Three-dimensional Elastic-plastic Finite Element Analysis Research Articles

A simple method to determine opening stress for the cracked plate considering thickness effect

In this paper, an approach is proposed to determine crack opening stress (COS) based on the variable quantity of maximum crack opening displacement (VMCOD) considering thickness effect. Based on the three-dimensional elastic-plastic finite element analysis of center cracked tension (CCT) specimens and single-edge cracked tension (SET) specimens, the explicit expressions of relationship between COS and VMCOD are put forward, considering the effect of specimen thickness, crack length, stress ratio, Young's modulus, yield stress and strain hardening. These expressions avoid adopting parameters around crack tip and are applicable to different specimen thicknesses. Further studies show these relationships can be applied to calculate the effective stress intensity factor range and predict crack growth rates for plates of different thicknesses, which correlate well with experimental results.

Evaluation of Tensile Shear Strength for Lap Joint of Dissimilar Steels

The influence of different thickness combinations was investigated on the strength of the lap joint of dissimilar steels. In this study, lap joints of dissimilar steels were welded by laser welding. The tensile shear test was conducted for the lap joints. Rotational deformation process around the weld bead of the lap joint was observed by a digital video camera during the test. Motion analysis from the video of the tensile shear test indicated that the rotation angle around the weld bead was reduced by overlapping higher strength grade steel. Three-dimensional elastic-plastic finite element analysis was performed for the tensile shear test of the lap joint. The numerically calculated deformation behavior of the lap joint subjected to tensile shear loading showed reasonable agreement with the experimental record. It was found that the rotation angle was reduced and tensile shear strength of the lap joint increase by overlapping higher strength grade steel sheet.

Determination of localized stress–strain behavior of fused silica: Inverse numerical analysis from nanoindentation test

Because the localized mechanical properties of fused silica are unlikely to be obtained via conventional tensile testing, an inverse numerical analysis has been applied to deduce these properties using the load–displacement curve from nanoindentation testing. The mechanical properties were initially assumed, and the load–displacement curve was numerically simulated using three-dimensional elastic–plastic finite element analysis. The mechanical properties were adjusted until the numerical curve corresponded to the experimental curve, and then the localized mechanical properties in the vicinity of an indentation could be estimated. Unfortunately, the inverse numerical analysis requires time-consuming numerical calculation, involving many repetitions, by experienced researchers. In the present work, the influence of mechanical properties on the nanoindentation parameters of fused silica was evaluated, and the systematical adjustment of mechanical properties to obtain a satisfactory load–displacement curve has been proposed. It is considered that this procedure can be applied for the evaluation of localized stress–strain behavior of fused silica.

Constraint analysis of thickness effects on fracture resistance behavior of clamped single-edge notch tension specimen

The correlation between the out-of-plane stress and the in-plane stress is established based on the bending modified J-Q theory and the out-of-plane constraint parameter TZ. Accordingly, an improved J-QZ-M constraint theory is developed to characterize the crack-tip fields by taking into account opening- and bending-dominated deformations in the ligament of the clamped single edge notch tension (SE(T)) specimens. Three-dimensional elastic-plastic finite element analyses (FEA) with a wide range of in-plane and out-of-plane constraints are performed to validate the proposed approach. It is found that the proposed J-QZ-M constraint theory can effectively quantify the crack-tip fields of SE(T) specimens, and the constraint parameter QZ exhibits approximately load- and distance-independence until large scale yielding (LSY).

Prediction of fully plastic J-integral for weld centerline surface crack considering strength mismatch based on 3D finite element analyses and artificial neural network

This work mainly focuses on determination of the fully plastic J-integral solutions for welded center cracked plates subjected to remote tension loading. Detailed three-dimensional elastic–plastic Finite Element Analyses (FEA) were implemented to compute the fully plastic J-integral along the crack front for a wide range of crack geometries, material properties and weld strength mismatch ratios for 900 cases. According to the database generated from FEA, Back-propagation Neural Network (BPNN) model was proposed to predict the values and distributions of fully plastic J-integral along crack front based on the variables used in FEA. The determination coefficient R2 is greater than 0.99, indicating the robustness and goodness of fit of the developed BPNN model. The network model can accurately and efficiently predict the elastic-plastic J-integral for weld centerline crack, which can be used to perform fracture analyses and safety assessment for welded center cracked plates with varying strength mismatch conditions under uniaxial loading.

Determination of Crack-Tip Opening Displacement in T-Type Wedge Opening Loaded Specimen

The protective layer at the crack tip of an alloy component can be damaged, and the resistance to crack propagation can be reduced by the combined effects of stress and a corrosive environment. Therefore, the measurement of crack-tip opening displacement (CTOD) can be applied to characterize the crack propagation rate (da/dt) during stress corrosion cracking (SCC) experiments. In the present work, CTOD of a T-type wedge opening loaded (T-WOL) specimen with a built-in loading bolt was initially determined using three-dimensional elastic-plastic finite element analysis (FEA). The influence of stress concentration from side groove on CTOD was clearly evaluated, i.e., the fluctuation of CTOD occurred near the groove-tip plane. However, CTOD became stable on >90% of thickness of T-WOL specimen. Therefore, CTOD at mid-thickness plane of T-WOL specimen could be applied for SCC experiment.

Finite element analysis of deformation in early stage of multi-pass circumferential dissimilar welding of thick-walled pipes with narrow gap

Three-dimensional thermal elastic-plastic finite element analyses were conducted in order to reveal the mechanism of gap shrinkage in early stage of multi-pass narrow gap welding of thick-walled dissimilar pipes and thick plates. The gap shrinkage up to the 8th pass indicates that the shrinkage of plates becomes to be much larger than that of pipes with increasing the weld passes. In addition, through the decomposition of gap shrinkage to transverse shrinkage and angular distortion, it is found that the gap shrinkage of pipes is mainly governed by the transverse shrinkage, while the shrinkage of plates is influenced by both the transverse shrinkage and angular distortion. Moreover, the serial computational results with various groove shapes suggest that the transverse shrinkage of pipes almost linearly increases with increasing the weld pass, and its increment can be predicted by a linear approximation function obtained by the transverse shrinkage of plates regardless of the groove shape.

Numerical simulation and experimental validation of angular distortion and residual stresses in a T-joint

Abstract Welding is the most important method in modern industry. However, welding distortion and residual stress after welding are inevitable. In this paper, experiments were performed to obtain the angular distortion, temperature field and longitudinal residual stress in two T plate structures after welding and post-weld heat treatment, respectively. Then, a three-dimensional thermal elastic-plastic finite element analysis using internal heat generation was carried out to simulate the deformation and stress. The FE analysis results were in good agreement with the measurements. The results showed that both, the thickness of the plates and the heat treatment, could influence the angular distortion and residual stress distribution. Finally, the welding process at a bogie was also simulated by using the same heat source model as for the T-joint. The deformation and stresses were shown and explained.

Incremental Variable Plastic Three-Dimensional Elastic-Plastic Finite Element Analysis in Soft Rock Tunnel Excavation

The plane finite element analysis is mostly adopted in soft rock tunnel excavation instead of three-dimensional nonlinear finite element analysis at present, but almost every underground engineering is a spatial nonlinear problem which, in many cases, cannot be simplified into a plane problem. This paper presents a three-dimensional elastic-plastic finite element analysis of incremental variable plastic in soft rock tunnel excavation, through analyzing the tunnel excavation and support, and combining the incremental variable plastic stiffness method into three-dimensional elastic-plastic model in light of the advantage of increment variable stiffness method and the incremental additional load method. Simulation results show that, the three-dimensional elastic-plastic finite element analysis model presented in this paper changes little final deformation under different load release coefficients, together with small support stress.

418 有限要素解析を用いたAZ31展伸用マグネシウム合金の冷間ロール成形プロセス(OS4-(4),OS4 オーガナイズドセッション《材料・組織と加工》)

As a manufacturing method of the structural pipe according AZ31 magnesium alloy, subjected to a three-dimensional elastic-plastic finite element analysis of cold roll forming, the strain at the time of forming were investigated and spring back.

Development of Central Minute Cavity in the Workpiece of Cross Wedge Rolling

Central cavity in the workpiece of cross wedge rolling is a high-level product defect which would seriously weaken the strength of material. Based on the three-dimensional elastic-plastic finite element analysis method, numerical simulation of cross wedge rolling parts with minute central cavities was performed. The area changes of the minute central cavities were obtained, and combined with the internal stress state during the rolling process, the viewpoint that tensile stress in the three-dimensional directions is one factor that leads to cavity growth was expound.

Two-parameter characterization of elastic–plastic crack front fields: Surface cracked plates under uniaxial and biaxial bending

In this paper the J–Q two-parameter characterization of elastic–plastic crack front fields is examined for surface cracked plates under static uniaxial and biaxial bending. Extensive three-dimensional elastic–plastic finite element analyses are performed for semi-elliptical surface cracks in a finite thickness plate, under remote uniaxial and biaxial bending conditions, covering from small-scale to large-scale yielding. Surface cracks with aspect ratios a/c=0.2, 1.0 and relative depths a/t=0.2, 0.6, corresponding to four specimen configurations, are investigated. The full stress field solutions are obtained in topological planes perpendicular to the crack fronts. The question of J–Q characterization is addressed by comparing these elastic–plastic crack-front stress fields with J–Q family of stress fields. It is found that the J–Q characterization provides good estimate for the constraint loss for crack front stress fields. It is also shown that for medium load levels, reasonable agreements are achieved between the T-stress based Q-factors and the Q-factors obtained from the finite element analyses. Complete distributions of the J-integral and Q-factors for the wide range of geometry and loading conditions are obtained. Size requirements in terms of crack depth (for shallow cracks) or ligament size (for deep cracks) that are necessary to ensure J–Q characterization of crack front fields in surface cracked plates are also discussed.

A three-dimensional analysis of fracture mechanics test pieces of different geometries – Part 1 Stress-state ahead of the crack tip

An extensive series of detailed three-dimensional elastic–plastic finite element analyses has been carried out to investigate the influence of fracture mechanics test specimen geometry on the near-tip stress fields. The specimens studied were pre-cracked plain-sided and side grooved bend specimens of Charpy specimen size, plain-sided and side-grooved compact tension specimens of thickness B = 25 mm and plain-sided compact tension specimens of thickness B = 100 mm. The standard ratio of the crack length to the specimen width a/W = 0.5 was employed in all the cases considered. Stress-strain curves of materials of different yield strength and strain hardening behaviour spanning the range of practical interest for typical structural steels were implemented into the finite element models.Variations of the local crack tip driving forces in terms of the J-integral and crack tip opening displacement (CTOD) over the crack front have been investigated. The near-tip stress fields in the fracture toughness specimens were analysed in detail with the emphasis on the opening mode stress. Further studies on the constraint parameter Q and hydrostatic and equivalent stress components are reported in a separate paper, Part 2 of this work.

A three-dimensional analysis of fracture mechanics test pieces of different geometries part 2 - Constraint and material variations

This paper reports the second stage of an extensive series of detailed three-dimensional elastic-plastic finite element analyses on the influence of fracture mechanics test specimen geometry and different material properties on constraint and triaxiality in the near crack tip region. The specimens studied were pre-cracked plain-sided and side-grooved Charpy sized specimens, plain-sided and side-grooved compact tension specimens of thickness B = 25 mm and plain-sided compact tension specimens of thickness B = 100 mm all with the ratio of the crack length to the specimen width a/W = 0.5. Stress–strain curves of materials of different yield strength and strain hardening behaviour spanning the range of practical interest for typical structural steels were implemented into the finite element models.The level of constraint in the specimens modelled has been characterised in terms of both the Q-stress parameter and the ratio of hydrostatic to the equivalent stress components. It has been established that in-plane constraint in the fracture toughness test pieces is significantly affected by the absolute ligament size of the specimen. It has also been shown that the strain hardening behaviour is one of the major material parameters defining constraint level in the fracture toughness specimen.

Creep Stress Analyses Affected by Load Properties on P91 Pipe with Local Wall Thinning under High Temperature

The local wall thinning defect is very normal on pipes in power plants, which may result in stress redistribution of the pipes during the service process at elevated temperature. For the purpose of understanding the stress redistribution and strain accumulation of pipes with local wall thinning affected by load properties under creep condition, three groups of models were calculated, using three-dimensional elastic-plastic finite element analyses (FEA) based on FEA codes ABAQUS. In this study, the pipes has an identical defect of local wall thinning, the load properties and values are changed. Three groups of load properties, considering here, were monotonic internal pressure, monotonic moment and both internal pressure and moment, respectively. The numerical simulation conducted on P91 full-scale steel pipes at 625°C, with local wall thinning located at the inner surface. Then, von Mises stress and creep strain of pipes after 100,000h could be obtained corresponding to different models. Based on the analysis, the figures of creep stress and strain varying with load properties were plotted. Then, the stress and strain of pipes with local wall thinning affected by load properties were discussed. The results indicate that creep stress and creep strain increase with load properties. The variation laws have been summarized. The research results can provide the possibility on safety assessment and structure integrity analysis of the pipe with local wall thinning at high temperature effectively.

Application of the dissipated energy criterion to predict fatigue crack growth of Type 304 stainless steel following a tensile overload

This paper presents the results of numerical simulations of fatigue crack growth performed using three-dimensional elastic–plastic finite element analysis. A simple node release scheme is used to simulate crack advancement. The crack front is assumed to be straight. Crack growth following a tensile overload is simulated. The total energy dissipated per cycle is calculated directly from the finite element analysis and used to predict fatigue crack growth. For comparison, fatigue crack growth rate experiments were performed on Type 304 stainless steel C( T) specimens to determine the effect of a single tensile overload. The dissipated energy per cycle is found to correlate well with the measured fatigue crack growth rate following an overload.

Finite Element Analysis for Wall Thickness Variation of Seamless Tube in Stretch Reducing Rolling Process

According to the geometrical characteristic of workpiece and groove in the stretch reducing rolling process, three-dimensional elastic-plastic finite-element analysis model was established to simulate the metal deformation, the regularities of distribution of wall thickness of transverse direction longitudinal direction were investigated. The analysis was verified by comparing finite element analysis results with on-line measurements. The length of crop ends was determined as well as product bore polygonization. The study provides the foundation for analyzing product defeat and instructing technological design.

Analytical study of fatigue crack growth in AA7050 notched specimens under spectrum loading

Abstract An analytical study of fatigue crack growth in aluminium alloy 7050-T7451 notched specimens under a fighter aircraft wing root bending moment spectrum was conducted. The crack growth data were measured by quantitative fractography for three groups of specimens with different stress concentration geometrical features. Under spectrum loading and for each spectrum peak stress level, a minimum of five specimens were tested. Based on the analysis of the measured spectrum crack growth data using linear elastic fracture mechanics, it was found that the concept of geometry factors formulated in the stress intensity factor could not collapse the crack growth rate data derived from each stress concentration feature, particularly near the small crack growth region. In order to investigate the possible reasons for this, three-dimensional elastic–plastic finite element analysis was used to determine notch plastic zone sizes for each stress concentration geometry. As a consequence, an alternative crack growth driving force by considering both notch elastic–plastic stress field and gross net-section stress field was proposed and used to interpret the fatigue crack growth data under spectrum loading. It was found that the predictions of crack growth under spectrum loading for different stress concentration factors at different peak load levels agree reasonably well with the experimental results.

Enhancement of leak rate estimation model for corroded cracked thin tubes

During the last couple of decades, lots of researches on structural integrity assessment and leak rate estimation have been carried out to prevent unanticipated catastrophic failures of pressure retaining nuclear components. However, from the standpoint of leakage integrity, there are still some arguments for predicting the leak rate of cracked components due primarily to uncertainties attached to various parameters in flow models. The purpose of present work is to suggest a leak rate estimation method for thin tubes with artificial cracks. In this context, 23 leak rate tests are carried out for laboratory generated stress corrosion cracked tube specimens subjected to internal pressure. Engineering equations to calculate crack opening displacements are developed from detailed three-dimensional elastic-plastic finite element analyses and then a simplified practical model is proposed based on the equations as well as test data. Verification of the proposed method is done through comparing leak rates and it will enable more reliable design and/or operation of thin tubes.

Two-parameter characterization of elastic–plastic crack front fields: Surface cracked plates under tensile loading

In this paper the J–Q two-parameter characterization of elastic–plastic crack front fields is examined for surface cracked plates under uniaxial and biaxial tensile loadings. Extensive three-dimensional elastic–plastic finite element analyses were performed for semi-elliptical surface cracks in a finite thickness plate, under remote uniaxial and biaxial tension loading conditions. Surface cracks with aspect ratios a/c=0.2, 1.0 and relative depths a/t=0.2, 0.6 were investigated. The loading levels cover from small-scale to large-scale yielding. In topological planes perpendicular to the crack fronts, the crack stress fields were obtained. In order to facilitate the determination of Q-factors, modified boundary layer analyses were also conducted. The J–Q two-parameter approach was then used in characterizing the elastic–plastic crack front stress fields along these 3D crack fronts. Complete distributions of the J-integral and Q-factors for a wide range of loading conditions were obtained. It is found that the J–Q characterization provides good estimate for the constraint loss for crack front stress fields. It is also shown that for medium load levels, reasonable agreements are achieved between the T-stress based Q-factors and the Q-factors obtained from finite element analysis. These results are suitable for elastic–plastic fracture mechanics analysis of surface cracked plates.