Thermal residual stresses and stress distributions under tensile and compressive loadings of short fiber reinforced metal matrix composites

The thermal residual stresses and the stress distributions of short fiber reinforced metal matrix composite under tensile and compressive loadings were studied using large strain axisymmetric elasto plastic finite element method. It is demonstrated that the thermal residual stresses can result in asymmetrical stress distributions and matrix plasticity. The thermal residual stresses decrease the stress transfer in tension and enhance the stress transfer in compression. The fiber volume fraction has more important effects on the thermal residual stresses and the stress distributions under tensile and compressive loadings than the fiber aspect ratio and the fiber end distance. [

Distribution of Stresses in Particulate Half Space under Surface Pressure

Reducing the linear system of two first order equilibrium equations involving normal stress σ(ρ,θ) and shearing stress v(ρ,θ), by elimination, to two decoupled second order equations in σ and v, we find that, for pressure only case, v(ρ,θ) vanishes in the half space. Consequently, the second order equation in σ can be simplified. In the language of linear system analysis, the medium(system) function, characterizing the mechanical behavior of a particulate medium in pressure only case, is obtained from the simplified second order equation ( 2 ρ+ 2 θ)σ(ρ,θ)=0 and can be inverted to give impulse reponse explicitly. Thus, response σ α(ρ,θ) may be computed directly from input, i.e., the surface pressure φ α(ρ) , by integration. Some explicit formulas for transmission problems, including response to input of strip linearly increasing pressure, are given in the paper.

Finite element analysis of stress distribution and burst failure of SiC_f/Ti-6Al-4V composite ring

A three-dimensional cyclic symmetry finite element model of titanium-matrix composites（TMCs） ring was developed to investigate the stress distribution and burst failure. The effects of fiber volume fractions, reinforced areas, thermal residual stresses and two different temperatures on stress distribution were studied. The burst speed was obtained through analyzing the hoop tensile stresses under a series of rotating speeds. The results indicate that at the two different temperatures, the influences of fiber volume fractions and reinforced areas on stress level and distribution are different. Some proposals are provided for the structure design of the TMCs ring. With regard to thermal residual stresses, a larger reinforced area is an advisable choice for design of the ring at higher temperature.

Nonlinear Analysis of Axial-load and Stress Distribution for Threaded Connection

Analytical method for the distributions of axial-load and stress is based on elastic assumption, but the threaded connections are often in plastic deformation stage in practice. Meanwhile the strain in the threaded connection is difficult to measure. So it is necessary to study the reliable numerical method. At present neither the convergence analysis of the computational results nor the elastic-plastic analysis in the loading-unloading process are studied. In this paper, von Mises plasticity and kinematic hardening model is used to describe the material response. A new convergence criterion for nonlinear finite element analysis of the loading-unloading process is proposed. An axisymmetric finite element model according to the proposed convergence criterion is developed and used to analyze the distributions of axial-load and stress. It can be conclude that the stress distribution analysis is more dependent on the mesh density than the axial-load distribution analysis. The stress distribution result indicates that with increasing of applied load, the engaged threads close to the nut-bearing surface become plastic firstly. The axial-load distribution result reveals that the load percentage carried by single thread depends on the position of thread and load intensity. When the load is relatively small, the applied load is mainly carried by the engaged threads near the nut-bearing surface, when the load is larger, the differences of percentages for all threads become small. The proposed convergence analyzing procedure is applicable for other nonlinear analyses. The obtained distributions of axial-load and stress can be a reference of engineering application.

Deformation characteristics and reinforcement technology for entry subjected to mining-induced stresses

The entry at Zhangcun coal mine in Lu＇an coal mining area in Shanxi Province suffered from severe mining-induced stresses with the heading face driven oppositely to an adjacent working face. In this paper, the characteristics of deformation and failure of the entry were investigated in terms of the tempo-spatial relations between heading and working faces through field study and numerical modeling. The three-dimensional （3D） finite difference models were built to investigate stresses, displacements and damages in the surrounding rocks of the entry and the working face. The field study includes selection of reinforcing methods and materials, design parameters, and determination of cable prestress. The monitoring data of entry deformation and stress along the cables during every stage were presented. The state of the reinforced entry was evaluated based on the monitoring data. The results demonstrate that before the heading face of the entry crosses the adjacent working face, the influence of advanced abutment pressure caused by adjacent working face upon the entry is not significant. After they cross each other, however, the lateral abutment pressure will have an evident impact on the entry. The displacement rate of the entry will be greatly increased and reaches a certain value within a certain distance between the heading face and the working face. Then, it will increase again with the presence of secondary mining-induced pressure on the entry when the present working face advances. The fully-grouted cable with short length, high strength and high prestress is an effective way to reinforce the entry suffering from severe mining-induced stresses, which greatly reduces the displacement and failure possibility of the entry. Finally, the principles and recommendations for reinforcing design of entries suffering from severe mining-induced stresses were proposed according to field study, numerical modeling and experiences from other coal mines. Problems encountered in field study and suggestions for reinforcement were also discussed.

Analytical model and application of stress distribution on mining coal floor

Given the analysis of underground pressure, a stress calculation model of coal floor stress has been established based on a theory of elasticity. The model presents the law of stress distribution on the relatively fixed position of the mining coal floor： the extent of stress variation in a fixed floor position decreases gradually along with depth, the decreasing rate of the vertical stress is clearly larger than that of the horizontal stress at a specific depth. The direction of the maximum principal stress changes gradually from a vertical direction to a horizontal direction with the advance of the working face. The deformation and permeability of the rock mass of the coal floor are obtained by contrasting the difference of the principal stress established from theoretical calculations with curves of stress-strain and permeability-strain from tests, which is an important mechanical basis for preventing water inrush from confined aauifers.

Predicting the present-day in situ stress distribution within the Yanchang Formation Chang 7 shale oil reservoir of Ordos Basin, central China

The Yanchang Formation Chang 7 oil-bearing layer of the Ordos Basin is important in China for producing shale oil.The present-day in situ stress state is of practical implications for the exploration and development of shale oil;however,few studies are focused on stress distributions within the Chang 7 reservoir.In this study,the present-day in situ stress distribution within the Chang 7 reservoir was predicted using the combined spring model based on well logs and measured stress data.The results indicate that stress magnitudes increase with burial depth within the Chang 7 reservoir.Overall,the horizontal maximum principal stress(SHmax),horizontal minimum principal stress(Shmin) and vertical stress(Sv) follow the relationship of Sv≥SHmax>Shmin,indicating a dominant normal faulting stress regime within the Chang 7 reservoir of Ordos Basin.Laterally,high stress values are mainly distributed in the northwestern parts of the studied region,while low stress values are found in the southeastern parts.Factors influencing stress distributions are also analyzed.Stress magnitudes within the Chang 7 reservoir show a positive linear relationship with burial depth.A larger value of Young's modulus results in higher stress magnitudes,and the differential horizontal stress becomes higher when the rock Young's modulus grows larger.

Characteristics of stress distribution in floor strata and control of roadway stability under coal pillars

Given the difficulties encountered in roadway support under coal pillars,we studied the characteristics of stress distribution and their effect on roadway stability,using theoretical analysis and numerical simulation.The results show that,under a coal pillar,vertical stress in a floor stratum increases while horizontal stress decreases.We conclude that the increased difference between vertical and horizontal stress is an important reason for deformation of the surrounding rock and failures of roadways under coal pillars.Based on this,we propose control technologies of the surrounding rock of a roadway under a coal pillar,such as high strength and high pre-stressed bolt support,cable reinforcement support single hydraulic prop with beam support and reinforcement by grouting of the surrounding rock,which have been successfully applied in a stability control project of a roadway under a coal pillar.

Study of electromagnetic characteristics of stress distribution and sudden changes in the mining of gob-surrounded coal face

The incidence of dynamic coal or rock disasters is closely related to the distribution of stress in the surrounding rock. Our experiments show that electromagnetic radiation （EMR） signals are related to the state of stress of a coal body. The higher the stress, the more intense the deformation and fractures of a coal body and the stronger the EMR signals. EMR signals reflect the degrees of concentrated stress of a coal body and danger of a rock burst. We selected EMR intensity as the test index of the No.237 gob-surrounded coal face in the Nanshan coal mine. We tested the EMR characteristics of the stress distribution on the strike, on the incline and in the interior of the coal body. The EMR rule of rock bursts, caused by sudden changes in stress, is analyzed. Our research shows that EMR technology can be not only used to test qualitatively the stress distribution of the surrounding rock, but also to predict a possible occurrence of rock burst. Based on this, effective distress measures are used to eliminate or at least weaken the incidence of rock bursts. We hooe that safetv in coalmines will be enhanced.

Study of Stress and Strain Distributions of First Pass Conventional Spinning Under Different Roller-trace

Based on simplified axisymmetrical forming model, a elasto-plastic FEM simulation system of multi-pass conventional spinning is developed. Taking the typical draw-spinning as the study object, and establishing reasonable mechanics model, research on the first pass of spinning process is carried out with FEM system developed. The distributions of the stress and strain are obtained by three types of roller-trace curves: straight line, involute curves and quadratic curves. The results are as follows: (1) The values of equivalent stress and strain are the lowest under involute curve compared to other two curves, and they change relatively small and decrease with the increase of radius. The values of equivalent stress and strain is the highest under quadratic curves, and increase with the increase of radius. (2) The value of radial stress is smallest under involute curve, and is the largest under straight line. Value of radial stress is often used as the criterion of cracking limit, so its distribution laws can provide references for studying the condition of cracking in multi-pass conventional spinning under different roller-trace. (3) Tangential stress is compressive stress. Absolute value of tangential stress is the smallest under involute curve, and values of tangential stress are close between other two curves. The distribution laws of tangential stress can serve as a significant guide to research the critical condition of wrinkling in multi-pass conventional spinning under different roller-trace. (4) The reduction of thickness is the smallest under involute curve. The distribution of the thickness strain is very unequal under quadratic curves. The results obtained can provide references for selecting reasonable roller-trace in multi-pass conventional spinning.

Numerical analysis of stress distribution in the upper arm tissues under an inflatable cuff：Implications for noninvasive blood pressure measurement

An inflatable cuff wrapped around the upper arm is widely used in noninvasive blood pressure measurement.However, the mechanical interaction between cuff and arm tissues, a factor that potentially affects the accuracy of noninvasive blood pressure measurement, remains rarely addressed. In the present study, finite element（FE） models were constructed to quantify intra-arm stresses generated by cuff compression, aiming to provide some theoretical evidence for identifying factors of importance for blood pressure measurement or explaining clinical observations. Obtained results showed that the simulated tissue stresses were highly sensitive to the distribution of cuff pressure on the arm surface and the contact condition between muscle and bone. In contrast, the magnitude of cuff pressure and small variations in elastic properties of arm soft tissues had little influence on the efficiency of pressure transmission in arm tissues. In particular, it was found that a thickened subcutaneous fat layer in obese subjects significantly reduced the effective pressure transmitted to the brachial artery, which may explain why blood pressure overestimation occurs more frequently in obese subjects in noninvasive blood pressure measurement.

Effects of Rock Bolting on Stress Distribution around Tunnel Using the Elastoplastic Model

To ensure the stability of a tunnel during construction, rock bolts are usually installed, which affects the stress distribution around the tunnel. Therefore, it is necessary to study the effects of rock bolting on the stress distribution around the tunnel. In this article, the effects of rock bolting on the stress distribution around the tunnel, including the pesition and orientation of bolts, the overburden depths, and the bolt lengths, are simulated using the ANSYS software with an elnstoplastic model. The effect of multiple bolts of 2 m and 1 m lengths on the stress distribution in the roof and on the lateral sides of a tunnel and at different overburden depths is considered. An important finding is that the tensile stress region that is very dangerous for rock in the bottom of the tunnel grows rapidly with increasing overburden depths when rock bolts are installed only in the roof or on the lateral sides of a tunnel. The determination of the length of the rock bolt used around a tunnel is dependent on the loads and the integrity of the rock mass around the tunnel. In addition, rock bolting around the tunnel can obviously reduce the coefficients and the size of the region of stress concentration, especially when installed in high-stress areas. This fact is very important and essential for the design of tunnels and ensures engineering safety in tunnel engineering.

Numerical Modeling of Neotectonic Movements and State of Stresses in the Central Seismic Gap Region,Garhwal Himalaya

This paper presents finite element modeling （FEM） to simulate the present-day stress field and crustal deformation using NE-SW structural section in the central Seismic Gap region of the Garhwal Himalaya. Our study deals with the effect of geometrical characteristics and rock layer parameters on the upper crust. Modeling results show that two types of tectonic regimes developed in the central Seismic Gap region： the geotectonics of the northern part has been controlled by regional compression, whereas southern part is characterized by regional extension. Correspondingly, thrust faults are induced in the northern part and normal faults are extensively developed in the southern front. Those evidences noticeably indicate that the compressive tectonic environment of the Himalaya becomes change into the extensional tectonic regime in its front. The computed shear stress accumulation along the northern fiat of Main Himalayan Thrust （MHT） implies that considerable amount of interseismic stress is building up along the MHT system in the Himalaya, which ultimately release through the possible future great Himalayan earthquake （M 〉 8）. The comparison between our modeled stress field, faulting pattern and horizontal shortening rate with the distribution of the microseismic events, focal mechanism solutions, active faulting and GPS data in the central Seismic Gap region shows good agreement.

Measurement and study of the distributing law of in-situ stresses in rock mass at great depth

To solve the technical cruxes of the conventional system in deep rock mass, an automatic testing system for hydraulic fracturing that includes a single tube for hydraulic loop, a pressure-relief valve, central-tubeless packers, and a multichannel real-time data acquisition system was used for in-situ stresses measurement at great depths （over 1000 m） in a coalfield in Juye of Northern China. The values and orientations of horizontal principal stresses were determined by the new system. The virgin stress field and its distributing law were decided by the linear regression from the logged 37 points in seven boreholes. Besides, the typical boreholes arranged in both the adjacent zone and far away zone of the faults were analyzed, respectively. The results show that a stress concentration phenomenon and a deflection in the orientation of the maximal horizontal stress exist in the adjacent zone of the faults, which further provides theoretical basis for design and optimization of mining.

Study on Longitudinal Load Distribution on Gear Tooth

Regularity of longitudinal load distribution on gear tooth when tooth faces are contacted uniformly and when only tooth ends are contacted, and influence on distribution exerted by longitudinal correction and flexible gear structure, are studied in the paper with method of finite element calculation combined with experiment. Research shows that load concentration exists on the conditions of uniform contact or one-end contact, and in the later case the stress nonuniformity factor on root is 1.5 to 2.0 times larger than in the former case. It also verifies that longitudinal correction and increased flexibility of gear structure are effective to improve longitudinal load distribution.

Simulation of Stress Distribution around Tunnels and Interaction between Tunnels Using an Elasto–plastic Model

This article presents a computer simulation of stress distribution around tunnels and interaction between tunnels using an elasto-plastic model. A finite element method using ANSYS software has been used for the analyses of one and two tunnels at different overburden depths with different separating distances between the tunnels. The results of numerical analyses indicate that stress distribution and stress concentration around the tunnels vary with the overburden depths. It is found that the coefficients of stress concentration for elasto-plastic medium are smaller than those for elastic one by 1.9%. Furthermore, the interaction between the two tunnels rapidly decreases with the increase of separation distance between them. In addition, for quantitatively describing the interaction between the two tunnels, a critical separation distance is introduced. The critical separation distances between the two tunnels at different overburden depths are 8 m, 12 m, and 14 m respectively. This fact is very important and essential for the design of mining tunnels and to ensure safety in tunnel engineering.

Distribution of ground stress on Puhe Coal Mine

Puhe Coal Mine is a typical Tertiary coal in Shenbei mining area. With an increase in mining depth, tectonic stress field becomes more complex, leading to increased deformation and failure of the soft rock roadway. Stress becomes an important factor of mine safety and stability. This paper analyzes the distribution of the regional tectonic field, and determines the distribution of situ stress measurement through measuring the ground stress field in the main mining area level of Puhe Coal Mine using stress relief method. The acquired in situ stress data at different locations and depths provide a reference for the rational arrangement of the stop and mine roadway supporting design, which are of great significance for the efficient safety production of the mine.

Stresses induced by post-tensioned anchor in jointed rock mass

A new analytical study on stresses around a post-tensioned anchor in rocks with two perpendicular joint sets is presented. The assumptions of orthotropic elastic rock with plane strain conditions are made in derivation of the formulations. A tri-linear bond-slip constitutive law is used for modeling the tendon-grout interface behavior and debonding of this interface. The bearing plate width is also considered in the analysis. The obtained solutions are in the integral forms and numerical techniques that have been used for evaluation. In the illustrative example given, the major principal stress is compressive in the anchor free zone and compressive stress concentrations of 815 k Pa and 727 k Pa(for the anchor load of 300 k N) are observed under the bearing plate and the bond length proximal end, respectively. However, large values of tensile stresses with the maximum of-434 k Pa are formed at the bond length distal end. The results obtained using the proposed solution are compared very those of numerical method(FEM).

Finite element analysis of stress and strain distributions in mortise and loose tenon furniture joints

We studied the effect of loose tenon dimensions on stress and strain distributions in T-shaped mortise and loose tenon （M＆amp;LT） furni-ture joints under uniaxial bending loads, and determined the effects of loose tenon length （30, 45, 60, and 90 mm） and loose tenon thickness （6 and 8 mm） on bending moment capacity of M＆amp;LT joints constructed with polyvinyl acetate （PVAc） adhesive. Stress and strain distributions in joint elements were then estimated for each joint using ANSYS finite element （FE） software. The bending moment capacity of joints increased significantly with thickness and length of the tenon. Based on the FE analysis results, under uniaxial bending, the highest shear stress values were obtained in the middle parts of the tenon, while the highest shear elastic strain values were estimated in glue lines between the tenon sur-faces and walls of the mortise. Shear stress and shear elastic strain values in joint elements generally increased with tenon dimensions and corre-sponding bending moment capacities. There was consistency between predicted maximum shear stress values and failure modes of the joints.

Mechanism of stress distribution and failure around two different shapes of openings within fractured rock-like materials

The complexity of a rock masses structure can lead to high uncertainties and risk during underground engineering construction.Laboratory tests on fractured rock-like materials containing a tunnel were conducted,and twodimensional particle flow models were established.The principal stress and principal strain distributions surrounding the four-arc-shaped and inverted U-shaped tunnels were investigated,respectively.Numerical results indicated that the dip angle combination of preexisting fractures directly affects the principal stress,principal strain distribution and the failure characteristics around the tunnel.The larger the absolute value of the preexisting fracture inclination angle,the higher the crushing degree of compression splitting near the hance and the larger the V-shaped failure zone.With a decrease in the absolute value of the preexisting fracture inclination angle,the compressive stress concentration of the sidewall with preexisting fractures gradually increases.The types of cracks initiated around the four-arc-shaped tunnel and the inverted U-shape tunnel are different.When the fractures are almost vertical,they have a significant influence on the stress of the sidewall force of the four-arc-shaped tunnel.When the fractures are almost horizontal,they have a significant influence on the stress of the sidewall of the inverted U-shaped tunnel.The findings provide a theoretical support for the local strengthening design of the tunnel supporting structure.