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The prediction accuracy of ductile damage models is subject to a sound calibration strategy, which normally involves the execution of complex multiaxial tests and requires dedicated facilities. In addition, finite element (FE) analysis is mandatory to retrieve the stress and strain states at the critical point, which cannot be directly measured from experiments. To overcome this complexity, a minimal set of simple multiaxial tests is selected, and an analytical‐numerical approach is proposed to evaluate, without resorting to FE, both the stress evolution with plastic deformation and the fracture strain, under any different loading condition of each test. This is achieved from the sole knowledge of the material bilinear stress–strain relation and of the applied test displacement at fracture. The obtained results are compared with a traditional testing and calibration methodology, and the robustness of the approach is proved on a 17‐4PH steel, an X65 steel, and a Ti6Al4V alloy. Highlights: Ductile damage models are calibrated by an analytical approach based on multiaxial tests.Local stress and strain in tests can be calculated from experiments without resort to FEM.Uniaxial and different shear‐tension stress states are investigated.The method works on a wide range of alloys; only test displacement at failure is required. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A coupled thermomechanical non-ordinary state-based peridynamics (NOSB-PD) model is developed to simulate the dynamic response arising from temperature and to predict the crack propagation with thermal shocks in brittle and ductile solids. A unified multiaxial constitutive model with damage growth is proposed to simultaneously describe the ductile and brittle fracture mechanisms. The main idea is the use of Lemaitre's model to describe ductile damage behavior and the use of tensile strength instead of yield stress in Lemaitre's model to describe brittle damage behavior. A damage-related fracture criterion is presented in the PD framework to predict crack propagation, which avoids numerical oscillations when using the traditional bond stretch criterion. To capture the dynamic plastic response induced by thermal shocks, the time and stress integration are achieved by an alternating solving strategy and implicit return-mapping algorithm. Several numerical examples are presented to show the performance of the proposed model. Firstly, a thermomechanical problem simulation based on both the proposed model and the FEM illustrate the accuracy of the proposed model in studying the thermal deformation. Moreover, a benchmark brittle fracture example of the Kalthoff–Winkler impact test is simulated, and the crack path and angle are similar to the experimental observations. In addition, the simulation of ductile fracture under different loads illustrates the effect of temperature on crack propagation. Finally, the simulation of the 2D quenching test shows the ability of the proposed model in predicting crack propagation under thermal shocks. [ABSTRACT FROM AUTHOR]

Summary: We present a phase‐field fracture model for a stress resultant geometrically exact shell in finite deformation regime where the configuration manifold evolves according to deformation and fracture. The Reissner–Mindlin shell problem is first solved via the finite element method, where the independent unknown fields are the displacement and director. The phase‐field ductile fracture model is then coupled with the verified geometrically exact shell by enriching the three‐field elasto‐plastic free energy with a regularized crack surface energy. To capture the geometrical nonlinearity due to the large plastic deformation exhibited in the processing zone, the corresponding finite‐strain stress resultant elasto‐plasticity model is coupled with the phase field model. This coupling between the stress resultant elasto‐plasticity model and the phase‐field fracture model enables us to predict the different amounts of energy dissipation attributed to plastic deformation and fracture and hence simulate the crack propagation in the ductile regime properly. We introduce a mixed finite element model with displacement, director, and phase‐field order parameters as the nodal degree of freedoms formulated on the mid‐surface. An energy‐based arc‐length method is generalized to track the equilibrium path and mitigate instabilities arising from material nonlinearity. Four numerical examples are presented to validate the implementation of the model and demonstrate its capability to simulate ductile fracture in shell structures. These examples include a plane‐stress tension/shear fracture model, the Muscat‐Fenech and Atkins plate, axial tension of a notched cylindrical shell, and ductile fracture of a simply supported plate under uniform pressure. [ABSTRACT FROM AUTHOR]

In this paper, we present a robust exploration of the Gologanu–Leblond–Devaux (GLD) model, an advanced iteration of the Gurson model, designed to predict ductile fractures in porous metals. Going beyond the limits of the original Gurson model, the GLD model accounts for cavity shape effects and non-local strain localization, marking a significant leap in fracture mechanics. We also present a comprehensive exposition of the GLD model and its non-local extension, establishing their compatibility with the concept of GSMs. Notably, we emphasize the uniqueness of solutions in the numerical implementation, underlining the imperative need for a meticulously devised mixed implicit/explicit algorithm. Furthermore, we set out to validate the GLD model through rigorous comparisons of our numerical simulations with experimental data. Employing a damage delocalization approach rooted in the natural logarithm of porosity, our study provides compelling evidence of the model's performance. This approach mitigates issues observed with the original porosity rate, preventing excessive smoothing of porosity and maintaining the fidelity of stress–strain curves. In addition, we gave a profound theoretical elucidation of this phenomenon via Fourier's analysis of porosity rate. Through this work, we not only enhance our understanding of ductile fracture behavior but also establish a robust numerical framework for its predictive modeling. The GLD model emerges as a powerful tool for the accurate analysis and prediction of fracture phenomena in porous materials, further advancing the field of materials science and engineering. [ABSTRACT FROM AUTHOR]

(1) Modeling and characterization of ductile fracture in metals is still a challenging task in the field of computational mechanics. Experimental testing offers specific responses in the form of crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM) implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model (PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed, with a threshold to propose a new relationship between critical fracture energy and critical total strain value. In addition, the threshold value of potential internal energy—which controls damage evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test. The PFDM model is validated against the experimental results obtained in the fracture toughness characterization test, with the simulation results being within 8% of the experimental measurements. (4) The novel implementation offers the possibility for better control of the ductile behavior of metallic materials and damage initiation, evolution, and propagation. [ABSTRACT FROM AUTHOR]

Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper describes a study into the evolution of damage in commercial-purity titanium (CP–Ti) sheets subjected to cyclic bending under tension (CBT) and uniaxial tension (simple tension, ST). Sections were taken from sheets that were strained to various levels under both methods and were imaged using X-ray computed tomography (XCT) to reveal insights into the size, density, and distribution of microvoids in the sheets. Digital image correlation (DIC) was also used to observe the surface strain of CBT and ST sheets during testing. These results showed that elongation to failure (ETF) for CBT deformation is about 2.5× higher than for ST, local longitudinal strains in the bulk of the CBT sample are around 1.3× higher than the peak strain in the ST necked region, and 1.7× higher in the localized region of CBT failure. It was found that the volume-density of voids in both sheets followed a similar exponential increase with strain, reaching nearly 45× higher in the CBT than the ST sheets before the onset of failure, mainly due to the higher strain levels achieved. A higher volume density of voids developed in the center of sheets at high levels of strain, for both processes, with the density in the sheet center becoming approximately double that found near the edges. Scanning electron microscopy (SEM) was used to examine the fracture surface of CBT and ST sheets after failure. The observations are presented and discussed highlighting the CBT process as effective to delay ductile fracture of the CP-Ti sheets.

Summary: This study presents a diffusive‐discrete crack transition scheme for stably conducting ductile fracture simulations within a finite strain framework. In the developed scheme, the crack initiation and propagation processes are determined according to an energy minimization problem based on crack phase‐field theory, and the predicted diffusive path is transformed to a discrete representation using the finite cover method during the staggered iterative scheme. In particular, for stably conducting ductile fracture simulations, three computational techniques, the staggered iterative configuration update technique, the subincremental damage update technique, and the crack opening stabilization technique, are introduced. The first and second techniques can be used regardless of whether discrete cracks are considered, and the third technique is specialized for diffusive‐discrete crack transition schemes. Accordingly, ductile fracture simulations with the developed scheme rarely encounter troublesome problems such as oscillations in the displacement field and severe distortion of finite elements that can lead to divergence of calculations. After the crack phase‐field model for ductile fractures is formulated and discretized, the numerical algorithms for realizing the diffusive‐discrete crack transition while maintaining computational stability are explained. Several representative numerical examples are presented to demonstrate the performance and capabilities of the developed approach. [ABSTRACT FROM AUTHOR]

Advanced high-strength steels (AHSS) have revolutionized the automotive industry by reducing weight without compromising crashworthiness. The new third-generation steels, such as quenching and partitioning (QP) steels, offer exceptional strength and ductility. However, despite the extensive strength-ductility studies, there is a wide knowledge gap in the literature on the fracture behavior of QP steels under a large range of stress states and loading conditions for material forming operations. This study aims to systematically investigate the fracture behavior of QP1000 sheet metal through a combination of experimental and numerical approaches. In addition to the classic fracture dependency on stress states, we particularly focus on the anisotropic behavior in terms of both plasticity and fracture. Mechanical tests with digital image correlation are performed along three loading directions covering stress states from simple shear to plane-strain tension. The evolving non-associated Hill48 (enHill48) model is employed to describe anisotropic plasticity, while the fracture behavior is represented by a partially coupled anisotropic fracture model and a fully anisotropic fracture model. It is concluded that the investigated QP steel shows moderate anisotropic plasticity behavior yet strong fracture anisotropy, which intensifies with the increase of stress triaxiality. The partially coupled anisotropic fracture model, which has shown success for materials with minor anisotropic plasticity, fails to describe the anisotropic fracture and a fully anisotropic model provides significantly improved predictive capability.

Additive manufacturing (AM) provides exceptional geometrical freedom to the architects and designers and enables the construction of architecturally exposed steel structures. However, the AM structural elements inherently possess microscale defects that can affect their ductility. This study aims to identify the fracture-initiating mechanism in AM 17-4 stainless steel that is popularly used owing to its excellent engineering properties. To this end, axisymmetric cylindrical notched and unnotched tension specimens are manufactured employing direct metal laser sintering from 17-4 stainless steel powder with established processing and build parameters. The test specimens were manufactured using a 90° build orientation with the build plate and a layer thickness of 40 μm. Postprocessing heat treatment was avoided as the study focused on understanding the failure mechanism in as-built AM test specimens. Detailed metallurgical analysis is performed employing scanning electron microscopy (SEM) and electron backscatter diffraction. Subsequently, micro–computed tomography (CT) studies are conducted on the tension specimens before and after mechanical testing. Although the SEM analyses of fracture surfaces are inconclusive, the micro-CT analysis revealed evidence of nucleation of new microvoids, growth of existing voids, and void coalescence in the vicinity of the fracture surface, which is unequivocal evidence for ductile fracture. Furthermore, the larger AM defects were found to play an important role in lowering the ductility in addition to stress concentration, and the fracture was initiated when the AM defects coalesced over a length of around 600 μm. The conclusions of this study emphasize the importance of controlling the maximum size of defects in AM structural elements to improve their performance. [ABSTRACT FROM AUTHOR]

Low yield point (LYP) structural steels had been developed and used for the seismic energy dissipating, however, the fracture of various LYP steel energy dissipation components may lead to progressive collapse of structures. To address this issue, the fracture behavior of LYP steels under various stress states were comprehensively investigated using experiments, theoretical analysis, and numerical simulations in this work. There are three meaningful contribution points. First, an improved weighted average (WA) method and dichotomy-based optimization are proposed to calibrate true stress–strain relation after necking onset. The maximum deviation for the prediction of full-range tensile load-displacement behavior based on the proposed WA method is less than 3%, which is better than the existing WA methods. Second, a modified ductile fracture model is developed to identify the fracture of LYP steels under various stress states. Comparison results among existing fracture models, the proposed fracture model and tests indicate that the fracture plastic strain can be more reasonably predicted by the proposed ductile fracture model than the existing models. Thirdly, an advanced ductile fracture prediction framework is proposed to simulate the complete tensile behavior of structural steels. Based on the proposed framework and object-oriented programming technique, the complete tensile behavior can be accurately and conveniently predicted by employing the proposed WA model, proposed ductile fracture model and developed user defined material subroutine. The verified WA method and ductile fracture model would contribute to predicting the failure of structural steel members, connections, welds and structures. It is meaningful to prevent casualties and property losses resulting from the subsequent structural progressive collapse. [ABSTRACT FROM AUTHOR]

The experimental measurements of ${2D}$ 2 D micro/nanolayered dimples' dimensions (both geometry and pattern) on the published tensile fractographs of a series of austempered high-strength low-carbon bainitic steel are carried out and interpreted with the corresponding initial microstructural features and tensile mechanical responses as a function of austempering temperature. [ABSTRACT FROM AUTHOR]

Metal parts undergo a blanking test that involves experimentation with different process parameters across multiple levels. The presence of uncontrolled burrs (measured as Hbv) significantly affects the precise geometry of the blanked parts, making it a primary concern in precision blanking. Moreover, the maximum blanking force (Fmax) holds considerable significance, as it aids in forecasting fracture mechanisms and plays a pivotal role in the design of blanking tools. The aim of this study is to assess the predictive capabilities of an elasto-plastic model coupled with damage in capturing the behavior of sheet material during the blanking process. Additionally, integrating the rate-dependent aspect into the model is crucial for accurately modeling the mechanical behavior of sheet metal. Our focus remains on demonstrating the efficacy of the model in predicting blanking force and burr formation. The numerical model incorporates modified plasticity and damage Johnson–Cook models to achieve this objective, considering the combined effect of strain and strain rate fields in the sheet blanking process. Experimental validation proves the efficacy of the proposed model in accurately predicting blanking outcomes. The experimental results confirm the model's capability to provide a consistent prediction of the blanking force and burr dimensions. In addition, it was proved experimentally that the sheet thickness has the most influence on Hbv and Fmax. [ABSTRACT FROM AUTHOR]

This article aims to compare three plasticity models, namely Bai-Wierzbicki (BW), von Mises and Drucker Prager, to predict the failure modes in double-lap metallic bolted joints under shear loading. The double-lap bolted joint finite element model has been validated against literature data, which demonstrated the application of BW ductile fracture model to bolt joint failure prediction. Taguchi Design is used to investigate the effects of geometrical parameters, preload and stress triaxiality on the failure modes. Force–displacement response amongst the three models differs up to 20% when failing in shear and a different prediction of the failure mode (shear out vs. net section) under the same loading and geometry conditions is observed. [ABSTRACT FROM AUTHOR]

In this study, the effect of the Lode angle on failure and plasticity is considered, and a new Lode angle function on plasticity is developed. Meanwhile, a new temperature coefficient function is proposed in this model, and the application of the model is extended to the range from room temperature to 650°C. The tensile specimens of different shapes have been designed to calibrate the parameters of the model. The tensile tests are carried out on the in situ micro‐tensile machine. For the notched tensile specimens at room temperature to validate the constitutive model, numerical results are consistent with experimental ones well, with an error of 7%. Then, the calibrated model is applied to FE simulations to numerically study the fracture phenomena observed in the test. The fracture positions and damage initiation positions of the shear specimen and the notched tensile specimen can be predicted by FE simulations well, while the smooth tensile specimen cannot be predicted well due to real specimens' imperfections. Highlights: A coupled plasticity‐damage model is proposed.A new Lode angle function and temperature coefficient function are developed.The experimental and numerical damage evolution and fracture edges are in agreement. [ABSTRACT FROM AUTHOR]

In this research, the load-bearing capacities of epoxy-based nanocomposite specimens containing rounded-tip V-shaped notches made of epoxy resin LR 630 and nanographene oxide were studied both experimentally and theoretically under pure opening mode conditions. In order to fabricate the studied specimens, first, the tensile properties and fracture toughness of pure epoxy resin and nanocomposite materials were determined by uniaxial monotonic tension and three-point bending tests. Rectangular plates containing a central rhombic hole with four blunt V-shaped corners with a notch angle of 60° and radii of 1, 2, and 4 mm were utilized as the samples for fracture tests. Then, the samples were subjected to uniaxial tensile loading, and their load-carrying capacities (LCC) were measured. For theoretical predictions, due to the ductile behavior of the studied specimens, a combination of the equivalent material concept (EMC) with the well-known brittle fracture criterion, maximum tangential stress (MTS), was employed. Then, experimental and theoretical results were compared. The results of the experiment showed that by adding nanoparticles to the epoxy resin, its strength improved by about 8%, and it was found that the maximum discrepancy between the theoretical and experimental results was related to the groove with a radius of 4 mm, approximately 9.2%. Finally, it was observed that the new criterion (EMC-MTS) could predict the experimental results well without performing any time-consuming and complex elastic-plastic analysis. [ABSTRACT FROM AUTHOR]

Repair of NPP pipelines with erosive and corrosive wear defects is an urgent problem of the nuclear power industry of Ukraine. When repairing the pipeline, the defective section is cut out and a new pipe coil is installed by welding. But for a large number of technological pipelines with identified isolated defects, inadmissible wall thinning, replacement of a pipe section is associated with a large volume of repair work. To extend the service life, the defective section of the pipeline can be reinforced, for example, by welding an external overlay, building-up, installing a bandage or a welded sleeve. In order to justify the expediency of using reinforcing structures of welded external overlay type at pipeline repair, a finite-element analysis of the stress-strain state of a straight section of the pipeline with an erosion-corrosion wear defect under the action of internal pressure before and after repair was carried out. The results of the analysis showed a high efficiency of reinforcing the defective section of the pipeline in the case of using a welded external overlay at repair. The obtained results can be used at justifying the introduction of alternative pipeline repair technologies at NPPs of Ukraine. [ABSTRACT FROM AUTHOR]

Cast steels are inherently suitable for fabricating complex joints in steel constructions. These joints may suffer from ductile fracture under ultralow cycle fatigue (ULCF) loadings during earthquakes. This problem could be even worse for cast steel joints working at subzero temperatures. In this investigation, ULCF tests on 48 smooth notched tensile specimens were carried out at 20°C, −20°C , −40°C , and −60°C for G20Mn5QT cast steel. Notches with three different radii were designed for different stress triaxialities. Two load patterns, cycle to fracture and cycle and pull to fracture, were applied for the tests. Ductile fracture caused by the ULCF loadings was observed and fatigue lives were obtained for all test specimens. The characteristic lengths were determined for G20Mn5QT cast steel at the four temperatures through scanning electron micrograph analysis of the fracture surfaces. The cyclic damage degradation parameters in the cyclic void growth model were then calibrated for G20Mn5QT cast steel at 20°C, −20°C , −40°C , and −60°C based on test results and complementary finite element (FE) analysis. The cyclic damage degradation parameter decreases with the drop of temperature, which indicates that the material's resistance to ductile fracture degrades faster at lower temperatures under ULCF loadings, especially when the temperature drops below −40°C. [ABSTRACT FROM AUTHOR]

This study introduces a modified DF2016 criterion to model a ductile fracture of sheet metals from shear to equibiaxial tension. The DF2016 criterion is modified so that a material constant is equal to the fracture strain at equibiaxial tension, which can be easily measured by the bulging experiments. To evaluate the performance of the modified DF2016 criterion, experiments are conducted for QP980 with five different specimens with stress states from shear to equibiaxial tension. The plasticity of the steel is characterized by the Swift–Voce hardening law and the pDrucker function, which is calibrated with the inverse engineering approach. A fracture strain is measured by the XTOP digital image correlation system for all the specimens, including the bulging test. The modified DF2016 criterion is also calibrated with the inverse engineering approach. The predicted force–stroke curves are compared with experimental results to evaluate the performance of the modified DF2016 criterion on the fracture prediction from shear to equibiaxial tension. The comparison shows that the modified DF2016 criterion can model the onset of the ductile fracture with high accuracy in wide stress states from shear to plane strain tension. Moreover, the calibration of the modified DF2016 criterion is comparatively easier than the original DF2016 criterion. [ABSTRACT FROM AUTHOR]

A procedure is outlined for calibrating a finite element model to simulate ductile cracking that employs a continuum damage criterion for ductile fracture initiation, termed the Stress Weighted Ductile Fracture Model, with an Adaptive Cohesive Zone method to simulate crack propagation. The proposed procedure is implemented and validated with data from 44 coupon‐scale tests of an A913 structural steel. The fracture model calibration is performed in two stages to determine parameters to evaluate: (1) the continuum damage mechanics criterion and (2) ductile crack initiation and propagation. Sensitivity of the calibration to parameter uncertainty is evaluated using synthetic data, followed by calibration and validation against experimental test data. The results indicate that the computational model can accurately simulate the overall response of experimental specimens, as well as other key aspects of observed behavior, including crack tunneling and crack face closure. Guidelines are provided for practical calibration of the model components. Highlights: A calibration method for simulating ductile crack propagation in steels is proposed.The calibration method is validated against the results of experimental tests.The proposed model may be used to simulate ductile cracking in steel structures. [ABSTRACT FROM AUTHOR]

Formation of erosion-corrosion wear defects in Npp pipelines is one of the urgent problems of nuclear power engineering. During pipeline repair, a defective section is cut out and a new pipe spool is mounted using welding, which is a rather labour-consuming process, and requires draining of the transported liquid. To prolong the service life, a defective pipeline section can be reinforced by mounting a repair structure, for instance a band or a welded coupling. In order to substantiate the rationality of application of reinforcing structures in pipeline repair, the finite element analysis of the stress-strain state of a rectilinear pipeline section with an erosion-corrosion wear defect under the impact of internal pressure, as well as evaluation of the effectiveness of unloading a defective section in the case of application of a reinforcing structure of the type of a band or a welded coupling in repair were performed. The analysis results have shown a high effectiveness of applying such structures. The obtained results can be used in substantiation of introduction of alternative technologies for repair of pipelines in the Ukrainian NPP, predominantly technological ones, particularly in those cases when repair by traditional methods is not possible or rational for technical or economic reasons. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration has considerable influence on the plastic deformation and resulting fracture responses of metallic alloys. This manuscript critically aims at quantification and assessment of two-dimensional ductile dimple geometry of Ti-6Al-4V alloy generated through the variation of ultrasonic vibration with different powers during tensile experiments. The analyzed dimple geometry statistics as a function of ultrasonic power are completely based on a published article. The alteration of microstructural states, leading to different dimple appearances after inducing different ultrasonic vibrations during tensile deformation, have been extensively quantified/assessed, compared and interpreted with respective mechanical responses of the alloy as a function of ultrasonic power. Moreover, the change in strain hardening path patterns through the variation of ultrasonic power has clearly reflected on the dimple statistics/dimensions on their respective tensile fractographs. This novel 'dimple geometry-ultrasonic power-tensile response' interpretation allows the use of two-dimensional ductile dimple fracture appearances in a quantitative way. The remarkable manifestation of ultrasonic vibration on tensile responses of Ti-6Al-4V alloy and hence the change in fracture appearances have been convincingly revealed. [ABSTRACT FROM AUTHOR]

AbstractWith the increasing focus on reducing carbon emissions, hydrogen has emerged as a promising alternative energy source. However, the safe transportation of hydrogen poses challenges due to its potential impact on the integrity of pipeline materials. This study aims to investigate the effect of hydrogen charging time on the plastic behavior and ductile fracture characteristics of API 5L X42 pipelines, which are commonly used for transporting hydrocarbons. Tensile tests were conducted on various types of hydrogen-charged specimens at room temperature to assess different fracture modes. Hydrogen was introduced into the specimens using a cathodic electrolytic method, and 24-h charging time durations were considered. Finite element analyses were performed on standard dog-bone and notched tension specimens to evaluate the plastic behavior, employing the Swift hardening law to model the flow stress. Numerical analyses were conducted to determine the loading path leading to fracture initiation. A damage framework based on the Hosford–Coulomb model was utilized to predict ductile fracture under non-proportional loading conditions. The findings of this study provide insights into the fracture behavior of pipelines under hydrogen exposure, aiding in the design and assessment of safe and reliable hydrogen transport systems. [ABSTRACT FROM AUTHOR]

The effectiveness of a ductile fracture model in accurately predicting fracture initiation has been demonstrated. In this study, we concentrate on applying the ductile fracture model to pre-cracked structures constructed from SUS304L stainless steel with experimental and numerical analyses. The Swift hardening law was employed to extend the plastic behavior beyond the onset of necking. Additionally, the Hosford–Coulomb model, integrated with a damaged framework, was utilized to predict ductile fracture behavior, particularly under non-proportional loading conditions. Tension tests were conducted on various specimens designed to illustrate various fracture modes resulting from geometric effects. Numerical analyses were conducted to explore the loading histories, utilizing an optimization process to calibrate fracture model parameters. The proposed fracture model is validated against pre-cracked structures detailed in a reference paper. The results convincingly demonstrate that the fracture model effectively predicts both fracture initiation and propagation in pre-cracked structures. [ABSTRACT FROM AUTHOR]

A CPB06-based Stewart-Cazacu micromechanical damage model is implemented and validated for Ti6Al4V material. It provides accurate numerical predictions in terms of macromechanical material response and damage accumulation. The Stewart & Cazacu–Tvergaard & Needleman–Thomason (SC11–TNT) based damage model presented here is developed and implemented in the finite element software Lagamine following a semi-implicit cutting plane algorithm and a well-chosen flow rule approach. The damage of the material is characterized by the porosity ratio contained within the material. It is modelled by void nucleation, growth and coalescence mechanisms. The onset of the coalescence is established by a criterion based on Thomason's approach. The macroscopic results obtained by the implemented model demonstrate a strong ability to predict the experimental elastoplastic mechanical behaviour of the material across a full deformation range and different types of loadings. At the microscopic level, the predicted accumulated porosity ratio of the material matrix at fracture exhibits a good correlation with the experimental observations. The element deletion feature, activated when a certain damage threshold is reached, provides a physical description of the loss of load-carrying capacity of the material during fracture. [ABSTRACT FROM AUTHOR]

Mechanical tests of commercially pure lead grade C2 were carried out, cylindrical samples of lead were destroyed in the process of creep with a constant tensile force. The tests were carried out initially without the inclusion of a magnetic field during deformation, then with the inclusion of a magnetic field with an induction of 0.5 T. Based on the data obtained, characteristic curves of the creep process were constructed. A change in the nature of the curve is revealed. At the discovered linear stage of the process, the creep rate was calculated. A decrease in the creep rate is shown compared to the process without the action of an external magnetic field. The duration of the creep process is analyzed depending on the induction and the percentage of residual relative elongation of the samples. Analysis of the fractograms showed a difference in the morphology of fractures in the studied samples. With the use of a magnetic field during the destruction of the sample, the number of pits on the surface decreased, the fibrous zone increased, and the fracture morphology changed. [ABSTRACT FROM AUTHOR]

During collisions, base metals may incur ductile fracture without evident defects under complex stress conditions. Herein, we propose a test method for evaluating the initiation behavior of internal ductile cracks in metals under shear stress conditions. The applicability of the developed specimen to the evaluation of ductile crack initiation condition was discussed based on the results of tensile fracture tests and finite element analyses. It is found that the critical equivalent plastic strain for crack initiation was lower in the shear stress state than the tensile stress state under equivalent stress triaxiality conditions. [ABSTRACT FROM AUTHOR]

A coupled thermomechanical non-ordinary state-based peridynamics (NOSB-PD) model is developed to simulate the dynamic response arising from temperature and to predict the crack propagation with thermal shocks in brittle and ductile solids. A unified multiaxial constitutive model with damage growth is proposed to simultaneously describe the ductile and brittle fracture mechanisms. The main idea is the use of Lemaitre’s model to describe ductile damage behavior and the use of tensile strength instead of yield stress in Lemaitre’s model to describe brittle damage behavior. A damage-related fracture criterion is presented in the PD framework to predict crack propagation, which avoids numerical oscillations when using the traditional bond stretch criterion. To capture the dynamic plastic response induced by thermal shocks, the time and stress integration are achieved by an alternating solving strategy and implicit return-mapping algorithm. Several numerical examples are presented to show the performance of the proposed model. Firstly, a thermomechanical problem simulation based on both the proposed model and the FEM illustrate the accuracy of the proposed model in studying the thermal deformation. Moreover, a benchmark brittle fracture example of the Kalthoff–Winkler impact test is simulated, and the crack path and angle are similar to the experimental observations. In addition, the simulation of ductile fracture under different loads illustrates the effect of temperature on crack propagation. Finally, the simulation of the 2D quenching test shows the ability of the proposed model in predicting crack propagation under thermal shocks.

(1) Modeling and characterization of ductile fracture in metals is still a challenging task in the field of computational mechanics. Experimental testing offers specific responses in the form of crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM) implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model (PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed, with a threshold to propose a new relationship between critical fracture energy and critical total strain value. In addition, the threshold value of potential internal energy—which controls damage evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test. The PFDM model is validated against the experimental results obtained in the fracture toughness characterization test, with the simulation results being within 8% of the experimental measurements. (4) The novel implementation offers the possibility for better control of the ductile behavior of metallic materials and damage initiation, evolution, and propagation.

A method is developed for predicting creep and long-term strength based on the behavior of a previously tested sample (leader sample, prototype) in the case of ductile fracture. It is assumed that a loaded material does not undergo instantaneous plastic deformation and the first stage of creep. The incompressibility hypothesis is fulfilled in this case. It is shown that, if a constant-stress creep curve and the time to fracture are known for a leader sample, then obtaining a diagram of rheological deformation and long-term strength of the material at other stress values requires knowing only the initial (at the initial time) minimum creep strain rate of the samples for these stress values. The relevance of the developed method is checked with experimental data in two types of tests. The first type is tension tests of 12Kh18N10T corrosion-resistant steel samples at a temperature of 850°C and titanium alloy samples at a temperature of 600°C and the second type is tension and torsion tests of D16T alloy samples at a temperature of 250°C. It is shown that the prediction results are independent of the choice of a leader sample from many samples tested at different stresses. The possibility of using the developed method in experimental studies of creep of materials until their fracture is discussed. [ABSTRACT FROM AUTHOR]

This paper addresses the prediction of ductile fracture and hardening behavior of AA7075-T651 sheets under different stress states. Tests from shear to balanced biaxial tension are carried out up to fracture to determine ductile fracture. Considering the effect of different loading conditions on the plastic behavior of the material, stress triaxiality T, representing different stress states, and Lode parameter L are introduced to the Voce hardening model. After calibration by an inverse engineering approach, the improved hardening model is analyzed numerically, and an accurate description of the material strength under different stress states is verified. Based on the hardening model, four uncoupled ductile fracture criteria (Oh, Rice-Tracy, DF2012 and DF2015) are calibrated and utilized to predict the onset of fracture for the specimens. All fracture strains are obtained by a hybrid experimental-numerical method. A comparison of the predicted fracture strokes indicates that the DF2015 criterion predicts the fracture behavior in better agreement with the experimental results, especially for the Nakajima specimen. [ABSTRACT FROM AUTHOR]

This paper presents an upset geometry sequence to determine the fracture forming limits in a wide variety of strain loading paths ranging from uniaxial compression to equibiaxial tension. The strains at fracture in principal strain space are obtained by combination of digital image correlation and experimental evolutions of the compression force versus time, and their representation in the effective strain versus stress triaxiality space is accomplished by means of a new analytical framework that uses the instantaneous slope of the strain loading paths. Modeling of the experimental strains at fracture by means of an uncoupled ductile fracture criterion built upon combination of the Cockcroft-Latham and McClintock criteria and fractography analysis using a scanning electron microscope allow understanding and characterizing the crack opening modes by shear and tension as well as the uncertainty region inside which mixed crack opening modes are observed. Results confirm that the overall philosophy and objectives underlying the new upset geometry sequence for determining the fracture forming limits in bulk forming resemble those of the Nakajima test that is commonly used in sheet forming. [ABSTRACT FROM AUTHOR]

Abstract The evolution of preexisting voids causes damage to metal structures with large plastic deformation. In the ABAQUS-Explicit computer code, the damage by the Gurson–Tvergaard–Needleman model (GTN model) is included in the porous failure criteria law. The numerical predictions using the GTN model are very sensitive to the calibrations of these parameters of the experimental results. This model describes until the damage, the mechanism of the evolution of the voids, which begins with their growth and their nucleation with the particles until the coalescence of these voids of a critical level, which causes the damage to the structure. This analysis uses Voce’s hardening model and von Mises’ equivalent stress flow theory. After validation with experimental results, this work aims to analyze the sensitivity of these GTN parameters to the response to damage and to the evolution of the gaps. This objective is applied on a plate notch. [ABSTRACT FROM AUTHOR]

Formation of erosion-corrosion wear defects in NPS pipelines is one of the urgent problems of nuclear power engineering. At pipeline repair the defective section is cut out and a new pipe spool is mounted using welding, which is a rather labour-consuming process, and requires draining of the transported liquid. To prolong the service life, the defective pipeline section can be reinforced by mounting a repair structure, for instance a band or welded sleeve. In order to substantiate the rationality of application of reinforcing structures in pipeline repair, finite element analysis of the stress-strain state of the rectilinear pipeline section with a defect of erosion-corrosion wear under the impact of internal pressure was performed, as well as evaluation of the effectiveness of unloading the defective section in the case of application of a reinforcing structure of the type of a band or welded sleeve in repair. Analysis results showed the high effectiveness of application of such structures. Obtained results can be used in substantiation of introduction in the Ukrainian NPS of alternative technologies of repair of pipelines, predominantly technological ones, particularly in those cases when repair by traditional methods is not possible or rational for technical or economic reasons. 18 Ref., 2 Tabl., 9 Fig. [ABSTRACT FROM AUTHOR]

It is mathematically shown that ductile fracture after finite plastic strain is a necessary consequence of the polycrystalline nature of the materials. A closed–form equation for the plastic strain to fracture of a fine–grained polycrystal with no voids is derived. The mathematical model for the plastic deformation is grounded on the physical hypothesis that adjacent grains slide with a relative velocity proportional to the local shear stress resolved in the plane of the shared grain boundary, when exceeds a finite threshold. Hence plastic flow is governed predominantly by the in–plane shear forces making grain boundaries to slide, and the induced local forces responsible for the continuous grain reshaping are much weaker. The process is shown to produce a monotonic hydrostatic pressure variation with strain that precludes a stationary flow. The hydrostatic pressure dependence on strain has two solutions. One of them leads to superplasticity, the other one is shown to diverge logarithmically at a finite fracture strain and then represents ductile behaviour. Emphasis is done in the mathematical aspects of the deformation of the polycrystal up to the initiation of fracture. Although theoretical predictions agree well with mechanical tests of commercial alloys, technical issues like the effects of the presence and evolution of porosity and other imperfections, or how fracture evolves after initiation are left for a more specific communication.