Elasto-plastic Finite Element Method Research Articles

Study of Construction Method on Sole-Hole Double Deck Tunnel

2D elasto-plastic finite element method was adopted to analyze the forced state of the surrounding rock and the tunnel lining in every step of the construction project for Fulongping double-decked tunnel. In the analysis,Mohr-Coulombs yield criterion was employed incoporating associated flow law to account for the elasto-plastic characteristics of materials. The tangent stiffness method was adopted to solve the equation of equilibrium, and the stresses which exceeded yielded point were adjusted.

Design of Virtual Prototype for Cold Roll Forming Machine of Side Panel of Engineering Vehicles and Numerical Simulation of the Forming Process

In this paper, based on the engineering vehicle’s side plate cold roll forming machine developed by a company, we use 3D solid modeling software Solid Works to complete the establishment of a 3D model. On the basis of explicit dynamics elastoplastic finite element method basic theory, we make numerical simulation analysis of the metal plate’s forming process by using ANSYS/LS-DYNA module. According to the simulation results, we make repeated adjustment and optimization on its pass system and parameters. Through the numerical simulation of the forming process, we conclude the stress-strain distribution of the sheet metal. For similar products, the result has a certain reference value to the research of cold roll forming process and the design of cold roll forming equipments.

Simulation of Microstructure Evolution and Deformation Behavior for Dual-Phase Steel by Multi-Phase-Field Method and Elastoplastic Finite Element Method

A coupled simulation method is developed by using a Multi-Phase-Field (MPF) method that is recognized as a powerful numerical method for simulating microstructure formation in material and ElastoPlastic Finite Element Analysis (EP-FEA) based on a homogenization method. We apply the developed simulation method to investigate the deformation behavior of DP steel that includes various volume fractions and morphologies of the ferrite (α) phase. To obtain morphological information on the α phase of DP steel, we performed MPF simulation of austenite-to-ferrite (γ → α) transformation during continuous cooling transformation. MPF simulation gives us the digital image of the distribution of the simulated α phase. Furthermore, we model the representative volume element, which describes the DP microstructure, on the basis of the obtained morphology of the α phase, and perform tension-compression testing of DP steel, including the simulated α phase. Through these simulations, it is confirmed that the developed simulation method enables us to clarify the effect of the volume fraction and the configuration of the α phase on macroscopic deformation behavior of DP steel, such as the Bauschinger effect.

Numerical Analysis of Bi-Adhesive Boded Single Lap Composite Joint with Mechanics Analysis

The effect of dual adhesives with different length ratio on the stress distributed in adhesively bonded single lap steel joint was investigated using elasto-plastic finite element method (FEM). The results from the numerical simulation showed that the peak stress along the bondline moves from the ends of the overlap to the middle part of lap zone. Compared with the results from the mono-adhesive system, appropriate bond-length ratios is beneficial to optimize the stress distribution and it is 0.4 for bi-adhesive bonded single lap composite joint.

Effect of the Metal Block on the Stress Distributed in the Adhesively Bonded Single Lap Steel Joint

The effect of 4 mm long metal block bonded to the end of the overlap zone on the stress distributed in adhesively bonded single lap steel joint was investigated using elasto-plastic finite element method (FEM). The results from the numerical simulation showed that the stress is varied a little when the joints with a couple of 4 mm long metal block adhered to both ends of the over lap or with a couple of adhesive fillet. Compared to the joint without the metal block, it is advantageous of reducing the peak stress in the adhesive layer near the ends of the lap zone in adhesively bonded single lap steel joints but its effect is less than that of the joint with a couple of adhesive fillet. There is no evidential difference in the effects between the steel and aluminum block.

The Numerical Simulation of the Crack Elastoplastic Extension Based on the Extended Finite Element Method

In the frame of the extended finite element method, the exponent disconnected function is introduced to reflect the discontinuous characteristic of crack and the crack tip enrichment function which is made of triangular basis function, and the linear polar radius function is adopted to describe the displacement field distribution of elastoplastic crack tip. Where, the linear polar radius function form is chosen to decrease the singularity characteristic induced by the plastic yield zone of crack tip, and the triangle basis function form is adopted to describe the displacement distribution character with the polar angle of crack tip. Based on the displacement model containing the above enrichment displacement function, the increment iterative form of elastoplastic extended finite element method is deduced by virtual work principle. For nonuniform hardening material such as concrete, in order to avoid the nonsymmetry characteristic of stiffness matrix induced by the non-associate flowing of plastic strain, the plastic flowing rule containing cross item based on the least energy dissipation principle is adopted. Finally, some numerical examples show that the elastoplastic X-FEM constructed in this paper is of validity.

Effect of Metal Block on Stress Distribution in Weld-Bonded Steel Joint

The effect of metal block as the fillet on the stress distributed in weld-bonded single lap steel joint was investigated using elasto-plastic finite element method (FEM). The results from the numerical simulation showed that it is beneficial when the joints with a couple of right triangle metal block were adhered to both ends of the over lap. It is advantageous of reducing the peak stress in the adhesive layer near the ends of the lap zone in weld-bonded single lap steel joints so that the stress distribution in overlap zone was improved. The load-bearing capacity of the weld-bonded single lap steel joints may be elevated. There is no evidential difference in the effects between the steel and aluminum block.

Investigation on blanking of thick sheet metal using the ductile fracture initiation and propagation criterion

In metal forming processes such as sheet blanking, severe plastic deformation localizes in a narrow shear band near blanking clearance, and ductile fracture occurs at the final stage. Because the combinations of large nonlinear strain localization, displacement discontinuity and ductile fracture brought obstacles to numerical simulation, a ductile fracture initiation criterion model and an elasto-plastic finite element method (FEM) were presented to simulate localized severe plastic deformation. Initiation and propagation of cracks were treated by deletion-and-replacement approach. The distributions and developing trends of effective strain and damage were predicted, the influence of blanking clearance on fracture was discussed, and an experiment was performed to explore the forming mechanism.

Failure model of soil around enlarged base of deep uplift piles

This paper presents an investigation into the failure behaviours of low-cohesive (c ≤ 10 kPa) or non-cohesive (c = 0) soils around the enlarged bases of deep uplift piles. An axisymmetric elasto-plastic finite-element method is used for analysing displacements and plastic strains in the soil–pile system induced by uplifting. Numerical results are examined in detail to reveal the relationships of the accumulated equivalent plastic strain contours in soils and the uplift displacements of piles with the diameters of enlarged bases. The investigation finds that for the pile to reach ultimate uplift failure, the pile has to experience a large upward displacement. A serviceability failure limit of pile upward displacement equal to 10% of pile shaft diameter is adopted for determining pile uplift resistance capacity. At serviceability failure limit, examination of the accumulated equivalent plastic strain contours in the soils leads to the establishment of two logarithmic spiral functions for the estimation of the plastic zone envelope and the slip surface around the enlarged base. The plastic zone envelopes and slip surfaces are axisymmetrical, peach-shaped, closed and curved surfaces, completely beneath the ground surface. The models and functions have been used to formulate analytical solutions for estimating uplift resistance capacity for deep piles with enlarged bases.

Stress integration schemes for novel homogeneous anisotropic hardening model

Numerical formulations and implementation of stress integration algorithms in the elasto-plastic finite element method are provided for the homogeneous yield function-based anisotropic hardening (HAH) model. This model is able to describe complex material behavior under non-monotonic loading conditions. Two numerical algorithms based on the semi-explicit and fully implicit schemes are compared in terms of accuracy. To efficiently treat the yield locus distortion when the strain path changes, a multi-step Newton–Raphson method is proposed to calculate the first and second derivatives of the HAH yield surface. For the validation of the developed numerical algorithms, the r-value anisotropy is compared for the conventional yield model with classical isotropic hardening and for the HAH model. Moreover, detailed error analysis is presented using iso-error maps. The results show that the fully implicit stress integration algorithm based on the closet point projection method leads to better accuracy in general. However, the semi-explicit algorithm also provides comparable accuracy if an appropriate time increment is chosen. Furthermore in spite of the yield surface distortion, the developed numerical algorithms can successfully update stress with the equivalent level of the error for the conventional yield model.

2D and 3D finite element analysis of crack growth under compressive residual stress field

In the present study, plasticity induced crack closure (PICC) concept and three dimensional (3D) finite element method (FEM) were used to study the effect of compressive residual stress field on the fatigue crack growth from a hole. Furthermore, a new methodology on the basis of a correction factor was presented to increase the PICC precision. The result obtained was compared to two dimensional (2D) FEM, superposition method and Liu’s experimental data. To simulate the elasto-plastic behavior of the material, isotropic hardening was assumed and the Von-Mises yield criterion was implemented. A 3D mesh was built using eight-node hexahedral elements and one half of the specimen was modeled. The simulation results were fairly well correlated with experimental data. Furthermore, the 3D elasto-plastic FEM predicted a slightly smaller fatigue life than a 2D plane stress FEM. Applying the modified PICC method reduces the 3D FEM fatigue life prediction errors.

Effect of Temperature on the Thermal Stress in the Single Lap Joint

The effect of the thermal shock temperature on the thermal stress distributed in the adhesively bonded steel single lap steel joint under a 10 s thermal shock was investigated using elasto-plastic finite element method (FEM). The results showed that both the highest temperature at the surface and the lowest one at the mid-bondline increases as the temperature of the thermal shock raised (80 C to 140 C) and all the peak values of the stresses at the mid-bondline and the zone of negative Sx in adherend increased as the temperature of the thermal shock elevated.

The Analysis of Fu Longping Double-Decked Tunnel with 3D Finite Element

The article analyzed the forced state of the surrounding rock and the tunnel lining for Fu longping double-decked tunnel by the Elasto-plastic finite element method. In the analysis, DP’s yield criterion was employed for the elasto-plastic characteristics of materials. It studied the construction method with the theory, and guided the construction for the double-decked tunnel ,too.

Three-dimensional strength-reduction finite element analysis of slopes: geometric effects

The vast majority of slopes, both natural and constructed, exhibit a complex geometric configuration and three-dimensional (3D) state, whereas slopes satisfying the assumption of plane strain (infinite length) are seldom encountered. Existing research mainly emphasizes the 3D dimensions and boundary effect in slope stability analysis; however, the effect of complex geometric ground configuration on 3D slope stability is rarely reported. In this paper, an elastoplastic finite-element method using strength-reduction techniques is used to analyze the stability of special 3D geometric slopes. A typical 3D slope underlain by a weak layer with groundwater is described to validate the numerical modeling, safety factor values, and critical slip surface for the 3D slope. Furthermore, a series of special 3D slopes with various geometric configurations are analyzed numerically, and the effects of turning corners, slope gradient, turning arcs, and convex- and concave-shaped surface geometry on the stability and failure characteristics of slopes under various boundary conditions are discussed in detail.

Slope Stability Analysis by SSR Based on Connectivity of Plastic Zone Failure Criterion

While the elasto-plastic finite element method based on the shear strength reduction(SSR) technique is employed to analyze slope stability, the overall factor of safety computed numerically is，in a certain degree，dependent on the failure criteria used for evaluating critical instability condition of slope. In the present paper, the connectivity of plastic zone criterion is chosen with its close physical meaning to the LEM , and the farther 3D critical slip surface searching procedure is presented. The results of stability analysis of a certain initial quarry slope show that the chosen failure criterion and the 3D critical slip surface searching procedure is reasonable and can be widely applied to slope engineering practice．

Effect of Shock Time on the Thermal Stress in the Single Lap Joint

The effect of the thermal shock time on the thermal stress distributed in the adhesively bonded steel single lap steel joint under a 100 C thermal shock was investigated using elasto-plastic finite element method (FEM). The results showed that the temperature is symmetrically distributed to the bondline in the overlap region and the lowest one at the mid-bondline increases as the time of the thermal shock elongated (4 s to 40 s). And all the peak values of the stresses at the mid-bondline and the zone of negative Sx in adherend decreased as the time of the thermal shock elongated.

Press cutting of thin-walled round pipe for producing curvilinear end

In order to obtain a basic understanding of the unwanted distortions in the pipe wall during the press cutting process, the deformation of a thin-walled round pipe to form a curvilinear end was numerically and experimentally studied. Vector analysis was used to study the relationship between the punch shape and the collapse of the cut-end. Stamping experiments on AISI 1020 steel pipe were conducted using different angles α and β defining the shape of the punch. The elasto-plastic finite element method that allows consideration of a ductile fracture was also employed to study the process. The results show that the deformation of the pipe end after press cutting is influenced mostly by the shape of the punch. A satisfactory quality of the curvilinear end of the pipe can be obtained if the appropriate geometric parameters of the punch are chosen. The pipe-wall collapse in the upper part of the section is decreased when α and β increase. The recommended values for α and β lie within 30°–50°. The hole on the underside of the punch has less influence on the quality of the cut-end, and the wall distortion and the generation of burr on the cut-end can be satisfactorily simulated using the fracture criterion of Brozzo or the normalized criterion of Cockcroft and Latham.

OS0105 弾塑性有限要素法による浸炭焼入鋼の残留応力解析

OS0105 弾塑性有限要素法による浸炭焼入鋼の残留応力解析

地中構造物の耐震補強効果に関する地盤改良体の引張軟化特性を考慮した定量的評価

近年では地中構造物の耐震補強として，構造物周辺地盤を固化改良する方法が検討されている．しかし，固化改良体を設計する場合には通常弾性体として取り扱っており，レベル2地震動を想定した場合には，引張応力による損傷などを考慮した方が合理的な設計が可能である．そのため，改良土の強度が小さい粘性土地盤を対象とした土槽載荷試験を実施し，地盤との相互作用を考慮した場合の改良体の補強効果や破壊挙動について明らかにした．また，固化改良体の引張軟化特性を考慮した弾塑性FEM解析により，土槽載荷試験における地盤，改良体および構造物の変形挙動を再現できることを示し，より合理的な設計方法に用いるべき解析手法を示した．さらに，この引張軟化特性を考慮した弾塑性FEM解析を用いた地震応答解析を実大構造物に対して実施し，実大レベルでの改良体による耐震補強効果について検討を行った．

Fatigue Modeling of a Notched Flat Plate Under Variable Amplitude Loading Supported by Elastoplastic Finite Element Method Analyses

Although intensive research has been carried out to understand the fatigue behavior of steel notched components, under variable amplitude loading, no definite and general robust models have been derived so far. Therefore, every effort to augment the knowledge in this topic is welcomed. Within this context, existing variable amplitude data, derived by the authors for a notched low carbon pressure vessel steel (P355NL1) flat plate, is used to assess a local approach to fatigue. A linear damage summation framework, supported by elastoplastic finite element analyses, is used. Several variable amplitude loadings were selected and analyzed, using alternative configurations of kinematic hardening plasticity models (e.g., Chaboche’s model with distinct constants superposition). The predictions are assessed using available experimental data and data derived with simplified empirical elastoplastic tools. This paper highlights the difficulties of performing such elastoplastic analysis and compares the obtained results with those obtained using more classical tools for elastoplastic analysis (Glinka and Seeger–Heuler). It was found that fatigue predictions based on an elastoplastic finite element analysis, made using the Chaboche’s model, were significantly more accurate than predictions based on simplified elastoplastic analysis. These results have important practical relevance.