Stress Redistribution Analysis Research Articles

Residual Stress Redistribution Analysis in the Repair Welding of AA6082-T6 Aluminum Alloy Joints: Experiment and Simulation.

Residual stress has a three-dimensional scale effect (length, depth, and width) in the process of repair welding, which has a detrimental impact on the service of the aluminum alloy welded structures in high-speed trains. This paper aims to systematically analyze the effects of the repair welding dimension on the residual stress redistribution and obtain the optimal repair welding principles. A combination of blind-hole drilling method and stress linearization in BS7910 was adopted to investigate residual stress redistribution under various repair welding dimensions. The results indicate that repair welding dimension was in accordance with the principle of “SNL (shallow, narrow and long)” and the optimal repair length, depth, and width of butt joints in this study were 15t, 0.25t, and t, respectively (t is the plate thickness of butt joints).

Statistical assessment of stress redistribution in loaded polycrystals

This work deals with the analysis of stress redistribution in a polycrystal due to external loading, anisotropy of elastic properties, and microstructure characteristics. A statistical method that enables assessing relationships between stress fields and microstructure features of interest is suggested. The notion of generalised semivariogram is introduced and used to determine the extent of spatial dependence in multivariate random fields. Afterwards, it is allowed to perform the tests of independence based on the distance correlation coefficient. The detected non-spatial dependencies are further examined, focusing on the identification of the actual type of heteroscedasticity. The method is aimed at analysing large computational datasets resulting from numerical simulations of stress redistribution in polycrystals under external loads. It is demonstrated on datasets computed on a realistic microstructure of a NiTi wire subjected to tension while considering uniform and preferential lattice orientation distributions and various degrees of elastic anisotropy. The method shows for the considered microstructure and loading that the degree of elastic anisotropy does not affect the dependencies contrarily to the lattice orientation distribution.

Health monitoring and dynamic analysis of an earth-fill dam at the stage of first impounding: case study—Siahoo dam of Iran

First impounding of the earth-fill dams is considered as one of the most critical stages of these earth structures during their lifespan such that it demands careful monitoring of the dam’s safety. In this study, behavior of Siahoo dam, an earth-fill dam in Iran, is evaluated by numerical modeling at the stage of first impounding to (1) back-analysis and calibration of the numerical model using data of instrumentation measurements, gathered during the dam construction. (2) Determine the optimized plan of the dam’s first impounding so that the dam safety is secured against hydraulic fracturing. (3) Predict the displacements of the dam in the future under seepage and consolidation using the calibrated numerical model. (4) Analyze the dam under seismic loading condition. The material properties were chosen through a two-step procedure based on numerical simulation of laboratory tests in the software and calibration between the stress–strain analysis of the dam and instrumentation measurements at the end of construction stage, so that the real behavior of the dam can be represented. To find the maximum rate of dam’s first impounding in safe condition, a sensitivity analysis was performed assuming eight number of impounding scenarios. Having performed the steady-state seepage analysis, seismic loading was applied using the equivalent linear method and the permanent displacements were predicted using the method of Newmark sliding blocks. Liquefaction analysis was also performed to recognize liquefiable zones of the foundation. Finally, stress redistribution analysis was carried out to estimate the post-earthquake displacements.

Hygrothermal Creep and Stress Redistribution Analysis of Temperature and Moisture Dependent Magneto-Electro-Elastic Hollow Sphere

In this article, the time-dependent stress redistribution analysis of magneto-electro-elastic (MEE) thick-walled sphere subjected to mechanical, electrical, magnetic and uniform temperature gradient as well as moisture concentration gradient is presented. Combining constitutive equations of MEE with stress-strain relations as well as strain-displacement relations results in obtaining a differential equation in which there are the creep strains. At the first step, discounting creep strains in the mentioned equation, an analytical solution for the hygro-thermo-magneto-electro-elastic behavior is achieved at the initial state. After that, the creep stress rates can be achieved by keeping only the creep strains in the differential equation for the steady-state condition. The analysis is done by applying the Prandtl-Reuss equations as well as Norton’s law in creep behavior modeling. Finally, the history of stresses, displacement as well as magnetic and potential field, at any time, is achieved using an iterative method. Results show that the increase in tensile hoop stress resulted from creep progress must be considered in design progress. Also, the effect of hygrothermal loading is more extensive after creep evolution.

Unloading responses of pre-flawed rock specimens under different unloading rates

Abstract Based on the stress redistribution analysis of rock mass during the deep underground excavation, the unloading process of pre-flawed rock material was simulated by distinct element method (DEM). The effects of unloading rate and flaw inclination angle on unloading strengths and cracking properties of pre-flawed rock specimens are numerically revealed. The results indicate that the unloading failure strength of pre-flawed specimen exhibits a power-function increase trend with the increase of unloading period. Moreover, combined with the stress state analysis on the flaws, it is found that the unloading failure strength increases with the increase of flaw inclination angle. The cracking distribution of pre-flawed specimens under the unloading condition closely depends on the flaw inclination angle, and three typical types of flaw coalescence are observed. Furthermore, at a faster unloading rate, the pre-flawed specimen experiences a sharper and quicker unloading failure process, resulting in more splitting cracks in the specimens.

Hygrothermomechanical creep and stress redistribution analysis of thick-walled FGM spheres with temperature and moisture dependent material properties and inelastic radius changes

In the present research, effects of the hygrothermal degradation of the material properties on rates of the creep strains and stresses and stress redistributions of thick-walled FGM spheres subjected to internal and external pressures, temperature rises, and diffusions are investigated. In this regard, the non-linear time-dependent governing equations of the sphere are derived based on the theory of elasticity, Prandtl-Reuss flow rule, and Norton's creep law and solved using a special iterative solution scheme. The main novelties of the present research are: (i) analyzing the FGM sphere as it is; without dividing it into isotropic homogeneous sub-spheres, (ii) considering the temperature and moisture dependencies of the elastic modulus of the FGM material, (iii) proposing a more general numerical procedure instead of the traditional successive elastic or Taylor's expansion procedures, and (iv) successively updating of the inner and outer radii of the vessel to consider the resulting inelastic creep deformations. Results reveal that the moisture absorption generally increases the maximum values of both the elastic and creep portions of the stresses, strains, and stress and strain rates. The creep process reduces the circumferential stresses in the interior regions and increases them in the outer regions, but even in presence of moisture absorption, the area beneath the radial distribution curve of the circumferential stress remains unchanged.

Simulation of Fastener Pull-through Failure for Honeycomb Sandwich Structures with Inserts

Honeycomb sandwich structures are commonly assembled using a local reinforcement called “inserts” at the junction. In this paper, fastener pull-through tests are firstly conducted to investigate the strength properties and failure process of Nomex honeycomb sandwich structures with carbon fiber-reinforced composite skins and inserts. Loading capability and failure modes are analyzed and discussed. Based on these experiments, an analytical model simulating the failure process is then developed and implemented using the finite element code ANSYS, and a degradation model is proposed for the stress redistribution analysis. The database for determining the stiffness degradation factors Di of the honeycomb core is established by means of parametric fitting. The simulated results of the fastener pull-through failure process are will coincided with experimental results.

Numerical analysis of seismic stability of a high centerline tailings dam

Rapid growth of mining activities parallel with recent technological progresses in this field has led to continuous production of great amounts of mining waste. Tailings dams are constructed to safely store these materials in order to protect the environment and water resources against mineral and chemical contaminations. However, the high rate of failure in these structures -especially under dynamic loads- has become a major concern for the mining industry as well as environment protection authorities. Considering the importance of these dams’ role and their stability in protecting the environment, this paper analyzes the dynamic behavior of a high centerline tailings dam in order to evaluate its stability. To achieve this goal, a coupled stress-pore pressure analysis is carried out by SIGMA/W software to study the dam's behavior during and at the end of staged construction. Then, the structure's dynamic response to different seismic criteria relevant to the area of interest is investigated using the QUAKE/W software to determine the history of acceleration at the dam's crest and liquefied zones in the impoundment. Permanent deformations are then determined by a stress redistribution analysis conducted by SIGMA/W software and performance of the dam is evaluated accordingly. Analyses results show that the studied dam is stable under weak ground motions, but unstable under stronger seismic inputs.

Rib/snook design in mechanised depillaring of rectangular/square pillars

A field study at different mechanised depillaring (MD) operations in Indian coalfields (with depth ranging from 60–377m and caveability Index variation from 2300–10500) found mixed performances of adopted sizes of the ribs/snooks. Formation of an irregular shaped rib/snook during MD of the existing square/rectangular pillars by a continuous miner and uniqueness of the existing geo-mining conditions also limit scope of application of the conventional rib/snook design approaches. Taking guidance from the field studies, a parametric investigation is conducted in laboratory on the calibrated simulated models using FLAC3D. An analysis of stress redistribution for different stages of the MD in simulated models provided a different characteristic of an irregular shaped ribs/snooks failure. Presence of moderate roof strata is found to be, relatively, more significant for the rib/snook design. Based on the simulation results, an attempt is made to provide a model for the rib/snook design in MD.

A physically based fatigue damage model for fibre-reinforced plastics under plane loading

The subject of the present article is a new layer-based fatigue damage model (FDM) for laminated multidirectional laminates exposed to general states of plane stress, which allows for simulating the stiffness and the strength degradation by means of a FEM analysis. The essential of the new model is its use of an energy approach which makes the fatigue life prediction of composites more physical and therewith its characterisation much less extensive. Since the failure analysis bases on an interacting failure criterion, the material degradation depends also on the failure mode and is layer-based. (Typical fatigue phenomena as stress redistributions and sequence effects can be analysed with the new model and due to its efficiency it is also applicable to larger structures.)The paper presents a partial validation of the model based on experimental results from the literature and different application examples. These are a shell with a hole and a rotor blade of a wind energy converter demonstrating the analysis of stress redistribution, sequence effects and the applicability of the model to large structures respectively.

2D numerical simulation on excavation damaged zone induced by dynamic stress redistribution

The formation of an excavation damaged zone (EDZ) around an opening in a deep rock mass is associated with the dynamic stress redistribution that starts from transient release of high in situ stress to the final quasi-static stress state after the excavation. This study applies a theoretical analysis of stress redistribution due to transient unloading in surrounding rock under hydrostatic stress field, and develops a numerical elastodynamics model for finite element analysis. Coupling the theoretical and the numerical solutions, a general damage model for heterogeneous rock mass is proposed by taking the dynamic stress redistribution due to excavation into account. Finally, the dynamic stress redistribution, as well as the induced damage zone around the excavation under different lateral pressure coefficients is numerically simulated. The numerical result indicates that, the stress wave induced by the transient unloading will initially cause the damage only in the 1/3 radius vicinity of excavation perimeter. The damage zone may then develop further under the constant quasi-static far-field stress. Therefore, the EDZ development during deep excavation is closely dependent on in situ stress, rock strength and excavation method.

Analysis of stress redistribution in soil and earth pressure on tunnel lining using the discrete element method

This paper analyzes the stress redistribution in the surrounding soil and the earth pressure acting on the shield tunnel lining due to tunneling. The construction of a 6m diameter tunnel buried at a 12m depth with a gap of 4cm with the surrounding soil is modeled using DEM, utilizing the equivalent mass method. The principal stresses and their inclination angle in the surrounding soil are examined together with the earth pressure acting on the tunnel lining. Soil arching and unloading effects due to tunneling are also investigated. Furthermore, the construction of the tunnel at different buried depths and with different tail gaps is modeled. All the comparisons show that increasing the buried depth up to 12m and the tail gaps up to 8cm result in a significant soil arching effect. The soil arching effect ceases to increase for buried depths of more than 12m and for tail gaps of more than 8cm.

콘크리트 주탑의 시간 의존적 거동을 고려한 인천대교의 비선형 해석

최근의 토목분야의 프로젝트에 있어 장대교량의 건설이 주를 이루고 있으며, 장대교량의 여러 형식 가운데서도 사장교가 현재 계획, 설계 중인 프로젝트에서 상당한 비중을 차지하고 있다. 사장교가 대형화 및 장경간화 됨에 따라, 구조물의 경량화를 위하여 강재를 사용한 사장교가 건설되어 왔다. 그러나 많은 사례에서 주탑은 구조적, 경제적인 이유로 콘크리트로 시공되고 있다. 콘크리트는 재료적 특성상 크리프와 건조수축에 의한 장기거동의 영향을 크게 받는데, 이러한 특성으로 인하여 응력의 재분배와 시공 중 구조계의 변화 등 해석상 고려해야 할 부분이 많아진다. 본 연구에서는 철근콘크리트의 비선형성을 고려한 유한요소해석 프로그램 RCAHEST를 사용하여 콘크리트 주탑을 채택한 사장교 중에 국내 최장의 강사장교인 인천대교를 선택하여 해석을 수행하였다. 실제 시공된 교량의 시공단계해석과 완공 후 시간해석을 통하여 콘크리트 주탑만의 시간 의존적 효과가 사장교 전체계에 미치는 영향을 파악하였다. Recently, building of long span bridge is increasing and cable stayed bridges have large portion in civil projects. As the spans of bridges become longer, steel cable-stayed bridges have been constructed mainly for slim structure. But in many case, pylons are constructed by concrete for the stability of structures and the economy. Concrete is greatly influenced by the long-term behavior like creep and drying shrinkage, so analysis of stress redistribution and structural change in construction is required. In this study, as a cable stayed bridge with concrete pylon, Incheon Bridge is analyzed by nonlinear FEM analysis program RCAHEST. Through this analysis, time dependent effect of concrete pylon to whole cable stayed bridge system is studied.

Time-dependent creep stress redistribution analysis of thick-walled functionally graded spheres

Time-dependent creep stress redistribution analysis of thick-walled spheres made of functionally graded material (FGM) subjected to an internal pressure and a uniform temperature field is performed using the method of successive elastic solution. The material creep and mechanical properties through the radial graded direction are assumed to obey a simple power-law variation. Total strains are assumed to be the sum of elastic, thermal and creep strains. Creep strains are time, temperature and stress dependent. Using the equations of equilibrium, compatibility and stress–strain relations a differential equation, containing creep strains, for radial stress are obtained. Ignoring creep strains, a closed-form solution for initial thermoelastic stresses at zero time is presented. It has been found that the material in-homogeneity parameterβ has a substantial effect on thermoelastic stresses. From thermoelastic analysis the material identified by β=2 in which a more uniform shear stress distribution occurs throughout the thickness of the FGM sphere is selected for time-dependent stress redistribution analysis. Using the Prandtl–Reuss relations and Norton’s creep constitutive model, history of stresses and strains are obtained. It has been found that radial stress redistributions are not significant, however, major redistributions occur for circumferential and effective stresses. It has also been concluded that stresses and strains are changing with time at a decreasing rate so that there is a saturation condition beyond which not much change occurs. Indeed after 50 years the solution approaches the steady-state condition.

Time-dependent thermoelastic creep analysis of rotating disk made of Al–SiC composite

Time-dependent creep stress redistribution analysis of rotating disk made of Al–SiC composite is investigated using Mendelson’s method of successive elastic solution. All mechanical and thermal properties except Poisson’s ratio are radial dependent based on volume fraction percent of SiC reinforcement. The material creep behavior is described by Sherby’s constitutive model using Pandey’s experimental results on Al–SiC composite. Loading is an inertia body force due to rotation and a distributed temperature field due to steady-state heat conduction from inner to outer surface of the disk. Using equations of equilibrium, stress strain, and strain displacement, a differential equation, containing creep strains, for displacement is obtained. History of stresses and deformations are calculated using method of successive elastic solution. It is concluded that the uniform distribution of SiC reinforcement does not considerably influence on stresses. However, the minimum and most uniform distribution of circumferential and effective thermoelastic stresses belongs to composite disk of aluminum with 0% SiC at inner surface and 40% SiC at outer surface. It has also been found that the stresses, displacement, and creep strains are changing with time at a decreasing rate so that after almost 50 years the solution approaches the steady-state condition.

Magnetothermoelastic creep analysis of functionally graded cylinders

This paper describes time-dependent creep stress redistribution analysis of a thick-walled FGM cylinder placed in uniform magnetic and temperature fields and subjected to an internal pressure. The material creep, magnetic and mechanical properties through the radial graded direction are assumed to obey the simple power law variation. Total strains are assumed to be the sum of elastic, thermal and creep strains. Creep strains are time, temperature and stress dependent. Using equations of equilibrium, stress–strain and strain–displacement a differential equation, containing creep strains, for displacement is obtained. Ignoring creep strains in this differential equation a closed form solution for the displacement and initial magnetothermoelastic stresses at zero time is presented. Initial magnetothermoelastic stresses are illustrated for different material properties. Using Prandtl–Reuss relation in conjunction with the above differential equation and the Norton’s law for the material uniaxial creep constitutive model, the radial displacement rate is obtained and then the radial and circumferential creep stress rates are calculated. Creep stress rates are plotted against dimensionless radius for different material properties. Using creep stress rates, stress redistributions are calculated iteratively using magnetothermoelastic stresses as initial values for stress redistributions. It has been found that radial stress redistributions are not significant for different material properties, however major redistributions occur for circumferential and effective stresses.

Bearing strength and failure behavior of bolted composite joints (part II: modeling and simulation)

In part II of this study, an analytical model for simulating the bearing failure and response characteristics of bolted composite joints is developed. The model was implemented using the general-purpose finite element code ABAQUS. The analytical model has taken into account the contact conditions at the pin/hole boundary, progressive damage, finite deformation and nonlinear material behavior. A complex approach based on combining the nonlinear shear elasticity theory with a continuum damage mechanics approach was utilized to represent the nonlinear material behavior during loading. The damage accumulation criteria based on Hashin and Yamada-Sun’s hybrid failure criteria were adopted and a degradation model for the damaged layers is proposed for the stress redistribution analysis. The numerical simulation results for joint’s progressive damage and strength response agreed well with existing experimental data.

Benchmark for finite element analysis of stress redistribution induced by creep damage

A benchmark test for finite element analysis of stress redistribution induced by material creep damage is proposed using a two-bar model structure. It is directly based on the analytical solution reported earlier by Gonçalves Filho [Int. J. Solids Struct. 32 (1995) 3087] and actual creep data for the Ti–6Al–2Cr–2Mo titanium alloy. The new benchmark is used to assess the accuracy of the implicit time integration scheme employed in the in-house finite element code developed by this author for solution of engineering creep damage problems. By allowing the calculation of the true relative errors in alternative numerical solutions, the designed test enhances the set of benchmark tests recently proposed by Becker et al. [Comput. Mater. Sci. 25 (2002) 34].

損傷力学手法に基づく複合材料機械的継手部の面圧破壊挙動シミュレーション

This paper presents the development of an accumulative damage model based on continuum damage mechanics (CDM) to simulate the bearing failure and response in the bolted composite joints. The simulation is implemented into a general-purpose FEM code ABAQUS. The main damage mechanisms observed from experimental study are described as accumulated compressive damage that appeared by matrix compression failure and fiber compression-shear failure. The fundamental approach consists of contact problem at the pin/hole interface, progressive damage, large deformation problem and material nonlinear problem. A complex approach based on a nonlinear shear elasticity theory combined with a continuum damage mechanics approach can be also utilized to represent the material nonlinear behavior during loading. The damage accumulation criteria using the hybrid method based on Hashin and Yamada-Sun’s failure criteria are adopted, and the stress redistribution analysis using a degradation model for the damaged ply is performed. The accurate prediction results include progressive damage and strength response of the joints that agrees well with the existing experimental data.

Bearing failure in bolted composite joints: analytical tools development

This paper presents an analytical tool development for simulating the bearing failure and response of bolted composite joints. It is implemented into a general-purpose finite element code ABAQUS. The main damage mechanisms observed from the experiments are described as accumulated compressive damage, induced by shear and compression failures of fiber and matrix. The contact problem at the pin/hole boundary, progressive damage, finite deformation and nonlinear material behavior are taken into account when developing the analytical tool. A complex approach based on a nonlinear shear elasticity theory combined with a continuum damage mechanics approach can also be utilized to represent the nonlinear material behavior during loading. The damage accumulation criteria based on the hybrid failure criteria of Hashin and Yamada-Sun are adopted, and a degradation model for the damaged ply is proposed for the stress redistribution analysis. The computed results, including progressive damage and strength response of the joints, agreed well with the existing experimental data.