Stress Concentration Coefficient Research Articles

Study of Structural and Mechanical Properties of Mineral Fertilizer Granules

The results of a study of the structural–mechanical properties of granules of various types of mineral fertilizers prepared on the basis of ammonium phosphates by measuring the force necessary for the destruction of the granule upon uniaxial compression between two parallel planes and deformation along the compression axis are given. Using X-ray microtomography and raster electron microscopy, the structure of granules is studied. The results of the calculation of the coefficient of local stress concentration, as well as activation energy of destruction and strength of the granules, are given.

Research on Distribution Law of Advanced Abutment Pressure in Deep Soft Rock Working Face

In view of the characteristics of deep buried depth and weak rock strata in Tangkou coal mine, the method of combining RFPA numerical simulation and field measurement is used to study the peak position of the advanced abutment pressure and the influence range of the advanced abutment pressure in the fully mechanized caving face, fully mechanized mining face and hard rock face. According to the results, when other conditions are met, the influence range, peak position and coal wall damage depth of the advanced abutment pressure of the caving mining face are greater than those of the fully mechanized mining stope. When other conditions are certain, the two soft working faces show that the advanced abutment pressure has a wide influence range, a far peak position, a large depth of damage of the coal wall, a small peak of the advanced abutment pressure, and a small stress concentration coefficient.

Photoelastic Stress Analysis of Crankpin Fillets of a Crankshaft

The aim of this work was to investigate the stress analysis of crankpin fillets of a crankshaft. Fatigue failure in the crankpin fillet zone is one of the primary causes of the breakdown of crankshafts. In this paper, a polarization–optical method (photoelasticity) was used to study the distribution of stresses from bending in the crank-throw plane of a crankshaft on flat transparent photoelastic models. Results showed that the influence of the radius of crankpin fillet on the value of the stress concentration coefficient is estimated. Results achieved can be used in fatigue life calculation and optimization of this component.

Instability Mechanism and Control Countermeasure of a Cataclastic Roadway Regenerated Roof in the Extraction of the Remaining Mineral Resources: A Case Study

Most accessible mineral deposits are nearly exhausted. Consequently, some resources that were previously abandoned are now being considered for remining. This paper describes a case study that aims at revealing the instability mechanism and selecting the optimal control countermeasures for a cataclastic roadway regenerated roof (CRRR) during the extraction of the remaining mineral resources. Based on the structural model of a cataclastic regenerated roof (CRR) of a remaining lower slice, a modified natural arch mechanical model for a CRRR was established by considering the lateral pressure and stress concentration coefficient of the bearing arch, through which the modified bearing arch curve equation and arch rise expression were deduced. The relationship between the modified arch rise and the lateral stress was obtained through a practical case. Next, a numerical model of a CRRR, which accounted for the cataclastic features, was built in the Universal Distinct Element Code (UDEC). The development of subsidence and fractures in the roadway roof was determined through modeling under various roof support scenarios, namely no support, rock bolt (RB) support, rock bolt and cable (RBC) support and a combined support of the rock bolt, cable and steel beam (RBCS). The theoretical analysis, numerical simulation and monitoring results of the RB and RBC stress all indicated that a bearing arch existed in the CRRR and that the arch rise underwent changes during the roof hanging time and with different support scenarios. The support structure should exceed the bearing arch rise in height and should be leak proof to avoid roof leakage. After a comparative analysis of the numerical and field support effects provided by various supporting scenarios, the RBCS support scenario was shown to be the optimal roof support choice, providing a good controlling effect for a CRRR and meeting the production requirements.

Experimental and Theoretical Study on the Mechanical Characteristics of Perforated Casings

Due to the perforated holes on casings after perforating, the strength of perforated casings will be decreased and the well integrity will be influenced during sequential well services. To get the remaining strength of perforated casings, experimental and theoretical study were completed. The samples of perforated casings were obtained from conventional oil field casings perforated in simulation well according to oilfield perforating practice, and the stress concentration coefficients around perforated holes were measured and confirmed by experiments and finite element analysis. Taking the perforated holes as semi-elliptical surface cracks on casings, the formula for calculating stress intensity factors and revised coefficients of perforated holes were derived. Then, both strength safety and stress intensity factors were applied to evaluate the safety of perforated casings. So, the safety analysis method for perforated casings is improved and more considerate. Considering the similarity of compressed rod and pipe, the formula for calculating the remaining collapse strength of thin walled casings were developed, taking account the stress concentration of perforated holes. The experimental and theoretical study shows that: the stress concentration coefficients around perforated holes were about 1.3 and the remaining strength will be decreased more when both stress concentration and stress intensity factors are took into consideration. Taking the mostly used perforating parameter as an example, the collapse strength of a perforated casing with 16 perforations/m and 90°helix may be decreased 12%. Based on the results of the experimental and theoretical study of this paper, the working parameters were decided and guidelines were developed to ensure the safety of perforated casing and well integrity.

Numerical Calculation of Mechanical Characteristics of Composite Materials with Embedded Piezoactive Structural Elements

Within the framework of the present work, numerical studies are carried out to calculate the mechanical characteristics of a fragment of thermoplastic composite material (TCM) with an embedded piezo actuator (MFC – Macro Fiber Composite). An algorithm for predicting the physico-mechanical properties of a composite material using a structural-phenomenological model of a composite material with an embedded piezo actuator was developed. For numerical prediction of the elastic characteristics of the TCM with MFC, six boundary-value problems were solved: stretching along the axes and a net shift in the planes. Based on the results of numerical experiments, the values of the effective elastic properties and stress concentration coefficients for the fragment were obtained. The analysis of the obtained results revealed that the introduction of a piezo actuator leads to a decrease in the structural strength and to the appearance of a stratification in the plane of the actuator position.

Similar Material Simulation Study on Protection Effect of Steeply Inclined Upper Protective Layer Mining with Varying Interlayer Distances

Protective layer mining, as a dominating regional prevention measure, is generally adopted to prevent and control gas disasters in highly gassy or outburst mines of China. Interlayer distance is one of the most important factors that influences protection effect. However, how does interlayer distance affect the protection effect of steeply inclined upper protective layer mining is not understood fully. According to the engineering practice in Nantong mining district, a new method for similar material simulation experiment of steeply inclined upper protective layer mining is proposed, in which an orthogonal test of similar materials comprising of sand, cement (containing gypsum and fly ash), and water mixture is conducted to obtain relations between proportioning parameters and mechanical properties using a multiple regression method. And then the method is applied to study the protection effect of steeply inclined upper protective layer mining with varying interlayer distances. The results show the following. (1) The proportioning parameters of similar material have strong linear relations with its mechanical properties, and mechanical behaviors of such similar material denote that it can simulate most coal‐rock lithologies in coal mine. (2) Both pressure‐relief curves and swelling strain curves for protected layer present convex shapes; protection angles at lower excavation boundary are greater than those of upper excavation boundary; with the increase of interlayer distance, the pressure‐relief curve evolves from pattern “∩” to pattern “∧” and corresponding pressure‐relief region becomes narrower, the center of pressure‐relief region tends to transfer to the corresponding center of upper protective layer excavation region, the stress concentration coefficient decreases, the protection angles change little, and the length of the protection region reduces dramatically. (3) The protection region and protection angle calculated based on swelling strain of 3‰ are less than the empirical values based on the dip angle in Provisions, denoting that the method proposed in this study is safer than that in Provisions. The research results provide a useful guide for layouts of roadway and gas drainage boreholes to prevent gas disaster in Nantong coal mine district.

Experimental and Numerical Study of Rock Stratum Movement Characteristics in Longwall Mining

The roof fracture is the main cause of coal mine roof accidents. To analyze the law of movement and caving of the roof rock stratum, the roof subsidence displacement, rock stratum stress, and the rock stratum movement law were analyzed by using the methods of the particle discrete element and similar material simulation test. The results show that (1) as the working face advances, regular movement and subsidence appears in the roof rock strata, and the roof subsidence curve forms a typical “U” shape. As the coal seam continues to advance, the maximum subsidence displacement remains basically constant, and the subsidence displacement curves present an asymmetric flat‐bottomed distribution. (2) After the coal seam is mined, the overburden forms an arched shape force chain, and the arched strong chain is the path of the overburden transmission force. The farther away from the coal seam, the smaller the stress concentration coefficient is, but it is still in a high stress area, and the stress concentration position moves toward the middle area of the goaf. The stress concentration in front of the coal wall is the source of force that forms the abutment pressure. (3) Above the coal wall towards the goaf, a stepped fracture was formed in the roof rock stratum. The periodic fracture of the rock stratum is the main cause of the periodic weighting of the working face. Understanding the laws of rock movement and stress distribution is of great significance for guiding engineering practice and preventing the roof accidents.

Stress Concentration in Vertical Tank Weld Seams

The article describes a new method for analyzing and predicting the stress concentration coefficient in a rolled vertical tank weld seam under hydrostatic loading. Vertical tanks are widely used for storing petroleum products. The use of roll-to-roll assembly technology is advisable for a quick and inexpensive installation of oil tanks. However, the use of this technology in the installation of large-capacity tanks leads to the need to use thick rolled steel. This leads to the appearance of significant angularities of the weld seams used to fasten steel sheets in a roll. Such angularities are mechanical stress concentrators and can damage the tank. Therefore, the problem of modeling the dependence of stress concentration factors on the geometrical parameters of angularity is relevant and important to ensure both the economic and environmental efficiency of operation of the oil tanks assembled by the roll-to-roll method. The approach described in this article is based on a combination of a numerical experiment and an approximation approach. The stress concentration factor depends on two dimensionless parameters of the dent. Thus, a method of approximation of a two-dimensional problem is described. This method is applied to the data collected by numerous computational experiments using the finite element approach to construct an approximate model of the stress concentration factor. Such a model can be used to predict stress values, as well as tank strength and durability. The change in material properties in the weld seam is not taken into account. Thus, the estimated stress is higher than the real one and represents a majorant estimate. An approximating model of the stress concentration factor was constructed in the area of angularity of the weld seam of a 3,000 m3 complex structure oil tank under hydrostatic loading. The tank consists of four belts made of steel of various thickness. The density of the tank contents is close to that of water. It has been found that stress concentration increases as the distance to the tank bottom becomes smaller. Therefore, when building an approximating model, the results in the most strained region are considered.

Application of quasi-optimal correlation algorithm for surface quality assessment

The article describes the application of a new approach to assessing the surface roughness of the GTE blade profile after vibration contact polishing. The basis for the calculation of the microgeometry of the surface of the back and the trough of the blades is the average amplitude of the variable component of the autocorrelation function obtained as a result of computer processing of the video image of the surface on the optical-electronic complex. The use of an optoelectronic method for evaluating the microgeometry of the surfaces of compressor and turbine blades allows obtaining the roughness distribution on the surface and the stress concentration coefficient, as well as a more in-depth analysis of the final processing technology.

Investigation of the stressed state of a cut-out plate

The results of the numerical and physical experiments aimed at studying of the flat element’s stress state with an oval cut and ten crack - simulating cuts are presented in the article. It was estimated the influence of the cuts inclination angle on the stress values. The stress concentration coefficients at the cracks’ vertices were obtained.

Research of Construction Elements of Structure-inhomogeneous Materials

The paper concentrates on strain-stress state research in construction elements of structurally heterogeneous materials which is of current importance. Classical concepts of solid, homogeneous, isotropic, linearly elastic body do not suit the construction practice, as nearly all materials used in construction and technics are structurally heterogeneous. Present article deals with the most typical structurally heterogeneous materials – polycrystalline materials. Finite element model of structurally heterogeneous body – polycrystal is developed. The problem of determination of body minimum volume, which could be endued with averaged properties by averaging elastic properties, is solved. It allows analyzing structurally heterogeneous body at different volumes. Stress concentration is investigated for small-scale plates with circular or ellipse holes and with various stress states considering microstructural aspects of stress concentration. It is shown, that coefficients of stress concentration depending on anisotropy of elastic properties can have values, which considerably differ from values for isotropic body.

Geomechanical justification based on the results of numerical modeling of combined technology parameters of working areas development with the use of robotized means of underground mining

Based on the results of numerical modeling the assessment of the options for selective and sequential development of the working areas and coal mine blocks by fully-mechanized longwalls with a complete collapse of the roof and short faces with the roof controlled by rib pillars. As the criteria for assessing the effectiveness of geotechnological options, the coefficients of vertical stress concentrations in the selvedge of the coal seam in the vicinity of extraction galleries and the height of the unloading zone of the roof rocks over the gob are adopted. Factors that limit the use of longwall faces are the presence of disjunctive disturbances within the mine field, which leads to coal losses and irrational use of subsoil. It was established that successive development of excavation sites with long and short faces results in a more even distribution of the vertical stress concentration coefficients, reduces the probability of zones with increased rock pressure and gas dynamic phenomena, and also provides an opportunity to increase the coal extraction factor.

Research on Nonlinear Dynamic Simulation and Fatigue Reliability Life Prediction for Synthesis Transmission System of Self-Propelled Gun

Aiming to the puzzle that the inner load of nonlinear synthesis transmission system is difficult to obtain, a new kind of virtual prototype establishment and simulation method is put forward. The influence on nonlinear vibration with flexible rotor, bearing backlash is analyzed based on a virtual prototype. To validate the virtual prototype of nonlinear gear transmission system, the corresponding test platform is established. The consistency between simulation results and test results proves that the simulation results of the virtual prototype can be used to calculate the fatigue reliability life of key components. A new kind of fatigue reliability life prediction method of gear system considering multi-random parameter distribution is put forward based on the fatiguestatistic theory. Considering the periodicity of gear meshing, linear interpolation method is adopted to obtain the stress-time course of random load spectrum based on the gear’s complicated torque provided by virtual prototype. The gear’s P-Sa-Sm-N curved cluster can be simulated based on material’s P-S-N curve. The simulation process considers the parameter distributions of stress concentration coefficients, dimension coefficients and surface quality treatment coefficients, and settles the puzzle that traditional test methods cannot acquire the gear’s fatigue life of all reliability levels. This method can provide the distribution function and the interval of fatigue reliability life of gear’s danger region, and has a guide meaning for the gear maintenance periods determination and reliability evaluation.

A study of the cyclic damage to buried pipelines during the passage of seismic waves

THE SEISMIC STRENGTH of underground pipelines is assessed based on the axial stresses on the pipeline from the so-called particular combination of loads and impacts. When calculating the stresses from seismic impact, several standard coefficients are introduced, which assume some damage to the pipeline while ensuring the safety of people and the integrity of equipment. These coefficients also take into account anchoring, which depends on the backfill soil and the degree of pipeline criticality. Permissible stresses are accepted in accordance with regulatory documents for design (SNiP 2.05.06-85). The seismic strength of the pipeline in operation is assessed taking into account the seismic impact intensity which is actually reached during an earthquake, and the loads and impacts which affect a pipeline in an earthquake, as well as any defects present in the pipeline wall. When a seismic wave passes through an underground pipeline, the girth welds are exposed to an alternating cyclic impact. Here, it is relevant to estimate the fatigue damages accumulated over the course of the earthquake. The magnitude of this damage depends on the intensity of the earthquake, the seismograph of the earthquake, the speed with which the longitudinal seismic wave travels along the longitudinal axis of the pipeline, the degree to which the pipeline is anchored by the soil, and the stress concentration coefficient in any defects. This article studies the accumulation of cycle-induced damage caused by a longitudinal seismic wave. The results may be applied for evaluations of the cyclic longevity of girth welds with defects in pipelines operating in seismic zones.

A new effective stress constitutive equation for cemented porous media based on experiment and derivation

The stress-strain of porous media is totally different from that of continuous solid materials. Terzaghi effective stress principle, as the cornerstone of soil mechanics, fits well for stress-strain of soils but fails to fit for cemented porous media. Many researchers are dedicated to propose a more comprehensive effective stress principle. By combining previous effective stress equations proposed by Skempton, Bishop, and Lade & de Boer, a more accurate and comprehensive effective stress constitutive equation is derived. A homogeneous coefficient ω, a stress concentration coefficient β, and a cemented coefficient λ for effective stress principle of all types of pore media are proposed. Appropriate experiments including three types of porous media, namely soils, rocks, and ceramics are designed. The strains of soils, rocks, and ceramics are tested in different confining pressure and fluid pressure. The results show that (a) the strain of soils is mostly caused by intergranular strain and λ is nearly 0, (b) the strain of ceramics is mainly caused by grains strain and λ is more close to 1 − φ, (c) the strain of rocks is combined with grains strain and intergranular strain and 0 < λ < 1 − φ. Three strain patterns of porous media are controlled by the cemented coefficient and the stress conditions. Demonstrated by theoretical derivation and experimental test, the new effective stress can be widely used to all types of porous media.

Analysis of Pressure Relief Effect on the Protective Layer of Hard Roof and Extra-Thickness Coal Seam Mining

The roof of Tashan coal mine was hard and difficult to fall. In the process of fully mechanized coal caving in the Carboniferous extra-thick coal seam, the strong pressure and rock burst appeared in the working face. To obtain the pressure relief effect of the exploitation of Shan 4# protective seam in Tashan coal mine, The stress distribution and displacement variation of the roof and floor of Shan 4# protective layer were obtained by numerical simulation. And by mine pressure observation in the 8107 working face of the un-mining protective seam and in the 8108 working face of mining protective layer, the pressure relief effect of mining Shan 4# protective layer was analyzed. It was shown that the lateral of the open-off cut and the rock mass in front of the working face produced stress concentration when 3–5# coal was mined separately. The stress concentration coefficient of k was 3. The liberated layer was in the floor relief area from the open-off cut after the upper protective layer being mined owing to internal misaligned arrangement of the liberated layer when the protective layer and the liberated layer were mined. The stress concentration of the lateral of open-off cut and working face of the liberated layer was greatly reduced, and the stress concentration coefficient was about 1.5. The middle of the goaf would be re-compacted with the advance of the working face. The maximum principal stress of the liberated layer was W type distribution. The expansion deformation of 3–5# coal was M type distribution. The working resistance of the 8107 working face was mainly distributed in 8000–12,000 kN. The working resistance of the 8108 working face was mainly distributed in 4000–10,000 kN. The vertical stress of the roof of the 3–5# coal was decreased by about 30% after mining the protective layer. The mining of the protective seam effectively reduced the pressure strength of the roof of the fully mechanized coal seam. The reference was provided for the rational layout of coal seam safe mining with impact tendencies.

Effect of Shot Peening on the Surface Integrity and Notched Fatigue Properties of a Single-crystal Superalloy at Elevated Temperature

The surface integrity and notched fatigue property of a shot-peened single crystal superalloy were investigated. The surface texture of the peened material was determined using a white light interferometer, while the microstructural characterization was performed using a scanning electron microscopy, high resolution transmission electron microscopy from the plane and cross-section view directions and electron backscatter diffraction. The gains, expressed in term of high temperature fatigue limit, were established by rotating-bending fatigue tests and discussed in relation to the microstructure evolution in the shot peening states. Results show that the beneficial effect provided by shot peening is more than 14.8% against the as-machined in a temperature range from 760 °C to 850 °C because of the high-density tangled dislocation, cold work and disorientation. Furthermore, the stress concentration coefficient is reduced by the shot peening procedure while the average profile height Ra increases according to the calculation of the surface stress concentration.

Forecasting the stress concentration coefficient around the mined panel using soft computing methodology

Stress analysis around the mined panel is one of the most critical topics in longwall mining for stability analysis of surrounding pillars and access tunnels. Actually, stress redistribution due to roadway extraction along with the longwall mining-induced stress must be considered in designing the panel surrounding structures. In this research, three new methods, i.e., radial basis function neural network (RBFNN), fuzzy inference system (FIS) and statistical analysis (SA) models have been developed to predict the stress concentration coefficient (SCC) around a mined panel. The transferred stress due to longwall mining has been also considered in predicted SCC from these models. Proposed models have been constructed based on the sufficient datasets gathered from the literatures. For SCC prediction, the height of destressed zone above the mined panel, rock mass unit weight, overburden depth and horizontal distance from the panel edge have been regarded as input variables. Based on the actual testing datasets, performance of the suggested models has been evaluated using the statistical indices. Accordingly, it was proved that RBFNN and FIS models have better capability compared to the SA model and their results are in a great agreement with the real values. Moreover, proposed models were practically applied in Tabas longwall coal mine of Iran and verified by comparing their results with the results of existing models. Finally, conducted sensitivity analyses of the proposed models indicate that height of destressed zone and unit weight are the most and least influencing variables on the SCC in all models.

Measurement of the Strong Pressure Appearance Laws with Hard Roof and Full Mechanized Mining Extra Thick Coal Seam

To master the laws of strong strata behavior of Tashan coal mine under Carboniferous coal mining process, the laws of strong strata behavior in 8107 working face was measured and analyzed. It was shown that the average initial weighting step of 8107 working face was 59.4 m. The average periodic weighting step of main roof was 16.2 m. The maximum working resistance during periodic weighting was 14,711.1 kN. The maximum working resistance during non-periodic weighting was 11,339.9 kN. The average dynamic load factor K during periodic weighting was 1.31. The stress of coal column on the side of the goaf could be divided into four zones (stress stabilization zone, stress slow-increasing zone, significant—increasing stress zone, stress reduction zone) along the strike of 8107 working face. There was a peak of lateral support pressure along the trend of 8107 working face. And the peak position was biased to the side of return airway roadway. With the increase of the distance from the down-side of return airway, the pressure peak of the inner coal body along the strike of 8107 the working face increased and the peak position decreased from the coal wall. The peak stress of coal column tended to be close to the up-side of return airway. And the distance from the down-side of return airway for the peak of inner coal was larger than that for the peak of coal pillar. The peak position of abutment pressure of hard roof was in the range of 10–25 m in front of 8107 working face under full mechanized mining extra thickness coal seam conditions. The relative stress concentration coefficient of k was 1.3–6.5. The range of 10–25 m from the front of the working face to coal wall was stress reduction zone. And the influence range of abutment pressure was about 80 m. It was of great significance to the control and practice of the surrounding rock of the stope for the mining of the hard extra-thick coal seam.