Stress Concentration Phenomenon Research Articles

Research on bearing capacity of honeycomb plate box-type hollow roof structure

• A new type of honeycomb plate box-type hollow roof structure is prepared with good ductility. • The validity of the numerical analysis model was verified by comparing the results of experiment with the results of the coupling model. • Influential factors on the bearing capacity of honeycomb plate box-type hollow roof structure obtained by parametric analysis. In this paper, a new type of honeycomb plate box-type hollow roof structure was prepared. The failure modes and mechanical properties of the box-type hollow roof structure were analyzed by bearing capacity test and numerical simulation. The validity of the numerical analysis model was verified by comparing the results of experiment with the results of the coupling model. The influence of specification of honeycomb plate, height of the side plate, rise-span ratio of the structure, configuration of box-type hollow roof structure, and initial geometric defect on the bearing capacity of the honeycomb plate box-type hollow roof structure were analyzed. The results show that the failure mode of the specimen is tensile failure of the surface plane of the honeycomb plate with strengthened frame and buckling instability of the plate near the joint. The results of coupling model are in good agreement with the results of experiment. The stiffness of honeycomb plate box-type hollow roof structure can be improved by the thickness of plate and the height of core layer of honeycomb plate. The ultimate bearing capacity of the honeycomb plate box-type hollow roof structure increases with the increase of the height and rise-span ratio. The bottom plate of box-type hollow roof structure can make the force transmission path of the structure more reasonable and effectively reduce the phenomenon of stress concentration. Compared with the structure without initial geometric defect, the stable bearing capacity of the structure is reduced by 18.6 % and the ultimate bearing capacity is reduced by 28 % when the initial geometric defect of 80 mm is applied to the structure.

Research on Soft Rock Damage Softening Model and Roadway Deformation and Failure Characteristics.

To determine a reasonable control strategy for deep buried soft rock roadways, a study on deformation and failure characteristics was carried out. The Weibull distribution damage variable was introduced to construct a damage-softening model considering the lateral deformation of the rock mass, and the functional relationship between the model parameters F0 and m and the confining pressure were discussed. The nonlinear fitting method was used to correct the model parameters. Using the model, the failure characteristics of deep buried soft rock roadways were analyzed. A comprehensive and step-by-step joint support control strategy was proposed based on the numerical simulation results. The research results showed that the damage-softening model curve established could genuinely reflect the whole process of mudstone failure. The apparent stress concentration phenomenon occurred in the surrounding rock. The surrounding rock deformation showed that roadway floors had larger plastic failure areas than sides and vaults. The plastic failure depth could reach 2.45 m. After a comprehensive and step-by-step joint support control strategy was adopted, the deformation rate of the roadway at the section was less than 0.1 mm/d. The optimized support scheme can effectively improve the stability of the roadway.

Static analysis and boundary effect of FG-CNTRC cylindrical shells with various boundary conditions using quasi-3D shear and normal deformations theory

In this paper, static analysis and the stress concentration phenomenon of functionally graded carbon nanotubes reinforced composite cylindrical shells with various boundary conditions are explored by using higher-order shear-normal deformation theory and an analytical approach. Five types of distributions of reinforced carbon nanotubes are considered, that is, uniform and four kinds of functionally gradient distribution of carbon nanotubes along with the thickness of the shell. Effective material properties of carbon nanotubes reinforced composite are estimated to the rule of mixture. The governing equations for FG-CNTRC cylindrical shells with various boundary conditions are solved analytically using simple trigonometric series and the Laplace transform. Moreover, the transverse shear and normal stress are reconstructed using 3D linear elasticity equilibrium equations. The present model is validated by comparing its numerical results with those of published works, including the 3D exact model. Using higher-order shear-normal deformation theory, this article has focused on investigating the stress concentration phenomenon, the distribution of stress components in the near-boundary region, and also assessing the effects of various parameters on the stress state of the FG-CNTRC cylindrical shells.

Research on the Characteristics of Coal Bump and Monitoring and Early Warning in Hujiahe Coal Mine

Under the high intensity mining disturbance, coal bump is easily triggered by the sudden release of large amount of elastic energy contained in the coal body, which seriously affects coal mine safety production. Triaxial experiments were used to study the damage characteristics of coal samples subjected to loading at the 401103 working face of Hujiahe coal mine, and the critical value of peak strength of coal samples was investigated. Based on the characteristics of the mechanical damage behavior of coal samples obtained from the triaxial experiment, the statistics of the occurrence of coal bump events at the 401103 working face were conducted through numerical simulation and field monitoring to study the areas that need to be focused on prevention and control, with a view to providing basic research for deep coal mining. The results show the following: (1) the strength of coal samples is “weakened” by stress loading, and the fracture penetrates the coal body interface leading to the formation of tensile-shear damage of coal samples. The value of the damage variable for the coal sample in the initial damage stage is 0; at the damage stabilization stage, the values of damage variables were derived to be located at 0.03~0.14. The bearing capacity of the coal sample decreases rapidly during the accelerated development period. (2) According to the simulation and field monitoring, it is known that 0~100 m in front of the coal mining face belongs to the key monitoring area. (3) With the advancement of the working face, different coal pillar widths have obvious effects on the vertical stress, and stress increase and decrease zones appear on both sides of the coal column, and the peak stress shows the characteristics of increasing first and then decreasing with the advancement of the working face. The width of the working face has a great influence on the change of vertical stress. When the sensitivity of the vertical stress to the width of the working face increases, the stress concentration phenomenon will occur, and a large amount of elastic energy gathered in the coal body is suddenly released to induce coal bump.

Fretting wear evolution model of the metal filaments inside metal rubber

Metal rubber (MR) is a porous material which possesses macroscopic damping properties through the dry friction between the internal helical metal wires. Due to its complex topological structure, the research on the fretting wear of MR is rarely reported in the literature. In the present work, a double-body wear model of metal filaments is constructed by the master-slave composite method. The friction and wear conditions of the dynamic and static metal wires inside the MR are analyzed under different contact angles, loads, and vibration amplitudes. The results indicate that the wear area and volume of the dynamic wire under each working condition are significantly larger than those of the static wire, while the case for the wear depth is the opposite. After wear, the wires exhibit an obvious stress concentration phenomenon, which is distributed along the wire wear contour area, and the wear profile has a high sensitivity to the contact angle. In order to further investigate the difference in the wear degree of the static and dynamic wires inside the MR, the fretting amplitude is introduced to describe the wear scar area of the dynamic wire, the special wear scar area is reorganized regularly, and the wear volume of the wire is approximated by the regional combination, deriving and constructing a fretting wear evolution model suitable for MR wires. This evolution model can simultaneously predict the wear degree of dynamic and static wires, and its prediction accuracy is high. The prediction accuracy under each working condition is basically less than 10%; thus, the proposed model can be effectively applied to the fretting wear prediction of MR ultra-fine wire contact pairs. This work provides theoretical guidance for the life prediction and other aspects of MR materials.

Investigation of the punching shear behaviors of reinforced concrete slab–steel reinforced concrete L-shaped column connections

To study the punching behaviors of reinforced concrete (RC) slab–steel reinforced concrete (SRC) L-shaped column connections, four slab–column connection tests were designed and completed, and a new punching shear resistance measure proposed. The test variables were column section shape, slab thickness and column cap. The test results show that the failure mode of L-shaped column was mainly two-way shear. Meanwhile, increasing slab thickness and installing column cap can effectively improve the ultimate bearing capacity of the slab–column connection. The punching angles formed by the punching cone and horizontal direction at the final failure of the connection were between 23.5° and 49.5°. In addition, a numerical simulation analysis was carried out using ABAQUS software, and the effects of various parameters on the performance of slab–column connections were studied. It was found that the change of column section shape will lead to more complex shear stress distribution and stress concentration phenomenon. However, the punching capacity of the special-shaped column was higher than that of the equivalent square column with the same section area. As a new punching shear resistance measure, inverted T-shaped steel can effectively improve the ultimate bearing capacity of the connections. In addition, when the ratio of slab thickness to web width of inverted T-shaped steel was less than 0.75, the failure mode of the connection changed from brittle punching failure to flexural failure.

FAILURE CHARACTERISTICS OF SURROUNDING ROCKS IN COAL SEAM MINING ROADWAY

In order to provide technical support for grouting engineering of broken surrounding rock in roadway. Taking a certain mine in Jin coal mine area as a test mine, drilling TV and segmented water injection tests were used to detect the damage characteristics of surrounding rocks, and the numerical simulation of stress characteristics during the failure process was carried out. The research results show that the crack width of the surrounding rock can be reduced to four areas from the inside to the outside, and the crack widths are different. After the excavation of the roadway, the stress concentration occurs inside the coal and rock mass. With the excavation, the stress exceeds the strength of the coal and rock mass, and the failure occurs, and the stress concentration phenomenon continues to develop deep; the radial direction of the roadway is divided into four areas: completely broken zone, fracture reduction zone, fractured compression zone and proto-rock-like area.

Numerical Simulation on Thermal Stresses and Solidification Microstructure for Making Fiber-Reinforced Aluminum Matrix Composites.

The fabrication of fiber-reinforced metal matrix composites (MMCs) mainly consists of two stages: infiltration and solidification, which have a significant influence on the properties of MMCs. The present study is primarily focused on the simulation of the solidification process and the effect of the active cooling of fibers with and without nickel coating for making the continuous carbon fiber-reinforced aluminum matrix composites. The thermomechanical finite element model was established to investigate the effects of different cooling conditions on the temperature profile and thermal stress distributions based on the simplified physical model. The predicted results of the temperature distribution agree well with the results of the references. Additionally, a three-dimensional cellular automata (CA) finite element (FE) model is used to simulate the microstructure evolution of the solidification process by using ProCAST software. The results show that adding a nickel coating can make the heat flux smaller in the melt, which is favorable for preventing debonding at the coating/fiber and alloy interface and obtaining a finer microstructure. In the presence of the nickel coating, the number of grains increases significantly, and the average grain size decreases, which can improve the properties of the resultant composite materials. Meanwhile, the predicting results also show that the interfaces of fiber–coating, fiber–melt, and coating–melt experience higher temperature gradients and thermal stresses. These results will lead to the phenomenon of stress concentration and interface failure. Thus, it was demonstrated that these simulation methods could be helpful for studying the solidification of fiber-reinforced MMCs and reducing the number of trial-and-error experiments.

Design and Analysis of Optical Window Encapsulation Structure for Laser Doppler Deep-Sea Hydrothermal Velocity Measurement System

The optical window is an essential channel for optical signal transmission and return of a deep-sea hydrothermal velocimetry system. Due to its unique structural design, the stress concentration of the optical window will occur under the action of deep-sea high pressure, resulting in cracks at the corner of the high-pressure surface of the optical window, which leads to the inaccurate convergence of the optical signal. A pressure self-balancing optical window package structure is designed to solve the problem. The stress at the optical window is numerically analyzed, and the forces of self-balancing and nonpressure self-balancing optical windows under the same seawater pressure are compared. The results show that the maximum stress at the stress concentration can be reduced by 53% using the pressure self-balancing method, and the phenomenon of stress concentration can be effectively eliminated. In addition, to verify the feasibility of the design and the accuracy of the numerical calculation results, the optical window and its encapsulation structure were experimentally studied, and the deep-sea performance test experiment was carried out on the “Jiaolong” submersible, which further verified the accuracy of the results.

Study on the supporting performance of concrete filled steel tube arches with three different cross-sections

At present, there are a variety of concrete-filled steel tube (CFST) supporting arches with different cross-sections, but a method for selecting a section that fits the site conditions is still lacking. In this paper, laboratory tests and numerical tests were carried out, and three mechanical conditions, the local compression-bending loads, the simplified ideal global loads and the simulated arch-rock contact loads, were investigated for the three most commonly used cross-section types, namely circular, square and D-shaped cross-sections. For the local compression-bending capacity, the axial bearing capacities of D-shaped cross-section specimens are 1.45% and 4.58% higher than those of the circular and square cross-section specimens, respectively; the bending bearing capacities of the square cross-section specimens are 11.19% and 22.13%/21.27% (D-shaped specimens under reverse eccentric compression) higher than those of the circular and D-shaped cross-section specimens, respectively. For the simplified ideal global loads, the straight-leg arches with square, circular and D-shaped cross-sections have bearing capacities from high to low, while the order of the bearing capacities is circular, square and D-shaped for circle arches; the difference values are not more than 10%. For the simulated arch-rock contact loads, the bearing capacities of the D-shaped type arches are 12.42% and 5.89% higher than those of the circular and square arches, respectively, under the full contact condition; the stress distribution of the surrounding rock is irregular, the stress concentration phenomenon appears near the cavity under the non-full contact condition, and the square cross-section arches have better bearing capacity behaviour with cavity widening. Finally, suggestions for the cross-section selection of the CFST supporting arch are proposed according to the quantitative test data and combined with the processing technique, production cost, construction technique and connecting joint property.

Understanding on interlaminar nano-reinforcement induced mechanical performance improvement of carbon/carbon composites after silicon infiltration

In structural materials research, lightweight composites for extreme environments are currently a hot issue. Although the layered architectural carbon/carbon (C/C) composites with pack cementation (PC) coatings are currently the most often viable option, free silicon penetration as a side effect of the PC process has the potential risk factors to damage the interlayer properties and hence greatly weaken the mechanical performance of the materials. Herein, the nanoscale enhancement technique is used to create a three-dimensional silicon carbide nanowire network/coating/matrix interlaminar structure to enhance the bonding strength between the coatings and the matrix. This strategy is employed in order to investigate the effect of interlaminar nano-reinforcement on the mechanical behavior of C/C composites after the silicon infiltration process. The mechanism of the influence of interlaminar reinforcement on the packing composition and stress distribution is investigated by using both experimental and multiscale modeling methodologies. Taking advantage of the improved interlayer bonding, the as-obtained composites do not only optimize the residual thermal stress concentration phenomenon caused by the high temperature treatment, but also promote a high level of interfacial shear strength, resulting in a simultaneous significant improvement in the strengthening of the load transfer and the toughening of the crack bridging. Thus, our approach contributes to a better understanding of the PC coating damage process while also providing novel insights into the creation of high-strength and lightweight structural materials.

Study on the Effect of Milling Surface Plastic Deformation on Fatigue Performance of 20Cr and TC17 Specimens

In addition to the micro-topography of machined surfaces, plastic deformation is an important factor affecting the machined surface integrity and the fatigue performance of specimens. For 20Cr and TC17 materials, the effect law of milling surface plastic deformation on high- and low-cycle fatigue performance of specimens was studied. Experimental results show that the effect law of milling surface plastic deformation on high- and low-cycle fatigue performance of specimens is different. When the high-cycle fatigue life is about 2 × 105 cycles, severe surface plastic deformation can increase the maximum stress suffered by TC17 specimens from 1060 MPa to 1080 MPa; when the low-cycle fatigue life is about 6 × 104 cycles, severe surface plastic deformation can reduce the maximum stress suffered by 20Cr specimens from 680 MPa to 660 MPa. Therefore, severe surface plastic deformation can improve the high-cycle fatigue performance and, on the contrary, it has a negative effect on the low-cycle fatigue performance. Combined with the analysis of the surface integrity index and the fatigue fracture topography of specimens, it is concluded that the machined surface plastic deformation significantly reduces the plastic deformation capacity of surface layer material and enhances the stress concentration phenomenon caused by the surface micro-topography, so that when a specimen is subjected to a large load, it is very easy to make microcracks appear on the machined surface and form the “over-plastic deformation” phenomenon, resulting in a sharp decrease in the low-cycle fatigue performance of specimens. This suggests that the plastic deformation degree of machined surfaces needs to be optimized depending on the magnitude of the working load and the micro-topography.

Biomechanical Changes on the Typical Sites of Pressure Ulcers in the Process of Turning Over from Supine Position: Theoretical Analysis, Simulation, and Experiment.

Pressure ulcers are mainly caused by prolonged pressure on local tissues. The current method of preventing pressure ulcers is mainly to change the patient's position by turning, so it is significant to study the biomechanics of the typical site of pressure ulcers. Based on anatomical theory, a three-dimensional model of the shoulder and hip was established, and the theoretical contact pressure between the body and the bed was calculated by force analysis. Then, finite element models of typical parts of pressure ulcers were established, and the maximum stresses under different boundary conditions were obtained by finite element analysis. Finally, a human body turning experiment was conducted using a pressure distribution sensor, and the pressure distribution clouds and maximum contact pressure curves under different turning angles were obtained. The results show that the extreme point of maximum stress occurs at [Formula: see text], producing a stress concentration phenomenon; the peak stresses at the shoulder and hip are more balanced in the angular threshold range of [Formula: see text] to [Formula: see text], the stresses are more dispersed, and there exists an angular threshold for optimal integrated pressure, which can improve the efficiency of the use of assisted turning equipment. The relevant results help to explain the causes of pressure ulcer disease and can provide clinical references to improve the effectiveness of care.

응력 집중 저감을 위한 머드 모터 커넥팅 로드 설계 개선에 관한 연구

Ground drilling technology for drilling has an environment where the major parts are prone to damage due to high stress, torque, and harsh operating conditions that can occur in the rotary power transfer structure. Research for preventing this damage is very important, as it can be coupled with the nature of drilling operations that take a long time in operation, which can lead to enormous cost and time consumption. Previous work investigated the cause of damage by analyzing the working environment and breakage of drilling holes for connecting rods, and a power transfer component of directional mud motors used in ground drilling systems. The material properties by heat treatment conditions for applied materials were analyzed. Based on prior work, we evaluated whether the stress concentration part shown in the analysis results matched the actual damage occurring point by conducting a structural analysis of the connecting rod, a damaged part, using the finite element analysis. We also analyzed how to reduce the stress concentration phenomenon that occurs during the mud motor operation by conducting part shape and design changes between the connecting rod and key parts.

Simulation Analysis and Fabrication of a Silicon Carbide-Based Piezoresistive Accelerometer

This paper proposes a Micro Electro Mechanical Systems piezoresistive accelerometer based on a whole SiC substrate. Compared with Si-based sensors, SiC-based sensors have stronger mechanical advantages and unique advantages for applications in ultra-high temperature environments. The characteristics of the accelerometer are designed and numerically simulated, and the accelerometer is evaluated in terms of stress load and working frequency band. An innovative design is carried out to eliminate the stress concentration phenomenon in the corner area of the sensor, which guarantees the working safety of the fragile structure of SiC. After fabrication, packaging and vibration experiment, it is found that the sensor’s working sensitivity can reach 0.21mv/g, and its linearity can reach 98%.

Microstructure of laser cladding nickel-based superalloy: characterization, finite element modeling, and fatigue analysis

Abstract After laser cladding, the mechanical response of nickel-based single crystal superalloy is more complex when the loading direction is perpendicular to the columnar grain growth direction. In order to understand the deformation at grain level, a representative volume element (RVE) model based on the randomness of columnar grain texture was established for DD6 single crystal alloy, and the finite element model simulation of crystal plasticity (CPFEM) was performed. The results show that the stress and strain responses of the cladding microstructure are related to the grain distribution. The orientation difference between columnar grains in the epitaxial growth microstructure leads to non-uniform deformation and local stress concentration. The greater the crystal orientation difference is, the more obvious the stress concentration phenomenon is. On this basis, the statistical standard deviation of strain component is chosen to represent the fatigue damage of material, and the relationship between the statistical standard deviation of strain component and the external load strain is studied, which has certain reference value for the fatigue damage research of micro-cladding.

Rock fragmentation mechanism and engineering application by shaped water pressure smooth blasting

In recent years, various regions are vigorously promoting road infrastructure construction, and the tunnel is one of the essential ways of road infrastructure in mountainous areas, but the traditional smooth blasting has problems such as large disturbance of surrounding rock, easy to exceed and underdog, high dust concentration, etc., which delays the construction process of tunnel drilling, time-consuming and laborious. To solve these problems, this paper, relying on the newly built Guantian tunnel project of the ZJHZQ-9 section of Zhangjiajie to Jishou-Huaihua railway Project, studied the stress propagation law of rock blasting, vibration and displacement changes generated by seismic waves and analyzed them through theoretical analysis and numerical simulation, and drew the following conclusions: (1) Based on the basic theory of rock blasting, the principle of shaped charge action and forming mechanism of shaped charge jet are introduced. The effect of water medium and mortar on rock breaking in the blasting process and the movement law of mortar in the hole are analyzed; (2) ANSYS/LS-DYNA software was used for numerical simulation, and the blasting stress propagation law and surrounding rock damage were analyzed. The results showed that the stress propagation of the shaped water pressure smooth blasting was outstanding, and there was an obvious stress concentration phenomenon at the water bag, which verified the shaped energy jet effect of the shaped energy tank; (3) ANSYS/LS-DYNA software was used for numerical simulation, and the changes of vibration velocity and displacement of blasting simulation were analyzed respectively. The results showed that the vibration velocity of shaped charge hydraulic smooth blasting was the smallest, indicating that the water medium had certain energy storage and buffering effect, while the displacement change was on the contrary. Under the joint action of water bag and mortar, the water wedge enlarges the surrounding rock fissures so that the displacement variation of the shaped water pressure smooth blasting is the largest; (4) Through the field engineering application, the direction and width of blasting cracks correspond to the simulation results, which verifies the accuracy of the simulation.

A biodegradable magnesium alloy vascular stent structure: Design, optimisation and evaluation

The existing biodegradable magnesium alloy stent (BMgS) structure is prone to problems, such as insufficient support capacity and early fracture at areas of concentrated stress. Herein, a stent structural design, which reduced the cross section of the traditional sin-wave stent by nearly 30% and introduces a regular arc structure in the middle of the support ring. The influence of the dual-parameter design of bending radius (r) and ring length (L) on plastic deformation, expansion and compression resistance performances are discussed. The non-dominated sorting genetic algorithm II (NSGA-II) was used to search for the optimal solution. It was found that the introduction of parameter r effectively improved the plastic deformation and expansion performance, and the reduction of L improved stent compression resistance. Finally, an optimized stent configuration was obtained. In vitro mechanical tests, including balloon inflation, radial strength and flexibility, verified the simulation results. The radial strength for the optimised stent increases by approximately 40% compared with that for the sinusoidal stent. Microarea X-ray diffraction result shows that the circumferential residual stress for the optimised stent decreases by half compared with that for the sinusoidal stent, thus effectively reducing the stress concentration phenomenon. Statement of significanceDespite current progress in BMgS research, the optimal design of the structure is limited. We present a new type of structurally designed stent. The performance of this stent was analysed by a finite element method and experimentally verified. The structural design positively influenced stent performance.

Investigation on mechanical characteristics of non-pneumatic tire with rhombus structure under complex pavement conditions

Non-pneumatic tires (NPTs) have gained more and more attention in recent years due to the advantages of no run-flat, maintenance-free and excellent load-bearing capacity. In this paper, a mechanical model of rhombic porous structure was derived based on the theory of the hexagonal honeycomb structure, and the difference of mechanical characteristics for rhombic NPT tread on horizontal pavement as well as complex pavement was studied. The results show that the average contact pressure of NPT with rhombic structure on horizontal road is much lower than that of pneumatic tire, the shape of its spoke bearing area is inverted trapezoid, and the stress concentration phenomenon is formed in the contact part corresponding to the connection between spokes and tread at different contact positions. Furthermore, the vertical displacement and contact pressure of NPT are decoupled on complex pavement. The maximum stress concentration point is shifted from the tire surface to the spoke-tread connection and then to the spokes of the rhombic bearing structure as the contact area between the tire and the ground increases. This study provides guidance for structural optimization of NPT applied to complex working conditions.

Free-Edge Effects in Composite Laminates—A Review of Recent Developments 2005–2020

AbstractThe design and analysis of composite structures in the form of layered plates or shells is often driven by stress concentration phenomena that occur due to geometric or material discontinuities. One prominent example is the so-called free-edge effect that manifests itself in the form of significant localized interlaminar stress fields in the vicinity of free laminate edges and that is given rise to due to the mismatch of the elastic properties of the individual laminate layers. The free-edge effect has been under scientific investigation for more than five decades, and this paper aims at providing an overview of recent developments and scientific advances in this specific field wherein an emphasis is placed on investigations that were published in the time range between the years 2005 and 2020. This paper reviews closed-form analytical methods as well as semi-analytical and numerical analysis approaches and summarizes the recent state of the art concerning the investigation of stress singularities and experimental characterization of free-edge effects. This paper also reviews advanced problems such as free-edge effects in curved laminated structures and in piezoelectric laminates as well as in the vicinity of holes and other geometric discontinuities, and two new aspects in the field of free-edge effects, namely, the development and application of a new semi-analytical method (the so-called scaled boundary finite element method (SBFEM)) and the fracture mechanical strength assessment, also by novel approaches such as finite fracture mechanics, are also discussed. This paper closes with a summary and an outlook on future investigations.