Stability assessment of landslide-prone road cut rock slopes in Himalayan terrain:A finite element method based approach

Large-scale slope destabilization could be aggravated due to swift urbanization and ever-rising demands of geoengineering projects such as dams,tunnels,bridges and widening roads.National Highway-58 connects Delhi to Badrinath in India,which passes through complex geomorphological and geological terrain and often encounters cut slopes susceptible to slope failures.In the present investigation,a detailed geotechnical appraisal is conducted along the road cut slopes from Rishikesh to Devprayag in the Himalayas.Twenty vulnerable road cut slopes were demarcated for detailed slope stability analysis using Phase2D finite element modeling simulator.Nonlinear generalized Hoek-Brown(GHB)criterion was adopted for stability analyses.Out of 20 slopes,five slopes(S6,S7,S18,S19 and S20)are unstable with factor of safety(FoS)less than or equal to 1,and thus needs immediate attention.The FoS values of four slopes(S2,S9,S13 and S17)lie between 1 and 1.3,i.e.marginally stable,and slopes S1,S3,S4,S5,S8,S10,Sll,S12,S14,S15 and S16 are stable.Mohr-Coulomb(MC)criterion was also adopted to compare the slope stability analysis with GHB criterion.The FoS calculated from GHB criterion is close to that using MC criterion for lower values of FoS whereas for higher values,the difference is marked.For the jointed rock in the Himalayan region,the nonlinear GHB criterion gives better results as compared to MC criterion and matches with the prevailing field conditions.Accordingly,some suggestions are proposed to strengthen the stability of cut slopes.

3D FINITE ELEMENT ANALYSIS OF THE DAMAGE EFFECTS ON THE DENTAL COMPOSITE SUBJECT TO WATER SORPTION

The damage effects of water sorption on the mechanical properties of the hydroxyapatite particle reinforced Bis-GMA/TEGDMA copolymer （HA/Bis-GMA/TEGDMA） h-ave been predicted using 3D finite cell models. The plasticizer effect on the polymer matrix was considered as a variation of its Young＇s modulus. Three different cell models were used to determine the influence of varying particle contents, interphase strength and moisture concentration on the debonding damage. The stress distribution pattern has been examined and the stress transfer mode clarified. The Young＇s modulus and fracture strength of the Bis-GMA/TEGDMA composite were also predicted using the model with and without consideration of the damage. ine Iormer results with consideration of the debonding damage are in good agreement with existing literature experimental data. The shielding effect of our proposed model and an alternative approach were discussed. The FCC cell model has also been extended to predict the critical load for the damaged and the undamaged composite subject to the 3-point flexural test.

Thermo-hydro-mechanical-air coupling finite element method and its application to multi-phase problems

In this paper, a finite element method （FEM）-based multi-phase problem based on a newly proposed thermal elastoplastic constitutive model for saturated/unsaturated geomaterial is discussed. A program of FEM named as SOFT, adopting unified field equations for thermo-hydro-mechanical-air （THMA） behavior of geomaterial and using finite element-finite difference （FE-FD） scheme for so/l-water-air three-phase coupling problem, is used in the numerical simulation. As an application of the newly proposed numerical method, two engineering problems, one for slope failure in unsaturated model ground and another for in situ heating test related to deep geological repository of high-level radioactive waste （HLRW）, are simulated. The model tests on slope failure in unsaturated Shirasu ground, carried out by Kitamura et al. （2007）, is simulated in the framework of soil-water-air three-phase coupling under the condition of constant temperature. While the in situ heating test reported by Munoz （2006） is simulated in the same framework under the conditions of variable temperature hut constant air pressure.

Finite Element Analysis of Elastic-Plastic Contact Mechanic Considering the Effect of Contact Geometry and Material Properties

Each surface of roughness has different shape of asperity which is modeled with various shapes of analytical models. In this paper, the differences among various models of shape of asperity investigate using the Finite Element Method (FEM) and various analytical models. The contact stresses in rough surfaces are calculated analytically using various asperity shape models. Finite element analysis is also carried out assuming three types of material properties namely, the linear, the elastic-perfect plastic and the elastic-nonlinear hardening. The analytical results are compared with the results obtained by the finite element method. The results illustrate for using a deterministic approach which the numerical models are suitable. In hertz model, the result of force is very big in interface of causing deformation plastic, while Model Zhao has almost same result with FEM nonlinear property model. It is observed that the results obtained from Zhao’s model are generally in a better agreement with the results obtained from various finite element models especially in elastic-plastic and plastic zones, hence it may be concluded that Zhao’s model can be used for analyzing the rough surfaces in contact mechanics.

Dynamic Characteristics of Inflated Torus Using Finite Element Analysis

In recent years, inflatable structures have been a subject of interest for space applications such as communication antenna, solar thermal propulsion and entry/landing systems. The inflatable structures characterized by high strength-to-mass ratios, minimal stowage volume, which makes them suitable for cost-effective large space structures. A typical example for the inflatable structure is the inflated torus which often used in order to provide structure support. In this study, our main focus is to understand the dynamic characteristics of an inflated torus in order to formulate an accurate mathematical model suitable for active vibration control applications. A commercial finite element package, ANSYS, is used to model the inflated torus. To verify the model the obtained frequencies and mode shapes are compared with the published results, which are derived using analytical approach, the verification shows a good agreement between the FEM and the analytical results. Based on the verified model, parametric study was investigated; the material thickness increase causes the natural frequencies decrease, while the increase of the inflation pressure simply results in stiffening the ring, which means that the natural frequency increased. The FEM analysis gives an easy and fast way for the vibration analysis of the structures compared with the complicated analytical solutions.

Free vibration characteristics of sectioned unidirectional/bidirectional functionally graded material cantilever beams based on finite element analysis

Advancements in manufacturing technology,including the rapid development of additive manufacturing(AM),allow the fabrication of complex functionally graded material(FGM)sectioned beams.Portions of these beams may be made from different materials with possibly different gradients of material properties.The present work proposes models to investigate the free vibration of FGM sectioned beams based on onedimensional(1D)finite element analysis.For this purpose,a sample beam is divided into discrete elements,and the total energy stored in each element during vibration is computed by considering either the Timoshenko or Euler-Bernoulli beam theory.Then,Hamilton’s principle is used to derive the equations of motion for the beam.The effects of material properties and dimensions of FGM sections on the beam’s natural frequencies and their corresponding mode shapes are then investigated based on a dynamic Timoshenko model(TM).The presented model is validated by comparison with three-dimensional(3D)finite element simulations of the first three mode shapes of the beam.

FEM simulation of flexible roll forming based on different material models

Flexible roll forming is a new roll forming process that produces parts with variable cross sections. This forming process is proposed to meet the demand of weight reduction of automobile industry. In order to study the mechanisms and material flow rules in this new forming process,the finite element mothod( FEM) model of a nine-step flexible roll forming of an ultra-high-strength steel bumper is established based on deep understanding and reasonable simplification of the process.Given that the material model is an important factor that influences the simulation accuracy,three material models which consist of different yield criteria and hardening models are adopted in the FEM models. Sheet thickness and springback amount calculated with three material models are studied comparatively. According to sheet thickness reduction and springback amounts,it is found that the MKi( Mises yield criterion and kinematic hardening law) model's result is larger than MI( Mises yield criterion and isotropic hardening law) model and HI( Hill's yield criterion and isotropic hardening law) model. Therefore,it is concluded that material models do have influences on the flexible roll forming simulation and need to be determined carefully.

Fracture of films caused by uniaxial tensions:a numerical model

Surface cracks are commonly observed in coatings and films.When structures with coatings are subject to stretching,opening mode cracks are likely to form on the surface,which may further lead to other forms of damage,such as interfacial delamination and substrate damage.Possible crack forms include cracks extending towards the interface and channeling across the film.In this paper,a two-dimensional numerical model is proposed to obtain the structural strain energy at arbitrary crack lengths for bilayer structures under uniaxial tension.The energy release rate and structural stress intensity factors can be obtained accordingly,and the effects of geometry and material features on fracture characteristics are investigated,with most crack patterns being confirmed as unstable.The proposed model can also facilitate the analysis of the stress distribution in periodic crack patterns of films.The results from the numerical model are compared with those obtained by the finite element method(FEM),and the accuracy of the theoretical results is demonstrated.

基于FEM/BEM的燃料电池轿车结构声预测和控制

采用有限元(FEM)和边界元(BEM)联合的方法对燃料电池轿车车内结构声进行预测和控制研究,提出了基于FEM/BEM的车内结构声分析方法和流程,建立了车身有限元模型和声学边界元模型,施加实测的激振力计算声学响应,通过试验数据验证了仿真模型,并进行误差分析.提出板件声学贡献分析的指导原则,介绍板件贡献分析原理和方法,进行所关注频率的车身板件声学贡献分析.最后根据分析结果对车身板件采取约束阻尼处理等控制措施,通过虚拟验证改进结果,车内低频噪声明显降低,其中后座椅和前地板改进最明显,证明所提出方法的可行性,达到优化燃料电池轿车车内噪声的目的.

基于FDM/FEM的挤压铸造收缩缺陷数值模拟

建立了模拟挤压铸造凝固过程中收缩缺陷形成的有限差分/有限元计算模型,该模型包括了凝固过程中的潜热释放和体积收缩效应。在温度场模拟中采用了交替隐式算法,在应力场模拟中采用了热粘弹塑性本构模型。为验证模型的正确性,对A356铝合金挤压铸造凝固过程进行了模拟计算,模拟结果与实验结果一致。

梁端削弱形式对火灾下钢框架抗连续倒塌性能影响

为探究不同梁端削弱形式对火灾下钢框架结构抗连续倒塌性能影响,对中柱失效2层2跨钢框架梁-柱子结构进行常温下Pushdown加载试验,研究其竖向抗力曲线和破坏模态。试验结果表明:中柱失效钢框架结构主要依靠弯曲机制和悬链线机制抵抗外加荷载,且悬链线机制具有滞后性。随后在试验的基础上,通过ABAQUS建立二层平面钢框架模型,并对其展开常温下和火灾下的拟静力模拟,对出现的削弱型梁翼缘、二次削弱型梁翼缘、开洞梁腹板和开洞梁翼缘4种梁端削弱方式进行抗连续倒塌分析。有限元结果表明:削弱型梁翼缘和二次削弱型梁翼缘不论在常温还是高温下,都能提供比未削弱情况下的模型更高的结构竖向抗力和变形能力。较于其他梁端削弱形式,考虑悬链线效应,二次削弱型梁翼缘变形能力最好。

State of the art in finite element approaches for milling process:a review

Over a century,metal cutting has been observed as a vital process in the domain of manufacturing.Among the numerous available metal-cutting processes,milling has been considered as one of the most employable processes to machine a variety of engineering materials productively.In the milling process,material removal occurs when the workpiece is fed against a rotating tool with multiple cutting edges.In order to maximize the profitability of metal cutting operations,it is essential that the various input and output variable relationships are analyzed and optimized.The experimental method of studying milling processes is costly and time demanding,particularly when a large variety of elements such as cutting tool shape,materials,cutting conditions,and so on,are included.Due to these issues,other alternatives emerged in the form of mathematical simulations that employ numerical methods.The finite element approaches have well-proven to be the most practical and commonly utilized numerical methods.The finite element model(FEM)can be used to determine the various physical interactions occurring during the machining process along with the prediction of various milling characteristics,such as cutting forces,cutting temperature,stresses,etc.,with the help of milling inputs.In the present article,various research studies in the broad milling process domain practiced with numerous finite element approaches have been critically reviewed and reported.It further highlights the several experimental and finite element approaches-based research studies that attempted to analyze and optimize the overall performance of the different milling processes.In recent years,various investigators have explored numerous ways to enhance milling performance by probing the different factors that influence the quality attributes.Some of the studies have also been found to be focused on the economic impacts of milling and various process inputs that affect milling performance.Furthermore,various milling factors’impact on the performance characteristics are presented and critically discussed.The issues related to the recent improvements in tool-work interaction modeling,experimental techniques for acquiring various milling performance measures,and the aspects of turn and micro-milling with finite element-based modeling have been further highlighted.Among the various available classifications in the milling process as employed in industries,face milling is more strongly established compared to other versions such as end milling,helical milling,gear milling,etc.The final section of this research article explores the various research aspects and outlines future research directions.

Accurate 3D Reconstruction of Subject-Specific Knee Finite Element Model to Simulate the Articular Cartilage Defects

The biomechanical relationship between the articular cartilage defect and knee osteoarthritis (OA) has not been clearly defined. This study presents a 3D knee finite element model (FEM) to determine the effect of cartilage defects on the stress distribution around the defect rim. The complete knee FEM, which includes bones, articular cartilages, menisci and ligaments, is developed from computed tomography and magnetic resonance images. This FEM then is validated and used to simulate femoral cartilage defects. Based on the obtained results, it is confirmed that the 3D knee FEM is reconstructed with high-fidelity level and can faithfully predict the knee contact behavior. Cartilage defects drastically affect the stress distribution on articular cartilages. When the defect size was smaller than 1.00cm2, the stress elevation and redistribution were found undistinguishable. However, significant stress elevation and redistribution were detected due to the large defect sizes ( 1.00cm2). This alteration of stress distribution has important implications relating to the progression of cartilage defect to OA in the human knee joint.

A STUDY OF B-P UNIFIED VISCOPLASTIC CONSTITUTIVE MODEL

By combining the Bodner-Partom constitutive model and equivalent stressfunction, finite element methods and program on analyzing non-elastic deformation and stress forthermal viscoplastic material are studied in this paper, and it's the first time that this materialmodel is used in a kind of engineering software-MARC. Thermal viscoplastic behavior of hightemperature alloy GH536 specimen with gap is analyzed by this program. The research results show itis feasible to analyze thermal viscoplastic behavior of specimen or structure by applying B-P model.

Investigation of mechanical behaviour of a quasi-brittle material using Karagozian and Case concrete (KCC) model

The mechanical behaviour of a quasi-brittle material,i.e.Pietra Serena sandstone,was investigated both numerically and experimentally in order to build a reliable numerical modelling system applicable to more complex cases.The Karagozian and Case concrete(KCC)model was exploited as the material constitutive law and a new method to utilise this model for efficient and accurate simulation of quasibrittle materials is discussed.The capability of this model is evaluated by comparing the results of the numerical simulations with the corresponding experimental results,and the method itself is critically assessed.

基于Java的OOFEM框架模型研究

面向对象的有限元(OOFEM)通用框架的构造对于有限元算法和并行有限元的研究具有重要意义。该文利用Java和面向对象技术,初步实现了这种非线性有限元框架模型,并且对其理论基础、功能构造、类库实现和算法设计等进行了研究。算例表明:数值结果与理论值是吻合的,框架模型是正确的和可靠的。

An anisotropic constitutive model of geomaterials based on true triaxial testing and its application

Series of testing on coarse grained soils were carried out with a true triaxial testing apparatus. The loads were applied from the major principal and minor principal directions, respectively, to simulate the construction and water impounding process of a rock fill dam. The stress and strain relationships induced by the different loading methods were investigated. A remarkable stress-induced anisotropy under complex stress state was observed. Contrary to popular assumptions in traditional numerical analysis and constitutive models, it was found that different elastic modulus and Poisson ratio exist in different principal directions in rock fill dams. From the testing results, an anisotropic constitutive model based on Duncan-Chang nonlinear model is presented to overcome the limitations of axi-symmetric assumptions in conventional triaxial experiments and constitutive models. Both models were then applied in FEM analysis of an under-construction earth core high rock soil filled dam with the focus on hydraulic fracturing. The study reveals the major biases that exist when numerical analysis and constitutive models do not give serious consideration to the intermediate principal stress and anisotropy effects in soil rock built structures.

Analysis of sp Pillar Stability Experiment: Continuous thermo-mechanical model development and calibration

The paper describes an analysis of thermo-mechanical （TM） processes appearing during the Aspo Pillar Stability Experiment （APSE）. This analysis is based on finite elements with elasticity, plasticity and dam- age mechanics models of rock behaviour and some least squares calibration techniques. The main aim is to examine the capability of continuous mechanics models to predict brittle damage behaviour of gran- ite rocks. The performed simulations use an in-house finite element software GEM and self-developed experimental continuum damage MATLAB code. The main contributions are twofold. First, it is an inverse analysis, which is used for （1） verification of an initial stress measurement by back analysis of conver- gence measurement during construction of the access tunnel and （2） identification of heat transfer rock mass properties by an inverse method based on the known heat sources and temperature measurements. Second, three different hierarchically built models are used to estimate the pillar damage zones, i.e. elas- tic model with Drucker-Prager strength criterion, elasto-plastic model with the same yield limit and a combination of elasto-plasticity with continuum damage mechanics. The damage mechanics model is also used to simulate uniaxial and triaxial compressive strength tests on the ,Aspo granite.

Development and application of an interface constitutive model for fully grouted rock-bolts and cable-bolts

This paper proposes a new interface constitutive model for fully grouted rock-bolts and cable-bolts based on pull-out test results.A database was created combining published experimental data with in-house tests.By means of a comprehensive framework,a Coulomb-type failure criterion accounting for friction mobilization was defined.During the elastic phase,in which the interface joint is not yet created,the proposed model provides zero radial displacement,and once the interface joint is created,interface dilatancy is modeled using a non-associated plastic potential inspired from the behavior of rock joints.The results predicted by the proposed model are in good agreement with experimental results.The model has been implemented in a finite element method(FEM)code and numerical simulations have been performed at the elementary and the structural scales.The results obtained provide confidence in the ability of the new model to assist in the design and optimization of bolting patterns.

基于特征的多分辨FEM模型快速生成

为了提高有限元分析效率,对零件进行不同精度的有限元分析应该使用不同分辨的零件有限元网格(FEM)模型。针对这一需要,提出了一种基于特征的多分辨FEM模型快速生成方法。首先确定出零件所有特征之间的接口;然后对零件所包含的每一个设计特征和分析特征进行了以相关接口为约束的网格划分;最后根据不同的特征层次结构选择相应的特征及其网格组合产生零件不同分辨的FEM模型。实验结果表明该方法快速而有效。