Three-dimensional Elasto-plastic Finite Element Analysis Research Articles

Finite element analyses of burst capacities of corroded pipelines containing pinhole-in-corrosion defects

This study carries out extensive parametric three-dimensional elasto-plastic finite element analysis to evaluate the burst capacity of oil and gas pipelines containing pinhole-in-corrosion (PIC) defects. The analysis results reveal that the burst capacity of the PIC defect is insensitive to the pinhole diameter but largely affected by the depth of the pinhole and length of the general corrosion. A pinhole located at the centre of the general corrosion is found to have a larger impact on the burst capacity than the same pinhole located near the edge of the general corrosion. The observed size and location effects on the burst capacity are attributed to the bulging deformation of a corroded pipeline under internal pressure. The findings of this study provide the basis for developing a practical, accurate engineering burst capacity model for PIC defects.

Elastoplastic Analysis of Timber Connections with Dowel-Type Fasteners at Ambient and High Temperatures

Three-dimensional elastoplastic finite element (FE) analysis models considering a damage zone and cleavage were developed, including plastic behavior of embedment tests parallel and perpendicular to the grain at ambient and high temperatures, in order to study the embedment behavior of timber. In a numerical analysis of compression tests to define material properties of timber, the post-yield behavior of the X-axis in the axial direction was larger than the test values when the post-yield slope of the test result were set to the plastic modulus. The reason was that the stress on the Y-axis and Z-axis increased after the yield point; thus, the equivalent yield stress decreased. In the numerical analysis of the embedment tests, the effect of the damage zone must be considered in the analytical models because the initial stiffness of the numerical results in compression parallel to the grain was considerably higher than that of the test results when the damage zone was not considered. In the numerical analysis of the embedment tests in compression perpendicular to the grain, the two models reproduced the stiffness and behavior after the yield point of the test results. The model that considered cleaving showed the stress distribution after cleavage.

Interaction Assessment of Diagonally Spaced Identical Corrosion Defects and Fully Aligned Unequal-Sized Corrosion Defects Under Combined Loads

Abstract In this study, the interaction effects of closely spaced corrosion defects on the burst capacity of oil and gas pipelines under combined internal pressure and longitudinal compression are investigated by using parametric three-dimensional elasto-plastic finite element analyses. Full-scale burst tests reported in the literature are used to validate the finite element model. It is observed that the interaction effects of diagonally spaced defects on the burst capacity are strongly related to the overlapping portion of the defect width or circumferential spacing between the two defects. The analysis results indicate that the strongest interaction between diagonally spaced defects under combined loads occurs if the defects have zero circumferential separation. The interaction weakens as the defects are more and more overlapped or separated circumferentially. It is also observed that the interaction effect associated with longitudinally or circumferentially aligned, unequal-sized corrosion defects is negligible under the internal pressure only or combined loads.

Assessment of the interaction of corrosion defects on steel pipelines under combined internal pressure and longitudinal compression using finite element analysis

Extensive parametric three-dimensional elasto-plastic finite element analyses are carried out to investigate the interaction effect on the burst capacity of oil and gas pipelines containing closely-spaced corrosion defects under combined internal pressure and load-controlled longitudinal compression. The analysis considers two identical, semi-ellipsoidal-shaped corrosion defects aligned circumferentially or longitudinally on the pipeline. The analysis results reveal that the interaction between circumferentially-aligned defects under combined loads is marked: the burst capacity corresponding to the two-defect case can be lower than that corresponding to the single-defect case by as much as 18% as a result of the enhanced bulging of the defect region due to the presence of the longitudinal compression. This is in direct contrast to the observation that the interaction effect is marginal for circumferentially-aligned defects subjected to internal pressure only. On the other hand, the interaction between longitudinally-aligned defects under combined loads is negligible due to the so-called shielding effect; this is again in direct contrast to the observation that the interaction between longitudinally-aligned defects under internal pressure only is marked. The adequacy of four practical interaction rules, which are developed for the loading condition of internal pressure only, for the combined loading condition is also examined. The findings of this study have important practical implications for the integrity assessment of corroded pipelines under combined loads.

Modeling and simulating nonhomogeneous non-Gaussian corrosion fields on buried pipelines and its use in predicting burst capacities of corroded pipelines

The present study proposes an iterative algorithm to simulate nonhomogeneous non-Gaussian corrosion fields on buried oil and gas pipeline's external surfaces. The algorithm incorporates the concepts of the discrete orthonormal S-transform and the iterative amplitude adjusted Fourier transform algorithm. This results in the space-wavenumber power spectral density function and marginal distribution function of the simulated corrosion field matching, respectively, their corresponding targets that could be determined from the high-resolution corrosion measurement data obtained from naturally corroded pipe segments. The simulation results demonstrate that the use of the proposed algorithm is able to capture the statistical characteristics of naturally occurring corrosion fields on pipelines. Three-dimensional elasto-plastic finite element analyses are carried out to evaluate the burst capacities of pipe segments containing simulated corrosion fields. Combined with finite element analyses, this algorithm can be employed to conduct virtual full-scale burst tests of corroded pipe specimens, which is of great value to the pipeline corrosion management practice.

Load-settlement response of piled raft foundations in sand

ABSTRACT The load-settlement behaviour of piled raft foundations (PRFs) resting on sand subjected to vertical uniformly distributed load is studied using three-dimensional elasto-plastic finite element (FE) analyses. The unified Clay and Sand Model (CASM), based on the critical state soil mechanics, is used as the soil constitutive model. In the present study, 38 rectangular, strip, and circular raft connected to different pile configurations resting on four different types of sands in their loose, medium, and dense states are considered. The accuracy of the finite element analysis is confirmed through verification and validation with other numerical and experimental studies. A detailed parametric study is conducted, which includes soil elastic and critical state parameters as well as different dimensions of PRFs. A guideline chart is provided, which will be helpful for a design practitioner to choose the suitable PRF configurations considering serviceability limit states of safety and economical design aspect. This flow chart is based on (i) combined effects of various parameters on PRF load settlement behaviour, (ii) load sharing between the raft and the pile groups, and (iii) a preliminary cost analysis.

Assessment of effects of idealized defect shape and width on the burst capacity of corroded pipelines

Abstract This study investigates the burst capacities of corroded pipelines using three-dimensional elasto-plastic finite element analyses validated by full-scale burst tests of corroded pipe specimens reported in the literature. The semi-ellipsoidal idealization of naturally-occurring corrosion defects in FEA is found to lead to more accurate predictions of the burst capacity than the rectangular idealization for defects that are less than 70% through the pipe wall thickness. Results of extensive parametric FEA based on the semi-ellipsoidal idealization of the corrosion defects indicate that the burst capacity in general increases as the defect width increases if the defect depth and length remain the same. The defect width effect is marked for deep, relatively short defects, and should therefore be taken into account accordingly in the empirical or semi-empirical burst capacity models. The defect width effect is marginal for long defects with w/l ≤ 1.5. The observed width effects are explained by considering the change in the membrane and bending stresses in the defect region as the defect width increases.

Nonlinear subgrade modulus of sandy soils for analysis of piled raft foundations

Continuum-based three-dimensional (3D) elasto-plastic finite element (FE) analyses of piled raft foundations (PRFs) resting on sandy soils and subjected to uniformly distributed vertical loads are performed using the software Abaqus, and equations are developed for estimating the nonlinear soil subgrade moduli (spring stiffnesses) beneath the raft, beneath the pile base, and along the pile shaft. The unified clay and sand model (CASM) is used as the soil constitutive model in the continuum-based 3D FE analysis. Four different types of sand with three different states (loose, medium and dense) and twenty different configurations of PRFs with rectangular, square, and strip rafts are considered in this study. The developed equations of the raft and pile spring stiffnesses are subsequently used in a soil spring-based nonlinear FE analysis of PRFs performed using a structural engineering software. It is shown through verification and validation studies that the developed equations of the raft and pile spring stiffnesses can be reliably used in spring-based FE analysis of PRFs, instead of the computationally expensive continuum-based 3D FE analysis, for quick and accurate estimate of PRF responses. The developed equations of spring stiffnesses are applicable to PRFs that are similar in dimensions considered in this study.

GROUND STRENGTHENING METHOD BY MULTISTAGE LOCAL CONSOLIDATION

Authors are investigating a ground strengthening method, which effectively consolidates the construction area of requisite minimum in a short time by local consolidation for the soft ground. In this paper, Authors research that the effect of increasing the strength of soft ground by using the three-dimensional elasto-plastic finite element analysis when the area of local loading is gradually changed. First, it was found that the strength of the soft ground just below the local loading surface increased with a short time by the local consolidation and ultimate bearing capacity increases to 2.6 times as much as the initial bearing capacity by the multistage loading. Next, analysis was carried out in the case of the multistage loading with cyclic loading. In the reloading process, loading area is reduced to 1/3 and 1/6 of the loading area of the previous stage. In this case, the ultimate bearing capacity increases to 8.25 times as much as the initial bearing capacity. In conclusion, it was found that the strength of the soft ground just under the loading surface is considerably increased by multistage local loading with reducing the loading area.

Bearing Capacity Characteristics of Steel Pipe Piles with Wings installed in Soil Cement Column

The steel pipe piles with wings installed in soil cement developed in Japan and Vietnam are composite foundation piles made of steel pipes with wings with foundation improvement pillars in soil cement and spiral wings attached to the shaft intermittently. This composite pile has large vertical and horizontal bearing capacities and is a construction method of foundation piles with consideration of environments with little surplus soil, using steel pipes with small diameters. In this study, several full scale loading tests on steel pipe pile with wings installed in soil cement column are presented, and bearing capacity of the composite pile is studied. Especially, combination effect of soil cement column and steel pipe with wings on bearing capacity performance are discussed. Threedimensional elasto-plastic finite element analysis based on the results of loading tests to help understand this composite pile’s mechanical characteristics is also performed.

Short rolling contact fatigue and thermal cracks under frictional rolling – A comparison through simulations

The relative severity of radial (thermal) and inclined rolling contact fatigue surface cracks of equal depth in a railway wheel is investigated by three-dimensional elastoplastic finite element analyses of a cracked wheel sector subjected to contact loading. Response is quantified by relative displacements of nodes close to crack tip and at the crack mouth. Highly inclined cracks give the highest magnitudes of crack tip shear displacements, which is the dominant deformation mode. Braking conditions are found to open the crack mouth. Initially higher temperatures on thermal cracks cause increased crack tip deformation and opening of the crack, whereafter subsequent mechanical load cycles impose crack closure.

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.

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.

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.

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.

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.

Stability of D-shaped tunnels in a Mohr–Coulomb material under anisotropic stress conditions

The near-face stability of D-shaped tunnels excavated in a Mohr–Coulomb material subjected to anisotropic in situ stress conditions is investigated in the present study. The construction of the intake tunnel of the Darlington Nuclear Generating Station is analyzed using three-dimensional elasto-plastic finite element analysis. The induced displacement and stresses around the tunnel opening as the face advances are compared to the field measurements recorded during the tunnel excavation. The effect of rock mass strength reduction on the tunnel deformation, face stability, and distribution of stresses at the tunnel circumference is investigated for different in situ stress conditions. When the ratio of rock mass strength to overburden pressure falls below 0.5, excessive deformation occurrs and squeezing of the rock mass becomes a problem that can cause instability of both the tunnel circumference and the face.Key words: weak rock, tunnelling, horizontal stresses, three-dimensional, finite element, excavation, face stability.

Stability analyses of dam abutments by 3D elasto-plastic finite-element method: a case study of Houhe gravity-arch dam in China

This paper studies the stabilities of the abutments of Houhe gravity-arch dam using elasto-plastic finite element analyses and block theory. The gravity-arch dam is constructed by expanding the existing gravity dam. Due to the complex geologic conditions, the natural abutments do not meet the stability requirements. Engineering measures including concrete plugs and concrete backfills are thus designed to increase the safety of both abutments. The effectiveness of these measures is evaluated in this study. The paper performs three-dimensional elasto-plastic finite element analyses to obtain the stress and deformation characteristics of the abutments and the dam. The stabilities of sliding blocks on the abutments are then evaluated by incorporating the results of finite-element method analyses. It is found that the use of concrete plugs significantly increases the factors of safety against sliding for both abutments. Concrete backfills not only provide the sliding resistance, but also are effective in reducing the deformation of the abutments and improve the stress conditions along the base of the dam. The dam works under satisfactory conditions as the results of applying these engineering measures.