations on local fracture. The ratio of edge toughness determined with the indentors of maximum and minimum tip radii (in this case, 400 and 11 μm) can serve as a measure of its sensitivity (in comparison to this characteristic for examined materials). Note that the edge toughness of Ti3AlC2 ceramics is almost one-third as large than, e.g., that of Y2O3 ceramics and 1.6 times smaller than that of TS nonlinearly elastic zirconia Mg-PSZ.

Experimental Study on the Evolution Law of Mesofissure in Full Tailing Cemented Backfill

To understand the mechanical properties of the backfill, to reveal the evolvement of micromechanical fissure of backfill, a uniaxial compression experiment was carried out for the full tailing cemented backfill. After loading, the microstructure of the specimens was observed by microscope and the pore characteristic parameters were analyzed. The results showed that the diameter of the initial damage hole of the backfill was mostly between 0 and 40 μm, the hole diameter increases gradually with the increase of pressure, and the hole diameter reached more than 5000 μm in the postpeak damage stage. The upper structure of the backfill specimen is compact while the lower structure is relatively loose. The cracks and interfaces between tailings particles and cement paste are mechanical weak surfaces, where the cracks are mainly generated and propagated. The tip of microfractures in the backfill is damaged by the influence of stress concentration. In the failure process, both surface porosity and fracture density decrease first and then increase, and the average pore diameter increases gradually. The results have guiding significance for the study of backfill mechanical properties and goaf filling design.

Micro-scale numerical study of fiber/matrix debonding in steel fiber composites

Fiber/matrix debonding behavior of steel fiber composites is analyzed using a parametric finite element modeling procedure and compared with conventional composites with carbon and glass fibers. Cohesive surfaces are applied to fiber–matrix interface to simulate the debonding behavior, while the interface strength properties of steel fiber are obtained with and without surface treatment. The effect of various parameters on the debonding behavior is investigated, including stress concentrations, fiber diameter, fiber shape, and fiber volume fraction, using the parametric model. The influence of stress concentrations is determined to be much lower than the debonding strength. Debonding damage is more evident in larger fibers compared to smaller ones. Earlier and sudden interface separation is observed with the polygonal steel fibers compared to the circular ones. Increase in the fiber volume ratio increases the debonding opening distance but does not affect the opening angle significantly. The results can be useful for assessing possibilities to use steel fibers to increase toughness of the composites in comparison with glass and carbon reinforcement.

Determination of Crack-Tip Opening Displacement in T-Type Wedge Opening Loaded Specimen

The protective layer at the crack tip of an alloy component can be damaged, and the resistance to crack propagation can be reduced by the combined effects of stress and a corrosive environment. Therefore, the measurement of crack-tip opening displacement (CTOD) can be applied to characterize the crack propagation rate (da/dt) during stress corrosion cracking (SCC) experiments. In the present work, CTOD of a T-type wedge opening loaded (T-WOL) specimen with a built-in loading bolt was initially determined using three-dimensional elastic-plastic finite element analysis (FEA). The influence of stress concentration from side groove on CTOD was clearly evaluated, i.e., the fluctuation of CTOD occurred near the groove-tip plane. However, CTOD became stable on >90% of thickness of T-WOL specimen. Therefore, CTOD at mid-thickness plane of T-WOL specimen could be applied for SCC experiment.

Experimental investigation and numerical prediction of static strength and fracture behaviour of notched epoxy-based structural adhesives

The influence of stress concentrations on the tensile static strength and fracture behaviour of notched bulk specimens was investigated by comparing the response of two epoxy-based structural adhesives (a rubber-toughened and a polyurethane-toughened). Numerical predictions of failure stress were carried out using a 3D-FEA model with a hydrostatic dependent elastoplastic material behaviour and the equivalent plastic strain for failure assessment. The ductile adhesive, which plastically deforms more under high stresses, provided experimental evidence of a notch strengthening effect. Conversely, the less ductile adhesive has shown a reduction in tensile strength compared to un-notched samples. For both adhesives fracture surface analysis showed the presence of stress whitening and voids close to the notch regions. These regions could be correlated to higher values of stress triaxiality using numerical simulation. The more ductile adhesive underwent widespread stress whitening prior to failure, whereas the response of the less ductile adhesive was more localised. Numerically based predictions showed excellent agreement with experimental results with average error of 5.1% for different notch types in both adhesives.

Influence of stress concentration and cooling methods on post-fire mechanical behavior of ASTM A36 steels

This study aims to investigate the influence of stress triaxiality and cooling methods on post-fire mechanical behavior of ASTM A36 steels. To this end, ASTM A36 notched steel specimens are designed to generate a range of stress triaxialities. These specimens are subjected to target temperatures of 500 °C, 600 °C, 700 °C, 800 °C, 900 °C and 1000 °C, and then cooled down to room temperature using air-cooling and water-cooling methods. These specimens are then uniaxially tested to determine their post-fire mechanical properties. Non-linear finite element analysis is conducted using post-fire mechanical properties to obtain stress triaxiality distribution in notched test specimens subjected to different target temperatures and cooling methods. Finally, a Scanning Electron Microscope (SEM) study is conducted on fractured surfaces of representative un-notched and notched test specimens to investigate the influence of high stress triaxiality and cooling methods on fracture initiation and propagation mechanisms. The post-fire mechanical properties of ASTM A36 steels are found to remain almost unaffected when cooled from 600 °C, irrespective of cooling method. ASTM A36 steels experienced up to 14% degradation in ultimate tensile strength and up to 22% increase in fracture strain when air-cooled from temperatures beyond 700 °C. Post-fire ultimate tensile strength is observed to increase by up to 146% whereas fracture strain is observed to decrease by up to 76% when ASTM A36 specimens are water-cooled from high temperatures. High stress triaxiality resulted in up to 37% increase in ultimate tensile strength and up to 74% reduction in ductility of air-cooled specimens. Presence of high stress triaxiality and water-cooling from temperatures beyond 700 °C is observed to significantly increase the ultimate tensile strength (up to 252%) and substantially reduced the ductility (up to 98%) of ASTM A36 steels.

Notch wear prediction model in high speed milling of AerMet100 steel with bull-nose tool considering the influence of stress concentration

Notch wear is one of the predominant types of tool failure in high speed milling of difficult-to-cut materials. This paper aims to reveal the formation and impact mechanisms of notch wear in bull-nose milling. Tool wear on rake face during dry milling of AerMet100 steel is investigated, severe notch wear is observed in lots of experiments. Based on the comparison of uncut chip thickness variations under two different cutting types, an attempt is made to explain the occurrence of notch wear from the view point of stress concentration. In order to quantitatively characterize the degree of stress concentration at any position on tool edge, a stress concentration factor is defined in this paper. The non-uniform and instantaneous variable characteristics of stress distribution along the cutting edge during bull-nose milling are taken into consideration. Then a predictive model of notch wear depth considering the influence of stress concentration is developed. Series of cutting tests are performed to validate the notch wear depth model, and the results indicate that the proposed model is feasible. In addition, the effects of different cutting parameters on notch wear are discussed. Further, this work can be applied to optimize process parameters for controlling notch wear, improving machining efficiency and reducing production cost.