Oyane Ductile Fracture Criterion Research Articles

Analysis of ductile damage changes of pipelines with unconstrained dents in rebound process

Dent is one of the most common defects in mechanical damage of oil and gas pipelines. Most of the dents generated during pipeline construction are unconstrained dents, and rebound will occur during service of the pipeline. The dent defect can be considered as ductile damage. Taking X52 steel pipe as the research object, the rebound process of unconstrained dents in service is numerically simulated. Based on the Oyane ductile fracture criterion, the ductile damage degree of dented pipes affected by multiple factors was studied. The change of the ductile damage integral value with the change of parameters during each loading process of the pipeline and the relationship between the pipeline damage and the depth of the dent were analyzed. The results show that the analysis results based on the ductile damage model are in accordance with the conclusions of the existing research, and the ductile damage integral value of the pipeline changes with the depth of the dent in a reasonable law, which shows that the ductile fracture criterion can be used for the safety evaluation of dented pipeline.

A calculating method of tube constants of ductile fracture criteria in tube free bulging process based on M-K theory

The purpose of this work was to obtain the accurate constants in ductile fracture criteria based on the M-K theory, which determined the condition of convergence in numerical simulations and predicted the ductile fracture during the tube free bulging process. In this paper, the equivalent stress was analyzed based on the M-K theory, and the constitutive equation of the tube free bulging was established. The ductile fracture criterion constants were obtained by the integral on the basis of the Freudenthal, Normalized C&L and Oyane theories. The comparison between the experimental and the simulation results regarding the free bulging, indicated that the Oyane ductile fracture criterion was more precise than the other criteria by the perimeter increase trend, the burst locations of the risky area and the crack length. The burst defects prediction became significantly accurate by the Oyane ductile fracture criterion utilization based on the M-K theory.

Identification of forming limits at fracture of DP600 sheet metal under linear and unloaded non-linear strain paths

Abstract The in-plane biaxial tensile test with a new cruciform specimen is used to investigate the forming limit strains at fracture of DP600 sheet metal. The experimental forming limits are determined under linear and non-linear strain paths without unloading provided by four independent dynamic actuators. The Oyane ductile fracture criterion is used to predict the experimental results under different strain paths.

Forming limit in thermal cruciform biaxial tensile testing of titanium alloy

In this study, a new cruciform biaxial tensile testing technology was employed to evaluate the thermal limit strains of a TA1 titanium alloy, which is widely used as an aircraft structural component, so as to prevent fracture defects during thermoplastic processing. The effect of specimen shape on the forming limit and its measurement range is discussed. The results of this study show that a design that reduces the semispherical thickness results in localized necking and fracture at the center of the specimen when normal stress is applied to it. The forming limit diagrams obtained at different angles with respect to the material rolling direction suggested that the limit strain was anisotropic in nature. The experimental results were in good agreement with the substituted values obtained from the finite element analysis and Oyane ductile fracture criterion. Finally, the efficacy of the related test and prediction methods was corroborated.

The analysis of damage degree of oil and gas pipeline with type II plain dent

Abstract Dent is a common type of defect in oil and gas pipelines and the assessment on dented pipelines is carried out with major international standards and specifications based on dent depth as the evaluation criteria. However, such evaluation criteria based on depth does not account for the impact of various parameters (e.g. parameters of dent, parameters of pipeline and the internal pressure of pipeline) on the evaluation result, as a result, many dented pipelines lose their efficacy, even though they meet the depth-based standards. The influence of parameters changes on the damage degree of II-type dented pipelines is investigated on the basis of Oyane's ductile fracture criterion and by the method adopting finite element numerical calculations. Finally, the non-linear regression analysis is conducted and based on the outputs, a specific expression of dent depth and pipeline damage degree is also acquired within a certain scope of application.

Establishment of a thermal damage model for Ti-6Al-2Zr-1Mo-1V titanium alloy and its application in the tube rolling-spinning process

Rolling-spinning of titanium alloy tubes is an advanced plastic forming technology that has been developed due to the urgent need for light-weight, high-precision, and high-reliability components in high-tech fields, such as aviation and aerospace. However, due to the complexity of the rolling-spinning process and the sensitivity of titanium alloy to temperature and strain rate, it is easy to crack, which severely restricts the improvement of the forming quality and forming limit of components. In this study, the critical deformation of Ti-6Al-2Zr-1Mo-1V was obtained by a hot compression test under various temperatures and strain rates. The damage threshold was obtained through FE simulation for the hot compression process under these temperatures and strain rates. The relationship among damage threshold, temperature, and strain rate was established by introducing the Zener-Hollomon factor. A thermal damage model for Ti-6Al-2Zr-1Mo-1V was established by combining the Oyane ductile fracture criterion with the relationship among damage threshold, temperature, and strain rate. By coupling this thermal damage model into the FE model for rolling-spinning of a Ti-6Al-2Zr-1Mo-1V tube, the damage prediction for the process was realized. The results show that the stress triaxiality at the top and bottom ends of the rolling zone is positive, the accumulation of damage is fast, and the strain rate is large in the zone. Thus, these ends are the zones most prone to damage in rolling process. The stress triaxiality at the local inner surface area of the spinning region is positive, the accumulation of damage is fast, and the strain rate is large in the zone. Therefore, the inner surface of the spinning region is the zone most prone to damage.

Influence of Roll Rotational Speed on inside Bore and Lamination Defects in Rotary Piercing Large Diameter Heavy Wall P92 Steel Pipe Process

To investigate the influence of different roll rotational speeds on tendency of inside bore and lamination defects of large diameter heavy wall seamless P92 (9Cr-0.5Mo-1.8WVNb) steel pipe pierced by two-high rotary piercing process, with the aid of commercial FE code MSC. SuperForm, 3D thermo-mechanical coupled simulations were presented. The damage field of the rolled piece during rotary piercing process, and the tendency of forming inside bore and lamination defects were analyzed using Oyane ductile fracture criterion. The results show that When roll rotational speed increases from 7rpm to 11rpm, the maximal damage characteristic value decreases from 0.4279 to 0.3340 in center area of rolled piece in front of the plug, but which increases from 0.3780 to 0.4858 in a certain depth zone (15~25mm) adjacent to the internal surface of the rolled piece contacting with the front end of the plug. With the increase of roll rotational speed, the tendency of forming inside bore defects of rolled piece reduces, but the tendency of forming lamination defects increases. Therefore, there exists a critical roll rotational speed to make the tendency of both inside bore and lamination defects reduce. This study provides scientific basis for formulating reasonable rotational speed schedule to prevent or reduce inner overlap and lamination defects.

An Efficient Approach for Identifying Constitutive Parameters of the Modified Oyane Ductile Fracture Criterion at High Temperature

The paper presents the theoretical part of a method for identifying constitutive parameters involved in the modified Oyane ductile fracture criterion at high temperature. Quite a general rigid viscoplastic model is adopted to describe material behavior. The ductile fracture criterion is in general path-dependent and involves stresses. Therefore, the identification of constitutive parameters of this criterion is a difficult task which usually includes experimental research and numerical simulation. The latter requires a precisely specified material model and boundary conditions. It is shown in the present paper that for a wide class of material models usually used to describe the behavior of materials at high temperatures, the criterion is significantly simplified when the site of fracture initiation is located on traction free surfaces. In particular, this reduced criterion does not involve stresses. Since there are well established experimental procedures to determine the input data for the reduced criterion, the result obtained can be considered as a theoretical basis for the efficient method for identifying constitutive parameters of the modified Oyane ductile fracture criterion at high temperature. The final expression can also be used in computational models to increase the accuracy of predictions.

Evaluation of Facture Criteria Considering Complex Loading Paths in Cobalt Alloy Tube Hydroforming

In this study, a free bulge test simulation was performed with conditions corresponding to experiments for a cobalt-alloy tube hydroforming. A 3D strain measurement scheme was introduced to obtain strain data after free bulge tests, and the measured strain values were used in the evaluation of ductile fracture criteria. Cockcroft ductile fracture criterion, Oyane ductile fracture criterion and the modified Cockcroft criterion were adopted for establishing the material constants by simple tensile test and notched tensile test. Experimental data from free bulge tests were used for fracture prediction with these criteria. The results revealed that for the purpose of tube hydrofoming, the modified Cockcroft criterion with strain paths is more accurate than either the Cockcroft ductile fracture criterion or the Oyane ductile fracture criterion. [doi:10.2320/matertrans.MF201119]

Incremental Sheet Metal Forming: Numerical Simulation and Rapid Prototyping Process to make an Automobile White‐Body

AbstractIn order to make an automobile body structure, incremental sheet metal forming is introduced as a rapid prototyping process. Numerical modeling of the process is initially used to predict the deformation of the sheet metal to avoid failure during the incremental forming process using ABAQUS/Explicit finite element code and OYANE's ductile fracture criterion via a VUMAT user material. An automobile CAD model is then designed, and segmented into several parts in order to accommodate the working space of the CNC machine and formability of sheet metal. After that, CAM software is used to generate a tool‐path for making wooden‐dies and all small parts. Finally, a welding process is applied to join all parts which were cut by laser cutting after incremental sheet forming process.

Prediction and Research of Single Point Incremental Forming Limit

Sing point incremental forming (SPIF) limit is much higher than the traditional processes. Currently, there are still no systematic theories and criterions to predict the limit. In this paper, the Oyane ductile fracture criterion is introduced to predict the forming limit of SPIF based on the stress-strain data by the finite element simulations. The predicted fracture initiation sites and the forming limit curve are consistent with the experiment results; further, the forming characteristic, stress state, local temperature are the main reasons of the higher forming limit in SPIF.

FLD OF AZ31 SHEET UNDER WARM STRETCHING AND ITS PREDICTION

Forming Limit Diagrams (FLDs) of a magnesium alloy (AZ31) sheet at various forming speeds (3 to 300 mm·mm-1) at several temperatures of 100-250°C were investigated by performing a punch stretch-forming test. The forming limit strains increased with temperature rise and with decreasing forming speed, where the effect of forming speed was stronger at higher temperatures. To describe such a characteristic of FLD of AZ31, the Marciniak-Kucznski type forming limit analysis was conducted using the Backofen-type constitutive equation (c = Cεnεm). In this analysis, the damage evolution in the necking zone was taken into account based on Oyane's ductile fracture criterion. The numerical results of the FLD show a good agreement with the corresponding experimental observations.

Improved FE Modeling of Center Crack Occurrence in Tube Rounds during Two-Roll Rotary Rolling Process

Using Oyane ductile fracture criterion, a 2-D coupled thermo-mechanical simulation of center crack occurrence in round billet during 2-roll rotary rolling process is presented with the aid of FE code MSC.Superform. Based on an existing flat-die-model, an improved FE model is advanced, in which not only the influence of roll feed angle and entry cone angle but also the diameter of the piercing roll on the process are taken into account. By adopting the parameters of the Diescher piercer in 140mm Mandrel Mill of Bao Steel in China, the distribution and development of strain/stress in tube rounds are analyzed, and the eigenvalue of ductile fracture as well. The critical percentage of diameter reduction is obtained from the simulation. The result shows a good agreement with the experimental value, and therefore is of widely guiding significance to practical process for rationally formulating deformation parameters of steel tube piercing.

Analytical and numerical approach to prediction of forming limit in tube hydroforming

Analytical and numerical analyses of forming limit in tube hydroforming under combined internal pressure and independent axial feeding are discussed in this paper. To predict the initiation of necking, Swift's criterion for diffuse plastic instability is adopted based on Hill's general theory for the uniqueness to the boundary value problem. In addition, in order to predict fracture initiation, Oyane's ductile fracture criterion is introduced and evaluated from the histories of stress and strain calculated by means of finite element analysis. From the comparison with a series of tube bulge tests, the prediction of the bursting failure based on the plastic instability and the ductile fracture criterion demonstrates to be reasonable so that these approaches can be extended to a wide range of practical tube hydroforming processes.

Finite element analysis for bursting failure prediction in bulge forming of a seamed tube

Finite element analyses for bursting failure prediction in bulge forming under combined internal pressure and independent axial feeding are carried out. By means of the FEM combined with Oyane's ductile fracture criterion based on the Hill's quadratic plastic potential, forming limit and bursting pressure level are investigated for a seamed tube that comprises of weldment, heat affected zone (HAZ) and base material parts. Especially, in order to determine the material property of HAZ tensile tests for the base material and the weld metal are executed based on iso-strain approach. Finally, through a series of bulge forming simulations with consideration of the weldment and HAZ it is concluded that the proposed method would be able to predict the bursting pressure and fracture initiation site more realistically, so the approach can be extended to a wide range of practical bulge forming processes.

A prediction of bursting failure in tube hydroforming processes based on ductile fracture criterion

Bursting is an irrecoverable failure mode in tube hydroforming, in contrast with buckling and wrinkling. To predict bursting failure in the hydroforming processes, Oyane's ductile fracture criterion is introduced and evaluated from the results of stress and strain productions obtained from finite element analysis. The region of fracture initiation and the bursting pressures are predicted and compared with a series of experimental results. It is shown that the material parameters used in the criterion can be obtained from the forming limit diagram. From the simulation results of tube bulging, the prediction of the bursting failure based on the ductile fracture criterion was demonstrated to be reasonable. This approach can be extended to a wide range of practical tube hydroforming processes.

Development of a Three-Dimensional Rigid-Plastic FEM Code and Its Application to Problem of Friction and Fracture.

In order to verify the accuracy regarding contact and friction, the two-dimensional (2D) penalty rigid-plastic FEM program (which was developed in previous reports) is applied to the ring compression problem. Then a 3D FEM code is developed by extension of this program. Using this code, the fiat-tool compression and spherical punch indentation of a block of various materials under various friction conditions are carried out. At the same time, the occurrence of fracture and change of relative density during deformation are inspected by using the Oyane's ductile fracture criterion and the change of relative density calculated by this code. From the results. this code is confirmed to be effective. Furthermore. it is shown that fracture is dependent on the forming type, material and friction condition, and that the prediction of fracture from the trivial change of relative density is possible using this code in which compressibility is not taken into account.