Gurson-Tvergaard-Needleman Parameters Research Articles

Plastic deformation and fracture of AlMg6/CNT composite: A damage evolution model coupled with a dislocation-based deformation model

Understanding the plastic deformation and fracture behavior of Carbon nanotube (CNT)-reinforced aluminum composites is crucial for determining the factors controlling their strength and ductility. This article presents a novel approach by proposing a coupled micromechanical dislocation-based constitutive model combined with the Gurson-Tvergaard-Needleman (GTN) damage evolution model. The objective of this research is to accurately predict the load-displacement behavior of an AlMg6/CNT composite, which is manufactured through accumulative roll bonding (ARB), from yield to fracture. The study investigates the correlations between the number of ARB passes, which affects the dislocation density of the matrix, and the distribution of CNTs in the composite, with the GTN parameters. The analysis reveals that the volume fraction of void nucleating particles (fN) is a critical parameter influencing the ductility of the composite ductility. Initially, due to CNT agglomeration, they act as nucleation sites for damage, resulting in an increase in fN and a decrease in ductility. However, as the number of ARB passes increases, leading to a homogeneous CNT distribution, fN decreases, and CNTs contribute to improved strength and ductility of the composite. The proposed model accurately predicts the load-displacement curve of the composite during uniaxial tensile testing, taking into account the effect of ARB passes. The research findings provide insights for future extensions of the GTN model, aimed at enhancing its theoretical framework and applicability in the field.

Experimental investigations on parameter identification and failure predictions of titanium alloy by Gurson–Tvergaard–Needleman model

This study focused on the experimental investigations on parameter identification and failure prediction of Ti-6Al-4 V by Gurson–Tvergaard–Needleman (GTN) model. Two approaches, i.e., direct (by image processing of SEM observations) and indirect measurements (by the reduction of effective Young’s modulus or FE trail-and-error), were used to determine the GTN parameters. Through digital image processed SEM micrographs of uniaxial tensile specimens at different deformation stages, the developments of void volume fraction (VVF) were obtained and compared with that from indirect measurements. The three nucleation parameters can then be analytically derived from this experimentally obtained VVF developments. The critical VVF at void coalescence was directly measured through a SEM observation of the section surface around the fracture region of uniaxial tensile specimen, and this value is also consistent with that from indirect measurement. However, as the matrix of a fracture surface is characterized with an obvious varying grayscale due to its dimple morphology, the VVF at final fracture is suggested to be determined from FE trial-and-error rather than a direct measurement of the fracture surface to avoid error induced by subjective judgements. Consistency of the determined GTN parameters was verified through failure predictions on notched tension (R = 6, 20, 100), notched Arcan tests (R = 1, 3, 5), and cracked Arcan tests (SECS, DECS, and CCS), which proved that GTN model with parameters from this experimental investigation cannot only predict the macroscopic mechanical behavior of ductile metals, but also well match the entire damage evolution, from void nucleation to final fracture.

Investigating effective yield surface of porous metals exhibit different hardening behaviors by cell models with randomly distributed spherical voids

AbstractThis study focuses on the development of effective yield surface of porous metals, which is characterized with the two constitutive parameters (i.e., q1 and q2) in the widely used Gurson–Tvergaard–Needleman (GTN) model. It was found that the influence of q1 and q2 on the mechanical responses may be masked by adjusting the two failure parameters (fc and fF), yielding a set of GTN parameters deviated from the actual situation and leading to the errors in failure predictions. Therefore, the two constitutive parameters should be carefully calibrated according to the hardening behavior of matrix. Further investigations on the void density and distributions proved that cubic cells containing 100 randomly distributed non‐intersecting spherical voids are sufficient in characterizing the homogenization. On this basis, effective yield surface of porous metals with a wide range of void volume fractions (from 0.4% to 20%) was investigated, and a correlation between the constitutive parameters and the power‐law hardening behavior of matrix was established. Finally, experimental verifications were conducted on low alloy steel SA508, indicating the q1 and q2 from this study can yield more accurate mechanical response predictions then the previously suggested values.

Predicting the forming limit diagram of the fine-grained AA 1050 sheet using GTN damage model with experimental verifications

In this research, forming limit diagram (FLD) of aluminum alloy 1050 (AA 1050) sheet produced by Accumulative Roll Bonding (ARB) is investigated numerically and experimentally. The Gurson-Tvergaard-Needleman (GTN) ductile damage model is used to predict sheet failure and obtain its FLD using numerical simulation in Abaqus/Explicit. Nucleation and growth of voids in the material during the deformation is the basic concept of the GTN damage model. This damage model has nine basic parameters that obtaining through experimental tests is time-consuming and costly, and in some cases, impossible. Thus, the present study tries to obtain the above parameters for fine-grained aluminum 1050 fabricated by ARB using the finite element method. Therefore, after considering each parameter’s interval, numerical simulation and the anti-inference method are used in the uniaxial tensile test to identify GTN parameters for the AA 1050 sheet using FEM. The optimum parameters of the GTN model are used in the FEM of the Nakazima test for FLD prediction. Also, The FLD of the fine-grained aluminum sheet is obtained experimentally using the Nakazima test. Finally, the numerical and experimental FLDs are compared for validation.

A Simplified Strategy to Address Effects of the Drop of Temperature on the Gurson-Tvergaard-Needleman Model for G20Mn5QT Cast Steels

G20Mn5QT cast steels have been widely used in cast steel connections, which may suffer from ductile fracture at ambient temperature. Northern climates make the problem even worse because the ductility of the cast steels deteriorates with the drop of temperature. For ductile fracture analysis of cast steel connections working at low temperatures, Gurson-Tvergaard-Needleman (GTN) models were calibrated and validated for G20Mn5QT cast steels at 20°C, −20°C, −40°C, and −60°C based on previous test results. The effects of the drop of temperature on material parameters in GTN models of G20Mn5QT cast steels were determined. A simplified strategy was proposed to address the effects of the drop of temperature by two GTN parameters, the void nucleation strain εN and the critical void volume fraction fc. It was found that εN decreased almost linearly with the drop of temperature, and fc had a similar relationship with the drop of temperature as the Charpy impact energy. The relationships between these two parameters and the drop of temperature were presented for the establishment of GTN models for G20Mn5QT cast steels at any possible low temperatures. Scanning electron microscope (SEM) micrographs indicated that the dimple-based ductile fracture mechanism was dominant in the fracture of G20Mn5QT cast steels, which was accompanied by possible quasi-cleavage fracture at low temperatures.

Micromechanical modelling of API X80 linepipe steel

Gurson–Tvergaard–Needleman (GTN) model parameters have been estimated for the API X80 linepipe steel; these parameters and mesh size are transferable from one geometry to another. Fracture data are non-transferable from the lab specimen to the component level. These issues are resolved by local approaches to fracture to predict damage. GTN model incorporates the local features of the fracture, i.e., nucleation, growth, and coalescence of voids. The void volume fraction of material at different stages of loading governs the load-carrying capacity. This research has explored the methodology to determine the parameters by metallographic examination, known as micromechanical modelling. Parametric study and calibration of the parameter are done to fit the load-displacement curve of the notched tensile bar. These parameters are validated on the single edge notch bend (SENB) test. Estimated GTN parameters can predict the damage behavior for moderate to low constraints; hence, these parameters and mesh size are transferable from one geometry to another.

Damage Analysis of Third-Generation Advanced High-Strength Steel Based on the Gurson–Tvergaard–Needleman (GTN) Model

The third generation of advanced high-strength steels (AHSS) brought attention to the steel and automotive industries due to its good compromise between formability and production costs. This work evaluated a third-generation AHSS (USS CR980XG3TM) through microstructural and X-ray diffraction (XRD) analyses, uniaxial tensile and plane-strain tension testing, and numerical simulations. The damage behavior of this steel is described with the Gurson–Tvergaard–Needleman (GTN) model using an identification procedure based on the uniaxial tensile and initial microvoids data. The microstructure of the CR980XG3TM steel is composed of ferrite, martensite–austenite islands, and retained austenite with a volume fraction of 12.2%. The global formability of the CR980XG3TM steel, namely the product of the uniaxial tensile strength and total elongation values, is 24.3 GPa%. The Lankford coefficient shows a weak initial plastic anisotropy of the CR980XG3TM steel with the in-plane anisotropy close to zero (−0.079) and the normal anisotropy close to unity (0.917). The identified GTN parameters for the CR980XG3TM steel provided a good forecast for the limit strains defined according to ISO 12004-2 standard from the uniaxial tensile and plane-strain tension data.

Visualization of the damage evolution for Ti–3Al–2Mo–2Zr alloy during a uniaxial tensile process using a microvoids proliferation damage model

Abstract Understanding the damage evolution of alloys during a plastic deformation process is significant to the structural design of components and accident prevention. In order to visualize the damage evolution in the plastic deformation of Ti–3Al–2Mo–2Zr alloy, a series of uniaxial tensile experiments for this alloy were carried out under the strain rates of 0.1–10 s−1 at room temperature, and the stress–strain curves were achieved. On the other hand, the finite element (FE) models of these uniaxial tensile processes were established. A microvoids proliferation model, Gurson–Tvergaard–Needleman (GTN) damage model, was implanted into the uniaxial tensile models, and the simulated stress–strain curves corresponding to different GTN parameter combinations were obtained. Based on the simulated and experimental stress–strain curves, the GTN parameters of this alloy were solved by response surface methodology (RSM). The solved GTN parameters suggest that higher strain rate can enhance the proliferation and coalescence of microvoids. Furthermore, the uniaxial tensile tests over different strain rates were simulated using the solved GTN parameters. Then, the damage processes were visualized and evaluated. The result shows that the degradation speed of this alloy is slow at the initial stage of the tensile deformation and then accelerates once the voids volume fraction reaches a critical value.

Sensitivity analysis of the GTN damage parameters at different temperature for dynamic fracture propagation in X70 pipeline steel using neural network

In this paper, the initial and maximum load was studied using the Finite Element Modeling (FEM) analysis during impact testing (CVN) of pipeline X70 steel. The Gurson-Tvergaard-Needleman (GTN) constitutive model has been used to simulate the growth of voids during deformation of pipeline steel at different temperatures. FEM simulations results used to study the sensitivity of the initial and maximum load with GTN parameters values proposed and the variation of temperatures. Finally, the applied artificial neural network (ANN) is used to predict the initial and maximum load for a given set of damage parameters X70 steel at different temperatures, based on the results obtained, the neural network is able to provide a satisfactory approximation of the load initiation and load maximum in impact testing of X70 Steel.

Study on the Influence of the Gurson–Tvergaard–Needleman Damage Model on the Fatigue Crack Growth Rate

The fatigue crack growth (FCG) process is usually accessed through the stress intensity factor range, ΔK, which has some limitations. The cumulative plastic strain at the crack tip has provided results in good agreement with the experimental observations. Also, it allows understanding the crack tip phenomena leading to FCG. Plastic deformation inevitably leads to micro-porosity occurrence and damage accumulation, which can be evaluated with a damage model, such as Gurson–Tvergaard–Needleman (GTN). This study aims to access the influence of the GTN parameters, related to growth and nucleation of micro-voids, on the predicted crack growth rate. The results show the connection between the porosity values and the crack closure level. Although the effect of the porosity on the plastic strain, the predicted effect of the initial porosity on the predicted crack growth rate is small. The sensitivity analysis identified the nucleation amplitude and Tvergaard’s loss of strength parameter as the main factors, whose variation leads to larger changes in the crack growth rate.

Determination of GTN Model Parameters Based on Artificial Neutral Network for a Ductile Failure

The Gurson – Tvergaard – Needleman (GTN) mechanical model is widely used to predict the failure of materials based on laboratory specimens, direct identification of Gurson – Tvergaard – Needleman parameters is not easy and time-consuming, and the most used method to determine them is the combination between the experimental results and those of the finite elements, the process consists of repeating the simulations several times until the simulation data matches the experimental data obtained at the specimen level.This article aims to find GTN parameters for the Compact Tension (CT) and Single Edge Tensile Test (SENT) specimen based on the Notch Specimen (NT) using the Artificial Neural Network (ANN) approach. . This work presents how the ANN could help us determine the parameters of GTN in a very short period of time. The results obtained show that ANN is an excellent tool for determining GTN parameters.

Evaluation of impact ductile fracture behaviour of low carbon austenitic stainless steel SUS304L using damage mechanics model

To clarify the applicability of the Gurson-Tvergaard-Needleman (GTN) model for impact ductile fracture behaviour, SHB test was reproduced by finite element analysis (FEA). The strain-rate dependence of the strength for austenitic stainless steel JIS SUS304L was obtained by tensile tests at quasi-static strain rate and impact strain rate. The CowperSymonds power law, which takes into the strain-rate dependence of strength, and the GTN model implemented in the commercial FEA code were used to simulate for impact ductile-fracture behaviour. GTN model parameters were determined by minimizing the difference between the simulated and measured stress-strain curve using response surface method. SHB test was simulated using GTN model obtained from quasi-static tensile test result. Simulation results did not occur the necking and fracture on the specimen. The fracture surfaces were observed by SEM micrograph. The appearance of ductile fracture since dimples are observed, regardless of the strain rate. It is necessary to adjust the parameter to accelerate the nucleation of the void. By identifying the GTN parameters in consideration of the strain rate dependence including impact strain rate. It would be possible to improve the simulation accuracy of impact ductile fracture behaviour.

Analysis of p-SPT specimens using Gurson parameters ascertained by Artificial Neural Network

Finite Element Analysis with Gurson-Tvergaard-Needleman (GTN) damage model is used to analyze p-SPT specimens of two structural steels. Load-displacement curves are calculated by parametric variation of GTN parameters. An ANN is trained using load-displacement data as input and GTN parameters as output. Trained ANN is used against p-SPT experimental data to ascertain GTN parameters. Three sets of p-SPT specimens are then analyzed for different a/W ratios. Computed load-displacement curves are in good agreement with experimental results. FE model output is used to calculate (a) J-R material data (b) crack growth at peak load. These are in good agreement with literature values.

Experimental Investigation of GTN model parameters of 6061 Al alloy

This research experimentally determines the Gurson-Tvergaard-Needleman (GTN) model damage mechanics parameters for 6061 Al alloys. Five different heat treatment conditions including T4 (natural aging) and T6 (peak strength) conditions of 6061 Al alloy were investigated. The GTN parameters considering different heat treatment conditions of the alloy were obtained by tensile tests. Scanning electron microscope (SEM) micrographs were used as inputs to determine initial and nucleated volume fractions. SEM and energy dispersive X-ray spectrography (EDX) analyses also revealed that the second-phase precipitates are the origin of the incipient voids. SEM analyses enabled the fractographic investigations where the primary and secondary voids were exhibited and thus showing nucleation strain. Density measurements clarify the critical and final void volume fractions and the standard deviation of the nucleated void volume fraction distribution. The results show that the void volume fraction increases exponentially along with increasing effective tensile plastic strain. Hence, a total of six different GTN parameters have been identified experimentally. Finite element method simulations based on GTN damage model were performed to verify the GTN model parameters. The results show that the experimentally obtained GTN model parameters could be used when performing tensile deformation simulations of 6061 Al alloys fabricated with different heat treatment conditions.

The Study of the Sensitivity of GTN Parameters

Gurson–Tvergaard–Needleman (GTN) model is a quite reliable tool that we can use to predict the failure of a component. Still, the determination of those parameters is not an easy task. It takes much time for computing, and sometimes we do find different sets of GTN parameters, with the same results after simulation. The purpose of this paper is to study how the change of the parameters affects the results, which means we are going to explore the non-uniqueness phenomena. We are going to conclude at the end, what are the main sensitive parameters.

The Effects of Forming Parameters on the Single Point Incremental Forming of 1050 Aluminum Alloy Sheet

The single point incremental forming (SPIF) is one of the dieless forming processes which is widely used in the sheet metal forming. The correct selection of the SPIF parameters influences the formability and quality of the product. In the present study, the Gurson-Tvergaard Needleman (GTN) damage model was used for the fracture prediction in the numerical simulation of the SPIF process of aluminum alloy 1050. The GTN parameters of AA 1050 sheet were firstly identified by the numerical simulation of tensile test and comparison of the experimental and numerical stress-strain curves. The identified parameters of the GTN damage model were used for fracture prediction in the SPIF process. The numerical results of the fracture position, thickness variation across the sample and forming height were compared with the experimental results. The numerical results had good agreement with the experimental ones. The effect of SPIF main parameters was investigated on the formability of samples by the verified numerical model. These parameters were tool rotation speed, tool feed rate, tool diameter, wall angle of the sample, vertical pitch, and friction between the tool and the blank.

Coupled identification of the hardening behavior laws and Gurson–Tvergaard–Needleman damage parameters - Validation on tear test of 12NiCr6 CT specimen

This work is devoted to the application of the micromechanical Gurson-Tvergaard-Needleman (GTN) model to study the ductile tearing of 12NiCr6 steel. GTN model is widely used to describe the three stages of ductile tearing: nucleation, growth and the coalescence of micro-voids. A new approach consists of a coupled identification of the GTN damage model with and without hardening laws using an inverse analysis is proposed. After identification, the obtained results show a good agreement between the experimental curve tensile test of an axisymetric notched bar (AN2) and those numerically obtained for GTN model coupled with the hardening laws. In order to validate the identified GTN parameters, a simulation of tear test is conducted on 12 NiCr6 steel CT specimen. The numerical results are compared with experimental results found in the literature and a good agreement is obtained. This identification procedure is more accurate than when the damage parameters are identified independently of the hardening laws.

Experimental and numerical study of hydro-mechanical deep drawing of 2024 aluminum alloy sheet at elevated temperatures

In the present study, hydro-mechanical deep drawing (HDD) of 2024 aluminum alloy sheet was investigated using the experimental tests and numerical simulations. The experimental tests were done at elevated temperature by considering four heating elements in the fluid chamber of HDD die which provided four temperatures of 25 °C (room temperature), 60 °C, 100 °C, and 140 °C for the HDD process. The effect of fluid chamber pressure was studied on the formability of AA 2024 by considering four pressures of 6, 10, 14 and 18 bar. The numerical simulations of the ABAQUS/Explicit and the Gurson-Tvergaard Needleman (GTN) damage model was used for fracture prediction of AA2024 in the HDD at room temperature. The anti-inference method and numerical simulation of the uniaxial tensile test of AA2024 sheet was used for identification of the GTN parameters. The experimental and numerical results indicated that the formability and forming height of AA2024 increased in the HDD by increasing of the pressure and temperature of the fluid chamber.

Determination of GTN parameters for SENT specimen during ductile fracture

The Gurson–Tvergaard–Needleman (GTN) model is widely used to predict the failure of materials based on lab specimens. The direct identification of the GTN parameters is not easy and it is time-consuming. The Gurson model is based on micro-mechanical behaviour of ductile fracture, containing void nucleation, growth and coalescence. The most used method to determine the GTN parameters is the combination between the experimental and FEM results but its time consuming as we have to repeat the simulations for many times until the simulation data fits the experimental data in the specimen level (axisymmetric tensile bar and CT specimens), but there are also other methods used to determine the GTN parameters, the aim of these methods is to determine the parameters in a short time as Artificial Neural Network, Hybrid Particle Swarm Optimization, Metallographic Method. In this paper, we determine the GTN parameters for the SENT specimen based on the fracture toughness test of CT specimen. The reason behind choosing the SENT specimen is because it can be a very good representative of the pipe for both uniaxial and biaxial loading conditions. The Results show that the GTN parameters concluded from CT simulations, predict very well the crack initiation and propagation of SENT specimen which confirms the validity of this model.

Failure Prediction of Superheater Tubes in Rotary Tube Bending Process Using GTN Damage Model

Superheater tubes are one of the main parts of boilers which are subjected to high temperature and stress. Fracture is one of the main defects which happen during the forming process of these tubes. In the present study, tube rotary draw bending (RDB) process is used for forming of superheater tube. Gurson–Tvergaard–Needleman (GTN) damage model is used for fracture prediction in the numerical simulation of tube RDB. Response surface methodology is coupled with the finite element to identify the GTN parameters. For this purpose, different sets of GTN parameters are used to simulate the uniaxial tensile test in the Abaqus software. Effect of GTN parameters is investigated on the predicted stress–strain curve of the uniaxial tensile test in the numerical simulation. The best-identified GTN parameters are used in the finite element simulation of tube RDB of superheater tube. Results indicate that there is an appropriate agreement between the predicted fracture location of the numerical and experimental sample after RDB.