Three-dimensional Elasto-plastic Finite Element Research Articles

Falling-weight impact response for prototype RC type rock-shed with sand cushion

In this paper, a prototype model of reinforced concrete (RC) type rock-shed is numerically examined by means of three-dimensional elasto-plastic finite element based model of RC rock-shed structure, having sand cushion, against the impact of 10 ton heavy weight. This study is undertaken in order to improve the knowledge for establishing a rational performance-based impact resistant design procedure for the RC type rock-sheds. Following results are obtained from this study: (1) the model fails in the punching shear mode when surcharged at the center of roof slab; and (2) the impact resistant capacity of the free edges of the model is greater than that at the center, as the free edges can behave more flexibly and absorb more impact energy in comparison with the center of the roof slab.

Finite Element Simulation of Shielding/Intensification Effects of Primary Inclusion Clusters in High Strength Steels Under Fatigue Loading

The change of potency to nucleate cracks in high cycle fatigue (HCF) at a primary nonmetallic inclusion in a martensitic gear steel due to the existence of a neighboring inclusion is computationally investigated using two-and three-dimensional elastoplastic finite element (FE) analyses. Fatigue indicator parameters (FIPs) are computed in the proximity of the inclusion and used to compare crack nucleation potency of various scenarios. The nonlocal average value of the maximum plastic shear strain amplitude is used in computing the FIP. Idealized spherical (cylindrical in 2D) inclusions with homogeneous linear elastic isotropic material properties are considered to be partially debonded, the worst case scenario for HCF crack nucleation as experimentally observed for similar systems (Furuya et al., 2004, “Inclusion-Controlled Fatigue Properties of 1800 Mpa-Class Spring Steels,” Metall. Mater. Trans. A, 35A(12), pp. 3737–3744; Harkegard, 1974, “Experimental Study of the Influence of Inclusions on the Fatigue Properties of Steel,” Eng. Fract. Mech., 6(4), pp. 795–805; Lankford and Kusenberger, 1973, “Initiation of Fatigue Cracks in 4340 Steel,” Metall. Mater. Trans. A, 4(2), pp. 553–559; Laz and Hillberry, 1998, “Fatigue Life Prediction From Inclusion Initiated Cracks,” Int. J. Fatigue, 20(4), pp. 263–270). Inclusion-matrix interfaces are simulated using a frictionless contact penalty algorithm. The fully martensitic steel matrix is modeled as elastic-plastic with pure nonlinear kinematic hardening expressed in a hardening minus dynamic recovery format. FE simulations suggest significant intensification of plastic shear deformation and hence higher FIPs when the inclusion pair is aligned perpendicular to the uniaxial stress direction. Relative to the reference case with no neighboring inclusion, FIPs decrease considerably when the inclusion pair aligns with the applied loading direction. These findings shed light on the anisotropic HCF response of alloys with primary inclusions arranged in clusters by virtue of the fracture of a larger inclusion during deformation processing. Materials design methodologies may also benefit from such cost-efficient parametric studies that explore the relative influence of microstructure attributes on the HCF properties and suggest strategies for improving HCF resistance of alloys.

Design approach to a method for reinforcing existing caisson foundations using steel pipe sheet piles

This paper proposes a steel pipe sheet pile (SPSP) reinforcement method for existing caisson foundations in water. The technique involves driving SPSPs around the caisson foundation and connecting them to it with reinforcing footing. To support the rational design of reinforcements using this method, the following factors influencing the technique׳s effectiveness and related mechanical behavior should be considered: (1) the conditions of the caisson/SPSP reinforcement footing connection; (2) the caisson/SPSP flexural rigidity ratio; (3) the distance between the caisson and the SPSP wall; and (4) the pile length. However, as the influence of these factors on the reinforcement effect and mechanical behavior has not yet been clarified, the current method has no standardization for the concept of the load transfer mechanism in reinforced foundation systems, and the ultimate lateral bearing capacity of existing caissons has been largely ignored in previous construction. This paper describes centrifuge model tests and three-dimensional elasto-plastic finite element total stress analysis conducted in relation to real cases in order to identify a more effective and rational reinforcement structure. The static lateral bearing capacity and seismic performance of reinforced foundations were investigated, and the following factors were considered: (1) the conditions of the caisson/SPSP reinforcement footing connection; (2) the caisson/SPSP flexural rigidity ratio; and (3) the pile length. Finally, a structural design flow is proposed based on the experimental and numerical simulation results. A chart to facilitate determination of appropriate reinforcement structures is also presented.

Springback prediction for incremental sheet forming based on FEM-PSONN technology

In the incremental sheet forming (ISF) process, springback is a very important factor that affects the quality of parts. Predicting and controlling springback accurately is essential for the design of the toolpath for ISF. A three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the process and the simulated results were compared with those from the experiment. The springback angle was found to be in accordance with the experimental result, proving the FEM to be effective. A coupled artificial neural networks (ANN) and finite element method technique was developed to simulate and predict springback responses to changes in the processing parameters. A particle swarm optimization (PSO) algorithm was used to optimize the weights and thresholds of the neural network model. The neural network was trained using available FEM simulation data. The results showed that a more accurate prediction of springback can be acquired using the FEM-PSONN model.

Dimensional Changes by Heat Treatment of Helical Gear

The dimensional change of tooth profile by heat treatment of helical gear was investigated by experimental and numerical approaches. Especially, the three-dimensional elasto-plastic finite element (FE) simulation was adopted to analyze the elastic deformation during load, unloading, ejecting of workpiece. Quenching simulation was also carried out to investigate the change of tooth profile on the forged gear. In experiments, the amount of elastic deformation of the forged gear was quantitatively determined by comparing the tooth profiles on the forged gear and die. The dimensional change of the forged gear tooth after quenching was also evaluated from the comparision of the cold forged and quenched gear teeth. From experimental works, it was found that the amounts of dimensional changes after forging and quenching of helical gear are 10 and 10 μm, respectively.

Assessment of three-dimensional crack growth in ductile layered material systems

Fatigue crack growth in three-dimensions may follow complex patterns that depend on the local and global conditions of the material around the crack front. In layered material systems, crack growth may be enhanced or delayed over portions of the crack front as the latter approaches a dissimilar layer. Three-dimensional elasto-plastic finite element analyses were developed for the study of the effects of dissimilar layers ahead of the crack front on the crack driving force (crack tip opening displacement) and crack growth; the simulation of the latter was based on previous experimental data obtained from a fatigued specimen with identical tri-layer architecture. The efficiency of the model under elastic conditions was first assessed by comparison of its predictions with an exact analytical solution. Crack growth in the top layer was simulated up to a depth of around 95% of its thickness. The modelling was based on a re-meshing scheme and was applied to bi-layer and tri-layer architectures subjected to three-point bending. The crack front was positioned as close as possible to the dissimilar layer so that shielding and anti-shielding effects would be clearly observed. These three-dimensional simulations revealed that such effects are less intense than those predicted by previous 2D analyses that assumed through-width cracks.

Effects of the ring-cut method as a settlement deterrent in a soft ground tunnel

This paper presents the results of centrifugal model tests and three-dimensional elasto-plastic finite element analyses carried out to clarify the effects of the ring-cut method on the restraint of the ground settlements ahead of a tunnel face. A model tunnel is excavated in a soft ground by a robot under a centrifugal loading state, and the ground settlements are measured during the progress of the face by a picture analysis system with high accuracy. The settlements generated by the full-face excavation method are compared with those generated by the ring-cut method for two kinds of grounds with different mechanical properties. The maximum settlement caused by the ring-cut method becomes about 36% of that caused by the full-face excavation method for the ground with low strength and about 58% for the ground with high strength. Considerations regarding these phenomena are given by conducting three-dimensional elasto-plastic finite element analyses.

Applicability of the Impact Response Analysis Method for Reinforced Concrete Beams Mixed with Polyvinyl Alcohol Short Fibers

Abstract The impact-resistant capacity of reinforced concrete (RC) structures can be rationally upgraded by mixing polyvinyl alcohol (PVA) short fibers into concrete. The static and dynamic post peak residual tensile strength of the concrete that occurs because of the bridge effects of PVA short fibers. In this paper, to establish a simple impact response analysis method for RC structures under impact loading, a method that treats PVA short fibers mixed into concrete as shell elements of PVA plates with an equivalent tensile strength to the post peak residual tensile strength of the concrete is proposed. The applicability of the method has been investigated by conducting a three-dimensional elastoplastic finite element analysis using LS-DYNA code and comparing the results with the falling-weight impact test results for RC beams. From this study, it was confirmed that the crack distributions and the failure mode of RC beams mixed with PVA short fibers can be predicted and that the effects of mixing PVA short fibers on improving the impact resistant capacity can be estimated by using the proposed numerical analysis method.

Study on the Vertical Rational Structure of Tunnel Lining in the Fault-Rupture Zone

Related to the actual project in the new Qi Daoliang tunnel between Lanzhou and Lintao highway, select 300-meter calculation range along the tunnel vertically including fault-rupture zone and effect fault-rupture zone, utilize 8 -node, 6-plane block element to scatter the calculating range, at the same time, use the deduced 8 -node, three dimensional jointed element to imitate the transformation gap of the tunnel lining, employ three-dimensional elasto-plastic static finite element program to analyze stress and transformation state of surrounding rock and lining in different construction stages of the new Qi Daoliang tunnel. Through the analysis and comparison of the calculation result of the three conditions: not placing transformation gap through, placing one transformation gap in the middle of the fault-rupture zone, placing two transformation gaps in the beginning and the end of the fault-rupture zone etc, we can get the following points: ①The gallery transformation in the fault-rupture zone and the plastic area in the surrounding rock are obviously bigger than the non-fault-rupture zone. ②Owing to the effect of fault-rupture zone, the increasing range of internal force of the initial support and twice lining is about 10% to 30%. ③Placing the transformation gap in the fault-rupture zone can obviously play a role in releasing lining internal force and transformation energy in the surrounding rock. ④In the start and end changing point of fault-rupture zone, the transformation gap should be placed in the tunnel lining.

Stability Analysis of a 3D Vertical Slope with Transverse Earthquake Load and Surcharge

The stability and failure mode for a 3D vertical slope with transverse earthquake load and surcharge have been an interesting issue, especially in building excavation and wharf engineering. In order to further reveal the seismic and surcharge effect, a three-dimensional elasto-plastic finite element(FE) code combined with a strength reduction procedure is used to yield a factor of safety and failure mode for a vertical slopes under two horizontal direction pseudo-static(PS) coefficient and surcharge on the slope top, respectively. Comparative studies are carried out to investigate the effect of seismic coefficient, surcharge intensity and location on the stability and the failure mechanism for a 3D vertical slope including an inclined weak layer. Several important findings are also achieved.

The Thermal-Mechanical Coupled FEM Analysis on 3-Roll Continual Tube Rolling PQF Deformation Process

Based on the characteristics of PQF deformation process, a thermal-mechanical coupled model of this process is established by the three-dimensional elasto-plastic finite element method. The simulation according to practical rolling process of a certain factory is completed. Some important parameters such as the finished size of the rolled product, the temperature variation curves of the key nodes on the tube, the rolling force and torque of each roller are predicted during this simulation. Comparison between simulation solutions and experiment results shows a good agreement, which means this model is capable of simulating PQF deformation process as well as forecasting product quality.

An applicability of dynamic response analysis of shear-failure type RC beams with lightweight aggregate concrete under falling-weight impact loading

In order to establish a simple and rational impact response analysis method for lightweight aggregate reinforced concrete (RC) beams, three-dimensional elasto-plastic finite element analysis was conducted for shear-failure type RC beams under falling-weight impact loading. The, tensile strength of concrete was assumed as 1/16th of the compressive one. An applicability of the proposed analysis method was confirmed by comparing with the experimental results of twelve beams. From this study, following results were obtained: (1) three response wave configurations: impact force; reaction force; and mid-span displacement, and crack patterns can be rationally predicted by using proposed analysis method; and (2) maximum response values of impact force, reaction force, and displacement can be estimated considering 20, 20, and 10% safety margin, respectively.

Studies on the Springback Mechanism of Incremental Sheet Forming Based on FEM Simulation

Incremental sheet forming (ISF) is an innovative and highly flexible sheet metal forming process for small batch production and prototyping, but springback is a very important factor to influence the quality of incremental sheet forming. This paper investigates the springback mechanism of incremental sheet forming using numerical method. A three-dimensional elasto-plastic finite element model was established for the simulation of the incremental sheet forming process. In this model, the combination of dynamic explicit algorithm and the static implicit algorithm was proposed to calculate the whole forming process including springback. The results of numerical simulation, such as, the strain history and distribution, the stress state and distribution, etc., are discussed in details. Moreover, the results confirm that residual stress has been releasing during forming process, which reveal the peculiar springback characteristic of incremental sheet forming process.

Numerical simulation and experimental investigation of incremental sheet forming process

In order to investigate the process of incremental sheet forming (ISF) through both experimental and numerical approaches, a three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the process and the simulated results were compared with those of experiment. The results of numerical simulations, such as the strain history and distribution, the stress state and distribution, sheet thickness distribution, etc, were discussed in details, and the influences of process parameters on these results were also analyzed. The simulated results of the radial strain and the thickness distribution are in good agreement with experimental results. The simulations reveal that the deformation is localized around the tool and constantly remains close to a plane strain state. With decreasing depth step, increasing tool diameter and wall inclination angle, the axial stress reduces, leading to less thinning and more homogeneous plastic strain and thickness distribution. During ISF, the plastic strain increases stepwise under the action of the tool. Each increase in plastic strain is accompanied by hydrostatic pressure, which explains why obtainable deformation using ISF exceeds the forming limits of conventional sheet forming.

Die Design of a Back Panel for a PDP TV Using 3-D Elasto-Plastic Finite Element Analysis

The objective of this research work is to design optimally dies and the blank sheet for manufacturing of the back panel of a PDP TV. The influence of design parameters of the dies and the blank sheet on the formation of wrinkling in the upper trimming area of the stamped part has been quantitatively investigated through three-dimensional elasto-plastic finite element analysis. The corner radius of the upper trimming area of the die and the blank gap, which is the distance from the outer line of the blank holder to that of the blank, have been chosen as design parameters to remove wrinkling associated with a stamping part in a upper trimming area. From the results of the analyses, it has been shown that a product without wrinkles and skid lines can be manufactured when the corner radius is 8 mm and the blank gap is 60 mm. Several stamping tests have been performed using the manufactured die set and the blank sheet according to the proposed optimum design. From the results of the stamping tests, it has been shown that a back panel of the PDP TV can be successfully manufactured using the proposed optimum design condition.

Influence of thickness and number of dielectric layers on residual stresses in micromultilayer ceramic capacitors

The residual stresses due to high-temperature processing in micromultilayer ceramic capacitors (MLCCs) with various thicknesses and numbers of dielectric ceramic layers were investigated by using a three-dimensional elastoplastic finite element model with temperature-dependent material properties taken into account. For comparison, an explicit analytical solution for the in-plane residual stress in the dielectric ceramic layer was derived. Both the numerical results and the analytical model showed that the thickness ratio of the dielectric layer to electrode layer has a dominant impact on the residual stress states. There exists a critical thickness for the dielectric ceramic layer in MLCCs in the case of a given thickness of the electrode layer, below which both high tensile out-of-plane stresses and high compressive in-plane stresses could cause the cracking of the brittle dielectric layers near the electrode tips and/or the debonding of the electrode/dielectric interface.

Tool design for the tubular press forming of a rear suspension member with the finite element analysis

Tool design is carried out for a press forming of a tubular axle in the rear suspension assembly based on the result of the finite element analysis. The analysis incorporates a three-dimensional elasto-plastic finite element method with the explicit time integration scheme by using LS-DYNA3D. The analysis simulates the two-stage stamping process and it fully evaluates the deformation mechanism by forming and springback. With the trial tool shape, simulation is performed in order to investigate failure by wrinkling, shape inaccuracy and the local deformation. This paper identifies such unfavourable mechanism in the tubular press forming and proposes a new tool design with a guideline for modification in the design of the process and sequential tool shapes. The finite element analysis result with the improved tool design confirms that the proposed design not only reduces the possibility of failure, but also improves the quality of a formed product.

An analysis of forming limit in the elliptic hole-flanging process of sheet metal

Abstract A methodology for formulating a three-dimensional elasto-plastic finite element model, which is based on Prandtl-Reuss flow rule and Hill's yield criterion, respectively, associates with an updated Lagrangian formulation, is developed to simulate the elliptic hole-flanging process. An extended r-minimum algorithm is proposed to formulate the boundary condition, such as the yield of element, maximum allowable strain increment, maximum allowable rotation increment, maximum allowable equivalent stress increment, and tolerance for nodes getting out of contact with tool. The fractured thickness of a specimen in simple tension test is adopted as the fracture criterion in simulation. The numerical simulation results include relationship between punch load and punch displacement, variation of the workpiece thickness, distribution of stress, distribution of strain, and limit forming ratio. The finite element model is developed to simulate anisotropic of the elliptic hole-flanging process. The accuracy of the finite element program is based on a comparison between the simulation and experiment outcomes. According to the experimental data, the prediction of the phenomenon of necking of the elliptic hole-flanging process occurs at the inner periphery of elliptic hole is studied. The simulation dearly demonstrates the efficiency of the model to simulate the elliptic hole-flanging process. This study has provided an improved understanding of the elliptic hole-flanging process for improving the manufacturing processes and the design of tools.

Analysis of subsurface crack propagation under rolling contact loading in railroad wheels using FEM

A general subsurface crack propagation analysis methodology for the wheel/rail rolling contact fatigue problem is developed in this paper. A three-dimensional elasto-plastic finite element model is used to calculate stress intensity factors in wheels, in which a sub-modeling technique is used to achieve both computational efficiency and accuracy. Then the fatigue damage in the wheel is calculated using a previously developed mixed-mode fatigue crack propagation model. The advantages of the proposed methodology are that it can accurately represent the contact stress of complex mechanical components and can consider the effect of loading non-proportionality. The effects of wheel diameter, vertical loading amplitude, initial crack size, location and orientation on stress intensity factor range are investigated using the proposed model. The prediction results of the proposed methodology are compared with in-field observations.

Development and Validation of Novel FE Models for 3D Analysis of Peening of Strain-Rate Sensitive Materials

In this paper, we provide two different symmetry cells to describe the shot-peening process. In this multiple impingement model, we study the dynamic behavior of TI-6Al-4V targets subjected to a large number of shots. Three-dimensional elastoplastic finite element analysis (FEA) of the process was conducted using these two symmetry cells for strain-rate sensitive targets and rigid shots. The basic symmetry cell is assigned a target surface area C×C, where C is one half of separation distance between adjacent shots. The second “enhanced” symmetry cell is assigned a target surface area 2C×2C thus allowing higher density of impact point locations. Average residual stresses inside the target predicted by FEA were compared with experimental measurements using the hole-drilling technique. In order to do this, a new averaged technique was developed to obtain the stress distribution inside the symmetry cell. The results reveal that both symmetry cell models could be used for shot-peening modeling. However, the use of the enhanced symmetry cell leads to a better agreement with the measured residual stresses. In addition, the enhanced symmetry cell model allowed us to overcome some of the shortcomings of the basic symmetry cell for cases involving high peening velocity and intensity.