Degree Of Stress Concentration Research Articles

Relationship between stress and magnetic signal of steel box girder based on magnetic memory method

Metal magnetic memory testing (MMMT) is a nondestructive testing technique that can detect early signs of damage in components. Many scholars have studied the effect of uniform stress on the self-leakage magnetic field (SLMF) strength of ferromagnetic materials. However, there is still insufficient research on the stress concentration caused by uneven stress, under the combined action of bending and shear. In this study, we studied the law of distribution of the magnetic signal, HP(y) and magnetic gradient, K, on a part of the surface of a steel box girder damaged by buckling, using a four-point bending pattern. The results showed that combining the three peak positions, namely, the magnetic signal, its newly added comparing initial magnetic signal, and magnetic gradient distribution curves, could accurately determine all stress concentration positions on the flange of the steel box girder, and reduce the interference of the initial complex residual magnetic field. Furthermore, we studied the quantitative relationship between normal stress, shear stress, and a magnetic signal. It was found that the stress-magnetic relationship conformed to the Jiles–Atherton model. The peak value of HP(y) – 𝜎, |HP(y)|a – 𝜎, and Kmax – 𝜎 relationship curves could be used as the characteristic point of the critical yield stress at the action of normal and shear stress. The degree of stress concentration of the flange and web could be quantitatively evaluated by fitting the Kmax – 𝜎 relationship. This study can provide an experimental reference for the application of MMMT in the evaluation and early warning of the state of damage to a steel box girder.

Effects of surface roughness on bending properties of rolled AZ31 alloy

This study investigated the effects of mechanical-polishing-induced surface roughness and the direction of polishing lines on the bending properties of a rolled AZ31 alloy. To this end, three-point bending tests were performed on one sample without polishing lines (SS sample) and two samples with polishing lines—one in which the polishing lines were parallel to the rolling direction (RS-RD sample) and the other in which they were parallel to the transverse direction (RS-TD sample). In all three samples, macrocracks were formed in the width direction on the outer surface, where tensile stress was predominantly generated in the longitudinal direction. However, the macrocracks formed in the SS sample were curved because of the merging of uniformly formed fine microcracks, whereas those formed in the RS-TD sample were linear owing to the formation of relatively coarse microcracks along the polishing lines. The bendability of the samples was in the order of SS > RS-RD > RS-TD, and their limiting bending depths were 4.8, 4.6, and 4.4 mm, respectively. In the presence of mechanical-polishing-induced surface roughness, polishing lines perpendicular to the direction of the major stress (i.e., tensile stress along the longitudinal direction) resulted in a greater degree of stress concentration on the outer surface of the bending specimen. This higher stress concentration promoted the formation of undesirable {10–11} contraction and {10–11}–{10–12} double twins—which typically act as crack initiation sites—and thereby facilitated crack generation and propagation. Consequently, the surface roughness caused premature fracture during bending deformation, which, in turn, caused deterioration of the bendability of the rolled Mg alloy.

A numerical simulation method of residual magnetic field signals for evaluating deformation-induced stress concentration in ferromagnetic materials

The metal magnetic memory (MMM) technique is a promising non-destructive inspection method that is sensitive to early damage due to stress concentration in ferromagnetic components. However, quantitative analysis methods for evaluating the stress concentration induced by local plastic deformation have not yet been sufficiently studied due to the lack of a reasonable numerical simulation method. Based on the Jiles-Atherton (J-A) magneto-plastic model, which considers the combined effects of residual stress and strain, the change in the behaviour of residual magnetic field (RMF) signals in an X80 pipeline steel specimen with an indentation is calculated in this paper using finite element (FE) simulations, while systematic experimental research is also carried out. The results show that the model-predicted RMF signals are consistent with the experimental data, which demonstrates the validity of the numerical simulation method. Moreover, the comparison indicates that the RMF FE simulations can provide an effective and reliable way to determine the location and the degree of deformation-induced stress concentration. In addition, the effect of the residual stress and strain on the surface magnetic field and the model is discussed. The results of this study help to improve the accuracy of the MMM technique for evaluating the stress concentration caused by local plastic deformation.

A butt shear joint (BSJ) specimen for high throughput testing of adhesive bonds

ABSTRACT Machine learning is extensively used in material research and development, including adhesion technology. However, it requires a large dataset to train the models for optimizing, developing, and designing new adhesives. This study proposes a novel testing machine that enables quick high-throughput measurements of the shear strength of adhesively bonded joints. A small cylindrical butt shear joint (BSJ) specimen placed in a holder was pushed by a metal specimen pusher until failure; during this process, the force and displacement were recorded. This testing machine can be used to quickly conduct the measurement by simply placing the specimen in a holder and pushing it. A comparison of the average shear strength measured by this method and that measured by single-lap shear tests, coupled with stress analysis using finite element simulation suggested that the proposed method can measure the shear strength more accurately, where a higher level of pure shear can be achieved in the adhesive layers with a lower degree of stress concentration and smaller peeling stress at the extremities of the adhesives. This indicates that the shear strength of adhesively bonded joints can be measured quickly using the proposed testing method, thereby facilitating the development of new adhesives using machine learning.

Shear testing on rock tunnel models under constant normal stress conditions

Large shear deformation problems are frequently encountered in geotechnical engineering. To expose the shear failure mechanism of rock tunnels, compression-shear tests for rock models with circular tunnel were carried out, including single tunnel and adjacent double tunnels. The failure process is recorded by the external video and miniature cameras around the tunnel, accompanied by real-time acoustic emission monitoring. The experiments indicate that the shearing processes of rock tunnel can be divided into four steps: (i) cracks appeared around tunnels, (ii) shear cracks and spalling ejection developed, (iii) floor warping occurred, and (iv) shear cracks ran through the tunnel model. Besides, the roughness of the sheared fracture surface decreased with the increase in normal stress. Corresponding numerical simulation indicates that there are tensile stress concentrations and compressive stress concentrations around the tunnel during the shearing process, while the compressive stress concentration areas are under high risk of failure and the existence of adjacent tunnels will increase the degree of stress concentration.

Study on Mechanical Characteristics of Rock Surrounding the Roadway under Different Section Shapes

In order to understand the instability characteristics of surrounding rock during deep roadway excavation, the influence of different section shapes on the stability of surrounding rock was systematically analyzed. Four sections of roadway with circular, rectangular, semicircular arch and three-center arch were studied. Simulation revealed that the maximum principal stress concentration and pressure relief degree of the three-center arch roadway is the highest, the minimum principal stress relief degree of the rectangular roadway is highest, the roof subsidence of the semicircular arch roadway is the lowest, the roof subsidence and left and right side displacement of the rectangular roadway are the highest, the surrounding rock failure areas of the circular roadway are evenly distributed, the surrounding rock failure areas of the other shape roadways are arch-distributed and the surrounding rock failure of the two sides of the rectangular roadway is the deepest. The mining stress environment coefficient is defined according to the stress state of the rock surrounding the roadway, and the range in which the coefficient is greater than 0.2 is defined as the destructive danger area. We found that the stability of the rock surrounding a circular roadway is greater than that of a semicircular arch roadway, a three-center arch roadway and a rectangular roadway.

Single-peak fitting based on wavelength recognition in FBGs spectra under quadratic strain distribution

The stress concentration appears in the form of a quadratic or higher-order strain distribution, which affects the measurement accuracy of fiber Bragg grating (FBG). The FBG spectrum presents asymmetric deterioration when the stress concentration exceeds a specific limit, making the symmetric Gaussian fitting algorithm no longer suitable for seeking its peak wavelength. In this paper, the degree of stress concentration is defined by the quadratic coefficient of the strain field. The bearing capacity of different length FBGs to the Gaussian fitting algorithm is investigated under the quadratic strain distribution. The experimental results show that the FBG with shorter length had a higher tolerance to the Gaussian peak-seeking algorithm. The Extreme fitting algorithm based on a single peak has been proposed to adapt to the asymmetric changes of FBGs spectra. The exceptional adaptability of the Extreme peak-seeking algorithm compared with Gaussian fitting has been proved, which provides a reliable reference for the accurate peak seeking of FBG reflect spectrum in a nonuniform strain field.

Interface structure and tensile behavior of high entropy alloy particles reinforced Al matrix composites by spark plasma sintering

Aluminum matrix composites (AMCs) reinforced with AlCoCrFeNi high entropy alloy (HEA) particles were fabricated by spark plasma sintering (SPS). The interface formation between the HEA particles and Al matrix, tensile properties and fracture behavior were investigated. The interface has a two-layer structure, the interface reaction layer close to the HEA particles was Al13(CoCrFeNi)4, and the interface reaction layer near the Al matrix was composed of Al9(CoFeNi)2 and Al18Cr2Mg3. The addition of HEA particles increased the yield strength, and reduced tensile strength and elongation of the composites. The fracture occurred at the interface reaction layer near the HEA particles, exhibiting obvious brittle fracture feature. The tensile fracture mechanism of the SPSed HEA/Al AMCs can be attributed to the poor plastic deformation ability of continuously distributed Al13(CoCrFeNi)4 and aggravated degree of stress concentration at interface reaction layer close to the HEA particles.

The relationship between storage-dissipation-release of coal energy and intensity of induced charge

Using uniaxial compression experiments, the evolution characteristics between energy and induced charge in each stage of coal deformation and failure are studied. Further, the relationship of energy conversion in the process of coal failure is analyzed. The calculation methods of energy storage, dissipation, and release of coal are proposed. The relationships between induced charge intensity and factors, including storage of elastic strain energy, increment of elastic strain energy, increment of dissipated energy, released energy, accumulated dissipated-released energy, are studied. A theoretical model of induced charge based on dissipated energy and released energy is established. The monitoring test of induced charge under the mine is conduced. The results show that the induced charge intensity is not related to the accumulation of elastic strain energy, but positively correlated to the dissipation and release of elastic strain energy. The induced charge intensity is not significantly correlated with the cumulative dissipated-released energy, but is significantly correlated with the slope of the cumulative dissipated-released energy curve and its variations. Especially when the escalation effect shows, the induced charge intensity accordingly increases in an abrupt manner. When the increment of dissipated energy rises to a certain degree, the intensity of induced charge suddenly increases. When the released energy suddenly increases, if the major part converts into the kinetic energy of coal chips and particles, a violent ejection phenomenon occurs, the induced charge intensity suddenly increases. The induced charge intensity is positively correlated with the increment of dissipated energy and the sudden increase of released energy. The higher the stress concentration degree and the greater the influence of mining for coal-rock, the larger amount of energy is dissipated and released, and thus the greater intensity of induced charge is monitored. The study can provide a theoretical basis for the monitoring and early warning of coal-rock dynamic disaster.

Structural design and mechanical properties of porous structured diamond abrasive tool by selective laser melting

Additive manufacturing is an important and promising way to realize the structural-functional integration of diamond abrasive tools. In the presented study, the porous diamond grinding heads with different pore structure and porosity were designed and fabricated by selective laser melting (SLM). By analyzing the stress distribution of overall structures and pore units, the 50 %-porosity square-pore structure with lowest stress concentration degree was optimized. The porous composite samples had good SLM formability, including good integrity and connectivity of pore units, and the diamond abrasives were evenly distributed and exhibited good retention and protrusion height. The high retention was attributed to the multiple interfacial system composed of carbide layer and solid solution strengthening layer. Compared with other porous samples, the 50 %-porosity square-pore structured sample with frame supporting unit and uniform stress distribution showed high deformation resistance of 430 MPa in yield strength and energy absorption capacity of 56.4 MJ/m3, which well verified the simulation results. The wear and grinding tests showed that the sharpness and self-sharpening ability of porous samples were significantly superior to the full-dense sample, and the grinding ratio increased with the increasing of the porosity.

Coal Wall Instability Evolution Law of Large Mining Height Face in Steeply Dipping Hard Roof Soft Coal Seam

The coal wall of large mining height longwall fully mechanized face in steeply dipping coal seam has poor self-stability and high probability of instability, which is likely to induce secondary hazards such as support instability and flying gangue once catastrophic occurs, increasing the difficulty of surrounding rock control and production risk. Coal wall disaster prevention and control can improve the productivity of this type of face, and this is based on the sufficient understanding of damage patterns such as internal and external dispersion of coal wall pressure, deformation, and displacement; in order to clarify the coal wall dynamic failure law of large mining height face in steeply dipping coal seam, numerical calculation, field measurement, theoretical analysis, and other methods are comprehensively applied to the study. The results show that the coal wall bearing of large mining height face in steeply dipping coal seam is distributed asymmetrically, the stress concentration position in the upper and middle part of the face is closer to the coal wall than the lower part, the stress concentration degree is also larger than the lower part, and the stress concentration coefficients from upper to lower are 1.37, 1.50, and 1.29, respectively. Soft coal wall bearing is mainly dispersed in the shape of “X” in its interior, forming intertwined pressure increasing and unloading zones, and most of the pressure increasing zones are at the edge of the outer end of the pressure relief zone, compression-shear type is the main failure form of the coal, and the middle and upper part of the coal wall in the height direction is easy to break and cause disaster. The coal wall of steeply dipping face partitioning migration features is obvious, and vertical displacement within 3.77 m from the coal wall is lower > middle > upper; after 3.77 m, it is upper > middle > lower; horizontal displacement is middle > upper > lower; coal migration volume in the middle region of the face is largest; and the coal wall instability has high frequency, wide influence area, and alternating evolution law.

Topologically optimized lattice structures with superior fatigue performance

The aim of this work is to study the effect of rounded fillets and minimal surfaces on the mechanical and fatigue performances of the topologically optimized lattice structure, especially a stress concentration assessment method is proposed to evaluate the fatigue performance. Results show that rounded corners and minimal surfaces are conducive to improving fatigue performances and the effect of the latter is better. Rounded fillet optimized lattice with the ratio of the fillet radius to the strut diameter of about 0.56 and minimal surface optimized lattice with k of 0.9 to 1.1 present the lowest degree of stress concentration.

Stress gradient effect in metal fatigue: Review and solutions

Under external loadings, notched components always show varying degrees of stress concentration. Accordingly, different kinds of approaches have been presented to characterize notch fatigue behaviours under complex loading histories. Among them, the considering of the stress gradient effect is a popular perspective, together with the fatigue damage zone and critical distance concepts. This work systematically reviews recent advances on notch fatigue analysis considering the stress gradient effect. Specifically, four approaches are summarized and explored, namely the local stress/strain-based approaches, critical distance-based approaches, critical plane-based approaches, and weighting control parameters-based approaches. This review aims to provide a systematic review and comparison on these methods, therefore to offer a reference for subsequent research on notch fatigue.

Collaborative detection and on-line monitoring of pipeline stress in oil and gas stations

The types of pipeline used in oil and gas stations is diverse, and it is difficult to comprehensively and accurately measure pipeline stress using a single detection method. Non-contact pipeline magnetic detection (NPMD), metal magnetic memory, ultrasonic stress measurement (USM) and ultrasonic thickness measurement (UTM)constitute a collaborative detection strategy for station pipelines. The pipeline magnetic abnormal evaluation parameter N is derived according to the sensor arrangement in NPMD devices. The magnetic field distribution based on different extraction heights is determined by the magnetic charge model and the experimental results, and a feature parameter E is constructed that can characterize the degree of stress concentration. The pipeline stress concentration points can be quickly determined in accordance with N and E. Reference stress values can be measured using USM and UTM. Monitoring is implemented at the stress concentration points, and the true stress values at the stress concentration points of the pipeline are established by combining the stress detection results. The collaborative detection method is applied to an oil and gas station, and two stress concentrations of 186.7 and 211.6 MPa are identified, respectively. The stress at the excavation pit is confirmed to be 196 MPa based on the monitoring data. Based on collaborative detection and on-line monitoring, fast and efficient collaborative detection and real-time mastering of station pipeline stress are achieved.

Design and Optimization of a Pressure Sensor Based on Serpentine-Shaped Graphene Piezoresistors for Measuring Low Pressure.

This thesis describes a novel microelectromechanical system (MEMS) piezoresistive pressure sensor based on serpentine-shaped graphene piezoresistors paired with trapezoidal prisms under the diaphragm for measuring low pressure. The finite element method (FEM) is utilized to analyze the mechanical stress and membrane deflection to enhance the degree of stress concentration in this unique sensor. The functional relationship between mechanical performance and dimension variables is established after using the curve fitting approach to handle the stress and deflection. Additionally, the Taguchi optimization method is employed to identify the best dimensions for the proposed structure. Then, the suggested design is compared to the other three designs in terms of operating performance. It is revealed that the recommended sensor can significantly improve sensitivity while maintaining extremely low nonlinearity. In this study, three different types of serpentine-shaped graphene piezoresistors are also designed, and their sensing capability is compared to silicon. The simulation results indicate that the pressure sensor with Type 2 graphene piezoresistors has a maximum sensitivity of 24.50 mV/psi and ultra-low nonlinearity of 0.06% FSS in the pressure range of 0–3 psi.

Electromagnetic and mechanical properties of CORC cable due to screening current

With the development of type II high temperature superconducting (HTS) ReBCO tape, it has been widely used in high field magnets. Conductor on round core (CORC) cable is highly flexible and fully isotropic, making it one of the most important types of HTS cables. In the condition of high field and current, the electromagnetic and mechanical behaviors of CORC cable under screening current effect are not clear. In this paper, the behaviors of CORC cable under high field and current are studied for the first time by combining electromagnetic and mechanical simulation. A three-dimensional shell model and a three-dimensional solid element model of single-layer CORC cable are established by finite element software to study the electromagnetic and mechanical properties of CORC cable, respectively. Compared with the case without taking screening current into account, two current loops are induced within a pitch of the CORC cable due to the screening current, and the magnetic field homogeneity is significantly reduced. Meanwhile, two pairs of shear force are generated at the current loops meeting zones, it results in a certain degree of stress concentration. Fortunately, because the copper core provides stable mechanical support for the HTS tape, there is no significant difference of the maximum stress between two cases with and without screening current in the CORC cable.

A NEW METHOD TO CONTROL THE REGIONAL STRATA MOVEMENT OF SUPER-THICK WEAK CEMENTATION OVERBURDEN IN DEEP MINING

In the western of china, the deep mining area with super-thick and weak cementation overburden is vast, sparsely populated and the ecological environment is extremely fragile. With the large-scale exploitation of deep coal resources, it is inevitable to face green mining problem, whose essence is the surface subsidence control. Therefore, it is necessary to study the control technology for the regional mining based on the evolution law of subsidence movement and energy-polling of super-thick and weak cementation overburden, and put forward the economically design scheme that can control strata movement and surface subsidence in a certain degree. Based on the key strata control theory, this paper puts forward the subsidence control scheme of partial filling -partial caving in multi-working face coordinated mining, and further studies its control mechanism through the numerical simulation and then analyzes the control effect of the strata movement and energy-polling in the fully caving mining, backfill mining, wide strip skip-mining and mixed filling mining method etc., the following conclusions are detailed as follows: (1) The maximum value of energy-polling occurs on the coal pillars or on both sides of goaf. With the width of goaf, the maximum value of energy-polling increases in a parabola. (2) In the partial filling-partial caving multiple working faces coordinated mining based on the main key stratum, the stress distribution of the composite backfill in the filling working face is parabolic, and it is high on both sides and low in the middle. Moreover, in the composite backfill, the stress concentration degree of a outside coal pillar is greater than that of the inside coal pillar. (3)The control mechanism of partial filling-partial caving harmonious mining based on main key layer structure is the double-control cooperative deformation system, formed by the composite backfill and the main and sub-key layers structure. They jointly control the movement and energy accumulation of overlying strata by greatly reducing the effective space to transmit upward, and absorb the wave subsidence trend of the overburden until it develops into a single flat subsidence basin. (4) Considering the recovery rate, pillar rate, area filling rate, technical difficulty and subsidence coefficient etc., the partial filling-partial caving multiple working faces coordinated mining based on the main key stratum is the most cost-effective mining method to control surface subsidence. This paper takes a guiding role in controlling the regional strata movement and surface subsidence of deep mining with super-thick and weak cementation overburden.

Plastic Deformation Mechanism and Slip Transmission Behavior of Commercially Pure Ti during In Situ Tensile Deformation

The plastic deformation modes of commercially pure titanium (CP-Ti) were studied using an in situ tensile test monitored by electron-backscatter-diffraction (EBSD) assisted slip trace analysis. The plastic strain was primarily accommodated by prismatic slip, followed by deformation twins and pyramidal slip. The slip transmission between two adjacent grains was predicted using the geometric compatibility factor m′, which influenced not only the degree of stress concentration but also the activity of dislocation slip systems. Stress concentration mainly occurred at GBs with an m′ less than 0.5 and could be released by the activities of pyramidal slip or deformation twins with high critical shear stress (CRSS).

Optimum Selection of Mining Plans for Pillars Containing Interlayers Based on Numerical Simulation

A reasonable selection of the pillar mining plan is the key to ensure smooth mining in the goaf group, which plays an important part in safe production. In formulating and optimizing the pillar mining plan, the influence of the ground pressure evolution law should be fully considered. This paper first introduces two mining plans for pillars, and then, numerical simulations were used to analyze the two mining plans from four perspectives such as stress evolution law, stress concentration degree, force state of pillars, and weak marble layers. The results show that the mining plan 1 that retreats from the middle of the ore body to the two wings is the optimal as it can realize sequential mining in high-stress concentration areas at the middle section. This effectively alleviates the stress on the surrounding rock during mining and will not aggravate the collapse of the marble-interbedded area.

Analysis method of micro stress sensitivity of aviation bearing based on Voronoi model

The micro-stress distribution of the bearing in actual work directly affects its service performance. This paper attempts to unify the bearing multi-field coupling service conditions with the micro-inhomogeneity of the internal material of the bearing steel, establish a micro-stress sensitivity analysis method for aviation bearings. The bearing motion parameters are solved based on the pseudo-dynamics method. The bearing fluid lubrication model was then established to calculate the lubricant state based on the CFD method. A bearing heat-fluid–solid multi-field coupling model is established based on the grid mapping method. According to EBSD, SEM and nanoindentation experiment, the microstructure model of bearing was established, and the micro stress of bearing was solved based on sub model method. A response surface model is established by the BOX-Behnen Design method. A multivariate random parameter evaluation method is proposed based on the SPEA coefficient. And the influence of inclusions on the bearing microscopic stress is quantitatively evaluated. The calculation results show that the inclusions' size and the inclusions' position significantly influence the degree of stress concentration. The degree of influence is divided into 0.478 and 0.650. The difference in stress components is mainly affected by the location of inclusions. The degree of influence exceeds 0.9. The overall effect of inclusion morphology is the smallest.